Silver Triflate Catalyzed Cyclopropyl Carbinol Rearrangement for Benzo[b]oxepine and 2H-Chromene Synthesis

An efficient AgOTf-catalyzed (TfO = trifluoromethanesulfonate) cyclopropyl carbinol rearrangement for the synthesis of benzo[b]oxepines and 2H-chromenes is reported by starting from 2-[cyclopropyl(hydroxy)methyl]phenols. The reactions proved to be general in scope and furnished a range of the corresponding functionalized oxygen heterocycles. The formation of the benzo-fused six-membered adduct is proposed to result from the ring-contraction of the benzo[b]oxepine derivative. Control of the product selectivity is achievable by fine-tuning the reaction time. The catalytic synergy between the silver(I) cation and the triflate anion was essential for optimal product yields. An efficient AgOTf-catalyzed (TfO = trifluoromethanesulfonate) cyclopropyl carbinol rearrangement to prepare benzo[b]oxepines and 2H-chromenes has been developed by starting from [cyclopropyl(hydroxy)methyl]phenols. A catalytic synergy was observed between the silver(I) cation and the triflate anion, which furnished the functionalized oxygen heterocycles.