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Our experimental survey provided evidence that catalyst-free reactions of phenylenediamine 3 with hydroxybenzaldehydes having no substitution in ortho-positions typically produce benzimidazole derivatives (e.g. 5, see the SI for synthetic and characterization details).This is in stark contrast to salicylaldehydes, i.e.Specifically, the reaction of 3,4-dihydroxybenzaldehyde (2) with 1,2-phenylenediamine (3) in methanol using the conditions reported by Yuan et al.consistently produced compound 1 being the sole isolated product in each of these experiments (Supplementary Table S1).
Structure 1 is expected to give a symmetric H NMR spectrum of the reaction product turned out to be more complex, and did not show the symmetry anticipated for structure 1 (Fig. After detailed NMR analysis using H, C-HSQC, H, C-HMBC, and H, H-COSY experiments, the identity of the product was shown to be consistent with the non-symmetric benzimidazole structure 1 having the benzimidazole moiety and two symmetrically non-equivalent dihydroxyphenyl units was obtained from single crystal X-ray structure analysis (Fig. This evidence provided unambiguous support for structure 1 also reported that carboxy-substituted diamine 4 reacts with aldehyde 2 to afford bis-imine 5 (Fig. They described the use of bis-imine 5 in a pull-down study to prove the existence of G-quadruplex structures in promoter region of oncogenes in vivo. Uncovering these assignment errors led us to formulate more general guidelines about additional misassignments in cases of published bis-imines derived from 1,2-phenylenediamine and hydroxybenzaldehydes having no substituent in ortho-positions.The main purpose of this article is to highlight this repetitive assignment error in the literature and thus increase the likelihood of correct assignments in future papers.In addition, the identity of compound 8 has been confirmed by our data from X-ray crystallography (8: CCDC 1418143, see S42). The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons license, users will need to obtain permission from the license holder to reproduce the material.The X-ray crystal structure of benzimidazole 11 (CCDC 852300) along with its synthesis has been reported previously in ref.