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

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, alpha,beta-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.

Automated summary

A series of highly functionalized carbocycles were 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 catalysts at room temperature. Different types of products with varying yields were obtained using Bi(OTf)3 and Fe(OTf)3 catalysis.