Synthesis of a key building block for a butyrolactone→1,3-diol approach to the polyol part of roflamycoin

For preparing tris(gamma-lactone) 3 the mono(gamma-lactone) 6 was synthesized from the dichlorodiol 12 (99.8% ee). Bisepoxide 9 - derived from dichlorodiol 12 (99.8% ee) - was ring-opened with the Gilman cuprate from 2-Lithio-1,5-hexadiene and CuI giving almost exclusively the monoepoxide 21; in five more steps, gamma-lactone 30 with the same stereotriad as the target molecule 6 but a different protecting group was obtained. Monoepoxide 33 - also derived from dichlorodiol 12 - was ring-opened with the same Gilman cuprate affording compound 35. It was transformed into the correctly protected gamma-lactone 6 in seven steps, key reactions being the ozonolysis 35 --> 36 and the diastereoselective reduction 36 --> anti-37.