Synthesis and Reactions of a Novel Furo[3,4-d]oxazole

The synthesis of a novel furo[3,4- d ]oxazole ( 7 ) starting from 2-hydroximino-3-oxopentanedioic acid dimethyl ester ( 4 ) and cycloadditions of 7 with dienophiles are reported. Density functional theoretical studies (B3LYP/6-31G*) for various c -annulated furans (benzo[ c ]furan, furo[3,4- d ]isoxazole, furo[3,4- d ]oxazole, furo[3,4- d ]thiazole, furo[3,4- b ]indole) and their Diels−Alder reactions with model dienophiles (ethylene, acetylene) are in qualitative agreement with experimental data.