Unexpectedcis-Selective 1,4-Addition Reaction of Lower Order Cyanocuprates to Optically Active 5-(tert-Butyldimethylsiloxy)-2-cyclohexenone

A remarkable cis selectivity has been observed in the 1,4-addition of lower order primary and secondary alkylcyanocuprates to 5-silyloxy- and 5-benzyloxy-substituted cyclohexenones. This enables the preparation of both enantiomers of the corresponding 5-alkyl-substituted cyclohexenones (S)- and (R)-3 by the reaction of the readily available 5-(tert-butyldimethylsiloxy)-2-cyclohexenone (1) with either the lower or higher order cyanocuprate. DBU=1,8-diazabicyclo[5.4.0]undec-7-ene.