Facile Construction of Novel Polycyclic Ring Systems Using a Metallocarbenoid-Induced Cyclization of Acetylenic Diazo Carbonyl Compounds

The Rh(II)-catalyzed reaction of diazo 2-propynyl maolonamic acid ester derivatives produce furo[3,4-c]furans in excellent yield. The methodology
was applied to the synthesis of several polyheterocyclic systems by first generating a 2-alkoxy-substituted furan and then allowing it to
undergo a subsequent intramolecular Diels−Alder cycloaddition. Ring opening of the resulting cycloadduct is followed by deprotonation to
furnish a rearranged keto lactone.