Bi(OTf)3-catalysed intramolecular cyclisation of unsaturated acetals

Abstract

A series of highly functionalized carbocycles was efficiently prepared via the selective cyclisation of unsaturated acetals and ketals in the presence of only 1 mol% of Bi(III) or Fe(III) triflates as the catalysts at room temperature, with yields ranging from 60 to 90%. With Bi(OTf)₃ catalysis, α,β-unsaturated ether carbocycles are formed selectively, whereas with the Fe(OTf)₃ system, a cycloisomerisation to carbocyclic diethers is mainly obtained. This acetal/olefin cyclisation could be run at a multi-gram scale and compound 2c could be obtained on a 300 gram-scale with a yield of 69% after precipitation in hexane.