Zinc Acetate Catalyzed Stereoselective 1,2-trans-Glycosylation Using Glycosyl Chlorides

The IICT Communication Number: IICT/Pubs./2022/169.

Abstract

We report a strategy for the stereoselective synthesis of 1,2-trans-glycosides in the absence of neighboring group participation. The present protocol for the selective glycosylation mainly relies on catalyst control rather than protecting group selection. By using this protocol, several glycosides were prepared. Zinc acetate was found to be the optimal catalyst, providing the desired 1,2-trans-glycosides from glucose- and mannose-derived glycosyl halides at room temperature instead of low-temperature conditions.

Key words

glycosyl chloride - no neighboring group participation - 1,2-trans-glycosylation - zinc acetate

Biological functionality of the carbohydrate molecules is highly dependent on the nature of the glycosidic bonds. Therefore, the stereoselective synthesis of 1,2-trans-glycosidic bonds in the absence of anchimeric assistance is one of the most important and challenging reactions in carbohydrate chemistry[.1] Several elegant methodologies have been developed for the synthesis of oligo- and polysaccharides with stereocontrol of the glycosidic linkages;[2] however, most of the developed methodologies rely on neighboring group participation for stereoselective control of the glycosidic linkages,[3] despite having certain limitations. Specifically, such protocols require the introduction of groups such as OAc, OBz, OPiv, OLev, OPicolyl, N-TCA, or N-Troc into the glycoside moiety to direct nucleophilic attack of the coupling partner.[3c] However, the incorporation of such groups is often troublesome, requiring additional steps for the regioselective introduction and removal of the participating group. In addition, this approach can limit substrate scope and often decreases overall efficiency.

Other methods that provide trans-glycosylated products in the absence of anchimeric assistance are fluorine-directed,[4] and alkoxymethyl-directed[5] glycosylation. However, most of these methods require several steps to synthesize orthogonally protected monomer building blocks as starting materials. Furthermore, they require excess of metal triflates to convert stable orthoester intermediates into the desired glycosides.[6] Therefore, the development of catalytic stereoselective methods for 1,2-trans glycosylation is highly desirable.

Recently, reagent-controlled glycosylation has become an effective strategy for activation of sugar donors using S_N2 displacement reactions with different nucleophiles.[7] Most often, the activation of glycosyl chlorides requires stoichiometric amount of reagents, such as silver(I) or mercury(II) salts.[8] There have been a few reports in which activation of glycosyl chlorides takes place in the absence of anchimeric assistance using FeCl₃ [9a] and bis-thioureas.[9b] However, the outcome of the stereochemistry was unpredictable and provided mixtures of α- and β-anomers. Separation of these diastereomers is extremely challenging. Another important strategy for 1,2-trans-glycosylation is S_N2 type displacement of highly unstable in situ generated per-O-TMS glycosyl iodides with suitable nucleophile in the presence of a suitable activator.[10] Other than glycosyl halides, recently Bennet et al.[11] reported activation of thioglycosides using aryl(trifluoroethyl)iodonium triflimide as an activator. However, this procedure requires the use of the bulky base 2,4,6-tri-tert-butylpyrimidine (TTBP) and a multiple solvent system. Thus, development of general and catalytic methodologies to stereocontrol glycosylations without neighboring group participation is highly desirable. The processes outlined herein rely on catalyst control rather than on neighboring group participation. As a prelude to this, we observed that the readily available and stable Zn(OAc)₂ catalyst in the absence of base, ligand, and promotors is a useful alternative metal catalyst for the Koenigs–Knorr type glycosylation at room temperature.

Optimization of the reaction parameters was explored using 2,3,4,6-tetra-O-benzyl-α-d-glucosyl halide (1a)[12] as the glycosyl donor and n-hexanol (2a) as the acceptor (Table [1]). Most of the classical Lewis acids [ZnCl₂, InCl₃, Cu(OTf)₂, Zn(OTf)₂] failed to promote the glycosylation reaction at room temperature, while, at higher temperatures, decomposition of the glucosyl halides was observed (entries 1–4). Interestingly, diethylzinc provided the desired 1,2-trans-glycoside product in moderate yield (entry 5).

Table 1 Screening of Reaction Condition for Synthesis of trans-Glycosides using Glucosyl Chloride 1a and n-Hexanol 2a ^a

Entry	Reagent (mol%)	Solvent	Temp. (°)	Time (h)	Yield (%) (4a/5a)b
1	ZnCl2(20)	CH2Cl2	40	24	NR
2	InCl3(20)	CH2Cl2	40	24	NR
3	Cu(OTf)2(20)	CH2Cl2	40	24	NR
4	Zn(OTf)2(20)	CH2Cl2	40	24	NR
5	Et2Zn (150)	toluene	60	12	58 (4a)
6	Zn(OAc)2 (20)	toluene	60	12	50:10
7	Zn(OAc)2 (50)	CH2Cl2	rt	5	75:10
8	Zn(OAc)2 (100)	CH2Cl2	rt	5	78:20
9	Zn(OAc)2 (100)	CH3CN	rt	12	45:24
10	Zn(OAc)2 (100)	Et2O/CH2Cl2 (1:1)	rt	12	40:20
11	Pd(OAc)2 (10)	CH2Cl2	40	24	NR

^a Reaction conditions: 2,3,4,6-tetra-O-benzyl-α-d-glucopyranosyl chloride 1a (1 equiv), n-hexanol 2a (1.2 equiv).

^b Isolated yields α/β ratio calculated from ¹H NMR analysis after column chromatography purification. NR: No Reaction.

To improve the yield of the desired product 4a, we further continued our screening with Zn(OAc)₂ in toluene, and found that 4a was obtained in moderate yield along with unwanted glucosyl acetate 5a (Table [1], entry 6). We then explored the reaction by replacing toluene with DCM. Zinc acetate successfully catalyzed Koenigs–Knorr glycosylation at room temperature in DCM, and provided the desired compound 4a in 75% yield with complete 1,2-trans-selectivity (entry 7). However, with increasing catalyst load, the amount of unwanted byproduct 5a also increased (entry 8). Anomeric α-participating solvents such as acetonitrile[13] (entry 9) did not change the selectivity, and β-participating solvents such as Et₂O[14] (entry 10) did not alter the selectivity either. Further attempts to improve yield of the desired product with Pd(OAc)₂-catalyzed activation of the glycosyl halide was also not successful (entry 11). These observations led us to choose Zn(OAc)₂ (50 mol%), in CH₂Cl₂ at room temperature as the optimal conditions (entry 7).

