33684-12-7Relevant articles and documents
A novel cycloaddition reaction of α-diazo-γ-amido ketones catalyzed by rhodium(II) acetate. Scope and mechanistic details of the process
Pawda, Albert,Price, Alan T.,Zhi, Lin
, p. 2283 - 2292 (2007/10/03)
α-Diazo ketones containing an amido group in the γ-position have been found to underdo a novel rhodium(II)-catalyzed cycloaddition reaction. Intramolecular cyclization of the keto carbenoid onto the oxygen atom of the amide group generates a carbonyl ylide dipole as a transient species. This highly stabilized dipole does not readily undergo 1,3-dipolar cycloaddition but ruther transfers a proton to produce a cyclic ketene N,O-acetal. The ketene acetale is unstable to moisture and upon standing is readily hydrolyzed to a γ-keto-δ-lactone and an amine. In the absence of any significant amount of water, the ketene N,O-acetal undergoes conjugate addition with the activated ?-bond of the dipolarophile to give a zwitterion intermediate. The anionic portion of the zwitterion adds to the neighboring carbonyl group. This is followed by epoxide ring formation with charge dissipation leading to an amido-substituted spiro cyclopentenyl epoxide. In certain cases a hydroxyl lactone was also isolated and its formation can be attributed to the competitive hydrolysis of the zwitterionic intermediate. The Rh(II)-catalyzed reaction of the diazo ketoamide derived from N-benzylpiperidone with DMAD afforded two different types of cyloadducts. In addition to the spiro cyclopentenyl epoxide, a product derived from trapping of the carbonyl ylide dipole was also obtained, thereby providing additional support for the proposed mechanism.
