Synthesis of Functionalized Cyclopropindenes via the Carbene Addition Route

Article abstract of DOI:10.1002/hlca.19940770729

The synthesis of 4,5-dihydro-1H,3H-cycloprop(f)inden-4-ol (1) and diethyl 4,5-dihydro-1H,3H-cyclopropindene-4,4-dicarboxylate 26 starting from diene 4 is described.The cyclopentene ring is constructed by condensation of diethyl malonate to the dibromide 21.The key-step in the synthesis of 1 consists in a twofold Curtius degradation of 22, with subsequent reduction of the carbonyl group and aromatization.The skeleton of the isomer 31 is synthesized via cycloaddition of butadiene to cyclopent-4-ene-1,3-dione (7) and addition of dichlorocarbene to the adduct 27 after ketalization.The attempted synthesis of dihydrocyclopropindene (2) by base-induced elimination of several appropriately substituted precursors failed.