The structure and anomeric selectivity for the formation of the desired glucoside 4a were confirmed from ¹H NMR spectroscopy, where the anomeric proton (H1) appeared at δ = 4.39 ppm (d, J = 7.8 Hz, 1H). The corresponding ¹³C NMR signal for the β-isomer carbon (C1) appeared at δ = 103.7 ppm.[15a] A very diagnostic ¹³C signal for the α-isomer would appear at δ = 96.8 (C1) ppm.[15b] We next examined the scope and generality of the optimized reagent system with a wide range of nucleophiles. Initially, we explored the utility of the protocol for the synthesis of β-glucosides. Scheme [1] lists the Zn(OAc)₂-catalyzed glycosylation reaction between glucosyl donor 1a and various aglycone O-nucleophiles, including primary and secondary alcohols. Various alcohols including n-hexanol, geraniol, citronellol, phenyl ethanol, cholesterol, fenchol, and menthol reacted with glucosyl chloride to give the corresponding 1,2-trans-glycosides 4a–r in 60–75% yields with complete 1,2-trans-selectivity. It is pertinent to mention that the current glycosylation strategy was extended to acid-sensitive TMS-protected alcohols such as TMS-ethanol (compound 4l), and the nitrogen containing 3-azido-1-propanol also reacted smoothly to yield desired compound 4m (62%).

Scheme 1 Zn(OAc)₂-catalyzed reaction between glucosyl chlorides and O-nucleophiles. Reagents and conditions: Glycosyl halide (1 equiv) reacted with corresponding alcohol (1.2 equiv) in the presence of Zn(OAc)₂ (50 mol%) at room temperature.

Having obtained excellent results with glucosyl chlorides, we turned our attention to mannopyranoside chloride and mannofuranoside chloride donors (Scheme [2]).[11] In this case, the reaction using donors 1b and 1c gave the desired mannopyranoside glycosides 6a–c and mannofuranoside glycosides 7a–f with good yields, but the stereoselectivity was compromised. We presume that, due to the strong endo-anomeric effect in mannose derivatives, competition between S_N2 and S_N1 pathways leads to diastereomeric mixtures with the trans-glycosylated product as the major stereoisomer.

Scheme 2 Zn(OAc)₂-catalyzed reaction between glycosyl chlorides1b, 1c with different alcohols. Reagents and conditions: Sugar donor (1 equiv) reacted with the corresponding O-nucleophile (1.2 equiv) in the presence of Zn(OAc)₂ (50 mol%) at room temperature.

The scope of the reaction was further tested with various nucleophiles to yield the desired glycosides in good yields (Scheme [2]). Furthermore, a gram-scale synthesis of β-allyl glucopyranoside 4s was achieved using allyl alcohol and glucosyl chloride in 60% yield (Scheme [3])[20].

The mechanistic pathway for this 1,2-trans-glycosylation is not currently conclusive, although a proposed mechanism is depicted in Figure [1]. The initial activation of the alcohol acceptor with Zn(OAc)₂ produces reaction intermediate I, which coordinates with the glucosyl chloride and delivers the nucleophile from the β-face via an S_N2 mechanism, resulting in the 1,2-trans-glycosylated product as the sole diastereomer. The catalytic cycle continues by the activation of the glycosyl chloride with intermediate II, which leaves ZnCl₂ in the reaction medium that reacts further with acetic acid to reform Zn(OAc)₂.[16a] In the case of mannopyranosides and furanosides, a mixture of diastereomers with the 1,2-trans-glycosylated product as major isomers was observed. This is probably due to the strong endo-anomeric effect operating via an S_N1 mechanism.[16`] [c] [d]

Scheme 3 Gram-scale synthesis of β-allyl-glucopyranoside (4s)

Figure 1 Plausible Zn-catalyzed activation of glucosyl chloride 1a

In summary, we have developed a 1,2-trans-glycosylation protocol of glycosyl chlorides with various O-nucleophiles in the presence of Zn(OAc)₂. The protocol described herein is efficient and furnishes the desired 1,2-trans-glycosylated products from glucopyranoside, mannopyranoside, and mannofuranoside chlorides. Mechanistic investigations as well as applications of this protocol in the synthesis of glycoconjugates are in progress.

Synthesis of 4a–r, 6a–c, and 7a–f; General Procedure

To a stirred solution of glycosyl chloride 1a–c (83 mg, 0.15 mmol) in anhydrous CH₂Cl₂ (3 mL) was added the requisite alcohol (0.18 mmol) and Zn(OAc)₂ (0.075 mmol) at room temperature, and the resulting solution was stirred at room temperature for 5 h. The reaction mixture was evaporated under reduced pressure, and the residue was purified using silica gel column chromatography (EtOAc/hexane, 2:8).

n-Hexyl-2,3,4,6-tetra-O-benzyl-β-d-glucopyranoside (4a)

Prepared by the General Procedure using 2,3,4,6-tetra-O-benzyl-α-d-glucopyranosyl chloride (0.15 mmol, 84 mg) and n-hexanol (0.18 mmol, 23 μL).[17] Column chromatography purification using ­EtOAc/hexane (2:8) gave 4a as a white solid (β-anomer only, 70 mg, 75%).

¹H NMR (500 MHz, CDCl₃): δ = 7.35–7.24 (m, 18 H), 7.16–7.14 (m, 2 H), 4.97–4.92 (m, 2 H), 4.83–4.80 (m, 2 H), 4.72 (d, J = 10.9 Hz, 1 H), 4.63–4.51 (m, 3 H), 4.39 (d, J = 7.8 Hz, 1 H), 3.97 (dt, J = 9.4, 6.5 Hz, 1 H), 3.74 (d, J = 10.7 Hz, 1 H), 3.71–3.61 (m, 2 H), 3.61–3.49 (m, 2 H), 3.47–3.43 (m, 2 H), 1.72–1.60 (m, 2 H), 1.47–1.35 (m, 2 H), 1.33–1.23 (m, 6 H), 0.88 (t, J = 7.0 Hz, 3 H).

¹³C NMR (100 MHz, CDCl₃): δ = 138.7, 138.5, 138.2, 138.1, 128.3, 128.1, 128.0, 127.9, 127.8, 127.6, 127.6, 103.7, 84.7, 82.3, 78.0, 75.7, 75.0, 74.9, 74.8, 73.5, 70.2, 69.0, 31.7, 29.8, 25.9, 22.6, 14.1.

Propargyl-2,3,4,6-tetra-O-benzyl-β-d-glucopyranoside (4d)

Prepared by the General Procedure using 2,3,4,6-tetra-O-benzyl-α-d-glucopyranosyl chloride (0.15 mmol, 84 mg) and propargyl alcohol (0.18 mmol, 11 μL).[18] Column chromatography purification using EtOAc­/hexane (2:8) gave 4d as a gum (β-anomer only, 53 mg, 62%).

