Cyclization Reactions of Tethered Radicals Derived From 4-O-Substituted α-D-erythro-Octa-2,6-dienopyranosides: Stereoselective Access to Carbocycles and Branched-Chain Sugars

Abstract

The chemo- and stereo- selectivities in the cyclization of tethered radicals, derived from α-D-erythro-octa-2,6-dienopyranosides, in which there is competition between 5-exo and 6-exo ring closures, have been examined. Use of silicon tethers resulted in a preferred 6-exo-trig addition. However, tethered mixed iodo acetals have shown an unprecedented relation between the stereogenic centre in the acetal and the preferred addition pathway. In addition, changes in the oxidation state at the termini of the olefins have a profound effect upon site selectivity, thus leading to 3-deoxy 3-C-substituted carbohydrates, off-template branched-chain sugars, or functionalized cyclopentanes.