Rhodium-catalyzed heterocycloaddition route to 1,3-oxazoles as building blocks in natural products synthesis

Rhodium(II) acetate serves as a catalyst for the heterocycloaddition reaction of diazodicarbonyl compounds with nitriles to give functionalized 1,3-oxazole derivatives in a simple one-step procedure. In particular, dimethyl diazomalonate undergoes this reaction to give 2-aryl-, 2-alkenyl-, or 2-alkyl-4-carbomethoxy-5-methoxy-1,3-oxazoles, and ethyl formyldiazoacetate (diazomalonate half-ester half-aldehyde) gives 2-aryl-, 2-alkenyl-, or 2-alkyl-4-carboethoxy-1,3-oxazoles. These products are of potential importance as key intermediates in the synthesis of several oxazole-containing natural products and other heterocyclic systems.