¹H NMR (400 MHz, CDCl₃): δ = 7.32–7.18 (m, 18 H), 7.09–7.07 (m, 2 H), 4.91–4.84 (m, 2 H), 4.76–4.69 (m, 2 H), 4.62 (d, J = 10.8 Hz, 1 H), 4.55 (dd, J = 9.9, 7.5 Hz, 2 H), 4.46 (dd, J = 11.5, 3.7 Hz, 2 H), 4.37 (qd, J = 15.8, 2.4 Hz, 2 H), 3.70–3.61 (m, 2 H), 3.60–3.51 (m, 2 H), 3.45–3.38 (m, 2 H), 2.39 (t, J = 2.4 Hz, 1 H).

¹³C NMR (125 MHz, CDCl₃ ): δ = 138.6, 138.4, 138.1, 128.4, 128.3, 127.98, 127.91, 127.8, 127.78, 127.72, 127.67, 127.64, 101.4, 84.6, 82.0, 79.0, 77.6, 75.7, 75.0, 74.9, 74.9, 74.8, 73.5, 68.8, 56.0.

cis-3-Nonene-2,3,4,6-tetra-O-benzyl-β-d-glucopyranoside (4g)

Prepared by the General Procedure using 2,3,4,6-tetra-O-benzyl-α-d-glucopyranosyl chloride (0.15 mmol, 84 mg) and cis-3-nonen-1-ol (0.18 mmol, 31 μL). Column chromatography purification using ­EtOAc/hexane (2:8) gave 4g as a white solid (β-anomer only, 66 mg, 67%).

Mp 93–95 °C; [α] _d ²² +2.42 (c = 0.019, CHCl₃).

¹H NMR (500 MHz, CDCl₃): δ = 7.32–7.14 (m, 18 H), 7.13–7.03 (m, 2 H), 5.44–5.29 (m, 2 H), 4.87 (dd, J = 16.0, 10.9 Hz, 2 H), 4.72 (dd, J = 16.3, 10.9 Hz, 2 H), 4.63 (d, J = 11.0 Hz, 1 H), 4.57–4.41 (m, 3 H), 4.32 (t, J = 7.6 Hz, 1 H), 3.90 (ddd, J = 9.3, 7.4, 6.2 Hz, 1 H), 3.67 (dd, J = 10.8, 1.9 Hz, 1 H), 3.63–3.58 (m, 1 H), 3.57–3.48 (m, 2 H), 3.47–3.43 (m, 1 H), 3.39–3.36 (m, 2 H), 2.35 (dt, J = 14.8, 7.4 Hz, 1 H), 1.97 (q, J = 7.0 Hz, 1 H), 1.29–1.24 (m, 2 H), 1.23–1.19 (m, 4 H), 0.80 (t, J = 7.0 Hz, 3 H).

¹³C NMR (125 MHz, CDCl₃): δ = 138.6, 138.5, 138.2, 138.1, 132.30, 128.39, 128.2, 128.0, 127.9, 127.8, 127.69, 127.63, 125.3, 103.7, 84.7, 82.3, 77.9, 75.7, 75.0, 74.9, 74.8, 73.5, 69.8, 69.0, 31.5, 29.3, 28.0, 27.4, 22.6, 14.1.

HRMS (ESI-TOF): m/z [M + NH₄]⁺ calcd. for C₄₃H₅₆NO₆: 682.4108; found: 682.4113.

Cyclopropylmethane-2,3,4,6-tetra-O-benzyl-β-d-glucopyranoside (4j)

Prepared by the General Procedure using 2,3,4,6-tetra-O-benzyl-α-d-glucopyranosyl chloride (0.15 mmol, 84 mg) and cyclopropylmethanol (0.18 mmol, 15 μL).[19] Column chromatography purification using EtOAc/hexane (2:8) gave 4j as a white solid (β-anomer only, 57 mg, 64%).

¹H NMR (500 MHz, CDCl₃): δ = 7.37–7.16 (m, 18 H), 7.08 (dd, J = 7.3, 1.8 Hz, 1 H), 4.93 (d, J = 10.9 Hz, 1 H), 4.86 (d, J = 10.9 Hz, 1 H), 4.78–4.62 (m, 3 H), 4.53 (d, J = 12.2 Hz, 1 H), 4.46 (dd, J = 11.5, 7.1 Hz,2 H), 4.37 (d, J = 7.8 Hz, 1 H), 3.71 (dd, J = 10.4, 6.8 Hz, 1 H), 3.66 (dd, J = 10.7, 1.7 Hz, 1 H), 3.59 (dd, J = 10.6, 5.2 Hz, 1 H), 3.56 (d, J = 9.0 Hz, 1 H), 3.49 (t, J = 9.3 Hz, 1 H), 3.42–3.36 (m, 2 H), 3.35–3.31 (m, 2 H), 1.11–1.00 (m, 1 H), 0.52–0.41 (m, 2 H), 0.19 (dd, J = 4.8, 0.7 Hz, 2 H).

¹³C NMR (125 MHz, CDCl₃): δ = 138.7, 138.6, 138.29, 138.20, 128.4, 128.3, 128.0, 127.9, 127.8, 127.7, 127.6, 103.3, 84.8, 82.3, 78.0, 75.7, 75.0, 74.9, 74.8, 74.6, 73.5, 69.1, 10.6, 3.4, 3.0.

3-Methylbutane-2,3,4,6-tetra-O-benzyl-β-d- glucopyranoside (4h)

Prepared by the general procedure using 2,3,4,6-tetra-O-benzyl-α-d-glucopyranosyl chloride (0.15 mmol, 84 mg) and 3-methylbutanol (0.18 mmol, 20 μL). Column chromatography purification using ­EtOAc/hexane (2:8) gave 4h as a yellow viscous liquid (β-anomer only, 64 mg, 70%).

[α] _d ²² +4.65 (c = 0.016, CHCl₃).

¹H NMR (400 MHz, CDCl₃): δ = 7.44–7.23 (m, 18 H), 7.16 (dd, J = 7.1, 2.2 Hz, 2 H), 4.98–4.91 (m, 2 H), 4.80 (dd, J = 12.8, 11.0 Hz, 2 H), 4.71 (d, J = 10.9 Hz, 1 H), 4.67–4.50 (m, 3 H), 4.38 (d, J = 7.8 Hz, 1 H), 3.88 (dd, J = 9.3, 5.6 Hz, 1 H), 3.75 (dd, J = 10.8, 1.8 Hz, 1 H), 3.70–3.61 (m, 2 H), 3.57 (t, J = 9.2 Hz, 1 H), 3.50–3.41 (m, 2 H), 3.29 (dd, J = 9.3, 7.2 Hz, 1 H), 1.73 (dd, J = 13.0, 6.4 Hz, 1 H), 1.48 (ddd, J = 13.3, 7.4, 5.7 Hz, 1 H), 1.24–1.16 (m, 1 H), 0.98 (d, J = 6.7 Hz, 3 H), 0.91 (t, J = 7.5 Hz, 3 H).

