Intramolecular N-H, O-H, and S-H Insertion Reactions. Synthesis of Heterocycles from α-Diazo β-Keto Esters

Article abstract of DOI:10.1021/jo00225a047

Several aspects of the Rh2(OAc)4-catalyzed intramolecular N-H, O-H, and S-H 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 α-diazo β-keto ester precursors (9a-c), whereas competing C-H insertion prevented formation of the seven-membered heterocycle.Variations in solvent, temperature, and catalyst concentration were found to play an important role in determining the product distribution in the cyclization of the 6-carbamoyl 2-diazo 3-keto ester 9c.The intramolecular X-H insertion reaction has also been successful in the synthesis of oxygen (39) and sulfur (49) heterocycles as well as a heterocycle containing two (N, O) heteroatoms (34).