Solid-Phase Rhodium Carbenoid Reactions:  An N−H Insertion Route to a Diverse Series of Oxazoles

The solid-phase synthesis of a series of oxazoles is described. The key step in the construction of these molecules involves the rhodium-catalyzed decomposition of polymer-bound α-diazo-β-ketoesters. These reactions are performed in the presence of primary amides and yield the corresponding N−H insertion products. Subsequent cyclodehydration of these α-(acylamino)-β-ketoesters provides the corresponding resin-bound 2,5-disubstituted oxazoles, which are further elaborated during cleavage from the resin.