Addition Mechanisms of Phenol toward Formaldehyde under Acidic Condition： a Theoretical Investigation

The reaction mechanisms of phenol with formaldehyde in the first and second addition at the ortho- and para-position in acid solution were theoretically investigated at the PW91/DNP level with solvent effects included. The reaction of phenol with protonated methanediol firstly forms an adduct intermediate, via a SN2 mechanism with a water molecule as the leaving group. From the adduct intermediate, there are two reaction channels involving a proton transfer to form the addition products. One is that a proton directly transfers via a four-membered ring transition state with a notable energy barrier (Four-member mechanism). Another mechanism involving a water molecule as catalyst to mediate the proton transfer (WCP mechanism), is a barrierless process, indicating that the formation of the adduct intermediate, the first reaction step, is rate-limiting. The reaction products are free hydroxymethyl phenols and/or hydroxybenzy carbocation (HOC6H4CH2+) which plays an important role in the following formation of methylene and methylene ether linkages. The second addition reactions between formaldehyde and hydroxymethyl phenol at all possible reaction sites of the phenol ring in acid solution were also investigated and discussed.     

Ab Initio Study of the Mechanism of Cycloaddition Reaction between H2Ge=Ge: and Acetaldehyde

The mechanism of cycloaddition reaction between singlet state H2Ge=Ge: and acetaldehyde has been investigated with the MP2/6-311++G** method. From the potential energy profile, it could be predicted that the reaction has two competitive dominant reaction pathways. The reaction rule presented is that the two reactants firstly form a four-membered Ge-heterocyclic ring germylene through the [2+2] cycloaddition reaction. As the 4p unoccupied orbital of Ge: atom in the four-membered Ge-heterocyclic ring germylene and the π orbital of acetaldehyde form a π→p donor-acceptor bond, the four-membered Ge-heterocyclic ring germylene further combines with acetaldehyde to give an intermediate. Because the Ge atom in intermediate exhibits sp3 hybridization after transition state, the intermediate isomerizes to a spiro-Ge-heterocyclic ring compound via a transition state. Simultaneously, the ring strain of the four-membered Ge-heterocyclic ring germylene makes it isomerize to a twisted four-membered ring product.     

Diverse synthesis of the C ring fragment of bryostatins via Zn/Cu-promoted conjugate addition of α-hydroxy iodide with enone

A convergent approach to 1,5-hydroxy ketones,the general precursors for constructing the C ring of bryostatins,has been developed via a Zn/Cu-promoted conjugate addition of a-hydroxy iodides with enones.The reaction leads to direct formation of the C21-C22 bond and tolerates diverse functionalities at the C17-,C18-and C24-positions.The approach also enables a more concise synthesis of the known C ring intermediate(10 longest linear steps and 14 total steps),in contrast to its previous synthesis(17 longest linear steps and 22 total steps) in our total synthesis of bryostatin 8.     

Ab Initio Study of the Mechanism of Forming a Spiro-Si-heterocyclic Ring Compound Involving Ge from Cl_2Ge=Si:and Formaldehyde

The X2Ge=Si:(X = H, Me, F, Cl, Br, Ph, Ar···) is a new species. Its cycloaddition reaction is a new area for the study of silylene chemistry. The mechanism of cycloaddition reaction between singlet Cl2Ge=Si: and formaldehyde has been investigated with CCSD(T)//MP2/6-31G* method. From the potential energy profile, it can be predicted that the reaction has two competitive dominant reaction pathways. The reaction rule presented is that the two reactants firstly form a four-membered Ge-heterocyclic ring silylene through the [2+2] cycloaddition reaction. Owing to the 3p unoccupied orbital of Si: atom in the four-membered Ge-heterocyclic ring silylene and the π orbital of formaldehyde forming a π→p donor-acceptor bond, the four-membered Ge-heterocyclic ring silylene further combines with formaldehyde to form an intermediate. Because the Si: atom in intermediate shows sp3 hybridization after transition state, the intermediate isomerizes to a spiro-Si-heterocyclic ring compound involving Ge via a transition state. Simultaneously, the ring strain of the four-membered Ge-heterocyclic ring silylene makes it isomerize to a twisted four-membered ring product. The research result indicates the laws of cycloaddition reaction between X2Ge=Si:(X = H, Me, F, Cl, Br, Ph, Ar···) and the asymmetric π-bonded compounds, which are significant for the synthesis of small-ring and spiro-Si-heterocyclic ring compound involving Ge. The study extends the research area and enriches the research content of silylene chemistry.     

