Ring-Expansion Reactions of the Biomass Derivative Cyrene via Enamine Dihalocyclopropanation

A ring-expansion process for the biomass derivative Cyrene obtained from levoglucosenone has been developed using gem-dihalocyclopropanes as intermediates. The process involves conversion of Cyrene to an enamine, reaction with an in situ generated dihalocarbene, and then ring-opening. Competition between endocyclic and exocyclic olefinic products was switchable using solvent and temperature, and ringexpanded alkenyl halides were obtained in 50–64% yield from Cyrene. Under extended heating, dehalogenation occurred giving homologated levoglucosenone in 25% overall yield from Cyrene in 3 steps.