Several aspects of the Rh2 (OAc) 4-catalyzed intramolecular NH, 0-H, and SH insertion reactions have been studied. Examination of the effect of ring size revealed that four-, five- and six-membered nitrogen heterocycles can be efficiently prepared from the corresponding a-diazo@-keto ester precursors (ga-c), whereas competing CH insertion prevented formation of the seven-membered heterocycle. Variations in solvent, temperature, and ...