Studies toward Total Synthesis of Non-Aromatic Erythrinan Alkaloids. 7. Synthesis of Cocculolidine Skeleton

Abstract

The skeletal structure of cocculolidine (1), a D-nor-erythinan alkaloid, was synthesized as the 8-oxo derivative 2 by several routes via the diester 4 as a key intermediate. One route was an ozonolysis of 14, 15, 17-trimethoxy-8-oxo-erythrinan (3) to directly yield 4 in 63%. The other was the Ce(IV) methanesulfonate oxidation of 16, 17-dimethoxy-8-oxo-erythinan (6) to yield the p-quinone 7 (94%), which was converted to the same diester 4 by ozonolysis and peroxide oxidation (70%). The diester 4 was transformed to the corresponding anhydride 5, which was regioselectively reduced with a bulky borohydride (K-selectride^[○!R]) to give the desired lactone 2.