types of cyclopropene-1,2-dicarboxylates 1 have been obtained by photochemical methods from the corresponding pyrazoles 11, 12, or 13. These pyrazoles were synthesized by 1,3-dipolarcycloadditions of alkynes 8 or 9 with either preformed diazoalkanes or diazoalkanes generated photochemically in situ, by use of oxadiazolines as diazoalkane precursors. The numerous substrates have clearly established the