A Boron Alkylidene-Alkene Cycloaddition Reaction

Abstract

Described herein is the exploration of a novel methodology whereby boronate-ester bearing cyclopentanes are produced by reaction between an unactivated olefin and what is described as a boron alkylidene. The mechanism is evaluated and concluded to proceed through a boracyclic intermediate that is achieved by a closed-shell, carbanion addition to the olefin. This mechanistic conclusion is arrived upon by considering two likely alternative routes (an open-shell, radical cyclization and a [2+2] concerted process) and providing evidence to refute them. A reaction scope is established as well as the utility of the methodology through the racemic synthesis of a natural sesquiterpene: aphanamal. Finally, the future of the reaction development will be considered by providing a single example of a 6-endo cyclization.