REGIOSPECIFIC HETERO-DIELS-ALDER SYNTHESIS OF FURO[2,3-G] AND FURO[3,2-G]QUINOLINE-4,9-DIONES

Diels-Alder reactions of 5- or 6-bromobenzofuran-4,7-diones 7 or 10 to wards azadienes 1 afford regiospecifically furo[2,3-g] or furo[3,2-g]q uinoline-4,9-diones 3 or 4. Assignment of the regioisomers, made by 2D NMR H-1-C-13 HMBC experiments, showed that the regiochemistry of the cycloadditions is under control of the bromine atom position. Calculat ions by the semiempirical method PM3 of the HOMO and LUMO orbital coef ficients of azadienes 1 and quinones 2 indicated that the larger ones are situated at C-4 for 1 and C-5 for 2. Copyright (C) 1996 Elsevier S cience Ltd