Synthetic studies on spiroketal natural products. III. Enantioselective synthesis of 1,6-dioxaspiro(4.5)decane compounds.

Abstract

Two enantiomers of 1, 6-dioxaspiro [4.5] decane (1) and all four stereoisomers of 2-methyl-1, 6-dioxaspiro [4.5] decane (an insect pheromone)(9) were successfully synthesized via a crucial step, an asymmetric five-membered ring cyclization induced by a sulfinyl chirality.The alcohol (6), prepared from the optically active sulfoxide (2), was treated with potassium hydride to give the spiroketal (7), which was transformed into the isomer (8) by acid. Reductive desulfurization of these products furnished R-1 and S-1, respectively.The ketone (10), also prepared from 2, was reduced with diisobutylaluminum hydride (DIBAL) or DIBAL-ZnCl2 to afford selectively 15a or 15b, respectively. Base-catalyzedicyclization gave 21a and 21b, which were convertible to 22a and 22b under acidic conditions. The four isomers (21a, 21b, 22a, and 22b) were efficiently transformed into 9a, 9b, 9c, and 9d by removal of the chiral auxiliary.