A convenient synthesis of homochiral δ-alkylated α,β-unsaturated δ-lactones

The tert-butyl propiolate ion serves as a convenient and efficient nucleophile in boron trifluoride-catalyzed openings of homochiral, mono-substituted epoxides. The resulting tert-butyl 5-hydroxy-2-alkynoates are converted into the title compounds upon semihydrogenation followed by acid hydrolysis. Specific examples include the synthesis of parasorbic acid and massoilactone, two naturally derived lactones of the present type. The scope of the synthetic protocol is discussed.