Acid-base equilibriums of lumichrome and its 1-methyl, 3-methyl, and 1,3-dimethyl derivatives

Lumichrome photophysical properties at different pH were characterized by UV-vis spectroscopy and steady-state and time-resolved fluorescence techniques, in four forms of protonation/deprotonation: neutral form, two monoanions, and dianion. The excited-state lifetimes of these forms of lumichrome were measured and discussed. The results were compared to those obtained for similar forms of alloxazine and/or isoalloxazine, and also to those of 1-methyl- and 3-methyllumichrome and 1,3-dimethyllumichrome. The absorption, emission, and synchronous spectra of lumichrome, 1-methyl- and 3-methyllumichrome, and 1,3-dimethyllumichrome at different pH were measured and used in discussion of fluorescence of neutral and deprotonated forms of lumichrome. The analysis of steady-state and time-resolved spectra and the DFT calculations both predict that the N(1) monoanion and the N(1,3) dianion of lumichrome have predominantly isoalloxazinic structures. Additionally, we confirmed that neutral lumichrome exists in its alloxazinic form only, in both the ground and the excited state. We also confirmed the existence and the alloxazinic structure of a second N(3) monoanion. The estimated values of pK(a) = 8.2 are for the equilibrium between neutral lumichrome and alloxazinic and isoalloxazinic monoanions, with proton dissociation from N(1)-H and N(3)-H groups proceeding at the almost the same pH, while the second value pK(a) = 11.4 refers to the formation of the isoalloxazinic dianion in the ground state.     

Synthesis of 2-methylthio-4H-1,3-thiazines

2-Methylthio-4H-1,3-thiazines or their mixtures with 5-alkylidene-4H-5,6-dihydro-1,3-thiazines were obtained by cyclization of methyl N-3-oxoalkyldithiocarbamates in sulfuric acid. The regiospecificity of the reaction is determined by the structures of the starting compounds. The structures of the synthesized thiazines were confirmed by spectral methods of analysis (IR and ¹H and ¹³C spectroscopy).Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 991–993, July, 1992.     

Synthesis of substituted 2-amino-4H-1,3-oxazines

4,4,6-Trimethyl-2-methylarylamino-4H-1,3-oxazines were synthesized by intramolecular cyclization of N-oxoalkyl-S-methylisothioureas.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 764–767, June, 1974.     

Synthesis and structural investigation of new isothiochromen-4-one 2,2-dioxide derivatives

This article presents a combined experimental and computational study of novel isothiochromene 2,2-dioxide derivatives, which were synthesized by the electrophilic substitution reactions. The compounds have been studied by NMR, IR spectroscopy and single-crystal X-ray analysis. According to X-ray diffraction data, the six-membered ring of 6 adopts a distorted half-chair conformation, but in case of compounds 7 and 8, we have a twist-boat conformation of the six-membered ring with deviation of the S1 and C8 atoms from the mean plane of the remaining atoms of the ring, respectively. Results of quantum-chemical calculations of possible isomers and tautomers of the isolated oxime 8 and azo compounds 10 at the B3LYP/aug-cc-pVDZ level indicate that the oxime-oxo tautomer (8a) is more stable than the nitroso-hydroxy tautomer (8b) in agreement with the crystal data and that the keto tautomer (II) is more stable than the hydroxyl tautomer (I) and zwitterion tautomer (III), because of a strong intramolecular hydrogen bond N–H···O.

     

2-异丙基-1,3-二氢-4(1H)异喹啉酮及其衍生物的合成

报道了异喹啉酮与格氏试剂反应合成四氢-4-羟基异喹啉酮化合物,NBS和混酸(HNO~3/HAc)与异喹啉酮反应合成异喹啉酮衍生物。6个新化合物的结构,通过元素分析,红外光谱和核磁共振氢谱,质谱给予证实。     

Diastereodivergent cis- and trans-fused [4 + 2] annulations of cyclic 1,3-dienes and 1-azadienes via ligand-controlled palladium catalysis

Despite the blossoming of reports of diastereodivergent synthesis over the past years, switchable control of the stereochemistry of the bridgehead atoms of the fused frameworks has been significantly underdeveloped. Here we disclose the ability of Pd⁰-π-Lewis base catalysis to finely reverse the concerted inverse-electron-demand aza-Diels–Alder cycloaddition reaction between cyclic 1,3-dienes and aurone-derived 1-azadienes. In contrast, the in situ-formed HOMO-energy-increased Pd⁰-η²-complexes of cyclic 1,3-dienes underwent a cascade vinylogous Michael addition/allylic amination process with 1-azadienes. Moreover, judicious selection of chiral ligands allowed for switchable diastereodivergent [4 + 2] annulations to be accomplished, resulting in the construction of both cis- and trans-fused tetrahydropyridine architectures in high yields with moderate to excellent stereoselectivity levels. A variety of acyclic 1,3-dienes and 1-heterodienes were also applied, and furnished a structural diversity of enantioenriched frameworks.

