Wittig-selectivity in mixed ketones: exploring 1,3-interaction and enolization

The present work explored the primary factors governing regioselectivity of Wittig olefination in bicyclo[2.2.2]oct-5-en-2-ones having 5-aroyl or acyl substitutions. In absence of steric congestion less enolizable ketone kinetically favored the initial formation of the oxaphosphetane ring whereas, in presence of 1,3-interaction between phosphonium ylide and ketone substitutions could switch over the selectivity in other direction.