Selective CS bond cleavage of a β-sultam ring was achieved by the reactions with Lewis acids. Aryl ketones or aldehyde were provided from 3-aryl-β-sultams whereas β-sultams bearing a poorly migratory substituent at C-3 gave trans-1,2,3-oxathiazolidine 2-oxides and/or cis-aziridines. These reactions were influenced by the cation-stabilizing capability of C-4 substituents and by the configuration of
Selective CN bond cleavage of 4-silyl-substituted 1,2-thiazetidine 1,1-dioxides with EtAlCl2: Stereospecific formation of (E)-vinylsulfonamides
作者:Tadashi Kataoka、Tetsuo Iwama、Atsuko Takagi
DOI:10.1016/0040-4039(96)00269-9
日期:1996.3
Monosilylation of 1,2-thiazetidine1,1-dioxides (β-sultams) furnished β-sultams stereoselectively. Treatment of 4-silylated β-sultams with a Lewis acid caused the selectiveCNbondcleavage because of the β-silyl stabilization against the resultant carbenium ion followed by desilylation to provide (E)-vinylsulfonamidesstereospecifically.
Reactions of 4-nonsubstituted β-sultams 1 with methyllithium gave only (E)-vinylsulfonamides2, whereas 2-aminoethyl sulfones 3 were obtained as minor products by use of methylmagnesium bromide. Reactions of 4-monosubstituted β-sultams 6 with organolithiums gave (E)-vinylsulfonamides 7 stereoselectively regardless of the configuration of 3- and 4-substituents. Treatment of 4,4-dimethyl-β-sultam 8a with
Stereospecific C-N Bond Cleavage of 4-Silylated 1,2-Thiazetidine 1,1-Dioxides with EtAlCl2 or AlCl3: Formation of (E)-Vinylsulfonamides.
作者:Tetsuo IWAMA、Atsuko TAKAGI、Tadashi KATAOKA
DOI:10.1248/cpb.46.757
日期:——
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.