1,1-Diphenylalkenes. Part V. C-1 vs. C-3 alkylation of allylic carbanions; applicability of the principle of least motion

Abstract

The product of C-1 alkylation is the only one observed when 1,3,3-triphenylprop-2-enylsodium (1) is alkylated in liquid ammonia. However, exclusive C-3 alkylation results when the 3-phenyl groups are linked by an ortho,-ortho' -bond, as in 2-(fluoren-9-ylidene)-1-phenylethylsodium (2), 2-(fluoren-9-ylidene)ethylsodium (3), or 2-(fluoren-9-ylidene)-1-methylethylsodium (4), or when the 1-phenyl group is reduced, as in 1-cyclohexyl-3,3-diphenylprop-2-enylsodium (5). It is concluded that the principle of least motion is generally applicable to these alkylation reactions and that the reactions of compound (1) are exceptions to the principle.