Stereoselective addition of organometallic reagents to N-(tosyl)vinylsulfoximines

Treatment of N-(toluene-p-sulfonyl)vinylsulfoximines 3 with methyllithium at -78 degrees C, followed by addition of chlorotrimethylsilane, results in the efficient formation of alpha-silyl vinylsulfoximines 6 in good to excellent yield, Nucleophilic addition of a range of simple alkyl and aryl organometallics (lithium, copper-lithium and Grignard reagents) occurs in variable yield to give the Michael adducts 8, with organolithium reagents most effective, The degree of stereoselectivity of each of the addition reactions was determined by H-1 NMR of the desilylated products 9, and proved to be synthetically useful for compounds in which the starting alpha-silylvinylsulfoximines were branched at the gamma-position, and also when phenyllithium was used as the nucleophile, The sense of stereoselectivity was determined in two cases by X-ray crystal structure analyses (of 9e and 9i), A one-pot process for the conversion of alpha-silylvinylsulfoximines 6 to alpha-substituted carboxylic acids 11 was developed, using an in situ phenylselenation-oxidation process following the initial conjugate addition, Use of enantiomerically pure starting materials allowed the assignment of configuration of two carboxylic acids (13e and 13h) by comparison with literature data, and hence indirectly of the relative stereochemistry of the initial Michael adducts 9e and 9h.