Stereospecific C-N Bond Cleavage of 4-Silylated 1,2-Thiazetidine 1,1-Dioxides with EtAlCl2 or AlCl3: Formation of (E)-Vinylsulfonamides.

Abstract

Monosilylation of 1, 2-thiazetidine 1, 1-dioxides (β-sultams) 3 gave (3R*, 4S*)-4-monosilyl-β-sultams 4 stereoselectively. Disilylated β-sultams 5 were obtained by the use of trimethylsilyl chloride. Treatment of 4-monosilyl-β-sultams 4 with EtAlCl2 caused stereospecific C-N bond cleavage owing to β-cation stabilization of the silicon group to provide (E)-vinylsulfonamides (E)-7. (E)-α-Silylstyrylsulfonamides (E)-7j-l were generated in the reaction of 4, 4-disilyl-β-sultams 5 with EtAlCl2. Reaction of 4-silyl-β-sultams with AlCl3 afforded N-dealkylated (E)-vinylsulfonamides in good yields. Reaction of (E)-α-silylstyrylsulfonamide (E)-10 with benzaldehyde in the presence of tetrabutylammonium fluoride and BF3·Et2O provided the allylic alcohol (E)-12.