Gold-Catalyzed Cyclization of O-Propargyl Carbamates under Mild ­Conditions: A Convenient Access to 4-Alkylidene-2-oxazolidinones

Abstract

On treatment with catalytic amounts of gold(I) chloride (AuCl) and a base co-catalyst, O-propargyl carbamates smoothly undergo a 5-exo-dig cyclization at room temperature to afford 4-methylene-2-oxazolidinones in high yield. Substrates with a sub­stituent at the alkyne terminus stereoselectively give rise to (Z)-4-alkylidene-2-oxazolidinones.

oxazolidinones - heterocycles - gold catalysis - alkynes

References and Notes

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<A NAME="RG23706ST-11">11</A>

Crystal data for compound 9a: colorless crystals (from cyclohexane); mp 87-88 °C; C₁₆H₁₉NO₄S, FW = 321.10, triclinic, space group P-1; a = 7.2854 (2) Å, b = 8.7222 (3) Å, c = 12.7763 (4) Å; α = 96.866 (2)°, β = 100.075 (2)°, γ = 99.598 (2)°; V = 778.85 (4) ų; Z = 2; d _calc = 1.370 g/cm³; R = 0.0391, R _w = 0.0837 for 2517 reflections having I > 2σ(I). Further crystallographic data have been deposited at the Cambridge Crystallographic Data Centre. Copies of the data (CCDC 613241) can be obtained free of charge from CCDC, 12 Union Road, Cambridge CB2 1EZ, UK [fax: [phone]; e-mail: [e-mail]].

<A NAME="RG23706ST-12">12</A> Such a mechanism was previously proposed for a related gold-catalyzed transformation (oxazole synthesis): Hashmi ASK. Weyrauch JP. Frey W. Bats JW. Org. Lett.  2004,  6:  4391 

