Allylic alcohol transposition by ortho ester-initiated carbonate extension. synthesis of the vasodilator 11(R),12(S),15(S)-trihydroxyeicosa- 5(Z),8(Z),13(E)-trienoic acid

reaction: see text] The title compound 1 was obtained via methyl ester 2, which was synthesized in four steps from an isomeric 11,14,15-triol ester 5. In the key step, Boc orthoformate 9 was treated with TMS triflate to initiate intramolecular nucleophilic substitution with allylic transposition, forming cyclic carbonates 10 and 11.