A number of 1- and 1,2-disubstituted cyclopropenes undergo [4+2]-cycloaddition to methyl vinyl ketone or acrolein at ambient temperature to produce 2-oxabicyclo[4.1.0]hept-3-enes. When 1-phenyl-2-trimethylsilyl-cyclopropene is treated with 0.4 mol. equiv. of m-chloroperbenzoic acid, the derived ring-opened enone undergoes [4+2]-cycloaddition to the remaining starting material at ambient temperature.