The synthesis of polycyclic benz‐fused pyrroles

Pyrrolo[1,2‐f]phenanthridine (2), benzo[f]pyrrolo[2,1‐a]isoquinoline (3), 5,6,7,8,9,10,11‐hexahydrobenzo[g]pyrrolo[2,1‐a]isoquinoline (5), and pyrrolo[2,1‐a]isoquinoline (6) dicarboxylic acid diesters were prepared in 1,3‐dipolar cycloaddition reactions between dimethyl acetylenedicarboxylate and the hydrofluoroborate salt of the appropriate Reissert compound. Several of the different methods to prepare Reissert compounds are compared and the carbon‐13 nmr spectra for the Reissert compounds are reported. Carbon‐13 nmr was used to assign the structures of isomers 10 and 11; the latter compounds arose from a prior reaction in which the cyclization of β‐(5,6,7,8‐tetrahydro‐2‐naphthyl)ethylamine N‐formate which gave a mixture of hexahydroisoquinolines, 8a and 9a. Pyrrolo[1,2‐b]isoquinoline (12) and pyrrolo[2,1‐a]isoquinoline dicarboxylic acid diesters were made in münchnone cycloaddition reactions. The latter compound was made from tetrahydroisoquinoline‐1‐carboxylic acid which was readily prepared from isoquinaldic acid by catalytic reduction. The dehydrogenation of several of the partially saturated compounds is also discussed.