BIMOLECULAR CYCLOADDITION REACTIONS OF ISOMUNCHNONES DERIVED FROM THE RHODIUM(II) CATALYZED CYCLIZATION OF DIAZO PYRROLIDINONES

Treatment of diazo substituted pyrrolidinones with a catalytic amount of rhodium(II) acetate in refluxing benzene results first in the formation of a rhodium carbenoid which then cyclizes onto the neighboring carbonyl oxygen to produce an isomunchnone ring system. Subsequent cycloaddition across the pi-bond of an added dipolarophile affords 1,3-dipolar cycloadducts in high yield. The isomunchnone derived from 2-diazoacetyl-2-pyrrolidinone reacts readily with both electron-rich (diethyl ketene acetal) and electron deficient (N-phenyl maleimide, methyl vinyl ketone) dipolarophiles. The regiochemical results are in full accord with FMO theory. The frontier orbital coefficients of the isomunchnone were determined by semi-empirical AMAC calculations. When acetylenic dipolaro-philes were used as the trapping agents, the expected dipolar cycloadducts were not isolated, but underwent a 4+2-cycloreversion instead to furnish furanoisocyanates. The isocyanates were characterized as their urethane derivatives by reaction with methanol.