π-Face selective azaspirocyclization of ω-(methoxyphenyl)-N-methoxyalkylamides

A novel method for the stereoselective preparation of 1-azaspiranes is described. Treatment of alpha- and beta-substituted 3-(methoxyphenyl)-N-methoxypropionamides 1 with phenyliodine(III) bis(trifluoroacetate) initiates efficient azaspirocyclization, via a putative N-acylnitrenium ion intermediate, to provide cyclohexa-2,5 and 2,4-dienone spirolactams 8 and 11 with good pi-facial selectivity. Furthermore, a preliminary study indicates that this strategy is also amenable to the preparation of 1-azaspiro[5.5] undeca-2,5-dienones. (C) 2003 Elsevier Science Ltd. All rights reserved.