Abstract
A mild and chemoselective dithioacetalization procedure for the protection of aromatic, aliphatic, and alkenyl aldehydes in presence of catalytic amount of N -bromosuccinimide under neutral conditions is described.
Key words
N -bromosuccinimide - aldehydes - dithioacetals - 1,3-dithiolanes - 1,3-dithianes
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Typical Experimental Procedure : To a stirred solution of NBS (15 mol%) and the appropriate aldehyde (1 mmol) in dichloromethane (10 mL) at r.t. was added 1,2-ethanedithiol or 1,3-propanedithiol (1.2 mmol) under nitrogen atmo-sphere. The mixture was stirred at r.t. for an appropriate time (Table). After completion of the reaction as indicated by TLC, the organic solvent was concentrated in vacuum and the crude product was purified by silica gel column chromatography to furnish the dithioalanes in good yields. Spectroscopic data for compound b : 1 H NMR (200 MHz; CDCl3 ): δ = 3.2-3.6 (m, 4 H), 5.6 (s, 1 H), 6.9-7.1 (m, 2 H), 7.4-7.6 (m, 2 H). Compound h : δ = 0.9 (t, 3 H, J = 5.88 Hz), 1.3-1.5 (m, 2 H), 1.9-2.1 (m, 2 H), 3.1-3.3 (m, 4 H), 5.0 (d, 1 H, J = 8.2 Hz), 5.3-5.6 (m, 2 H). Compound m : δ = 1.85-2.0 (m, 1 H), 2.1-2.2 (m, 1 H), 2.8-2.9 (m, 2 H), 2.95-3.1 (m, 2 H), 5.1 (s, 1 H), 7.2 (d, 2 H, J = 8.3 Hz), 7.4 (d, 2 H, J = 8.3 Hz). Compound n : δ = 1.85-2.0 (m, 1 H), 2.1-2.2 (m, 1 H), 2.8-3.1 (m, 4 H), 3.7 (s, 3 H), 5.1 (s, 1 H), 6.8 (d, 2 H, J = 7.3 Hz), 7.3 (d, 2 H, J = 7.3 Hz).
