INTRAMOLECULAR CYCLOADDITIONS WITH ISOBENZOFURANS XI(1)-SYNTHESIS OF ANNULATED INDOLES

Transition metal catalyzed decomposition of diazoester 4b results in t he formation of furo[3, 4-b]indol 5. This intermediate is trapped intr amolecularly in situ to give 6. Furo[3, 4-b]indoles of type 10 can be prepared similarly, but intramolecular Diels-Alder reactions seem to b e prevented for sterical reasons. Some quantum chemical calculations ( AM1, PM3, ab initio, density functional studies) concerning the geomet ry and different reactivity of benzo[c]furans and furo[3, 4-d]indoles are reported. The results are in agreement with observations.