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 ring-expanded 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. The ring-expansion of Cyrene has been developed via the enamine using a dihalocyclopropanation/ring-opening approach. The outcome for the ring-expansion was sensitive to solvent, with the ring-expansion favored in DMF, giving access to halogenated homologated levoglucosenone. A reductive dehalogenation was observed with extended heating in DMF. image