A spirodiepoxide-based strategy to the A-B ring system of pectenotoxin 4.

[reaction: see text] A synthesis of a pectenotoxin 4 C1-C15 segment is reported. Suitable C1-C7 and C8-C15 segments were prepared, coupled, converted to I and the C3-hydroxy variant, and then cyclized. Key findings include the stereoselective conversion of the allene to the corresponding spirodiepoxide, oxidative cleavage of the p-methoxybenzyl ether, and cyclization of the spirodiepoxide to spiroketal II.