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.