¹³C NMR (100 MHz, CDCl₃): δ = 138.7, 138.5, 138.2, 138.1, 128.3, 128.2, 128.0, 127.8, 127.7, 127.6, 127.6, 103.8, 84.8, 82.3, 78.0, 75.7, 75.1, 75.0, 74.9, 73.4, 69.0, 35.1, 29.7, 26.2, 16.9, 11.0.

HRMS (ESI-TOF): m/z [M + NH₄]⁺ calcd. for C₃₉H₅₀NO₆: 628.3638; found: 628.3642.

Cinnamyl-2,3,4,6-tetra-O-benzyl-β-d-glucopyranoside (4i)

Prepared by the General Procedure using 2,3,4,6-tetra-O-benzyl-α-d-glucopyranosyl chloride (0.15 mmol, 84 mg) and cinnamyl alcohol (0.18 mmol, 24 μL). Column chromatography purification using EtOAc­/hexane (2:8) gave 4i as a white solid (β-anomer only, 66 mg, 67%).

Mp 92–94 °C; [α] _d ²² +0.869 (c = 0.023, CHCl₃).

¹H NMR (400 MHz, CDCl₃): δ = 7.31–7.12 (m, 23 H), 7.11–7.03 (m, 2 H), 6.57 (d, J = 15.9 Hz, 1 H), 6.23 (dt, J = 15.9, 6.0 Hz, 1 H), 4.93–4.84 (m, 2 H), 4.78–4.64 (m, 3 H), 4.56–4.48 (m, 3 H), 4.47–4.42 (m, 2 H), 4.25 (ddd, J = 12.9, 6.4, 1.2 Hz, 1 H), 3.68 (dd, J = 10.7, 1.8 Hz, 1 H), 3.64–3.60 (m, 1 H), 3.60–3.56 (m, 1 H), 3.53–3.50 (m, 1 H), 3.46–3.38 (m, 2 H).

¹³C NMR (100 MHz, CDCl₃): δ = 138.6, 138.5, 138.2, 138.1, 136.6, 132.7, 128.6, 128.4, 128.1, 128.0, 127.9, 127.8, 127.6, 126.6, 125.4, 102.7, 84.8, 82.4, 77.9, 75.7, 75.0, 74.9, 73.5, 70.0, 69.0.

HRMS (ESI-TOF): m/z [M + Na]⁺ calcd. for C₄₃H₄₄NaO₆: 679.3036; found: 679.3037.

2-(Trimethylsilyl)ethane-2,3,4,6-tetra-O-benzyl-β-d-glucopyranoside (4l)

Prepared by the General Procedure using 2,3,4,6-tetra-O-benzyl-α-d-glucopyranosyl chloride (0.15 mmol, 84 mg) and 2-(trimethylsilyl)ethanol (0.18 mmol, 26 μL). Column chromatography purification using EtOAc/hexane (2:8) gave 4l as a white solid (β only, 57 mg, 60%).

Mp 102–104 °C; [α] _d ²² +9.198 (c = 0.014, CHCl₃).

¹H NMR (500 MHz, CDCl₃): δ = 7.35–7.20 (m, 18 H), 7.13 (d, J = 7.0 Hz, 2 H), 4.94–4.88 (m, 2 H), 4.80–4.74 (m, 2 H), 4.70 (d, J = 11.0 Hz, 1 H), 4.59–4.49 (m, 3 H), 4.37 (dd, J = 7.8, 1.0 Hz, 1 H), 4.04–3.98 (m, 1 H), 3.72 (d, J = 10.7 Hz, 1 H), 3.68–3.50 (m, 4 H), 3.45–3.39 (m, 2 H), 1.10–0.95 (m, 2 H), 0.00 (s, 9 H).

¹³C NMR (100 MHz, CDCl₃): δ = 140.06, 140.03, 139.6, 139.5, 129.7, 129.5, 129.3, 129.2, 129.1, 128.9, 104.5, 86.1, 83.8, 79.4, 77.0, 76.4, 76.2, 76.2, 74.8, 70.4, 68.8, 19.9, 0.02.

HRMS (ESI-TOF): m/z [M + Na]⁺ calcd. for C₃₉H₄₈NaSiO₆: 663.3118; found: 663.3186.

1,3,3-Trimethyl-2-norbornane-2,3,4,6-tetra-O-benzyl-β-d-glucopyranoside (4n)

Prepared by the General Procedure using 2,3,4,6-tetra-O-benzyl-α-d-glucopyranosyl chloride (0.15 mmol, 84 mg) and fenchol (0.18 mmol, 30 μL). Column chromatography purification using EtOAc/hexane (2:8) gave 4n as a yellow viscous liquid (β-anomer only, 61 mg, 60%).

[α] _d ²² +92.685 (c = 0.0175, CHCl₃).

¹H NMR (400 MHz, CDCl₃): δ = 7.31–7.16 (m, 18 H), 7.16–7.02 (m, 2 H), 4.97 (d, J = 10.8 Hz, 1 H), 4.87 (d, J = 11.0 Hz, 1 H), 4.73 (dd, J = 10.9, 8.3 Hz, 2 H), 4.66 (d, J = 10.8 Hz, 1 H), 4.52 (dd, J = 12.2, 6.1 Hz, 3 H), 4.22 (d, J = 7.7 Hz, 1 H), 3.62 (d, J = 2.6 Hz, 2 H), 3.58–3.50 (m, 2 H), 3.43–3.29 (m, 2 H), 3.08 (d, J = 1.5 Hz, 1 H), 1.80–1.58 (m, 4 H), 1.36 (dd, J = 12.9, 8.7 Hz, 2 H), 1.04 (s, 3 H), 1.02–0.98 (m, 1 H), 0.96 (s, 3 H), 0.85 (s, 3 H).

¹³C NMR (125 MHz, CDCl₃): δ = 138.8, 138.5, 138.3, 138.2, 128.4, 128.3, 128.1, 127.7, 127.69, 127.64, 127.5, 127.4, 105.0, 93.7, 84.8, 82.5, 78.0, 75.6, 75.0, 74.5, 73.6, 69.3, 49.2, 48.0, 41.1, 39.1, 29.7, 29.6, 26.3, 26.2, 21.7, 19.7.

HRMS (ESI-TOF): m/z [M + Na]⁺ calcd. for C₄₄H₅₂NaO₆: 699.3662; found: 699.3666.

Citronellyl-2,3,4,6-tetra-O-benzyl-β-d-glucopyranoside (4p)

Prepared by the General Procedure using 2,3,4,6-tetra-O-benzyl-α-d-glucopyranosyl chloride (0.15 mmol, 84 mg) and citronellol (0.18 mmol, 34 μL). Column chromatography purification using EtOAc/hexane (2:8) gave 4p as a white solid (β-anomer only, 63 mg, 62%).

