Metal-complex catalysis during the reduction of functional groups by sodium borohydride in the synthesis of pyrrolidine derivatives

A selective method was developed for the reduction of functional groups with sodium borohydride using complexes of CoCl₂ and CuCl₂ with triethylbenzylammonium chloride and cobalt and copper mesotetra[4-(2-hydroxyethyl)pyridyl]porphyrinates as catalysts. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 205–208, February, 2006.     

The first 4-dialkylamino-1,2-dihydropyridine derivatives: synthesis and basic reactions

The first two 4-dialkylamino-1,2-dihydropyridine derivatives 4a and 4b are prepared in good yield by addition of n-butyllithium or t-butyllithium to 4-dimethylaminopyridine 1 followed by quench with diethylcarbonate. Compound 4a can be hydrolyzed under mild conditions providing 4-dihydropyridone 5, an interesting acceptor building block. On the other hand reaction of 4a with dimethyl acetylene dicarboxylate gives benzene derivative 7 via a cycloaddition-cycloreversion path.     

The synthesis and borohydride reduction of some alloxazine derivatives

Unequivocal syntheses of N(1 or 3)-mono-substituted 7, 8-dimethylalloxazines are described. The borohydride reduction of various alloxazines has been studied under aerobic and anaerobic conditions, in the absence of light. These reactions are discussed in relation to other work on 7, 8-dimethylisoalloxazines (flavins) and on certain flavoproteins.     

Electronic structure and conformational flexibility of 1,2-dihydropyridine, 1,2- and 1,6-dihydropyrimidines,and their ylide derivatives

Molecular and electronic structures of 1,2-dihydropyridine, 1,2- and 1,6-dihydropyrimidine, and their oxo, imino, and methylene derivatives were studied by the semiempirical quantum-chemical AM1 method. In all compounds, the heterocycle exhibits a high conformational flexibility. The transition from a planar equilibrium conformation to a distorted sofa conformation with the =C-NH-C-C(N)= torsion angle of ±20° causes an increase in the energy by less than 1.7 kcal mol^–1. All molecules have similar -electronic structures, which, apparently, determines the similarity in their conformational behavior. The bending strain and the nonaromatic character of the cyclic -system are the factors that stabilize the nonplanar conformation of the ring in unsubstituted dihydroazines and ylide derivatives, respectively.Translated fromIzvestiva Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1934–1937, August, 1996.     

具有生物活性的1,4-二氢吡啶衍生物的水热法合成及结构表征

1,4-二氢吡啶衍生物具有很好的生理活性。在医学上用作心血管疾病的防治保健药物,不仅能治疗肠胃疾病、雷诺氏病、脂肪肝、中毒性肝炎,也有抗衰老、防早熟等作用,还可以用作治疗肺动脉高压和癫痫病的辅助药物[1-2]。近年又发现1,4-二氢吡啶衍生物不但是一类高效的钙拮抗剂,亦是一种绿色饲料添加剂。它的合成通常采用文献报道的Hantzsch法合成[3],即将干燥氨气通入乙酰乙酸乙酯与醛的混合溶液中。该反应时间长、操作复杂,且氨气易对环境造成污染。正因为此,越来越多的化学家和药物学家将有机合成的研究重点放在对环境无污染的绿色合成上。如…     

Free radicals in the electrochemical reduction of derivatives of 3,5-dinitro-1,2-dihydropyridine

The characteristics (potentials, limiting currents, reversibility) of the electrochemical reduction of 3,5-dinitro-1,2-dihydropyridines were determined by cyclic voltammetry and polarography. It was established by ESR that the free radicals formed in these processes have a radical-dianion structure in the case of both the N-unsubstituted and the N-substituted dihydropyridines. The hyperfine coupling constants of the interaction between the unpaired electron and the nuclei of the atoms at various positions of the heterocycle were determined.Latvian Institute of Organic Synthesis, Riga LV-1006. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 212–218, February, 1997.     

One-pot synthesis of quaternary pyridinium salts and tetrahydropyridine derivatives of fusidane triterpenoids

Chemistry of Heterocyclic Compounds - An efficient one-pot method was developed for the preparation of quaternary pyridinium salts and tetrahydropyridine derivatives of fusidane triterpenoids,...     

Synthesis and reactions of some derivatives of 1,2-dihydrothiazolo [3,2-a]pyridinium salts

The condensation of 2-mercaptopyridine, 2-mercapto-4-methylpyridine, and 2-mercapto-6-methylpyridine with -bromoacetaldehyde and its diethyl acetal has given cyclic products (3-hydroxy- and 3-ethoxy-2,3-thiazolo[3,2-a]pyridinium salts), from which cyanine dyes have been synthesized.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1254–1257, September, 1973.     

Convenient synthesis of fluorinated quinoline, 1,2-dihydroquinoline, and 1,2,3,4-tetrahydroquinoline derivatives

A convenient synthetic method for 2-polyfluoroalkylated quinoline systems through the efficient generation of perfluoroalkylated imine from o-vinylanilines with perfluorinated hemiacetals or aldehyde hydrates was developed. In most cases, the major products are 2-polyfluoroalkyl-1,2-dihydroquinoline derivatives 3, which can be converted to either quinolines or 1,2,3,4-tetrahydroquinolines.     

