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

[graphics] 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.