Tandem synthesis of [1,2,4]-triazoles mediated by iodine—a regioselective approach
摘要:
A tandem regioselective one-pot synthesis of 3-amino-[1,2,4]-triazoles has been achieved from 1,3-disubstituted thioureas using molecular iodine. In this one-pot strategy, the intermediate carbodiimide generated in situ from thiourea upon reaction with HCONHNH2 gives diaryl/alkylhydrazinecarboximidamide or acylureidrazone, which then undergoes an intramolecular cyclodehydration to afford the corresponding 3-amino-[1,2,4]-triazole. The product regioselectivity for unsymmetrical 1,3-disubstituted thioureas correlate well with the pK(a)s of the parent amines attached, in which the amine having higher pK(a) goes to the ring nitrogen while the other nitrogen remains flanked as an exocyclic nitrogen of the triazole core. This method is milder and environmentally sustainable giving good to excellent yields of the desired products. (C) 2012 Elsevier Ltd. All rights reserved.
A novel artificial receptor based on 2,2′-binaphthalene skeleton bearing two thiourea groups was prepared via nickel(II)-catalyzed homocoupling of the corresponding bromide. The receptor showed high binding ability for F− and AcO− in acetonitrile.
Synthesis and anion recognition properties of 2,2'-binaphthalene derivatives bearing two thiourea (1) and urea (2) groups at 8- and 8'-positions were studied. The structure of receptor 1 was determined by Xray crystallography. UV-vis spectra of the receptors showed characteristic changes around 300-400 nm through isosbestic points upon the addition of biologically relevant anions such as acetate, dihydrogenphosphate, and chloride in MeCN and DMSO due to restriction of the rotation around the single bond connecting two naphthyl moieties by cooperative guest binding of two recognition sites. Job's plots showed 1:1 complexation for guest anions. The fluorescence quantum yields of free form of 1 and 2 in MeCN were determined to be 0.021 and 0.57, respectively. The fluorescence intensities of the receptors diminished upon the addition of anions in MeCN. The association constants of receptors 1 and 2 were one or two orders of magnitude greater than the corresponding monothiourea and urea receptors 3 and 4 indicating cooperative hydrogen bonding with guest anions. The selectivity trends of association of anions were F->AcO->H2PO4->Cl->>HSO4- approximate to NO3- approximate to Br- approximate to l(-) for 1, and F->AcO- approximate to Cl->H2PO4-> Br->HSO4->l(-) approximate to NO3- for 2. Receptor 2 showed remarkable Cl- selectivity presumably owing to suitable orientation for effective hydrogen bond formation with Cl-. (C) 2010 Elsevier Ltd. All rights reserved.
Dyson; Hunter; Morris, Journal of the Chemical Society, 1932, p. 2283
作者:Dyson、Hunter、Morris
DOI:——
日期:——
Alpha-Naphthyl Isothiocyanate as a Reagent for Primary and Secondary Aliphatic Amines