Mp 110–112 °C; [α] _d ²² +1.25 (c = 0.008, CHCl₃).

¹H NMR (400 MHz, CDCl₃): δ = 7.35–7.15 (m, 18 H), 7.08 (dd, J = 7.1, 2.2 Hz, 2 H), 5.01 (t, J = 7.1 Hz, 1 H), 4.86 (dd, J = 10.9, 7.4 Hz, 2 H), 4.72 (dd, J = 13.1, 11.0 Hz, 2 H), 4.64 (d, J = 11.0 Hz, 1 H), 4.59–4.41 (m, 3 H), 4.31 (d, J = 7.8 Hz, 1 H), 3.95 (ddd, J = 9.2, 7.7, 5.4 Hz, 1 H), 3.67 (dd, J = 10.7, 1.7 Hz, 1 H), 3.63–3.54 (m, 2 H), 3.50–3.45 (m, 2 H), 3.40–3.35 (m, 2 H), 1.91 (m, 2 H), 1.75–1.61 (m, 2 H), 1.58 (s, 3 H), 1.51 (s, 3 H), 1.37–1.35 (m, 3 H), 1.18 (s, 3 H), 1.16–1.05 (m, 1 H), 0.83 (d, J = 6.6 Hz, 3 H).

¹³C NMR (100 MHz, CDCl₃): δ = 138.6, 138.5, 138.2, 138.1, 131.2, 128.3, 128.1, 128.0, 127.9, 127.8, 127.6, 127.6, 124.8, 103.7, 84.7, 82.3, 78.0, 75.7, 75.0, 74.9, 74.8, 73.5, 69.0, 68.3, 37.3, 36.7, 29.7, 29.4, 25.7, 25.5, 19.3, 17.7.

HRMS (ESI-TOF): m/z [M + Na]⁺ calcd. for C₄₄H₅₄NaO₆: 701.3818; found: 701.3827.

Allyl-2,3,4,6-tetra-O-benzyl-β-d-glucopyranoside (4s)

To a stirred solution of glycosyl chloride 1a (1.68 g, 3 mmol) in anhydrous CH₂Cl₂ (15 mL) was added allyl alcohol (244 μL, 3.6 mmol) and Zn(OAc)₂ (328 mg, 1.5 mmol) at room temperature, and the resulting solution was stirred at room temperature for 7 h. The reaction mixture was evaporated under reduced pressure, and the residue was purified using silica gel column chromatography (EtOAc/hexane, 2:8) to obtained the desired product 4s as a white solid (β-anomer only, 1.04 g, 60%).

¹H NMR (500 MHz, CDCl₃): δ = 7.29–7.17 (m, 18 H), 7.11–7.04 (m, 2 H), 5.89 (ddd, J = 15.8, 10.8, 5.5 Hz, 1 H), 5.27 (dd, J = 17.2, 1.5 Hz, 1 H), 5.12 (d, J = 10.4 Hz, 1 H), 4.87 (dd, J = 17.4, 10.9 Hz, 2 H), 4.72 (dd, J = 15.3, 10.9 Hz, 2 H), 4.65 (d, J = 10.9 Hz, 1 H), 4.54 (d, J = 12.2 Hz, 1 H), 4.51–4.42 (m, 2 H), 4.41–4.32 (m, 2 H), 4.07 (ddd, J = 13.0, 5.9, 1.2 Hz, 1 H), 3.67 (dd, J = 10.8, 1.6 Hz, 1 H), 3.64–3.47 (m, 3 H), 3.39 (ddd, J = 10.8, 6.5, 5.2 Hz, 2 H).

Cholesterol-2,3,4,6-tetra-O-Benzyl-α/β-d-mannopyranoside (6a)

Prepared by the General Procedure using 2,3,4,6-tetra-O-benzyl-α-d-mannopyranosyl chloride (0.15 mmol, 84 mg) and cholesterol (0.18 mmol, 70 mg). Column chromatography purification using EtOAc/ hexane (2:8) gave 6a as a yellow viscous liquid (α-/β-anomers = 2:1, 84 mg, 62%).

¹H NMR (400 MHz, CDCl₃): δ = 7.39–7.23 (m, 18 H), 7.22–7.12 (m, 2 H), 5.34–5.26 (m, 1 H), 5.01–4.98 (m, 1 H), 4.94–4.85 (m, 1 H), 4.78–4.72 (m, 1 H), 4.69–4.62 (m, 2 H), 4.60–4.56 (m, 1 H), 4.57–4.47 (m, 2 H), 4.04–3.90 (m, 1 H), 3.90–3.77 (m, 2 H), 3.77–3.67 (m, 1 H), 3.55–3.42 (m, 1 H), 2.32–2.25 (m, 2 H), 2.13–1.88 (m,2 H), 1.85–1.78 (m, 2 H), 1.65–1.44 (m, 6 H), 1.42–1.23 (m, 6 H), 1.21–1.05 (m, 6 H), 1.05–0.96 (m, 6 H), 0.92 (dd, J = 6.5, 2.7 Hz, 1 H), 0.87 (d, J = 1.7 Hz, 3 H), 0.86 (d, J = 1.7 Hz, 3 H), 0.68 (d, J = 5.6 Hz, 3 H).

¹³C NMR (100 MHz, CDCl₃): δ = 140.7, 140.6, 138.9, 130.7, 138.5, 138.2, 128.5, 128.3, 128.2, 128.1, 128.0, 127.86, 127.82, 127.6, 127.5, 127.4, 127.3, 121.8, 99.7, 95.8, 82.5, 80.4, 78.7, 77.2, 76.5, 75.9, 75.2, 75.0, 74.1, 73.8, 73.4, 73.3, 72.6, 72.1, 71.7, 71.4, 69.9, 69.4, 56.8, 56.2, 50.2, 50.1, 42.3, 39.9, 39.8, 39.5, 39.0, 37.3, 37.0, 36.8, 36.7, 36.2, 35.8, 31.9, 29.8, 29.7, 28.3, 28.0, 27.6, 24.3, 23.8, 22.8, 22.6, 21.1, 19.5, 19.4, 18.7, 11.9.

HRMS (ESI-TOF): m/z [M + Na]⁺ calcd. for C₆₁H₈₀NaO₆: 931.5853; found: 931.6009.

n-Hexyl-2,3,4,6-tetra-O-benzyl-α/β-d-mannopyranoside (6b)

Prepared by the General Procedure using 2,3,4,6-tetra-O-benzyl-α-d-mannopyranosyl chloride (0.15 mmol, 84 mg) and n-hexanol (0.18 mmol, 23 μL). Column chromatography purification using EtOAc/hexane (2:8) gave 6b as a yellow viscous liquid (α-,β-anomers = 1:1, 65 mg, 70%).

