Control of the Regio- and Diastereoselectivity for the Preparation of Highly Functionalized Terpenic Cyclopentanes through Radical Cyclization

The titanocene-mediated cyclization of suitably functionalized acyclic C10 epoxy-polyprenes leads, with moderate stereoselectivity, to high yields of functionalized terpenic cyclopentanes with three contiguous stereogenic centers. These highly functionalized cyclopentanes are useful intermediates for the synthesis of several natural compounds that include this interesting subunit in their structure. Both the regioselectivity of the process leading to cyclopentanes and the stereoselectivity of the cyclization could be controlled by using malonyl derivatives or α,β-unsaturated nitriles as radical acceptors.