Synthesis and nuclear magnetic resonance spectra of fused pyrimidines

Ethy phenylpropiolate reacted with 2-aminobenzothiazoles, benzimidazoles, thiazoline and thiazole to give the corresponding fused 2-oxopyrimidines. 2-Mercaptobenzimidazole reacted with ethyl phenylpropiolate to give 4-phenyl-2H-1-thiapyrimido(1,2-a ]benzimidazol-2-one in very good yield. The thiones, methylthio iodides and the hydrobromides of some of the products were prepared. Analysis of the nmr spectra of the benzothiazole and benzimidazole products and their 3-deuterio analogs showed that the proton at position 6 is shielded and absorbs together with the proton at position 3 near δ 6.0 ppm. The nmr and ir spectral data of all the products are tabulated and discussed.     

Synthesis and some properties of vanadocene isocyanate and isothiocyanate d1-complexes

Conclusions Vanadocene monochloride and vanadocene dichloride react with organotin and organosilicon pseudohalides, R₃MNCX (R₃M=Bu₃Sn, Me₃Si and X=O, S), to give the corresponding vanadium (IV) d¹-complexes, Cp₂V(NCX)₂ or Cp₂VCl(NCX).Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 678–681, March, 1988.     

Synthesis of fused pyrimidines from amines and cyclic β-formylesters

A highly efficient method was successfully developed for the synthesis of fused pyrimidines via aminoheterocyclic dihydrofuranone intermediates obtained from 2-aminoheterocycles and cyclic β-formylesters by three different methods.     

Ring-cleavage of isoxazoles with heterocyclic amines. Synthesis of fused pyrimidines

The reaction between 2-substituted ethyl 2,5-dihydro-5-oxoisoxazole-4-carboxylates ( 2a,b ) and heterocyclic amines 1, 4 , and 6 , having the amino group in position 2 with respect to the nuclear nitrogen afforded fused pyrimidines 3, 5 , and 7 .     

Synthesis and properties of isocyanate and isothiocyanate d1- and d2-complexes of vanadocene

The reactions of vanadocene and its halides Cp₂VCl and Cp₂VCl₂ with R₃MNCX (M  Sn, Si, X  O, S) and R₂M(NCX)₂ in various molar ratios have been studied. The reactions proceed either by an exchange of groups, with no change in the oxidation state of vanadium, or by an oxidative addition of pseudohalide ligand: V^II → V^III; V^III → V^IV. Oxidative addition results in the formation of (R₃M)₂ or gaseous hydrogen (in the reaction with HCl) in the reaction products.We have prepared the first ever monomeric and readily oxidisable d²-complexes of V^III of Cp₂VNCX-type and asymmetric d¹-complexes of Cp₂V(Cl)NCX type, which, although rather stable in air, undergo disproportionation into symmetric d¹-complexes on heating. In transmetallation reactions the ligand activity is found to increase in the order C1 < NCO < NCS. The complexes were characterised by GLC analysis, IR and ESR spectroscopy. A general scheme for the disproportionation reaction of asymmetric complexes of vanadocene is supported by differential thermal analysis data.     

Conformations and vibrational spectra of allyl isocyanate and allyl isothiocyanate

The infrared spectra of allyl isocyanate and allyl isothiocyanate as vapours and liquids were recorded in the region 4000-50 cm^?1. Additional spectra of the amorphous and crystalline solids at ?180°C were recorded between 4000 and 400 cm^?1. p]Raman spectra, including semiquantitative polarization measurements were obtained of the liquids, and spectra of the unannealed as well as of the crystalline solids at ?180°C were recorded.A considerable simplification of the vibrational spectra of the crystals compared to the liquids was observed as a consequence of the conformational equilibria in these compounds. It can be concluded with confidence that a cis conformation of the allyl group was present in the crystals of both compounds with additional gauche conformers in the liquids. No definite conclusions can be reached regarding the conformational arrangement of the -NCX groups. A remarkable similarity was observed between the spectra of the two compounds, and all the fundamental frequencies except the lowest C-N torsion have been assigned for the cis conformers. More than ten fundamentals for the gauche conformers have also been assigned.     

Synthesis of fused bicyclic pyridines with microwave-assisted intramolecular hetero-Diels-Alder cycloaddition of acetylenic pyrimidines

A series of acetylenic pyrimidines was synthesized and subjected to microwave irradiation. In contrast to conventional heating, the microwave irradiations generally gave clean conversion to fused bicyclic pyridines for all substrates reported with shorter reaction time. This method has been successfully applied to the synthesis of both fused lactones and lactams.     

