PRODUCTS AND MECHANISMS IN THE ANODIC-OXIDATION OF SOLANIDINE-TYPE STEROIDAL ALKALOIDS

Anodic oxidation of DELTA4-solaniden-3-one, 2,3beta-acetoxysolanidin, 5, and 3beta-acetoxy-5alpha-chlorosolanidin, 6, were performed in CH3CN-CH2Cl2 (1:1)-tetraethylammonium perchlorate electrolyte solution at platinum using controlled potentials. As a result of two-electron oxidation the corresponding N-22 immonium salts (2a, 5a, and 6a) and N-16 immonium salts (2b, 5b, and 6b) were isolated in good yield (75-82%) with a ratio of a/b products of approximately 1.1. The effect of solution conditions on regioselectivity, e.g., formation of 2a and 2b, has been shown to be remarkable. The oxidation of 2 in acetone solution gave 2a in 95 % yield, whereas the oxidation in methylene chloride solution gave 2b in 95% yield. On the basis of the electroanalytical and preparative results as well as molecular orbital calculations with model compounds the mechanism and regioselectivity of the reaction have been deduced.