ASYMMETRIC INDUCTION IN MN(III)-BASED OXIDATIVE FREE-RADICAL CYCLIZATIONS OF PHENYLMENTHYL ACETOACETATES AND 2,5-DIMETHYLPYRROLIDINE ACETOACETAMIDES

Mn(III)-based oxidative free-radical cyclization of phenylmenthyl ester 1e afforded 90% of 13 with 86% de. Cyclization of 31b provided 56% of (+)-podocarpic acid precursor 32e with 82% de. The direction of de was opposite in these two cases. Oxidative cyclization of a-methyl beta-keto ester 44b gave a 1:1.6 mixture of 46b and 47b while alpha-propyl beta-keto ester 44d produced a > 10:1 mixture of 46d and 47d indicating that the extent and direction of de is dependent on the size of the alpha-substituent The reaction proceeds through transition states 12 and 56 with large alpha-substituents and through transition states 19 and 57 with small a-substituents. The de depends on the double-bond substitution pattern as shown by the decreased de with 37b and 37d, and selectivity in the 5-exo cyclization of 64b, 65b, 70b, and 71b is low.