Synthesis of some new fused coumarin derivatives

2-Hydrazino-4-hydroxy-5H- [1] -benzopyrano- [ 4,3-d ] -pyrim-idin-5-one (3) was prepared via condensation of 2 with hy-drazine hydrate. Treatment of 3 with methylene chloride, ethyl chloroformate, ethyl chloroacetate and benzaldehyde yielded the corresponding 2 - ( substituted ) hydrazino - 4 -hydro-xy-5H-[1]-benzopyrano-[4, 3-d]-pyrimidin-5-one (4, 5, 6, and 10), followed by cyclization of 4, 5 and 6 with dimethyl fonnamide and fused sodium acetate under reflux, while compound 10 was cyclized with bromine and sodium acetate in acetic acid. Compound 3 reacted with β-(toloyl) acrylic acid, ethyl α-cyano-p-methoxytinnamate, diethyl mal-onate and acetyl chloride affording the corresponding 2-(substituted) hydrazino-4-hydroxy-5H-[1]-benzopyrano-[4, 3-d]-pyrimidin-5-one (12, 13, 14, 15 and 16).     

Synthesis and characterization of new planar butterfly-shaped fused oligothiophenes

A simple oxidative cyclization reaction was used to construct new seven-ring-fused butterfly-shaped oligothiophene backbone: dibenzothieno[1,2-b:4,3-b′:6,7-b″:9,8-b″′]tetrathiophene. The new materials show high stability and strong solid state fluorescence. X-ray crystallography results reveal that they exist in 2-D stacked structures in their crystals.     

Synthesis of new chiral N-substituted fused pyrazoles and pyrazolinols

Treatment of β-diketones and the corresponding β-enaminoketones, having modified carane (2-ethyl-6,6-dimethylbicyclo[3.1.0]hexane) and p-menthane (3-ethyl-1-isopropylcyclopentane) skeletons, with aryl- and alkylhydrazines results in regioselective formation of N-substituted pyrazoles or stable pyrazolinols depending on the nature of the substituent at the hydrazine nitrogen.     

Electron diffraction investigation of the molecular structures of isopropyl isocyanate and isopropyl isothiocyanate

The molecular structures of isopropyl isocyanate and isopropyl isothiocyanate have been determined by electron diffraction in the gas phase. For both molecules the data are consistent with the presence of a single conformer at room temperature, with the NCX group eclipsing one of the C---C bonds of the isopropyl group (a skew conformation). The structures found are consistent with the limited information available from microwave studies. The skeletal parameters found are (NCO, NCS; distances in pm, angles in degrees): r(C---N) 146.0(8), 145.9(13); r(C---C) 153.4(5), 15.8(7); r(N=C) 121.4(6), 120.1(6); r(C=O) 118.4(4); r(C=S) 159.8(5); NCC 110.0(5), 110.4(10); CCC 114.7(9), 115.7(13); C---N=C 132.6(10), 135.9(17); NCX 159(3), 166(3); C---N torsion 125(3), 115(6) (where a torsion angle of 120° corresponds to the skew form). The results are compared with those for some related molecules.     

Synthesis of new fused isoquinolines via reissert compounds

Reissert compounds 2 derived from isoquinoline, chloroformates and TMS‐cyanide were alkylated in position 1. The resulting alkylation products 3 as well as the precursors 2 reacted with Grignard reagents affording imidazoisoquinolines 4, 5, 7 and 8 by addition to the cyano group and Grignard reduction or by twofold addition to the cyano group, respectively. In both cases the alcohol of the 2‐alkoxycarbonyl moiety was eliminated by attack of the N‐atom at the carbonyl carbon atom. Under acid conditions, 1‐benzylated Reissert compound 3h cyclised by attack of the resulting N‐acyliminium C‐atom at the o‐position of the benzyl ring to form tetracyclic 1,3‐bridged tetrahydroisoquinolines 10 and 11. Bromocyclisation of 1‐allyl‐2‐menthyloxycarbonyl‐substituted Reissert compounds 3b, c led to tricyclic dibromo products 12, in which the menthol moiety was split off and addition to the enamine double bond occurred. A 2‐menthyloxycarbonyl group in Reissert compounds 2a and 3 failed to exert an asymmetric induction in all cases.     

Synthesis of fused pyrimidines with N‐, S‐heterocyclic moieties by double‐annelation reaction

A variety of tri‐ and tetracyclic hetero systems were obtained by reaction of heteroaromatic ortho‐aminoesters or ortho‐aminonitriles with iminothioether, yielding double‐annelation of a thiazolo[3,2‐a]‐pyrimidine, pyrimido[2,l‐b]thiazine, imidazo[1,2‐a]pyrimidine, and pyrimido[1,2‐a]pyrimidine moieties in a one‐pot process.     

Synthesis of substituted fused pyridines, pyrazines and pyrimidines by sequential Ugi/inverse electron demand Diels–Alder transformations

The synthesis of all four regioisomers of fused pyrrolidino-pyridines in a one-pot two-step sequential Ugi-inverse electron demand Diels–Alder reaction is described. Fused pyrrolidino-pyrazines, pyrrolidino-pyrimidines and azepinone pyridines can also be obtained in consecutive synthetic sequences.