Crystal Structure and Spectra Characters of 2-Benzoly-3-(4-(1,2,4-triazole)-5-anilino-thiophene and 2-(4-Methyl-benzoly)-3-(4- chlrolphenyl)-3-(1,2,4-triazole)-5-anilino-thiophene

Triazole derivatives are widely studied, because they represent the largest group of modern fungicides and are widely used both in human and veterinary therapy and in agriculture. We synthesized the title compound in which the thiophene ring was substituted by a 1,2,4-triazole group, a phenacyl group, a phenylaminol group and a benzene ring.     

Synthesis and mesomorphic properties of 4-(4-bromopropyloxy)-4’-(4-alkyloxybenzylidene)anilines

This article describes the preparation and liquid crystalline properties of a new homologous series of 4-（4-bromopropyloxy）-4’- （4-alkyloxybenzylidene）anilines in which the phenyl ring is armed by a bromopropyloxy chain.The thermal behavior and mesomorphic properties of the synthesized compounds were studied with particular attention given to the correlation between their phase transition temperatures and anisotropic change influenced by molecular structure.All the members displayed enantiotropic smectic phase except for the homologue with the longest alkyloxy chain(R = C₁₈H₃₇),exhibiting only monotropic characteristic. The presence of bromine atom from the propyloxy side chain is found to be capable of altering and influencing the mesomorphic properties.     

Ab Initio Study on the Mechanism of Cycloaddition Reaction between Silylene Carbene （H_2Si=C：） and Acetone

The mechanism of cycloaddition reaction between singlet silylene carbene and acetone has been investigated with CCSD(T)//MP2/6-31G method. From the potential energy profile, it can be predicted that the reaction has two competitive dominant reaction pathways. One consists of two steps: (1) the two reactants (R1, R2) firstly form a four-membered ring intermediate (INT4) through a barrier-free exothermic reaction of 585.9 kJ/mol; (2) Then intermediate (INT4) isomerizes to CH3-transfer product (P4.1) via a transition state (TS4.1) with energy barrier of 5.3 kJ/mol. The other is as follows: on the basis of intermediate (INT4) created between R1 and R2, intermediate (INT4) further reacts with acetone (R2) to form the intermediate (INT5) through a barrier-free exothermic reaction of 166.3 kJ/mol; Then, intermediate (INT5) isomerizes to a silicic bis-heterocyclic product (P5) via a transition state (TS5), for which the barrier is 54.9 kJ/mol. The presented rule of this reaction: the [2+2] cycloaddition effect between the π orbital of silylene carbene and the π orbital of π-bonded compounds leads to the formation of a four-membered ring intermediate (INT4); The unsaturated property of C atom from carbene in the four-membered ring intermediate (INT4) results in the generation of CH3-transfer product (P4.1) and silicic bis-heterocyclic compound (P5).     

Decomposition Mechanism of 5,5′-Bis(tetrazole)-1,1′-dioIate(TKX-50) Anion Initiated by Intramolecular Oxygen Transfer

Density functional theory calculations at the B3LYP/6-31+G^** and B3LYP/6-311++G ^** levels were perfonned on thermal decomposition of 5,5′-bis(tetrazole)-1 ,r-diolate(TKX-50) anion with an intramolecular oxygen transfer being an initial step. Tlie results show that the intramolecular oxygen transfers are the rate-limiting steps for the decomposition of title anion with activation energies being in the range of 287-328 kJ/mol. Judged by the nucleus- independent chemical shift values, the formation of antiaromatic ring in transition state or the decrease of aromaticity of the tetrazole ring of the reactant makes somewhat contribution to the high potential energies of the rate-limiting transition states. However, the activation energies of the following N2 elimination tlirough various pathways are in a low range of 136-166 kJ/mol. The tetrazole ring acts as an electron donor or acceptor in difierent pathways to assist the bond nipture or group elimination. The rate constants in a temperature range of 500-2000 K for all the intramolecular oxygen transferring reactions were obtained. The corresponding linear relationships between InA and 1/T were established.     

Oligouridylates Formation with N-(O,O'-Diisopropyl)-Phosphoryl Alanine in the presence of Poly(β-(N~7-Adeninyl)Ethyl Methacrylate)

Phosphoryl amino acids are a series of novel molecules, which not only are capable of self-assembly into oligopeptides but also can act as the phosphoryl donor to phosphorylate nucleosides to nucleotides and oilgonucleotides1. A systematic study of the latter reaction opens a new way to search for the interaction and recognition between amino acids and nucleotides. Nevertheless, the poor yield of this reaction brings difficulties in separation, characterization and data analysis process. Nucle…     

六氢茚满催化开环: 氢解和阳离子反应路径(英文)

