Rhodium(II)-catalyzed cyclization of amido diazo carbonyl compounds.
A series of acyclic diazo ketoamides were prepared from N-benzoyl-N-alkylaminopropanoic acids and were treated with a catalytic amount of rhodium(II) acetate. The resultant carbenoids underwent facile cyclization onto the neighboring amide carbonyl oxygen atom to generate seven-membered carbonyl ylide dipoles. Subsequent collapse of the dipoles with charge dissipation produce bicyclic epoxides which undergo further reorganization to give substituted 5-hydroxydihydropyridones in good yield. Depending on the nature of the substituent groups, it was possible to trap some of the initially formed carbonyl ylide dipoles with a reactive dipolarophile such as DMAD. In other cases, cyclization of the dipole to the epoxide is much faster than bimolecular trapping. A related cyclization/rearrangement sequence occurred when diazo ketoamides derived from the cyclic pyrrolidone and piperidone ring systems were subjected to catalytic quantities of Rh(II) acetate. With these systems, exclusive O-cyclization of the amido group onto the carbenoid center occurs to generate a seven-ring carbonyl ylide dipole. Starting materials are easily prepared, and the cascade sequence proceeds in good yield and does not require special precautions. The overall procedure represents an efficient one-pot approach toward the synthesis of various indolizidine and quinolizidine ring systems.
Padwa
A
A
Department of Chemistry, Emory University, Atlanta, Georgia 30322, USA.
Hasegawa
T
T
Liu
B
B
Zhang
Z
Z
D002384:Catalysis; D003500:Cyclization; D003979:Diazonium Compounds / Q000138:chemical synthesis*; D013058:Mass Spectrometry; D000644:Quaternary Ammonium Compounds / Q000737:chemistry; D012238:Rhodium
D003979:Diazonium Compounds; D000644:Quaternary Ammonium Compounds; D012238:Rhodium