Potentially synthetically useful reactions of the dilithium salts
of the title dianions have been
investigated. Electrophilic quenching with a variety of reagents
usually leads to the expected
products in good yield. Quenching the diphenylacetone dianion with
1 equiv of trimethylchlorosilane, however, gives a good yield of 1,3-diphenylallene obtained by
formal elimination of a
trimethylsiloxy anion from an intermediate monoquenched monoanion salt.
NMR studies, however,
do not reveal the intermediacy of the
1,3-diphenyl-2-(trimethylsiloxy)allyl anion but rather
suggest
that the initial reaction site is at carbon, rather than oxygen.
Oxidation of the dianions leads
either to ring closure or dimerization for the tribenzylidenemethane
dianion and to dimerization
for the diphenylacetone dianion. The dimerization reactions are
stereospecific, both with respect
to the two new stereocenters produced and for the double bonds of the
bis-silyl enol ether products
if the dimeric bis-enolate dianion products are quenched with
trimethylchlorosilane.