Cascade Radical Cyclization to Vinylogous Carbonates/Carbamates for the Synthesis of Oxa- and Aza-Angular Triquinanes: Diastereoselectivity Depends on the Ring Size of Radical Precursor

Published as part of the Special Topic Modern Radical Methods and their Strategic Applications in Synthesis

Dedicated to Professor Sambasivarao Kotha, IIT Bombay, on the occasion of his 60^th birthday.

Abstract

An efficient strategy was developed for the stereoselective construction of oxa- and aza-angular triquinanes employing a cascade 5-exo-trig radical cyclization to vinylogous carbonates and carbamates. The radical precursors are readily prepared from 2-(hydroxymethyl)cyclopentenone/cyclohexenones. High diastereoselectivity is observed for the formation of angular oxa- and azatriquinanes. Diastereoselectivity drops when six-membered radical precursors are used. The strategy is found to be useful to incorporate synthetically challenging moieties such as spiroindoline, lactone-bearing, and uracil-fused angular triquinanes in a concise manner.

Key words

oxatriquinanes - azatriquinanes - vinylogous carbonates - vinylogous carbamates - cascade/tandem radical cyclization - stereoselective synthesis

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