Free-radical cyclization of enantiomerically enriched 2-p-tolyl-thio derivatives of 2-allylcyclohexanones with Mn(III): asymmetric synthesis of bridged bicyclic ketones and thio-chroman-3-ones

Mn(III)-based oxidative intramolecular cyclization of enantiomerically enri ched 2-allyl-2-(p-tolylsulfonyl)cyclohexanone 4 and 2-allyl-2-(p-tolylsulfe nyl)cyclohexanone 9 are reported. The observed chemoselectivity (reaction o n the allylic double bond yielding bridged bicyclic ketones vs, reaction on the aromatic ring of the p-tolyl group affording thiochroman-3-ones) depen ds on the sulfur function (sulfone or thioether, respectively), which deter mines the electronic density of the p-tolyl ring and the conformational pre ferences of the starting compounds. The nature of the substituent at C-2 is related to the endolexo selectivity of the cyclization as well as the regi oselectivity in the formation of the enones. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.