DIHALOCARBENE ADDITION TO ARYLSUBSTTTUTED VINYL PHOSPHATES UNDER PHASE TRANSFER CATALYTIC CONDITIONS

Abstract

Dihalocarbene addition to aryl-substituted vinyl phosphates was carried out both in solid-liquid and in liquid-liquid two phase systems. The dihalocyclopropane adducts of vinyl phosphates could be obtained in better yield using dihalocarbenes generated by the latter method and no hydrolysis of the vinyl phosphate and of the adduct occurred under these circumstances. Eighteen new vinyl phosphate-dihalocarbene adducts were synthetized and characterized.     

Thioformaldehyde S-methylide and thioacetone S-methylide: an ab initio MO study of structure and cycloaddition reactivity

The mechanisms of cycloaddition of thioformaldehyde S-methylide and thioacetone S-methylide, as models for an alkyl-substituted ylide, to thioformaldehyde and thioacetone, as well as to ethene as a model for a C=C double bond have been studied by ab initio calculations. Restricted and unrestricted B3LYP/6-31G* calculations were performed for the geometries of ground states, transition structures, and intermediates. Although basis sets with more polarization functions were tested, the 6-31G* basis set was applied throughout. Single-point CASPT2 calculations are reported for analysis of the unsubstituted system. The stabilities of structures with high biradical character seem to be overestimated by DFT methods in comparison to CASPT2. The general trends of the results are independent of the level of theory. Thioformaldehyde adds to thioformaldehyde S-methylide without activation energy, and the activation energies for two-step biradical pathways to 1,3-dithiolane are low. C,S biradicals are more stable than C,C biradicals. The two-step cycloaddition is not competitive with the concerted cycloaddition. Methyl substitution in the 1,3-dipole and the dipolarophile does not change the mechanistic relationships. TSs for the concerted formation of the regioisomeric cycloadducts of thioacetone Smethylide and thioacetone were located. Concerted addition remains the preferred reaction. The reactivity of the C=S double bond is high relative to that of the C=C double bond.     

Synthesis of Novel Imines Containing Indolizine Moiety

Reaction of 2‐phenylindolizine‐3‐carbothialdehyde with amine derivatives provides a new, mild and efficient synthesis of a series of heterocyclic imines. The corresponding structures of products were established by IR, ¹H NMR, MS and elemental analysis. And the reaction mechanisms was also discussed.     

New reaction of thiocarbonyl ylides. Interaction ofS-alkyl-N,N-dimethylthiobenzimidium salts with activated acetylene derivatives leading to (E,E)-divinyl sulfides

The reaction of thiocarbonyl ylides with activated acetylene derivatives gives (E,E)-divinyl sulfides in good yields. The reaction mechanism is discussed and evidence in favor of the formation of a thiirane intermediate is presented. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 791–795, April, 1997.     

1,3-dithiolanes from cycloadditions of alicyclic and aliphatic thiocarbonyl ylides with thiones: regioselectivity

The regiochemistry of 1,3-dithiolanes obtained from thiocarbonyl ylides 9 and thiones 10 shows a striking dependence on substituents. Previously and newly performed experiments indicate that sterically hindered cycloalkanethione S-methylides and dialkylthioketone S-methylides react with alicyclic and aliphatic thiones to give the 2,2,4,4-tetrasubstituted 1,3-dithiolanes 11 exclusively. Aryl groups in one or both reactants lead to a preference for, or even complete formation of, 4,4,5,5-tetrasubstituted 1,3-dithiolanes 12. Several mechanisms appear to be involved, but the paucity of experimental criteria is troubling. Quantum-chemical calculations (see preceding paper) on the cycloaddition between thioacetone S-methylide and thioacetone furnish lower activation energies for the concerted process than for the two-step pathways via C,S- or C,C-biradicals; the favoring of the 2,4-substituted 1,3-dithiolanes over the 4,5-substituted type would be expected to increase with growing bulk of substituents. Aryl groups stabilize intermediate biradicals. Experimental criteria for the differentiation of regioisomeric dithiolanes are discussed. Thiocarbonyl ylides 9 are prepared by 1,3-cycloadditions between diazomethane and thioketones and subsequent N(2) elimination from the usually isolable 2,5-dihydro-1,3,4-thiadiazoles 17; different ratios of the two rate constants lead to divergent product formation scenarios.     

硫代羰基化合物激发态结构及光化学反应的理论预示

运用精确的量子化学计算方法，优化了几种硫代羰基化合物（H2CS，CH3CHS和 CH3CSCH3）的基态和激发态的结构，计算了它们的相对能量。不同的方法得到的结 构参数比较一致，并与可用的实验结果相符。计算结果表明，三个分子的S1，T1和 T2态的能量非常接近，而S2态的能量明显高于T2态，这个理论结果与先前关于CH2 ＝CH2，CH2CHO和CH2＝CH－CH＝CH2的研究的结论是一致的。用不同的方法对基态 和最低三态的角途径进行了理论优化，得到的结果较好地一致。并且利用优化的基 态和最低三态解离的势能剖面，和光激发到各个电子态的可用能量，对硫代羰基化 合物的光解离反应的机理进行了理论预示。     

Quantum mechanical studies of environmental effects on biomolecules

SCFab initio computations have been performed on the structure, molecular potential and hydration scheme of thiourea in view of a comparison with urea and more generally as a model of the conjugated S=CNH-group as compared to O=CNH-. In contrast to the carbonyl oxygen, both σ and π acceptor, the sulfur atom of the thiocarbonyl is a σ donor but a π acceptor and this results in an enhancement of the double-bond character of thiourea. The CN bond is less attractive for a proton than urea. The hydration scheme indicates a maximum number of four water molecules directly bound to thiourea.     

Density functional evaluation and a feasibility study of intramolecular thione–thiol tautomerization

Performance of various density functionals for use in geometry and energetics calculation of thiocarbonyl systems is evaluated. The three biologically significant systems such as 2‐methyl‐3‐thiosemicarbazide, 1‐acetyl‐2‐thiohydantoin and bornane‐2‐thione are selected for the geometry analysis. Energy of tautomerization of thioacetone and enthalpy of formation of 2‐thiohydantoin are considered for analyzing the performance in energetics. Minnesota functionals such as M05‐2X, M06‐2X and range separated hybrid functional wB97 give best results in both geometry and energetics calculations. Studies on basis set effect showed reliable performance by 6‐31 + G* and 6‐31++G** over higher basis sets. Feasibility of tautomerization in the aforementioned thiones has been investigated using the best performing density functionals. The proposed thione–thiol tautomerization step during PPC‐DC catalyzed decarboxylation reaction has also been investigated and the computed high energy barrier shows less feasibility of the reaction.