Synthetic studies on a picrotoxane sesquiterpene, coriamyrtin. II. An effective stereocontrolled synthesis of the picrotoxane skeleton except for a C1 unit at the C9 position and functionalization of the five-membered ring.

Abstract

The picrotoxane skeleton (5) except for a C1 unit at the C9 position was effectively synthesized starting from protoanemonin and 2-methyl-1, 3-cyclopentanedione through five steps. The key reaction of this synthesis was the Grignard reaction of the ester (6) with isopropenylmagnesium bromide. A synthetic approach for completing the total synthesis of coriamyrtin (4) by functionalization of the five-membered ring of the lactone (5) was also examined.