Highly Activated Vinyl Hydrogen in a Significantly Twisted Styrene

The novel example of a vinylic hydrogen more reactive than a benzylic hydrogen was found by treatment of a twisted styrene derivative with a strong base followed by D₂O quenching. In this paper, the full details of the examples of the highly activated vinyl hydrogens in twisted styrene derivatives are described, with a discussion on the correlation between the reactivity of the vinyl hydrogens and the magnitude of the twist. The highly reactive vinyl hydrogens could be rationalized by considering the novel orbital interaction between the π* orbital of the benzene ring and the σ orbital of the vinylic C−H bond in the twisted styrene derivatives.