“…A solution of 2-phenyl-4(5//)-oxazolone12 (0.8 g, 0.005 mol) and DMAD (2.5 mL) in acetic anhydride (5 mL) was heated at 130 °C for 18 h. The volatile components were removed in vacuo and the residue taken up in benzene and chromatographed (silica gel, 75 g, eluted with Et20petroleum ether, 2:3) to afford as the only isolable component dimethyl 2-phenylfuran-3,4-dicarboxylate (5; R = Ph; R1 = COOCH3), 0.32 g (26%). It crystallized from CH3OH as colorless plates: mp 70-71 °C; IR (KBr) 3170, 3030, 2980 (CH), 1730, 1720 (CO) cm-1; Xmax (CH3OH) 259 nm (log r 3.34); NMR (CDC13) 7.89 (s, 1, Cs-H), 7.16-7.84 (m, 5, phenyl), 3.82 In a similar fashion 2-(4-chlorophenyl)-4(5//)-oxazolone (1.0 g, 0.005 mol), DMAD (2.5 mL, ca. 0.02 mol), and Ac20 (7 mL) were heated at 130 °C for 18 h. The volatile components were removed by evaporation and the residue chromatographed (silica gel, 40 g, eluted with Et20-petroleum ether 1:1) to give as the first component dimethyl 2-(4-chlorophenyl)furan-3,4-dicarboxylate (5, R = p-ClCeH4; R1 = COOCH3) crystallizing from CH3OH as fine colorless needles: 0.43 g (29%); mp 93-93.5 °C; IR (KBr) 1760, 1735 (CO) cm-1; Xmax (CH3OH) 278 nm (log e 4.24); NMR (CDCI3) 7.97 (C5-H), 7.61 (d, 2, aromatic), 7.32 (d, A second fraction crystallized from CH3OH to afford tetramethyl 1-(4-chlorophenyl)-7-oxabicyclo [2.2.1 ] hepta-2,5-diene-2,3,5,6-tetracarboxylate (6, R = p-ClCgH^a s colorless irregular prisms: 0.42 g (19%); mp 126-127 °C; IR (KBr) 1753,1735 (CO) cm"1; Xmax (CH3OH) 332 nm (log e 3.69), 224 (4.15); NMR (CDC13) 7.42 (s, 4, aromatic), 6.10 (s, 1. bridgehead CH), 3.80 (b, 12, CH3); M+-377 (6), 294 (100).…”