Solid-phase rhodium carbenoid reactions: An N-H insertion route to a diverse series of oxazoles

[GRAPHICS] 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 alpha -diazo-beta -ketoesters. These reactions are performed in the presence of primary amides and yield the corresponding N-H insertion products, Subsequent cyclodehydration of these alpha-(acylamino)-beta -ketoesters provides the corresponding resin-bound 2,5-disubstituted oxazoles, which are further elaborated during cleavage from the resin.