Perhydroindan(bicyclo[4.3.0]nonane) was converted in a flow-type apparatus under a hydrogen pressure of 5 MPa on six different catalysts,namely on a bifunctional Pd/Na,H-Beta zeolite,on Ir/Na,H-Y and Pt/Na,H-Y zeolites with a low concentration of Br?nsted acid sites,and on three catalysts containing the three noble metals on the non-acidic support silica.On the bifunctional zeolite Pd/Na,H-Beta,skeletal isomerization of perhydroindan was the primary reaction followed by opening of one naphthenic ring,the formation of open-chain nonanes in low yields of ca.6%,and hydrocracked products C8-.The carbon number distribution of the latter was volcano-shaped with no C1,C2,C7,and C8 indicating a carbocationic hydrocracking of C9 precursors with one naphthenic ring.On Ir/Na,H-Y and Pt/Na,H-Y("high-performance ring-opening catalysts"),ring opening and hydrocracking to C8-occurred by hydrogenolysis on the respective metal.Opening of the five-membered ring was found to be much faster than opening of the six-membered ring,in agreement with literature reports.The maximal selectivities of open-chain nonanes(OCNs) attained on Ir/Na,H-Y and Pt/Na,H-Y were very high,viz.49% and 54%,respectively,and significantly better than those of the open-chain decanes observed previously with decalin as model hydrocarbon.The OCNs formed on Pt/Na,H-Y were much less branched than those formed on Ir/Na,H-Y which was interpreted in terms of the different hydrogenolysis mechanisms on both metals.Valuable ancillary mechanistic information was obtained from the selectivities of perhydroindan hydroconversion on the three noble metals on silica.In contrast to Pd/silica,Ir/silica and Pt/silica gave appreciable selectivities of OCNs as well,yet the maximum values of these selectivities were lower than those obtained on the two high-performance zeolite catalysts.     

The reversible and stereoselective N- to C-bonded rearrangement of tris(2-pyridylmethyl)-1,4,7-triazacyclononanecobalt(III)

The hexaaminecobalt(III) complex [Co(tmptacn)]3+ (tmptacn = 1,4,7-tris(2'-pyridylmethyl)-1,4,7-triazacyclononane) undergoes a novel base-catalyzed N- to C-bonded rearrangement in which a tacn nitrogen is displaced by the alpha-carbon which deprotonates and binds to the metal ion as a carbanion. The X-ray structure establishes the configuration for the regio- and stereoselectively (100%) formed product. The reaction involves both ring expansions and ring contraction. The carbanion is part of a strained four-membered ring. The kinetics are reported for the N- to C-rearrangement, shown to be retentive for the optically resolved (+)-[Co(tmptacn)]3+ reactant, and also the kinetics for a competitive and somewhat faster base-catalyzed racemization reaction of this complex. The reaction is completely but very slowly reversed in acid, also with retention, and in D2O/D+ there is 1:1 D-incorporation into the two sets of inequivalent tacn carbons. Extensive 1D and 2D NMR studies establish mechanistic details, and alternative mechanisms are proposed for the forward and reverse reactions. In neutral solution, there is a competitive oxidation reaction for the reverse C- to N-bonded process, involving the regio- and stereoselective (100%) incorporation of an alpha-OH substituent into the tacn ring.     

Microwave-enhanced synthesis of new (-)-steganacin and (-)-steganone aza analogues

[reaction: see text]. A novel, microwave-enhanced, highly efficient protocol for the synthesis of hitherto unknown (-)-steganacin and (-)-steganone 7-aza analogues containing a 1,2,3-triazole ring has been presented. Microwave irradiation was found to be highly beneficial in promoting the Suzuki reaction and the 1,3-dipolar cycloaddition reaction to generate the highly strained medium-sized ring system of the title molecules.     

Total synthesis of (-)-okilactomycin

A highly convergent synthesis of (-)-okilactomycin is described. Key reactions of this synthesis include a strategy-level diastereoselective oxy-Cope rearrangement/oxidation sequence, a Petasis-Ferrier union/rearrangement tactic, and an efficient RCM reaction to construct the 13-membered macrocyclic ring.     

Phosphazene Base tBu-P4 Catalyzed Methoxy–Alkoxy Exchange Reaction on (Hetero)Arenes

The organic superbase tBu-P4 catalyzes methoxy-alkoxy exchange reactions on (hetero)arenes with alcohols. The catalytic reaction proceeded efficiently with electron-deficient methoxy(hetero)arenes as well as with a variety of alcohols, including 3-amino-1-propanol, β-citronellol, menthol, and cholesterol. An intramolecular version of this reaction furnished six- and seven-membered ring compounds.     

