Qw. Zhang et al., ASYMMETRIC INDUCTION IN MN(III)-BASED OXIDATIVE FREE-RADICAL CYCLIZATIONS OF PHENYLMENTHYL ACETOACETATES AND 2,5-DIMETHYLPYRROLIDINE ACETOACETAMIDES, Journal of organic chemistry, 58(27), 1993, pp. 7640-7651
Mn(III)-based oxidative free-radical cyclization of phenylmenthyl este
r 1e afforded 90% of 13 with 86% de. Cyclization of 31b provided 56% o
f (+)-podocarpic acid precursor 32e with 82% de. The direction of de w
as 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 indicati
ng 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 su
bstitution 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.