Pyryliumverbindungen. XXII. 1H-NMR- und UV-spektroskopische Untersuchungen zur Isomerisierung von Pseudobasen unsymmetrisch substituierter 2, 4, 6-Triarylpyryliumsalze

Pyrylium Compounds. XXII. ¹H-N.M.R. and U.V. Spectroscopic Investigations on the Isomerization of Pseudobases of Unsymmetrically Substituted 2, 4, 6-Triarylpyrylium Salts The kinetics and mechanism of the isomerization of the title compounds, the pentene 1,5-diones 2 and 3 , were studied by ¹H-n.m.r. and u.v. spectroscopy. The equilibrium constants measured vary little near 1, indicating the small influence of substituents on the equilibrium position. The mutual rearrangement 2 ⇄ 3 proved to be a base-catalized reaction which is characterized by strictly linear Hammett correlation between 1g k and Σσ_p. The results obtained suggest resonance-stabilized anions of type 4 as intermediates. - Pseudobases of 3-alkyl-2, 4, 6-triarylsubstituted pyrylium salts do not undergo a reversible isomerization.     

Quantenchemische Untersuchungen zur Farbe und Stereodynamik von acyclischen Azinen. XV. Zum strukturellen Aspekt des Photochromie-Effektes

Quantum Chemical Studies on Colour and Stereodynamics of Acyclic Azines. XV. On the Structural Aspect of the Photochromic Effect For the longest-wavelength colour-determining electronic transition of selected arylsubstituted acyclic azines the curvature of λ=λ(θ_cc) has been adapted by means of polynomic and trigonometric functions. On this basis it is possible to discuss the structural aspect of the photochromic and aphotochromic behaviour being observed due to the (E, Z) isomerization.     

Organoarsen-Verbindungen. XXV. Synthese und Reaktionen von 1.3-Azarsolidin-2-thionen

Synthesis and Reactions of 1, 3-Azarsolidine-2-thiones Secondary 2-aminoethylarsines of the type RAs(H) CH₂CH₂ NHR′ react with CS₂ yielding 1,3-azarsolidine-2-thiones. Under suitable conditions the corresponding ammonium salts of the 2-arsinoethyl-dithiocarbamates are isolable as primary reaction products. 1,3-Azarsolidine-2-thiones are attacked by electrophilic agents on the sulfur atom yielding 2-alkylthio- and 2-organostannylthio-azarsolines, respectively, as well as 1,3-azarsolidine-2-ones.     

Spektroskopie und Photochemie indigoider Verbindungen. V. Quantenchemische Berechnungen zum unterschiedlichen UV/S-Spektralverhalten der trans- und cis-Isomeren thioindigoider Verbindungen

Spectroscopy and Photochemistry of Indigoid Compounds. V. Quantum Chemical Calculations on the Different UV/VIS Spectral Behaviour of trans- and cis-Isomers of Thioindigoid Compounds The concept of non-bonding S…O-interaction [3] has been proved for some thioindigoid compounds. The different spectral behaviour of trans- and cis-isomers with regard to the long wave absorption band is mainly dependent on the number of S…O-structural units and on the S…O-distance. As compared to a coplanar structure twisting about the central double bond can result both in an increasing and a decreasing spectral shift.     

Pyryliumverbindungen. XVIII, 2-Alkoxy-2H-pyrane aus tetra- und pentasubstituierten Pyryliumsalzen

Pyrylium Compounds. XVIII. 2-Alkoxy-2H-pyrans from Tetra- and Pentasubstituted Pyrylium Salts Alkali alkoxides add regioselectively to 2,3,4,6-tetrasubstituted pyrylium salts 7 (R' H), affording high yields of colourless crystalline 2-alkoxy-2H-pyrans 9 . The latte are also formed simply on refluxing 7 in the corresponding alcohol with triethylamine as proton acceptor. 3,5-Dialkylsubstituted 2,4,6-triarylpyrylium salts react analogously. The 2H-pyran structure of the adducts obtained follows from their n.m.r., i.r., u.v. and mass spectra as well as from their reaction with tetracyanoethylene to cycloadducts of type 10 . Acids regenerate from 9 the original pyrylium cations, whereas reaction of 9 with nitromethane or ethyl cyanoacetate provides benzene derivatives. -- The novel starting pyrylium salts 7b--o are characterized by u.v./vis data and by transformation into the corresponding pyridine derivatives     

Pyryliumverbindungen. XXI. Struktur und Tautomerie von Pseudobasen unsymmetrisch substituierter 2,4,6-Triarylpyryliumsalze

