New Indigoid Compounds by Reduction of Bis-Imidoylchlorides of Oxalic Acid – A Further Evidence for Dimeric Isocyanides?

Abstract

a cross-over experiment further evidences of intermediates corresponding to dimeric isocyanides could be verified. Mechanistical aspects are discussed. The structure of (V) is determined by X-ray analysis.

The Elusive 1,4‐Diazabutatrienes: Lurking in the Shadows

“…After almost two decades of absence the 1,4‐diazabutatrienes reappeared in the scientific literature in 1999 when Beckert et al attempted the systematic preparation of several 1,4‐diaryl‐1,4‐diazabutatrienes 13 by reduction of a range of bisimidoyl chlorides 12 derived from oxalic acid with magnesium under sonication . However, these processes led, presumably by means of the biradical intermediates 14 , to dimeric species as indigo dianils and dibenzo[ b,g ][1,5]naphthyridine‐6,12‐diimines 15 in low yields (Scheme b).…”

“Nindigo”: synthesis, coordination chemistry, and properties of indigo diimines as a new class of functional bridging ligands

“…Indigo N,N 0 -bis(arylimine)s 3 have been identified as minor decomposition products of aryl isonitriles 9 and can be made in low yields from oxalyl chloride N,N 0 -bis(arylimine)s; 10,11 none of these represent practical synthetic routes. The preparation of indigo N,N 0 -diphenylimine (3a) from the reaction of indigo with aniline was described over a century ago, 12 but this could not be reproduced by us or others.…”

Recent Advances in the Synthesis of 5‐MemberedN‐Heterocycles via Rhodium Catalysed Cascade Reactions

“…Isocyanide based reactions for instance multicomponent reactions, [31a,b] [3+2]‐cycloaddition of activated methylene isocyanides with polar multiple bonds, [31c,d] transition metal‐catalyzed isocyanide insertion and radical insertions, [31e,f] has its importance in constructive organic synthesis. Synthesis of fused heterocyclic compounds via in situ coupling‐cyclization of two isocyanides using 1,4‐diazabutatriene species has emerged as an efficient protocol [31g–l] . The existence of 1,4‐diazabutatriene was first proved by Beckert and co‐workers, in 1999 by reduction of bis‐imidoyl chlorides of oxalic acid [31g] .…”

“…Synthesis of fused heterocyclic compounds via in situ coupling‐cyclization of two isocyanides using 1,4‐diazabutatriene species has emerged as an efficient protocol [31g–l] . The existence of 1,4‐diazabutatriene was first proved by Beckert and co‐workers, in 1999 by reduction of bis‐imidoyl chlorides of oxalic acid [31g] . Afterwards, the related coupling‐cyclization reactions of 2‐pyridylisonitriles or o‐isocyanostyrenes were reported independently by Cheng and Kobayashi groups respectively [31h,i] .…”

“…Recently, Xu's and Li's group developed a new cross‐cyclization from non symmetrical 1,4‐diazabutatriene generated by the hetero dimerization of two different isocyanides [31j,k] . However, all of the above reactions were limited to functionalized aryl isocyanides [31g–l] . In 2020 a novel rhodium‐catalyzed homo dimerization‐cyclization reaction of two vinyl isocyanides 44 was developed by Wang and co‐workers.…”