Polar selectivity of carbene addition to 3-substituted propenes

Abstract

Relative rate constant for the addition of several carbenes to a series of allylic compounds have been determined by means of competititive experiments. These results and derived Hammett–Taft parameters show that polar selectivities of carbenes are generally low, but correlate with the polar natures of the carbene substituents. The selectivity of a singlet carbene was even lower than that of the corresponding triplet state. These facts support a mechanism of addition of singlet carbene involving a transition state having only a slight contribution from polar structures. Low selectivities of alkoxycarbonylcarbenes suggest that the –R effects of the alkoxycarbonyl groups do not affect the addition reactivities of the carbenes.