Pyrylium Compounds. XXI. Structure and Tautomerism of Pseudobases of Unsymmetrically Substituted 2,4,6-Triarylpyrylium Salts Hydrolytic ring opening of unsymmetrically substituted 2,4,6-triarylpyrylium salts 11 results in a mixture of two tautomeric pseudobases, the penten-1,5-diones 13 and 14 . In crystalline state as a rule one of these tautomers markedly predominates, whereas in solution a rapid equilibrium establishment occurs which can be followed by ¹H-n.m.r. and u.v. spectroscopy (equilibrium ratio nearly 1:1). The ¹H-n.m.r. spectroscopic structural assignment of the two isomeric forms was supported by u.v. spectroscopic studies using 1:1 mixtures of the chromophoric partial systems ArCOCHCHPh and ArCOMe or the pseudobases 10 of symmetrically substituted 2,4,6-triarylpyrylium salts 9 as reference systems. From the mass spectra of the pseudobases 10 and 13 / 14 follows that – if hydrolysis of 11 is performed in media containing H₂¹⁸O – mass spectrometric isotopic analysis of the resulting ¹⁸O-labelled pseudobases allows no information to be made about the regioselectivity of the ring opening. – Novel starting pyrylium salts of type 9 and 11 are characterized by u.v./vis data and by transformation into the corresponding pyridine derivatives.     

Quantenchemische Berechnungen zur Addition von CH3–XFX (X = 0,…,3) an Ethen. I. Semiempirische Untersuchungen mit der AM1-Methode

Quantum Chemical Calculations on the Addition of CH₃–_XF_X (X = 0,…,3) to Ethene. I. Semiempirical Investigations by Means of the AM1 Method AM1 calculations are reported for the homolytical addition of CH_3–XF_X (X = 0,…,3) to ethene. The structures of the reactants, the products and the transition states, as well as the reaction enthalpies are described reasonably. The calculated activation barriers are significantly different from the experimental activation energies, probably because the parametrisation is not well suited for the energetics of radical species, especially radical transition states. MNDO gives similar results, MINDO/3 fails completely.     

Pyryliumverbindungen. XXIII. 2-Dialkylamino-2H-pyrane aus tetra- und pentasubstituierten Pyryliumsalzen

Pyrylium Compounds. XXIII. 2-Dialkylamino-2H-pyrans from Tetra- and Pentasubstituted Pyrylium Salts. Tetra- and pentasubstituted pyrylium salts of type 6 react with secondary alkyl amines to give stable crystalline 2-dialkylamino-2h-pyrans 7 . In the case of tetrasubstituted pyrylium salts 6 , R′ = Me, R″ = H the reaction occurs regioselectively leading to 2H-pyrans with Me at C-3 of the heterocyclic ring. The structure of the reaction products was established by n.m.r., i.r., u.v. and mass spectroscopic methods. Electrophilic agents like protons, carboxylic acid chlorides or methyl iodide regenerate the original pyrylium cations from 7 . In refluxing methanol 7a is converted into the 2-methoxy-2H-pyran derivative 8 , whereas in aqueous acetone the pseudobase 9 and with ammonia the pyridine 10 are formed. Reaction of 7a with nitromethane or ethyl cyanoacetate provides the benzene derivatives 11 and 12 , respectively.     

Untersuchungen zur regioselektiven Halogenierung von 4-Amino-2-iodmethyl-6-methyl-pyrimidinen

Studies on the Regioselective Halogenation of 4-Amino-2-iodomethyl-6-methylpyrimidines In the presence of oxidants, 4-amino-2-iodomethyl-6-methylpyrimidines 2 undergo regioselective reactions in the positions 2 and/or 5. Thus, the reaction of 2a with hydrogen peroxide proceeds under dealkylation and iodination to give 4-amino-5-iodo-6-methylpyrimidine 7 . Depending on reaction temperature and molar ratios the reaction of 2a with bromine or chlorine leads to the corresponding 4-amino-5-halogeno-2-halogenomethyl-6-methyl-pyrimidines 2c, 9a and 9d . The 5-substituted pyrimidines 2b, c afford the 2-bromo (or chloro) methyl derivatives 9b, c .     

超声辅助合成2-氨基-3,5-二氰基-4H-吡喃衍生物

以苯甲酰乙腈、苯甲醛、丙二腈为原料,碳酸钠为催化剂,超声条件下三组分反应合成2-氨基-3,5-二氰基-4H-吡喃衍生物。单因素法筛选催化剂、溶剂,正交实验法考察反应时间及温度、原料物质的量比对产率的影响。获得的最优条件为:乙醇作溶剂,反应温度为70℃,反应时间25 min,n(苯甲醛)∶n(丙二腈)∶n(苯甲酰乙腈)=1.0∶0.9∶0.9,产率最高为98.1%。