Preparation and spectral properties of the nitrogen analogs of (E)-5,5 '-diaryl-3,3 '-bifuranylidene-2,2 '-diones and their derivatives

(E)-5,5'-bis(2-methylphenyl)- and (E)-5,5'-bis(2,4,6-trimethyphenyl)-3, 3'-bifuranylidene-2,2'-diones and their isomeric pyrano[4,3-c]pyran-1,5-diones were converted into the nitrogen analogs, in which the aryl groups were twisted relative to the parent skeletons, and had small conjugation effect. Another nitrogen analogs bearing coplanar aryl rings were prepared, and their UV-VIS and NMR spectral data were compared with those of the analogs having twisted aryl groups. Conjugation effect of the 2-alkylphenyl group is bathochromic shift by 24 nm. Steric compression due to coplanarity of the aryl rings causes a deshielding of a H-1 NMR signal by similar to 0.6 ppm, and a shielding of a C-13 NMR Signal by similar to 5 ppm.