(5‐Imino‐4,5‐dihydro‐3H‐pyrrol‐2‐yl)amines as Sterically Restrained 1,3,5‐Triazapenta‐1,3‐dienes: Useful Building Blocks for the Synthesis of Oligonitriles

Abstract

Abstract(5‐Imino‐4,5‐dihydro‐3H‐pyrrol‐2‐yl)amines 2 may be considered as sterically restrained 1,3,5‐triazapenta‐1,3‐dienes. They were easily prepared from 2,2,3,3‐tetramethylsuccinonitrile (1) and lithium amides with subsequent aqueous workup to give the monocyclic compounds 2a–d and the bi‐ and tricyclic compounds 2e–g. X‐ray diffraction studies of 2c and 2d, which contain a primary NH2 group, reveal the existence of homodimers held together with paired hydrogen bonds in the solid state. Trapping of the lithiated intermediate 2a‐Li by benzoyl chloride provided access to the 1‐oxa‐3,5,7‐triazahepta‐1,3,5‐triene 3b. It is characterized in the solid state by a planar heterocyclic subunit and a strongly twisted N‐acylamidine part. With 1‐oxa‐3,5‐diazinium salts 4, compounds 2a,b,d or 2a‐Li reacted to give 1‐oxa‐3,5,7,9,11‐pentaazaundeca‐1,3,5,7,9‐pentaenes 5a–d. Here again, the planar heterocyclic parts combine with longer, twisted (not helical) oligonitrile moieties. The X‐ray diffraction study of 5d indicates intermolecular N–H···O=C hydrogen bonding in the solid state, producing one‐dimensional strands. In a similar way as 1 the trinitrile 2,3,5‐trimethyl‐2,3,5‐tricyanohexane (6), a byproduct of the thermal decomposition of azoisobutyronitrile (AIBN), reacted with lithium benzylamide to give a bicyclic intermediate which was successfully converted into the corresponding 1‐oxa‐3,5,7,9,11,13‐hexaazatrideca‐1,3,5,7,9,11‐hexaene 7 when treated with 1‐oxa‐3,5‐diazinium salt 4b. Similar to 5d, this extended oligonitrile forms one‐dimensional hydrogen‐bonded polymers in the solid state. Its UV spectrum (λmax = 286 nm) is interpreted in terms of a planar conjugated π–π* azapolyene substructure forced into planarity by the heterocycles.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)