Studies on New Synthetic Pathways to ⊿^{α, β}-butenolides from α-Methylbutanolides. III. Regiospecific Preparation of α-Methyl-⊿^{α, β}-butenolides and α-Methylene-γ-butyrolactones by Electrolysis of α-Carboxy-α-methylbutanolides and

by Oxidation of α-Dimethylamino-α-methylbutanolides in a Fused Lactone System

Abstract

New methods have been developed for the preparation of α-methylene-γ-butyrolactones (exo-type olefin) and α-methyl-⊿^{α, β}-butenolides (endo-type olefin) starting from an α-carboxy-α-methyl-γ-butyrolactone in a fused lactone system, e. g., (+)-11β-carboxy-(2a) and (+)-11α-carboxy-3α, 4β, 5α, 6βH-hexahydrosantonin (2c). The method for exocyclic (⊿^{α, β'}) butenolides, e. g., ⊿¹¹⁽¹³⁾-dehydrohexahydrosantonin (5a), consists of the oxidative syn elimination of an 11β-oriented α-dimethylaminolactone (4b) derived smoothly with retention of the configuration of the α-substituent through several intermediates, starting from an α-carboxy-α-methylbutanolide, e. g., 11β-carboxy-3α, 4β, 5α, 6βH-hexahydrosantonin (2a) (11β-COOH/7α-H : trans). The method for endo-type butenolides, e. g., ⊿⁷⁽¹¹⁾-dehydrohexahydrosantonin (8a), consists of electrolytic oxidation of the trans- or cis-carboxylactone acid, e. g., 11β-carboxy-(2a) and 11α-carboxy-3α, 4β, 5α, 6βH-hexahydrosantonin (2c) (11α-COOH/7α-H : cis), irrespective of the configuration of the α-carboxyl group in the santanolide.