Investigations into the Regioselectivity of Fischer Indole and Friedländer Quinoline Syntheses with Octahydroisobenzofuran and Octahydroisoindole Derivatives

Abstract

A Fischer indole synthesis with a cis-configurated octahydroisobenzofuran-6-one yielded exclusively a furo[3,4-c]carbazole derivative as the product of a regioselective angular annulation reaction. A Friedländer quinoline synthesis from the same substrate gave a mixture of angular and linear annulation products, i. e. furo[3,4-a]acridine and furo[3,4-b]acridine derivatives. When submitting a mixture of cis- and trans-octahydroisoindole derivatives to Fischer and Friedländer syntheses, the trans-starting material gave regioselectively linear annulation products, i. e. pyrrolo[3,4-b]carbazole and pyrrolo[3,4-b]acridine derivatives. In contrast, the respective cis-configurated isoindole gavemixtures of angular and linear annulation products. The constitutions and relative configurations of nine new indole and quinoline derivatives were established by 2D NMR experiments and X-ray singlecrystal investigations.