Synthesis and carbon-13 NMR study of 2-benzyl, 2-methyl, 2-aryloctahydropyrrolo [3,4-c] pyrroles and the 1,2,3,5-tetrahydropyrrolo [3,4-c] pyrrole ring system

2-Benzyl, 2-phenyl, 2- (3-methoxyphenyl) and 2-(3-trifluoromethylphenyl) octahydropyrrolo[3,4-c]pyrrole (9a, 9b, 9c, and 9d, respectively) were prepared in five steps from 1-benzylpyrrole-3,4-dicarboxylic acid (2). 2-Methyloctahydropyrrolo [3,4-c]pyrrole (9′a) was prepared analogously in six steps from 1-methylpyrrole-3,4-dicarboxylic acid (3). Diborane reduction of 1-benzyl-N-methyl-1H-pyrrole-3,4-dicarboximide (7′a) and 1, N-dibenzyl-1H-pyrrole-3,4-dicarboximide (7a) gave 5-benzyl-2-methyl and 2, 5-dibenzyl-1,2,3,5-tetrahydropyrrolo [3,4-c]pyrrole (19′ and 19, respectively); the first reported members of the 1,2,3,5-tetrahydropyrrolo[3,4-c]pyrrole ring system. A detailed study of the carbon-13 nmr shifts permitted a complete assignment for all compounds. Mono and disubstituted products produce a systematic effect on the shifts for the bicyclic ring systems which can be readily interpreted in terms of substituent chemical shifts. The effect of protonation at nitrogen is also shown to produce a series of well defined chemical shifts for the octahydropyrrolo [3,4-c] pyrrole ring system.