Cis and Trans Selective 1,4-Addition of a Lithium Dithioester Enolate to 4-<i>O</i>-TBS-2-cyclohexenone

The 1,4-addition of the lithium enolate of methyldithioacetate (LMDTA) to (±)-4-<i>O</i>-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 <b>6t</b> and <b>6c</b> and derived bicyclic ketolactones <b>7t</b> and <b>7c</b>.