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CC BY-NC-ND 4.0 · Synlett 2022; 33(01): 45-47
DOI: 10.1055/a-1695-4516
DOI: 10.1055/a-1695-4516
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A Chiral Sulfoxide-Based C–H Acid
Authors
Generous support by the European Research Council (Advanced Grant ‘C–H Acids for Organic Synthesis, CHAOS’) and the Deutsche Forschungsgemeinschaft (Leibniz Award to B.L. and Cluster of Excellence RESOLV, EXC 1069) is gratefully acknowledged. Work at Tartu was supported by the Estonian Research Council grant (PRG690), and by the EU through the European Regional Development Fund under project TK141 (2014-2020.4.01.15-0011).
Abstract
We report the design and synthesis of a strong, chiral, enantiopure sulfoxide-based C–H acid. Single-crystal X-ray analysis confirms the proposed structure and its absolute configuration. The new motif shows a high acidity and activity in Brønsted and Lewis acid catalyzed transformations. So far, only little to no enantioselectivities were achieved.
Key words
sulfoxide C–H acids - stereogenic sulfur - triflyl groups - strong acids - noncoordinating anions - Brønsted acidsSupporting Information
- Supporting information for this article is available online at https://doi.org/10.1055/a-1695-4516.
- Supporting Information (PDF) (opens in new window)
Publication History
Received: 17 September 2021
Accepted after revision: 04 November 2021
Accepted Manuscript online:
12 November 2021
Article published online:
14 December 2021
© 2021. The Author(s). This is an open access article published by Thieme under the terms of the Creative Commons Attribution-NonDerivative-NonCommercial-License, permitting copying and reproduction so long as the original work is given appropriate credit. Contents may not be used for commercial purposes or adapted, remixed, transformed or built upon. (https://creativecommons.org/licenses/by-nc-nd/4.0/)
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References and Notes
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- 8 1-{[Bis(triflyl)methyl]}sulfinylnonafluorobutane (1) A Schlenk flask was charged with bis(triflyl)methane (0.46 g, 1.6 mmol, 1.0 equiv) and THF (3.5 mL) to give a colorless clear solution that was cooled to −78 °C. A 1.2 M solution of TMP·MgCl·LiCl in THF (3.1 mL, 3.8 mmol, 2.3 equiv) was added dropwise, followed by the diastereomerically pure sulfinyl oxazolidinone 6a (4.3 g, 14 mmol, 1.0 equiv; dr >99:1) in THF (3.5 mL). The mixture was allowed to reach RT overnight. All volatiles were then removed under reduced pressure to give an orange solid that was dissolved in CH2Cl2 (30 mL) and washed with sat. aq. NaHCO3 (3 × 10 mL). The pooled aqueous phases were extracted with CH2Cl2 (2 × 10 mL). The pooled organic phases were washed with concd aq HCl (3 × 30 mL), dried (MgSO4), filtered, and concentrated under reduced pressure. The resulting yellowish viscous oil was dissolved in CH2Cl2 (30 mL), washed with concd H2SO4 (3 × 10 mL), stirred over dried BaCl2 for 80 min, and filtered. All volatiles were removed under reduced pressure until 7 mL of liquid remained. This solution was stored at –29 °C overnight, which led to the formation of a precipitate. The mother liquor was removed to give a colorless solid; yield: 0.51 g (57%, 0.93 mmol). LC/MS (chiral): (150 mm Chiralpak IC-3, 4.6 mm i.d., 30:70 MeCN–0.2% TFA, 1.0 mL/min, 20.8 MPa, 298 K): t R,(S)-enantiomer = 21.06 min, t R,(R)-enantiomer = 22.69 min; e.r. = 1:99. 13C NMR (151 MHz, acetone-d 6): δ = 123.74 (t, J = 23.1 Hz, C 6), 120.22 (q, J = ~322.0 Hz, C 7,8), 117.14 (tt, J = 322.7, 36.6 Hz, C 1), 114.51 (qt, J = 287.0, 32.5 Hz, C 4), 111.21 (tp, J = 266.2, 34.0 Hz, C2), 108.76 (th, J = 271.0, ~35 Hz, C 3). 19F NMR (471 MHz, acetone-d 6): δ = –179.16 (br, 3 F, F7,8 ), –80.68 (br, 3 F, F7,8 ), –81.37 to –82.51 (td, J = 9.6, 5.1 Hz, 3 F, F4 ), –103.82 (br d, J = 220.6 Hz, 1 F, F1′ ), –121.02 (dt, J = 221.8, 10.3 Hz, 1 F, F1′′ ), –123.63 [br d (AB system), J = ~300.0 Hz, 1 F, F2′ ], –124.33 [br d (AB system), J = ~300.0 Hz, 1 F, F2′ ], –126.39 [br d (AB system), J = 293.0 Hz, 1 F, F3′ ], –127.19 [br d (AB system), J = 293.0 Hz, 1F, F3′′ ]. MS (ESI–): m/z = 545 [M –H]. HRMS (ESI–): m/z [M –H] calcd for C7F15O5S3: 544.8674; found: 544.8674. Anal.: Calcd for C7HF15O5S3 (546.24 g/mol): C, 15.39; H, 0.18; F, 52.17; S, 17.61; Found: C, 15.42; H, 0.17; F, 52.14; S, 17.60.
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