Two-Step Method for Constructing a Quaternary Carbon Atom with a Geminal Divinyl Group from a Ketone.

A two-step synthesis of geminal divinyl compounds from ketones was developed. An allyl titanium reagent prepared from 1-phenylthio-4-trimethylsilyl-2-butene was reacted with a ketone, and the resulting tertiary alcohol was subjected to a Brønsted acid-mediated rearrangement reaction to generate a geminal divinyl compound. Introduction of another alkene moiety followed by ring closing metathesis resulted in a bicyclic compound possessing a vinyl group at the bridgehead position.