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organic compounds
Bis(phenylazo)stilbene, (1), undergoes facile cycloaddition reactions with acetylenic and olefinic dipolarophiles to give the corresponding cycloadducts. The cycloadducts of (1) with dibenzoylacetylene (DBA), trans-1,2-dibenzoylethylene (trans-DBE) and acrylonitrile (AN) have been unambiguously identified through X-ray crystallographic analysis as, formally, 5,6-dibenzoyl-2,3a,4,6a-tetraphenyl-2,3a,4,6a-tetrahydro- 1,2,3,4-tetraazapentalene [C42H30N4O2, (5)], 2,3a,4,6a-tetraphenyl-2,3a,4,5,6,6a-hexahydro- 1,2,3,4-tetraazapentalene-6-carbonitrile [C29H23N5, (6a)], and 5,6-dibenzoyl-2,3a,4,6a-tetraphenyl-2,3a,4,6a-tetrahydro- 1,2,3,4-tetraazapentalene [C42H32N4O2, (6b)], in each of which their is a delocalized double bond over N1, N2 and N3 [N1N2N3: N1N2/N2N3 = 1.297 (2)/1.305 (2), 1.308 (2)/1.302 (1) and 1.298 (1)/1.298 (1) Å for (5), (6a) and (6b), respectively]. In (5), the C(O)C6H5 substituent on C6 is almost fully conjugated with the C5=C6 double bond [O2=C32-C6=C5 torsion angle 166.4 (2)°]. Compounds (5), (6a) and (6b) are examples of a new class of heterocyclic compounds.