Highly diastereoselective approach to methylenecyclopropanes via boron-homologation/allylboration sequences

A simple and efficient diastereoselective synthesis of methylenecyclopropanes is described, in which boron-homologation and allylboration are merged into a one-pot process, starting from in situ generated cyclopropenyllithium species. This unprecedented methodology opens a new route to strained alkylidenecycloalkanes containing a quaternary stereocenter, in high yields and excellent diastereomeric ratios.