Abstract
We and others have recently begun to develop the intramolecular [2 + 2] cycloaddition of ketenes to alkenes into a general synthetic method. Although many isolated examples are known, the development of this reaction has been hindered by the limited reactivity of simple alkylketenes. For instance, the ketene prepared by treatment of acid chloride 1 with triethylamine has been reported to provide only a 3% yield of the cycloadduct 2. The ketene derived from 3 does not give any cycloadduct. We chose to examine the intramolecular [2 + 2] cycloadditions of chloroketenes with alkenes, since methylchloroketene is much more reactive in intermolecular [2 + 2] cycloadditions than methylketene.