Three Cycloadducts Formed by the Reaction of Bis(phenylazo)stilbene with Acetylenic and Olefinic Dipolarophiles

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.

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