Cyclohexenone Construction by Intramolecular Alkylidene C−H Insertion: Synthesis of (+)-Cassiol

We report new procedures for stereoselective cyclopentene and cyclohexenone construction employing the alkylidene carbene C−H insertion reaction. Described are diastereoselective insertion into methylene and enantiospecific insertion into methine C−H bonds. The latter case leads directly to the enantioselective synthesis of (+)-cassiol ( 1 ).