Journal of Organic Chemistry p. 7640 - 7651 (1993)
Update date:2022-08-05
Topics:
Zhang, Qingwei
Mohan, Raju M.
Cook, Laura
Kazanis, Sophia
Peisach, Daniel
et al.
Mn(III)-based oxidative free-radical cyclization of phenylmenthyl ester 1e afforded 90percent of 13 with 86percent de.Cyclization of 31b provided 56percent of (+)-podocarpic acid precursor 32e with 82percent de.The direction of de was opposite in these two cases.Oxidative cyclization of α-methyl β-keto ester 44b gave a 1:1.6 mixture of 46b and 47b while α-propyl β-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 α-substituent.The reaction proceeds through transition states 12 and 56 with large α-substituents and through transition states 19 and 57 with small α-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.
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