Mechanism for annelation ([2+4] cyclocondensation) of Schiff bases by β-dicarbonyl and β,β′-tricarbonyl compounds in amphiprotic media (review)

The mechanism was established for annelation ([2+4] cyclocondensation) of Schiff bases or azomethines by β-dicarbonyl and β,β′-tricarbonyl compounds in amphiprotic media. The condensation was found to be a self-catalyzed pericyclic process achieved through six-membered transition states. The key reaction intermediates are dipoles of quaternized azomethine ions and enol-anions of the β-dicarbonyl and β,β′-tricarbonyl compounds, which display 1,4-dipolarophilicity. Dedicated to Academician A. A. Akhrem of the Belarus Academy of Sciences on the Occasion of His Ninety-Fifth Birthday __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 335–346, March, 2008.     

Thiosalicyloylhydrazones of aliphatic aldehydes and their cyclization to give 1,3,4-benzothiadiazepine derivatives

¹H and ¹³C NMR spectroscopy showed that the previously unknown thiosalicyloylhydrazones of aliphatic aldehydes, 2-HSC₆H₄CONHN=CHAlk (Alk = Me, Et, Pr, Bu, i-Pr, i-Bu) exist in solution as a tautomeric mixture of the linear and cyclic 1,3,4-benzothiadiazepine forms. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 460–464, March, 2008.     

Synthesis and structure of new 3-pyrazolinylcoumarins and 3-pyrazolinyl-2-quinolones

The reactions of substituted 3-cinnamoyl-4-hydroxycoumarins and 3-cinnamoyl-4-hydroxy-2-quinolones with different phenylhydrazines gave 3-hetaryl-1H-4,5-dihydropyrazoles. The product structures were studied by ¹H NMR spectroscopy and mass spectrometry. 4-Hydroxy-3-pyrazo-linylcoumarins exist in DMSO as two tautomers (4-enol and chromane-2,4-dione), while 4-hydroxy-3-pyrazolinyl-2-quinolones exist only in the enol form. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1479–1486, July, 2008.     

A Bistable Molecular Switch Driven by Photoinduced Hydrogen‐Atom Transfer

The occurrence of photoinduced hydrogen atom transfer between two remote spots of a molecule is experimentally demonstrated. This photoprocess involves the intermediacy of an intramolecular “crane”. In an experimental case study, 7‐hydroxy‐4‐methylquinoline‐8‐carbaldehyde monomers isolated in low‐temperature Ar matrices are investigated. On UV (λ>295 nm) irradiation, a hydrogen atom is transferred from the O⁷H group to the N¹ atom of the quinoline ring. Subsequent irradiation with UV (λ>360 nm) light reveals that the phototransformation is partially photoreversible. In the studied hydrogen‐atom‐transfer process, the exocyclic carbaldehyde group plays the role of an intramolecular crane. The possible application of systems analogous to 7‐hydroxy‐4‐methylquinoline‐8‐carbaldehyde as optically driven molecular switches is discussed.     

Experimental and theoretical study of the electronic absorption spectra of some 1,2‐benzoquinone diazides: Closed–open tautomerism

The electronic absorption spectra as well as molecular orbital (MO) calculations at the ab initio level of some 1,2‐benzoquinone diazides have been studied. The results of spectral study support the open isomer over the closed one (1,2,3‐oxadiazole derivative) and indicate the contribution of both the benzenoid and quinonoid structures to the molecule. Spectral results were confirmed by MO calculations. The results of the latter gave a lower total energy for a benzoquinone diazide than for 1,2,3‐benzoxadiazole structure. Bond length and charge density indicate the contribution of both quinonoid and benzenoid structures for the studied compounds. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 78: 52–62, 2000     

2-酰基-1,3-环二酮类化合物互变异构的理论计算

采用MP2/6-31+G**//B3LYP/6-31+G**方法,系统地研究了2-酰基-1,3-环二酮类化合物的互变异构性质,探讨了环的饱和性、环的大小、环上杂原子以及溶剂效应对各互变异构体相对稳定性的影响。结果表明:(1)未烯醇化的异构体由于无法形成分子内氢键而具有较高的能量;(2)环上杂原子的推电子效应提高了邻位羰基氧上的负电荷,从而有利于相应环外烯醇式异构体的稳定;(3)对化合物3-酰基-1H-吡啶-2,4-二酮,3-酰基吡喃-2,4-二酮,2-酰基环戊-4-烯-1,3-二酮和3-酰基吡咯-2,4-二酮,由互变异构形成的环的芳香性在各异构体的相对稳定性中扮演着决定性的作用。     

Synthesis and properties of polyamidines

Polymers with amidine groups  NH CRN in the main chain were prepared by acid catalysed melt polycondensation of 4,4′-diaminodiphenyl methane (DAPM) with various orthoesters. The resulting polyamidines were characterized by ¹H-, ¹³C- and ¹⁵N-NMR spectroscopy, differential scanning calorimetry (DSC), thermogravimetry (TGA) and wide angle x-ray scattering (WAXS) measurements. The properties of the polyamidines are strongly determined by the substituent R on the amidine group. Some peculiarities of the polyformamidine (RH) could be attributed to the conformation of the amidine group. Glass transition temperatures varied from 106 to 161°C depending on the substituent R. All polyamidines possessed good thermal stability up to 370°C and, with exception of the polyformamidine, good solubility in common solvents. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 929–938, 1998