Donald L. Hertzog

Intramolecular cycloaddition of isomünchnones derived from the rhodium(II) catalyzed cyclization of diazoimides

Abstract Rhodium(II) catalysis of various diazoimides containing tethered π-systems results in isomunchnone dipole formation followed by intramolecular dipolar-cycloaddition.

Synthesis of AZA substituted polycycles via rhodium (II) carboxylate induced cyclization of diazoimides

Abstract Treatment of several substituted diazoimide derivatives with rhodium (II) carboxylates results in nitrogen-containing cyclic carbonyl ylide formation followed by 1,3-dipolar cycloaddition.

Bimolecular cycloaddition reactions of isomünchnones derived from the rhodium(II) catalyzed cyclization of diazo pyrrolidinones

Abstract 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.

Azomethine ylide generation via the dipole cascade

Abstract A series of N-acyl 2-diazo-3-oxobutanoates, when treated with a catalytic quantity of a rhodium(II) carboxylate, were found to afford substituted pyrroles derived from an azomethine ylide intermediate. The initial reaction involves generation of the expected carbonyl ylide dipole by intramolecular cyclization of the keto carbenoid onto the oxygen atom of the neighboring amide group. The primary cycloadduct undergoes a subsequent rearrangement-fragmentation reaction to give the pyrrole derivative. When the α-position of the α-diazoketone was blocked with two methyl groups, the rhodium(II)-catalyzed cycloaddition with dimethyl acetylenedicarboxylate led to the carbonyl vlide cycloadduct in high yield. MNDO calculations show that the cyclic carbonyl ylide derived from ethyl 2-diazo-4-dibenzoylamino-3-oxobutyrate is 3.3 kcal lower in its heat of formation than the corresponding azomethine ylide. This thermodynamic difference in stability of dipoles nicely accounts for why the carbonyl ylide cycloadduct is the major product from the rhodium(II) catalyzed reaction of ethyl 2-diazo-4-dibenzoylamino-3-oxobutyrate.

Generation and cycloaddition reactions of transient alkyl-substituted anhydro-4-hydroxythiazolium hydroxides

Abstract Transient alkyl-substituted anhydro-4-hydroxythiazolium hydroxides undergo efficient inter- and intramolecular cycloaddition to provide the corresponding 1,3-dipolar cycloadducts in high yield.