Total Synthesis of (+)-Cyclobutastellettolide B.

A convenient enantioselective total synthesis of (+)-cyclobutastellettolide B via a strategy that involves a diastereoselective Johnson-Claisen rearrangement, a regioselective cyclopropoxytrimethylsilane ring-opening reaction, and a Norrish-Yang cyclization is described. The results of computational and experimental studies indicate that the regio- and stereoselectivity of the Norrish-Yang reaction are controlled by the C-H bond dissociation energy and restricted rotation of the C13-C14 bond.