Regio- and stereoselectivity in the amination of cyclohexanone enamines

The portionwise addition of ethyl N-[(4-methylbenzenesulphonyl)oxy]carbamate (TsONHCO2Et) in the presence of solid caesium carbonate enables the regioselective amination of 1-(1-cyclohexenyl)pyrrolidine, to give mainly the C-amination product 2-[(ethoxycarbonyl)amino]cyclohexanone in 38% yield. In the absence of base, the batchwise addition of TsONHCO2Et exclusively gives the N-amination product (48%). With ethyl N-[(4-nitrobenzenesulphonyl)oxy]carbamate (NsONHCO(2)Et) as the aminating agent, the regioselectivity is depending on the reaction conditions. The optically active enamine (S)-(-)-1-(1-cyclohexenyl)-2-(methoxymethyl)pyrrolidine reacts with NsONHCO(2)Et yielding a product whose stereoselectivity depends on the reaction conditions. In the presence of CaO, the major enantiomer has a configuration (S) opposite that of the major enantiomer obtained in the presence of EtaN. Amination of the same enamine by another electrophile, bis(tert-butoxycarbonyl)diazene [N-2(CO(2)t-Bu)(2)], gives 2-{[N,N'-bis(tert-butoxycarbonyl)]hydrazino]cyclohexanone in good yield (66%). The configuration of the major enantiomer was determined by chemical correlation.