PREPARATION OF SOME PYRROLE-3,4-DICARBOXYLIC ACID-DERIVATIVES AND THE CRYSTAL-STRUCTURE OF 2-METHYLPYRROLO[3,4-C]PYRROLE-1,3(2H,5H)-DIONE

A series of pyrrole-3,4-dicarboxylic acid derivatives has been prepared, and the crystal structure of one, 2-methylpyrrolo[3,4-c]pyrrole-1,3(2H,5H)-dione, has been determined by X-ray diffraction and refined to a residual R 0.049 for 1415 observed reflections. Crystals are monoclinic, space group P2(1)/c, with Z = 8 in a cell of dimensions a 14.775(3), b 7.0692(5), c 15.151(3) angstrom, beta 118.82(8)-degrees. Strain in the planar fused ring system is evident from the widening of the external interring angles to 143-degrees, and from the unusual substituent effects in the C-13 n.m.r. spectra.