<A NAME="RG23706ST-13">13</A>

General Procedure for the AuCl-Catalyzed Cyclization of O -Propargyl Carbamates: To a solution of an O-propargyl carbamate (6 or 8a-8f; 0.5 mmol) and a base co-catalyst (0.025 mol, 5 mol%) in solvent (2 mL) was added AuCl (0.025 mol, 5 mol%). The mixture was stirred at r.t. or 60 °C for the time specified in Tables [2] and [3] . Conversion was monitored by TLC and/or GLC analyses. The reaction mixture was filtered through a small pad of Celite^® (elution with CH₂Cl₂). Removal of the solvent under reduced pressure and purification of the residue by flash chromatog-raphy on SiO₂ (cyclohexane-EtOAc, 3:1) afforded the products (7 or 9) as colorless oils or solids.
4-Methylene-3-(toluene-4-sulfonyl)-1-oxa-3-azaspiro[4.5]decan-2-one ( 9a): ¹H NMR (300 MHz, CDCl₃): δ = 1.34-1.74 (m, 10 H), 2.41 (s, 3 H), 4.39 (d, ² J = 3 Hz, 1 H, C=CH), 5.46 (d, ² J = 3 Hz, 1 H, C=CH), 7.31 (d, ³ J = 8.3 Hz, 2 H), 7.89 (d, ³ J = 8.3 Hz, 2 H). ¹³C NMR (75 MHz, CDCl₃): δ = 21.36 (t), 21.65 (q), 24.28 (t), 36.64 (t), 84.83 (s), 90.14 (t), 127.92 (d), 129.75 (d), 134.31 (s), 144.96 (s), 145.94 (s), 150.26 (s). IR (ATR): 1782 (ss, C=O), 1660 (s, C=C) cm^-1. MS (DIP-EI, 70 eV): m/z (%) = 321 [M⁺], 166 (14), 155 (24), 105 (12), 94 (23), 91 (100), 81 (16), 65 (33). HRMS (EI): m/z [M]⁺ calcd for ¹²C₁₆H₁₉ ¹⁴N¹⁶O₄ ³²S: 321.1035; found: 321.104.
( Z )-4-Ethylidene-3-tosyloxazolidin-2-one ( 9b): ¹H NMR (250 MHz, CDCl₃): δ = 1.85 (td, ⁵ J = 1.8 Hz, ³ J = 7.36 Hz, 3 H, CH₃), 2.42 (s, 3 H), 4.62 (app pent, 2 H,), 5.24 (tq, ⁴ J = 1.8 Hz, ³ J = 7.4 Hz, 1 H), 7.33 (d, ³ J = 8 Hz, 2 H), 7.92 (d, ³ J = 8 Hz, 2 H). Characteristic signals of the minor isomer iso-9b: ¹H NMR (250 MHz, CDCl₃): δ = 4.56 (dt, ⁵ J _t = 1 Hz, ³ J _d = 6 Hz, 2 H), 5.43 (tq, ⁴ J _q = 1 Hz, ³ J _t = 5 Hz, 1 H). ¹³C NMR (75 MHz, CDCl₃): δ = 14.63 (q), 21.75 (q), 70.14 (t), 112.43 (q), 128.28 (d), 129.87 (d), 135.4 (s), 138.84 (s), 145.77 (s), 153.54 (s, C=O). IR (ATR): 2923 (w, C=CCH₃), 1782 (ss, C=O) cm^-1. MS (DIP-EI, 70 eV): m/z (%) = 267 [M⁺], 155 (34), 112 (11), 95 (32), 91 (100), 65 (23), 57 (44). HRMS (EI): m/z [M]⁺ calcd for ¹²C₁₂H₁₃ ¹⁴N¹⁶O₄ ³²S: 267.0565; found: 267.056.
( Z )-4-Benzylidene-3-(toluene-4-sulfonyl)oxazolidin-2-one ( 9c): ¹H NMR (250 MHz, CDCl₃): δ = 2.42 (s, 3 H), 4.82 (d, ⁴ J = 2 Hz, 2 H), 6.15 (t, ⁴ J = 2 Hz, 1 H), 7.25-7.31 (m, 7 H), 7.68 (d, ³ J = 8.5 Hz, 2 H). ¹³C NMR (75 MHz, CDCl₃): δ = 21.71 (q), 70.28 (t), 115.87 (d), 127.13 (s), 127.79 (d), 128.48 (d), 128.54 (d), 129.57 (d), 134.49 (s), 134.80 (s), 145.76 (s), 153.90 (s, C=O). IR (ATR): 3058 (w, C=CR), 1788 (ss, C=O) cm^-1. MS (DIP-EI, 70 eV): m/z (%) = 329 [M⁺], 174 (12), 155 (33), 130 (68), 103 (25), 91 (100), 77 (26), 65 (31), 51 (9). HRMS (EI): m/z [M]⁺ calcd for ¹²C₁₇H₁₅ ¹⁴N¹⁶O₄ ³²S: 321.0721; found: 321.072.
4-Methylene-3-phenyloxazolidin-2-one ( 9d): ¹H NMR (250 MHz, CDCl₃): δ = 4.12 (d, ² J = 2.5 Hz, 1 H, C=CH), 4.21 (d, ² J = 2.5 Hz, 1 H, C=CH), 5.01 (t, ² J = 2 Hz, 2 H), 7.30-7.46 (m, 5 H). ¹³C NMR (75 MHz, CDCl₃): δ = 67.10 (t), 82.00 (t), 126.91 (d), 128.94 (d), 129.15 (d), 133.55 (s), 141.72 (s), 155.97 (s, C=O). IR (ATR): 1757 (ss, C=O), 1680 (s, C=CH) cm^-1. MS (DIP-EI, 70 eV): m/z (%) = 175 [M⁺], 130 (100), 103 (56), 91 (8), 77 (68), 63 (10), 51 (46). HRMS (EI): m/z [M]⁺ calcd for ¹²C₁₀H₉ ¹⁴N¹⁶O₂: 175.0633; found: 175.063.
( Z )-4-Ethylidene-3-phenyloxazolidin-2-one ( 9e): ¹H NMR (250 MHz, CDCl₃): δ = 1.06 (td, ⁵ J = 2.3 Hz, ³ J = 7.3 Hz, 3 H), 4.47 (tq, ⁴ J = 2.3 Hz, ³ J = 7.3 Hz, 1 H), 4.91 (m, 2 H), 7.30-7.43 (m, 5 H). ¹³C NMR (75 MHz, CDCl₃): δ = 10.43 (q), 66.06 (t), 93.17 (d), 127.09 (d), 127.17 (d), 128.21 (d), 128.59 (d), 129.55 (d), 129.87 (d), 130.59 (s), 135.16 (s). IR (ATR): 1771 (ss, C=O), 1699 (s, C=CH) cm^-1. MS (DIP-EI, 70 eV): m/z (%) = 207 [M⁺], 189 (32), 149 (33), 132 (36), 119 (100), 104 (27), 91 (29), 84 (74), 77 (69), 57 (77), 49 (94). HRMS (EI): m/z [M]⁺ calcd for ¹²C₁₁H₁₁ ¹⁴N¹⁶O₂: 189.079; found: 189.079.
( Z )-4-Benzylidene-3-phenyloxazolidin-2-one ( 9f): ¹H NMR (300 MHz, CDCl₃): δ = 5.10 (d, ⁴ J = 2.1 Hz, 2 H), 5.67 (s, 1 H), 6.63 (d, J = 1.7 Hz, 2 H), 6.81-6.90 (m, 3 H), 6.98-7.06 (m, 5 H). ¹³C NMR (75 MHz, CDCl₃): δ = 68.03 (t), 99.89 (t), 125.88 (d), 126.96 (d), 128.12 (d), 128.16 (d), 128.68 (d), 129.74 (d), 132.27 (s), 132.83 (s), 134.60 (s), 156.95 (s, C=O). IR (ATR): 3053 (w, C=CR), 1769 (ss, C=O) cm^-1. MS (DIP-EI, 70 eV): m/z (%) = 251 [M⁺], 206 (23), 104 (100), 89 (9), 77 (32), 63 (8), 51 (22). HRMS (EI): m/z [M]⁺ calcd for ¹²C₁₆H₁₃ ¹⁴N¹⁶O₂: 251.0946; found: 251.094.

<A NAME="RG23706ST-14">14</A> During the preparation of this manuscript, a method for the gold-catalyzed synthesis of (isomeric) 3-alkylidene-2-oxazolidinones was reported, which nicely complements the work described here: Robles-Machin R. Adrio J. Carretero JC. J. Org. Chem.  2006,  71:  5023