Singlet oxygen in synthesis. Oxazoles as carbonyl 1,1-dipole synthons.

Abstract

2,5-Diphenyloxazole has been utilized in a two-step sequence as a carbonyl 1,1-dipole synthon as illustrated by the synthesis of 7-heptanolide, α-benzyloxy δ-valerolactone, and 9-nonanolide. Alkylation of 4-lithio-2,5-diphenyloxazole, followed by singlet oxygen oxidation yields a triamide which undergoes cyclization to the lactone.