An efficient approach to isoindolo[2,1-b]benzazepines via intramolecular [4+2] cycloaddition of maleic anhydride to 4-alpha-furyl-4-N-benzylaminobut-1-enes
Acylation of 4-alpha-furyl-4-N-benzylaminobut-1-enes with maleic anhydride gave 4-oxo-3-aza-10-oxatricyclo[184.108.40.206(1,5)]dec-8-ene-6-carboxylic acid via amide formation followed by intramolecular Diels-Alder reaction of furan (IMDAF). The cycloaddition proceeded under mild reaction conditions (25 degreesC) and provided only the exo-adduct in quantitative yield. Treatment of this compound with PPA gave isoindolo[2,1-b] benzazepine derivatives via ring opening, aromatization and intramolecular electrophilic alkylation. In order to extend the scope of the reaction sequence, 7-oxo-5,11b,12,13-tetrahydro-7H-isoindolo[2,1-b]benzazepine-8-carboxylic acids were further transformed into useful synthetic intermediates. (C) 2004 Elsevier Ltd. All rights reserved.