Abstract: Lithium dienolates derived from a, fl-unsaturated carbonyl compounds generally undergo alkylation reactions nearly exclusively at the a (rather than the y) carbon. Changing the counterion from lithium to copper (I), however, has a remarkable effect on the alkylation regioselectivity of these dienolates. A systematic investigation has been made of the reaction of dienolates derived from (Z)-and (E)-3-methyl-2-hexenoic (2a and 3a) and ...