Stereocontrolled total synthesis of (-)-ephedradine A (orantine)

The stereocontrolled total synthesis of (-)-ephedradine A has been accomplished. The synthesis features an asymmetric C-H insertion reaction, an intramolecular ester-amide exchange reaction, and a Sharpless asymmetric aminohydroxylation reaction. Construction of the complex macrocyclic ring was performed by Ns-strategy and an intramolecular aza-Wittig reaction.     

CpRu(PPh3)2SSiiPr3与SCNR(R=Ph,1-Naphthyl)反应的结构、成键与机理的理论研究

应用密度泛函理论(DFT), 通过CpRu(PH₃)₂SSiⁱPr₃ (Cp＝环戊二烯负离子; ⁱPr＝异丙基)与SCNH模型化反应, 探讨了CpRu(PPh₃)₂SSiⁱPr₃ 与SCNR (R＝苯基, 萘基)的反应机理, 分析了反应所涉及的各相关化合物的结构与成键特征. 反应中首先失去一个膦配体, 生成一个中间体. 该中间体中, 硫原子采取sp²杂化, 硫原子剩余的一个p轨道与金属中心上的d轨道具有相同的对称性, 因而该p轨道上的孤电子对可与金属中心上的d轨道形成π键, 导致Cp环中心, Ru, S1, P和Si原子在同一平面内, 而不是S1, P和Si原子偏离该平面. 计算结果预测, S＝C双键中的p键打开, 生成含金属中心的四元环螯合物一步为反应的决速步骤. 空间位阻的减小、p共轭体系的生成以及螯合环的存在, 是导致该反应热力学有利的重要原因.     

Synthesis of methyl epijasmonate and cis-3-(2-oxopropyl)-2-(pent-2Z-enyl)-cyclopentan-1-one

A novel and efficient synthesis of both (±)-methyl epijasmonate and (±)-cis-3-(2-oxopropyl)-2-(pent-2Z-enyl)-cyclopentan-1-one is described. The key step to establish the cis-stereochemistry on the 5-membered ring is an ionic Diels–Alder reaction, which is high yielding and highly regioselective. Subsequent key steps include oxidative cleavage of the six-membered ring, Wittig coupling and for the synthesis of epijasmonate, the haloform reaction.     

Ab initio Study of Mechanism of Cycloaddition Reaction between Germylene Silylene (H2GeSi:) and Acetone

The mechanism of the cycloaddition reaction between singlet germylene silylene (H₂GeSi:) and acetone has been investigated with CCSD(T)/6‐31G*//MP2/6‐31G* method. From the potential energy profile, we could predict that the reaction has two competitive dominant reaction channels. The present rule of this reaction is that the [2+2] cycloaddition reaction of the two (‐bonds in germylene silylene and acetone generates a four‐membered ring silylene with Ge. Because of the unsaturated property of Si atom in the four‐membered ring silylene with Ge, it could further react with acetone, resulting in the generation of a bis‐heterocyclic compound with Si and Ge. Simultaneously, the ring strain of the four‐membered ring silylene with Ge makes it isomerize to a twisted four‐membered ring product.     

Simplified analogues of qinghaosu (artemisinin)

Three new simplified analogues of qinghaosu have been designed and synthesized through simple routes without recourse to the commonly employed photosensitized oxidation. The peroxy bonds in the target molecules were taken from UHP with the first peroxy-carbon bond formed through a hemiketal exchange reaction and the second by either an intramolecular Michael addition or a Hg(II)-mediated ring-closure reaction. All three peroxides possess a seven-membered peroxy ring fused to an all-carbon six-membered ring, a structural motif required for generating the carbon-centered substituted ethyl radicals.     

Theoretical study of mechanism of cycloaddition reaction between 2,2-dimethyl(2-germavinylidene) [(CH3)2Ge=C:] and formaldehyde

The mechanism of the cycloaddition reaction between singlet 2,2-dimethyl(2-germavinylidene) [(CH₃)₂Ge=C:] and formaldehyde has been investigated with CCSD(T)//MP2/6-311G** method. From the potential energy profile, it could be predicted that the reaction has two competitive dominant reaction pathways. The first pathway consist of the transfer of formaldehyde oxygen π-electrons to the 2p unoccupied orbital of the C: atom in 2,2-dimethyl(2-germavinylidene) with a formation of intermediate which then isomerizes to a four-membered heterocyclic ring carbene (Ge and O in the 1,3-position). The second pathway is a direct [2 + 2] cycloaddition reaction in which the interaction of two π-bonds in 2,2-dimethyl(2-germavinylidene) and formaldehyde generates another four-membered heterocyclic ring carbene (Ge and O in 1,2-position). Because of the unsaturated property of the C: atom in the two four-membered heterocyclic ring carbenes, the two four-membered heterocyclic ring carbenes could further react with formaldehyde, generating two spiro-heterocyclic ring compounds.