Factors controlling the regioselectivity of additions to α-enones-VII

Reaction of phosphononitrile 2 with a series of a-enones in THF-n-BuLi gives different results according to the enone nature. C4-disubstituted enones are attacked at the carbonyl carbon; phenones and cyclopentenone are attacked at the double bond (except dypnone); benzalacetone, 3-penten-2-one and cyclo-hexenone give mixtures of C2 and C4 substituted products. Electrophilic assistance by complexation of the lithium cation by α-enone can be shown except for phenones.