Facile Alder-Ene Reactions of Silylallenes Involving an Allenic C(sp2)-H Bond

Facile and selective Alder-ene reactions of silyl-allenes involving the activation of an allenic C(sp(2))-H over an allylic C(sp(3))-H bond is described. In this ene reaction, the presence of a silyl substituent was found to be critical for the observed reactivity and selectivity since the corresponding alkyl-substituted allenes show different reaction profiles. Computational studies show that the origin of this unusual reactivity is the lower bond dissociation energy of the alpha-C(sp(2))-H bond in silylallenes compared to the corresponding nonsilylated allenes.