-cycloaddition of alkyl vinyl ethers to 3-aroylpyrrolo[1,2-a]quinoxaline-1, 2-dione

Reactions of 3-aroylpyrrolo[1,2-a]quinoxaline-1,2diones with activated alkenes were not studied previously. We examined reactions of 3-(4-chlorobenzoyl)4-(4-chlorophenyl)pyrrolo[1,2-a]quinoxaline-1,2-dione (I) with alkyl vinyl ethers IIa and IIb at a ratio of 1 : 5 in boiling toluene (20–30 min, until violet color typical of initial compound I disappeared) and obtained new difficultly accessible bridged heterocyclic compounds, 16-alkoxy-2,14-bis(4-chlorophenyl)-15-oxa-3,10-diazatetracyclo[8.7.0.0.0]heptadeca-2,4,6,8,13pentaene-11,12-diones IIIa and IIIb. Compounds IIIa and IIIb are likely to be formed via thermal [4 + 2]cycloaddition of the O=C–C=C conjugated bond system in pyrrolo[1,2-a]quinoxaline-1,2-dione I at the polarized double C=C bond in vinyl ether IIa or IIb. crystallized from toluene. Yield 78%, mp 224–225°C. IR spectrum, ν, cm: 1728 (C=O), 1713 (C=O). H NMR spectrum, δ, ppm: 0.81 t (3H, CH3, J = 7.0 Hz), 2.18 d.d (1H, 17-H, J = 13.4, 4.6 Hz), 2.36 d (1H, 17-H, J = 13.4 Hz), 3.37 m (1H, OCH2), 3.44 m (1H, OCH2), 5.62 d (1H, 16-H, J = 4.6 Hz), 7.40– 7.93 m (12H, Harom). Found, %: C 65.75; H 4.38; N 5.15. C30H24Cl2N2O4. Calculated, %: C 65.82; H 4.42; N 5.12.