¹H NMR (400 MHz, CDCl₃): δ = 7.47 (dd, J = 7.7, 1.6 Hz, 2 H), 7.39–7.23 (m, 34 H), 7.19–7.15 (m, 4 H), 4.99 (d, J = 12.5 Hz, 1 H), 4.92–4.85 (m, 4 H), 4.73 (d, J = 5.2 Hz, 2 H), 4.66 (d, J = 12.2 Hz, 1 H), 4.64–4.59 (m, 3 H), 4.58–4.48 (m, 4 H), 4.43 (d, J = 11.8 Hz, 1 H), 4.37 (s, 1 H), 4.02–3.94 (m, 2 H), 3.90 (dt, J = 4.8, 2.4 Hz, 2 H), 3.86–3.83 (m, 1 H), 3.82–3.69 (m, 6 H), 3.68–3.62 (m, 1 H), 3.50 (dd, J = 9.4, 3.0 Hz, 1 H), 3.46–3.42 (m, 2 H), 3.38–3.32 (m, 2 H), 1.68–1.57 (m, 4 H), 1.53–1.44 (m, 3 H), 1.36–1.22 (m, 16 H), 0.89 (m, 8 H).

¹³C NMR (100 MHz, CDCl₃): δ = 138.8, 138.6, 138.5, 138.49, 138.40, 138.2, 128.4, 128.3, 128.1, 127.89, 127.85, 127.80, 127.68, 127.61, 127.5, 127.49, 127.41, 101.7, 97.87, 82.4, 80.3, 75.9, 75.2, 75.09, 75.05, 74.9, 73.7, 73.6, 73.5, 73.3, 72.6, 72.2, 71.8, 71.4, 70.1, 69.8, 69.3, 67.7, 31.7, 31.6, 29.7, 29.4, 25.9, 25.8, 2 2.69, 22.62, 14.1.

HRMS (ESI-TOF): m/z [M + Na]⁺ calcd. for C₄₀H₄₈NaO₆: 647.3349; found: 647.3396.

n-Decyl-2,3,4,6-tetra-O-benzyl-α/β-d-mannopyranoside (6c)

Prepared by the General Procedure using 2,3,4,6-tetra-O-benzyl-α-d-mannopyranosyl chloride (0.15 mmol, 84 mg) and n-decanol (0.18 mmol, 36 μL). Column chromatography purification using EtOAc/­Hexane (2:8) gave 6c as a yellow viscous liquid (α-/β-anomers 3:1, 71 mg, 70%).

¹H NMR (500 MHz, CDCl₃): δ = 7.46 (t, J = 9.2 Hz, 1 H), 7.39–7.21 (m, 22 H), 7.17–7.15 (m, 2 H), 4.95–4.84 (m, 2 H), 4.73 (q, J = 12.5 Hz, 2 H), 4.68–4.59 (m, 3 H), 4.57–4.48 (m, 2 H), 4.47–4.34 (m, 1 H), 4.01–3.88 (m, 2 H), 3.83–3.70 (m, 4 H), 3.67–3.62 (m, 1 H), 3.51–3.48 (m, 1 H), 3.37–3.33 (m, 1 H), 1.64–1.50 (m, 3 H), 1.25 (bs, 19 H), 0.88 (t, J = 6.7 Hz, 4 H).

¹³C NMR (100 MHz, CDCl₃): δ = 138.6, 138.5, 138.4, 128.4, 128.3, 128.0, 127.9, 127.85, 127.81, 127.68, 127.61, 127.4, 10, 101.7, 97.8, 82.4, 80.4, 76.0, 75.2, 75.0, 74.9, 73.7, 73.6, 73.5, 73.3, 72.6, 72.2, 71.8, 71.4, 70.1, 69.8, 69.3, 67.7, 31.9, 29.6, 29.49, 29.41, 26.2, 22.7, 14.2.

HRMS (ESI-TOF): m/z [M + Na]⁺ calcd. for C₄₄H₆₀NO₆: 698.4421; found: 698.4411.

n-Decyl-2,3:5,6-di-O-isopropylidene-α/β-d-mannofuranoside (7b)

Prepared by the General Procedure using 2,3:5,6-di-O-isopropylidene-α-d-mannofuranosyl chloride (0.15 mmol, 42 mg) and n-decanol (0.18 mmol, 36 μL). Column chromatography purification using EtOAc/hexane (2:8) gave 7b as a yellow viscous liquid (α/β = 3:1, 45 mg, 75%).

¹H NMR (400 MHz, CDCl₃): δ = 4.90 (s, 1 H), 4.71 (dd, J = 5.9, 3.6 Hz, 1 H), 4.51 (d, J = 5.9 Hz, 1 H), 4.33 (ddd, J = 7.8, 6.3, 4.4 Hz, 1 H), 4.04 (dd, J = 8.7, 6.3 Hz, 1 H), 3.96 (dd, J = 8.7, 4.4 Hz, 1 H), 3.85 (dd, J = 7.8, 3.6 Hz, 1 H), 3.54 (dt, J = 9.7, 6.7 Hz, 1 H), 3.30 (dt, J = 9.7, 6.6 Hz, 1 H), 1.49–1.45 (m, 2 H), 1.40 (s, 3 H), 1.38 (s, 3 H), 1.31 (s, 3 H), 1.25 (s, 3 H), 1.19 (s, 14 H), 0.81 (t, J = 6.9 Hz, 3 H).

¹³C NMR (125 MHz, CDCl₃): δ = 112.6, 112.5, 109.2, 106.2, 106.0, 85.1, 84.8, 80.2, 79.5, 79.2, 73.2, 70.5, 67.5, 67.0, 64.6, 31.9, 30.9, 29.6, 29.5, 29.4, 29.3, 26.9, 26.1, 25.9, 25.2, 24.5, 22.7, 14.1.

HRMS (ESI-TOF): m/z [M + Na]⁺ calcd. for C₂₂H₄₀NaO₆: 423.2723; found: 423.2681.

cis-3-Nonene-2,3:5,6-di-O-isopropylidene-α/β-d-mannofuranoside (7c)

Prepared by the General Procedure using 2,3:5,6-di-O-isopropylidene-α-d-mannofuranosyl chloride (0.15 mmol, 42 mg) and cis-3-nonen-1-ol (0.18 mmol, 31 μL). Column chromatography purification using EtOAc/hexane (2:8) gave 7c as a yellow viscous liquid (α/β = 2:1, 39 mg, 68%).

