Cis and trans selective 1,4-addition of a lithium dithioester enolate to 4-O-TBS-2-cyclohexenone.

The 1,4-addition of the lithium enolate of methyldithioacetate (LMDTA) to (+/-)-4-O-TBS-2-cyclohexenone (3) can be varied from being highly 3,4-trans selective to being highly 3,4-cis selective simply by varying the reaction temperature. This stereodivergency allows expedient syntheses of the corresponding trans and cis methyl esters 6t and 6c and derived bicyclic ketolactones 7t and 7c.