-4-Ethoxycarbonyl-4-(phenylthio)-9-methylene-2-oxabicyclo-[3.3.1]nonan-3-ones (5a–c) and their related compounds 5e–h, -4-ethoxycarbonyl-4-(phenylthio)-8-methylene-2-oxabicyclo[3.2.1]octan-3-one (5d) were synthesized from α-diazomalonates 3 of 2-(phenylthio)cyclohex-2-en-1-ols (1a–c) and their related compounds e–h, and 2-(phenylthio)cyclopent-2-en-1-ol (1d), respectively, via the [2,3]sigmatropic