¹H NMR (400 MHz, CDCl₃): δ = 5.47–5.32 (m, 1 H), 5.31–5.21 (m, 1 H), 4.92 (s, 1 H), 4.70 (dd, J = 5.9, 3.6 Hz, 1 H), 4.51 (d, J = 5.9 Hz, 1 H), 4.33 (ddd, J = 7.7, 6.3, 4.4 Hz, 1 H), 4.04 (dd, J = 8.7, 6.3 Hz, 1 H), 3.96 (dd, J = 8.7, 4.4 Hz, 1 H), 3.86 (dd, J = 7.8, 3.6 Hz, 1 H), 3.54 (dt, J = 9.6, 7.0 Hz, 1 H), 3.33 (dt, J = 9.6, 6.9 Hz, 1 H), 2.23 (q, J = 7.0 Hz, 2 H), 2.00–1.90 (m, 2 H), 1.40 (s, 3 H), 1.39 (s, 3 H), 1.31 (s, 3 H), 1.26 (s, 3 H), 1.24–1.15 (m, 3 H), 0.82 (t, J = 6.9 Hz, 3 H).

¹³C NMR (100 MHz, CDCl₃): δ = 132.4, 125.1, 112.7, 112.5, 109.2, 106.2, 105.9, 85.1, 84.8, 80.2, 80.1, 79.5, 79.2, 73.1, 70.6, 67.0, 64.6, 31.5, 30.9, 29.7, 29.3, 27.6, 27.3, 26.9, 25.95, 25.92, 25.2, 24.6, 24.5, 22.5, 14.0.

HRMS (ESI-TOF): m/z [M + Na]⁺ calcd. for C₂₁H₃₆NaO₆: 407.2410; found: 407.2363.

3-Azido-1-propane-2,3:5,6-di-O-isopropylidene-α/β-d-mannofuranoside (7d)

Prepared by the General Procedure using 2,3:5,6-di-O-isopropylidene-α-d-mannofuranosyl chloride (0.15 mmol, 42 mg) and 3-­azido-1-propanol (0.18 mmol, 17 μL). Column chromatography purification using EtOAc/hexane (2:8) gave 7d as a yellow viscous liquid (α/β = 2:1, 33 mg, 65%).

¹H NMR (400 MHz, CDCl₃): δ = 4.91 (s, 1 H), 4.71 (dd, J = 5.9, 3.6 Hz, 1 H), 4.52 (d, J = 5.9 Hz, 1 H), 4.33 (ddd, J = 7.6, 6.3, 4.5 Hz, 1 H), 4.05 (dd, J = 8.7, 6.3 Hz, 1 H), 3.97 (dd, J = 8.7, 4.5 Hz, 1 H), 3.85 (dd, J = 7.6, 3.6 Hz, 1 H), 3.65 (dt, J = 10.1, 5.9 Hz, 1 H), 3.40 (dt, J = 10.0, 6.1 Hz, 1 H), 3.30 (t, J = 6.7 Hz, 2 H), 1.76 (p, J = 6.5 Hz, 2 H), 1.40 (s, 3 H), 1.39 (s, 3 H), 1.31 (s, 3 H), 1.26 (s, 3 H).

¹³C NMR (100 MHz, CDCl₃): δ = 112.7, 112.6, 109.2, 106.4, 106.1, 85.0, 84.8, 80.4, 80.1, 79.5, 79.2, 73.1, 70.3, 66.9, 64.3, 64.0, 63.9, 48.4, 48.3, 30.9, 29.7, 28.8, 26.9, 25.97, 25.92, 25.2, 24.6, 24.5.

HRMS (ESI-TOF): m/z [M + Na]⁺ calcd. for C₁₅H₂₅N₃NaO₆: 366.1641; found: 366.1590.

Phenylethane-2,3:5,6-di-O-isopropylidene-α/β-d-mannofuranoside (7e)

Prepared by the General Procedure using 2,3:5,6-di-O-isopropylidene-α-d-mannofuranosyl chloride (0.15 mmol, 42 mg) and phenylethanol (0.18 mmol, 22 μL). Column chromatography purification using EtOAc/hexane (2:8) gave 7e as a yellow viscous liquid (α/β = 2:1, 32 mg, 60%).

¹H NMR (400 MHz, CDCl₃): δ = 7.25–7.20 (m, 2 H), 7.14 (dd, J = 9.9, 4.5 Hz, 3 H), 4.92 (d, J = 7.0 Hz, 1 H), 4.67 (dd, J = 5.9, 3.6 Hz, 1 H), 4.50 (d, J = 5.9 Hz, 1 H), 4.30 (ddd, J = 7.8, 6.3, 4.5 Hz, 1 H), 4.02 (dd, J = 8.6, 6.3 Hz, 1 H), 3.89 (dd, J = 8.7, 4.5 Hz, 1 H), 3.82–3.67 (m, 2 H), 3.56 (dt, J = 9.8, 6.9 Hz, 1 H), 2.79 (t, J = 6.9 Hz, 2 H), 1.39 (s, 3 H), 1.37 (s, 3 H), 1.31 (s, 3 H), 1.24 (s, 3 H).

¹³C NMR (125 MHz, CDCl₃): δ = 138.7, 138.6, 128.8, 128.8, 128.4, 126.3, 112.6, 112.5, 109.2, 106.2, 105.8, 85.0, 84.8, 80.3, 80.1, 79.5, 79.1, 73.1, 70.5, 68.0, 67.9, 67.0, 64.5, 35.9, 30.9, 26.9, 25.9, 25.2, 24.6, 24.5.

HRMS (ESI-TOF): m/z [M + Na]⁺ calcd. for C₂₀H₂₈NaO₆: 387.1784; found: 387.1725.

Cholesterol-2,3:5,6-di-O-isopropylidene-α/β-d-mannofuranoside (7f)

Prepared by the General Procedure using 2,3:5,6-di-O-isopropylidene-α-d-mannofuranosyl chloride (0.15 mmol, 42 mg) and cholesterol (0.18 mmol, 70 mg). Column chromatography purification using EtOAc/hexane (2:8) gave 7f as a yellow viscous liquid (α/β = 1:1, 63 mg, 67%).

¹H NMR (500 MHz, CDCl₃): δ = 5.27 (d, J = 5.1 Hz, 1 H), 5.07 (s, 1 H), 4.72 (dd, J = 5.8, 3.6 Hz, 1 H), 4.50 (d, J = 5.9 Hz, 1 H), 4.36–4.29 (m, 1 H), 4.04 (dd, J = 8.6, 6.4 Hz, 1 H), 3.96 (dd, J = 8.7, 4.5 Hz, 1 H), 3.91 (dd, J = 7.7, 3.5 Hz, 1 H), 3.41–3.30 (m, 1 H), 2.30–2.13 (m, 2 H), 1.97–1.85 (m, 2 H), 1.85–1.68 (m, 3 H), 1.52–1.35 (m, 12 H), 1.33–1.28 (m, 3 H), 1.30–1.20 (m, 6 H), 1.21–1.13 (m, 2 H), 1.11–0.96 (m,7 H), 0.92 (s, 6 H), 0.84 (t, J = 7.5 Hz, 3 H), 0.80 (d, J = 2.2 Hz, 3 H), 0.79 (d, J = 2.2 Hz, 3 H), 0.60 (s, 3 H).