Skeletal remodeling of chalcone-based pyridinium salts to access isoindoline polycycles and their bridged derivatives

Simultaneous deconstructive ring-opening and skeletal reconstruction of an inert, aromatic pyridinium ring is of great importance in synthetic communities. However, research in this area is still in its infancy. Here, a skeletal re-modeling strategy was developed to transform chalcone-based pyridinium salts into structurally intriguing polycyclic isoindolines through a dearomative ring-opening/ring-closing sequence. Two distinct driving forces for the deconstruction of the pyridinium core were involved in these transformations. One was the unprecedented harnessing of the instability of in situ generated cyclic β-aminoketones, and the other was the instability of the resultant N,N-ketals. The desired isoindoline polycycles could undergo the Wittig reaction with various phosphorus ylides to achieve structural diversity and complexity. Notably, by tuning the Wittig conditions by addition of one equivalent of base, an additional bridged ring was introduced. A plausible mechanism was proposed on the basis of control experiments and theoretical calculations.

A novel skeletal remodeling strategy to transform chalcone-based pyridinium salts into structurally intriguing polycyclic isoindolines was achieved through a dearomative ring-opening/ring-closing sequence.     

A novel synthesis of amino-1,2-oxazinones as a versatile synthon for beta-amino acid derivatives

The radical addition-cyclisation of alpha, beta-unsaturated hydroxamates containing an oxime ether provides a novel method for the stereoselective synthesis of amino-1,2-oxazinones. Its synthetic utility is demonstrated by a stereoselective synthesis of beta-amino acid derivatives, such as alpha-alkyl-beta-amino-gamma-lactone and alpha,beta-disubstituted beta-lactam.     

Studies on the method of total synthesis of koumine: I. 4-Substituted 1,2-dihydropyridine derivatives and their function as a conjugated diene in Diels-Alder reaction

A route to the total synthesis of koumine has been suggested. Five 4-substituted 1, 2-d hydropyridine derivatives, which are supposed to be a conjugated diene of Diels-Alder reaction to produce the isoquinuclidine ring of koumine, have been synthesized. Only two of them were found to be able to undergo the Diels-Alder reaction. The stereochemistry of the reaction product has also been examined.     

Regioselective reduction of 3-substituted N-acylpyrazinium salts toward the synthesis of 1,2-dihydropyrazines

The regioselective reduction of 3-substituted N-acylpyrazinium salts with n-Bu(3)SnH has been developed for the synthesis of 3-substituted 1,2-dihydropyrazines in yields of 56-94%. Substitution of the pyrazinium salts with electron-donating groups favors the formation of the 1,2-isomers as a result of their better stability over the 1,6-isomers. Under mild acidic conditions, 3-methoxy substituted 1,2-dihydropyrazine was easily hydrolyzed in excellent yield to Δ(5)-2-oxopiperazine.     

Theoretical investigation of the reducing capacity of sodium borohydride and sodium acetoxyborohydride derivatives

The reducing capacity of sodium borohydride and its acetoxy derivatives was studied. Density functional theory using four different functionals were used to investigate the enthalpies, charges and molecular structures of four distinct reactions associated with hydride release. The theoretical results in the gas phase reinforce the experimental observations that the acetoxyborohydride derivative reducing capacities are a consequence of both the inductive electron-withdrawing ability of the acetoxy group and the steric bulk surrounding the BH bond. The electron acceptor effect of the acetoxy group provided a linear relation between the boron GAPT charges and the enthalpy necessary to remove the hydride from sodium borohydride, justifying the smaller or even nonexistent reductor capacity of more substituted borohydrides.     

Features of the molecular structure of pyridinium salts and their dissolving power with respect to cellulose

Main geometric parameters and electronic structure of molecules of alkylpyridinium chlorides, bromides, and acetates were calculated by a quantum-chemical method. The influence of the electronic structure of molecules on their dissolving power with respect to cellulose was analyzed.     

Ultrafast room-temperature reduction of graphene oxide by sodium borohydride,sodium molybdate and hydrochloric acid

Since graphene-based materials have shown great potential in many fields,it is important to explore ultrafast and high-efficient methods to synthesize reduced graphene oxide(rGO) using inexpensive reducing agents under mild conditions.Here,we reported a novel method for the ultrafast chemical reduction of graphene oxide(GO) at room temperature using sodium borohydride(NaBH₄),sodium molybdate(Na₂MoO₄) and hydrochloric acid(HCl).The reduction was carried out within 2 min.A series of characterization results revealed that the obtained reduced graphene oxide has higher reduction degree than that synthesized by NaBH₄ alone at high temperature.Moreover,rGO electrode based on the present reducing method exhibited a superior specific capacitance of 139.8 F/g at a current density of1 A/g,indicating that it can be used as electrode materials for supercapacitors.     

Dehydrogenation of 1,4-dihydropyridine derivatives by the action of hydroperoxides in the presence of metal salts

Conclusions Molybdenum, tungsten, vanadium, and other metal salt-catalyzed hydroperoxide oxidation is a convenient preparative method for the dehydrogenation of 1,4-dihydropyridines to pyridine bases.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 670–671, March, 1972.