New vanadium mediated one-pot in situ (L)-histidine based ligand cyclization and aerobic dehydrogenative aromatization

New vanadium mediated in situ cyclization and subsequent aerobic dehydrogenative aromatization of two (L)-histidine based ligands viz. salicylidene-L-histidine and 5-bromosalicylidene-L-histidine have been reported here. Oxidative cyclization resulted from the intra ligand C-C bond formation between C(sp(2)) of (L)-histidine imidazolyl ring and the imine C-H. The newly synthesized dioxovanadium(V) complexes of cyclized ligands namely [n-Bu4N][VO2(L-1)], 1 (H2L1 = 4-(2-Hydroxyphenyl)-1H-imidazo[4,5-c]pyridine-6-carboxylic acid) and [nBu(4)N][VO2(L-2)], 2 (H2L2 = 4-(5-Bromo-2-hydroxyphenyl)-1H-imidazo[4,5-c]pyridine-6-carboxylic acid) have been characterized by 1H NMR, ESI-HRMS and IR techniques. Further, the structure of complex [n-Bu4N] [VO2(L-1)], 1 has been determined unambiguously by single crystal X-ray crystallography.

Automated summary

A new vanadium mediated in situ cyclization and subsequent aerobic dehydrogenative aromatization of two (L)-histidine based ligands has been reported. The synthesized dioxovanadium(V) complexes of cyclized ligands have been characterized and the structure of one complex has been determined by single crystal X-ray crystallography.