¹³C NMR (100 MHz, CDCl₃): δ = 140.5, 121.9, 112.6, 112.4, 109.2, 104.9, 104.3, 85.4, 85.1, 80.2, 79.6, 79.2, 73.2, 70.5, 67.0, 64.6, 56.7, 56.1, 50.1, 42.3, 40.1, 39.7, 39.5, 37.0, 36.7, 36.2, 35.8, 31.9, 30.9, 28.2, 28.0, 27.9, 27.8, 26.9, 25.96, 25.91, 25.2, 24.6, 24.5, 24.3, 23.8, 22.8, 22.5, 21.0, 19.3, 18.7, 11.8.

HRMS (ESI-TOF): m/z [M + Na]⁺ calcd. for C₃₉H₆₄NaO₆: 651.4601; found: 651.4593.

Conflict of Interest

The authors declare no conflict of interest.

Acknowledgment

The authors are grateful to the Director of CSIR-IICT for providing necessary infrastructure.

• References and Notes

• 1a Crich D. Acc. Chem. Res. 2010; 43: 1144
• 1b Seeberger PH. Acc. Chem. Res. 2015; 48: 1450
• 1c Galonic DP, Gin DY. Nature 2007; 446: 1000
• 1d Zhu X, Schmidt RR. Angew. Chem. Int. Ed. 2009; 48: 1900
• 2a Pornsuriyasak P, Demchenko AV. Angew. Chem. Int. Ed. 2005; 44: 7123
• 2b Nukada T, Berces A, Zgierski MZ, Whitfield DM. J. Am. Chem. Soc. 1998; 120: 13291
• 2c Singh GP, Watson AJ. A, Fairbanks AJ. Org. Lett. 2015; 17: 4376
• 2d Speciale G, Farren-Dai M, Shidmoossavee FS, Williams SJ, Bennet AJ. J. Am. Chem. Soc. 2016; 138: 14012
• 2e Elferink H, Mensink RA, White PB, Boltje TJ. Angew. Chem. Int. Ed. 2016; 55: 11217
• 3a Nukada T, Berces A, Zgierski MZ, Whitfield DM. J. Am. Chem. Soc. 1998; 120: 13291
• 3b Jensen KJ. J. Chem. Soc., Perkin Trans. 1 2002; 2219
• 3c Boltje TJ, Buskas T, Boons G.-J. Nat. Chem. 2009; 1: 611
• 4 Aiguabella N, Holland MC, Gilmour R. Org. Biomol. Chem. 2016; 14: 5534
• 5 Karak M, Joh Y, Suenaga M, Oishi T, Torikai K. Org. Lett. 2019; 21: 1221
• 6a Helferich B, Zirner J. Chem. Ber. 1962; 95: 2604
• 6b Bock K, Meldal M. Acta Chem. Scand., Ser. B 1983; 37: 775
• 6c Conrow RB, Bernstein S. J. Org. Chem. 1971; 36: 863
• 6d Ogawa T, Matsui M. Carbohydr. Res. 1976; 51: C13
• 6e Mukherjee D, Ray PK, Chowdhury US. Tetrahedron 2001; 57: 7701
• 6f Li C, Liang H, Zhang ZX, Wang Z, Yu L, Liu H, An F, Wang S, Ma L, Xue W. Tetrahedron 2018; 74: 3963
• 6g Igarashi K, Honma T, Irisawa J. Carbohydr. Res. 1970; 15: 329
• 6h Hanessian S, Banoub J. Carbohydr. Res. 1977; 53: C13
• 6i Verlhac P, Leteux C, Toupet L, Veyrieres A. Carbohydr. Res. 1996; 291: 11
• 6j Kaeothip S, Pornsuriyasak P, Demchenko AV. Tetrahedron Lett. 2008; 49: 1542
• 7 Yao H, DuyVu M, Liu X.-W. Carbohydr. Res. 2019; 473: 72
• 8a Igarashi K, Honma T, Irisawa J. Carbohydr. Res. 1970; 15: 329
• 8b Matsuoka K, Terabatake M, Umino A, Esumi Y, Hatano K, Terunuma D, Kuzuhara H. Biomacromolecules 2006; 7: 2274
• 9a Geringer SA, Demchenko AV. Org. Biomol. Chem. 2018; 16: 9133
• 9b Park Y, Harper KC, Kuhl N, Kwan EE, Liu RY, Jacobsen EN. Science 2017; 355: 162
• 10 Kulkarni SS, Gervay-Hague J. Org. Lett. 2008; 10: 4739
• 11 Adam Chu A.-H, Minciunescu A, Bennett CS. Org. Lett. 2015; 17: 6262
• 12a Tatina MB, Khong DT, Judeh ZM. A. Eur. J. Org. Chem. 2018; 2208
• 12b Boettcher S, Matwiejuk M, Thiem J. Beilstein J. Org. Chem. 2012; 8: 413
• 13 Bracinni I, Derouet C, Esnault J, Penhoat CH, Mallet JM, Michon V, Sinay P. Carbohydr. Res. 1993; 246: 23
• 14 Wulff G, Rohle G. Angew. Chem., Int. Ed. Engl. 1974; 13: 157
• 15a Suna G, Wua Y, Liua A, Qiua S, Zhanga W, Wangb Z, Zhang J. Synlett 2018; 29: 668
• 15b Dong X, Chen L, Zheng Z, Ma X, Luo Z, Zhang L. Chem. Commun. 2018; 54: 8626
• 16a Thorat BR, Gurav A, Dalvi B, Sawant A, Lokhande V, Mali SN. Curr. Chin. Chem. 2021; 1: 30
• 16b Cai F, Wu B, Crich D. Adv. Carbohydr. Chem. Biochem. 2009; 62: 251
• 16c Crich D, Sun SX. Tetrahedron 1998; 54: 8321
• 16d Crich D, Sun SX. J. Am. Chem. Soc. 1997; 119: 11217
• 17 Guo H, Si W, Li J, Yang G, Tang T, Wang Z, Tang J, Zhang J. Synthesis 2019; 51: 2984
• 18 Geng Y, Kumar A, Faidallah HM, Albar HA, Mhkalid IA, Schmidt RR. Angew. Chem. Int. Ed. 2013; 52: 10089
• 19 Dubey A, Sangwan R, Mandal PK. Catal. Commun. 2019; 125: 123
• 20 Guo H, Sia W, Li J, Yang G, Tang T, Wang Z, Tang J, Zhang J. Synthesis 2019; 51: 2984

Publikationsverlauf

Eingereicht: 11. August 2022

Angenommen nach Revision: 07. September 2022

Accepted Manuscript online:
12. September 2022

Artikel online veröffentlicht:
12. Oktober 2022