Control of product formation
Reaction conditions usually employed to obtain rearranged products yielded
irreproducible mixtures of starting compound 1, mono-rearranged I4, and
double-rearranged I5 species.* Those difficulties could finally be overcome by
very slow inverse addition of LDA to the starting material.
It became evident that the ratio of composition depends solely on the amount of added base.
1.25 equiv. LDA gives mono-rearranged product while 2.5 equiv. LDA affords double-migration
*Lithium-Intermediates trapped as the corresponding TMS-compounds.