Diastereodivergent and asymmetric [4 + 2] annulations between cyclic 1,3-dienes and 1-azadienes via ligand-controlled Pd catalysis have been realized, furnishing both cis- and trans-fused tetrahydropyridines in good yields and stereoselectivity levels.     

Synthesis and mesomorphic properties of some derivatives of 2-methylcyclohex-2-ene-4-one-1-carboxylic and cis-2,6-dimethyl cyclohex-2-ene-4-one-1 -carboxylic acids

Mesomorphic derivatives prepared from ethyl esters of 2-methylcyclohex-2-ene-4-one-1-carboxylic and cis-2,6-dimethylcyclohex-2-ene-4-one-1-carboxylic acids have been synthesized. It has been shown that the compounds obtained are characterized by a lower nematic—isotropic transition temperature (10-20°C) and a considerably narrower nematic range in comparison with the analogous derivatives of 4-alkylcyclohex-3-ene-carboxylic and trans-4-alkylcyclohexane-carboxylic acid.     

Synthesis of substituted 2-amino-5,6-dihydro-4H-1,3-thiazines and 2-iminotetrahydro-1,3-thiazines

N-Aryl-N′-(2-methyl-4-hydroxy-2-pentyl)thioureas are cyclized in acidic media to 4,4,6-trimethyl-2-arylimino-5,6-dihydro-4H-1,3-thiazines, the methylation of which with methyl iodide gives 4,4,6-trimethyl-2-methylarylamino-5,6-dihydro-4H-1,3-thiazines. 3,4,4,6-Tetramethyl-2-aryliminotetrahydro-1,3-thiazines were synthesized by cyclization of Naryl-N′-methyl-N′-(2-methyl-4-hydroxy-2-pentyl)thioureas.     

Synthesis of derivatives of 1,3-dihydrospiro[2h-indole-2,2′-pyrrolidine]

Derivatives of 1,3-dihydrospiro[2H-indole-2,2-pyrrolidine] were synthesized by the reaction of 2-methylene-2,3-dihydro-1H-indoles with -iodoacetamide. Treatment of the products with alkyl iodides in the presence of potassium hydroxide gave 1-substituted spiroindole-2,2-pyrrolidines. The 1,3-dihydrospiro[2H-indole-2,2-pyrrolidines] were converted by the action of perchloric acid into 2-(2-carbamoylethyl)-3H-indolium perchlorates.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 57–59, January, 1989.     

Synthesis of substituted 2-arylimino-2,3-dihydro-4H-1,3-thiazines

The synthesis of 3,4,4,6-tetramethyl-2-arylimino-2,3-dihydro-4H-1,3-thiazines, which have a fixed imino structure, was accomplished by two methods: by intramolecular rearrangement of 1,4,6,6-tetramethyl-3-aryl-1,2,3,6-tetrahydropyrimidine-2-thiones and by amination of 3,4,4,6-tetramethyl-2,3-dihydro-4H-1,3-thiazine-2-thione methiodide.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 941–943, July, 1972.     

Comparative conformational analysis of 2,2-dimethyl and 2,2,5-trimethyl-1,3-dioxanes and their 2-heteroanalogs with silicon and germanium atoms

Comparative conformational analysis of 2,2-dimethyl- and 2,2,5-trimethyl-1,3-dioxanes as well as their 2-heteroanalogs with silicon and germanium atoms has been performed by means of computer simulation using HF/pVDZ, hybrid DFT PBE/3ξ, and RI-MP2/λ2 methods. The potential energy surface for all the studied compounds has revealed the presence of the chair and 2,5-twist conformers. The latter form, in the case of substituted 1,3-dioxa-2-silacyclohexanes at the HF/pVDZ level, is a transition state rather than an intermediate minimum. The molecules of 2-sila- and 2-germa-1,3-dioxacyclohexanes exhibit an enhanced conformational flexibility as compared to the 1,3-dioxanes.     

Synthesis of 2-sulfanylidene-1,3-thiazolidin-4-one derivatives

Three-component condensation of primary amines with carbon disulfide and dialkyl maleates afforded the corresponding alkyl (3-R-4-oxo-2-sulfanylidene-1,3-thiazolidin-5-yl)acetates whose structure was confirmed by independent synthesis and IR and ¹H NMR spectroscopy.