Thermal and photochemical Wallach rearrangement of azoxybenzene in zeolite cages

Acidic zeolites HY and CaY catalyse the Wallach rearrangement of azoxybenzene (I) leading mainly to the formation of para-hydroxyazobenzene (II) and ortho-hydroxyazobenzene (III). In this transformation, increasing the loading level of I results in the formation of a larger amount of para-isomer. As observed in isotropic media, photochemical Wallach rearrangement in the presence of various cation-exchanged faujasites results in the predominant formation of the ortho-isomer from the S₁ state and this rules out any appreciable heavy atom effect.     

Conformational Analyses of Glycinal and Alaninal: A Computational Study

We present computational results from detailed gas-phase conformational analyses of the -substituted aldehydes, glycinal and alaninal. A synplanar conformer of glycinal and a synperiplanar conformer of alaninal in which the C=O and C–N bonds are in an eclipsing orientation are found to be lowest in energy; the two amino hydrogen atoms in these conformers are both directed over the C–C bond, i.e., in a compact arrangement. For the Group VA analogs, H₂P–CH₂–CHO and H₂P–CH(CH₃)–CHO, skew conformers in which the C–H and C–Me groups, respectively, are in an eclipsing orientation with the C=O bond are found to be lower in energy than the syn(peri)planar conformers. The results of various self-consistent reaction-field calculations suggest that the lowest-energy conformer of glycinal in 1, 2-dichloroethane is still synperiplanar, although the orientation of the amino hydrogen atoms may be different from that in the gas phase. Similar reaction-field calculations for alaninal raise the possibility that in this solvent a skew conformer, in which the C–H bond is nearly eclipsing the C=O bond, is energetically competitive with synperiplanar conformers.     

Anionic Thia-Fries Rearrangement at Ferrocene: A Computational and Experimental Study

Ferrocenyl triflate ( 1 ) and 1,1′-ferrocenediyl ditriflate ( 5 ) undergo single and double anionic thia-Fries rearrangements at low temperatures in high yields with the latter forming exclusively the respective meso product. The detailed mechanisms of the anionic thia-Fries rearrangement of 1 , as well as that of the double anionic thia-Fries rearrangement of 5 , are examined with the aid of DFT calculations. Functionals, basis set and pseudopotentials applied were selected in accordance with a benchmark using the crystal structure analysis of the prime product 3 of the reaction of 1 before hydrolysis for comparison, which has so far not been reported. The unprecedented meso diastereoselectivity of the double anionic thia-Fries rearrangement of 5 is shown to be a result of a distinctive degree of chelation arising from two diastereomeric transition states.     

Structure Effect of Imidazolium-Based Dicationic Ionic Liquids on Claisen Rearrangement

A large group of imidazolium-based dicationic ionic liquids (DILs) has been prepared in good yields. Thermal stability of all DILs has been determined. The effects of the reaction time, cation, imidazolium C₂–H acidity, and anion on the Claisen rearrangement of allyl phenyl ether have been investigated. Type of anion and the presence of the acidic C₂–H bond in the imidazolium moieties have proven to be essential for this reaction. The simple procedure and the possibility of avoiding the use catalysts and volatile organic solvents make this synthetic method environmentally benign and adaptable for large-scale applications.     

A Theoretical Study on Chapman Rearrangement

Some Chapman rearrangements are investigated using HF and B3LYP methods combined with two different basis sets (6‐31G** and 6‐31++G**) and both finite difference model and Janak's approximation. It is shown that although minimum polarizability (MPP) and maximum hardness (MHP) principles are always valid in these reactions, minimum electrophilicity principle (MEP) is followed just when DFT method (B3LYP) is used. The Morrel's rules are also successfully applied in predicting the validity of MEP in these rearrangements. Therefore, it seems that in the study of this kind of reaction, the results of DFT are more reliable than those of HF.     

Rearrangement of azoxybenzocrowns into chromophoric hydroxyazobenzocrowns and the use of hydroxyazobenzocrowns for the synthesis of ionophoric biscrown compounds

The Wallach rearrangement was used as a method for preparing p-hydroxyazobenzocrown ethers starting from different azoxybenzocrowns as substrates. Synthesis of a series of p-hydroxyazobenzocrowns under modified conditions and characterization of the obtained products are presented. o-Hydroxyazobenzocrowns were identified among the products of the photochemical rearrangement of azoxybenzocrowns. Novel biscrowns were synthesized from p-hydroxyazobenzocrown ethers. The synthesized host molecules, differing in the size of the macrocycles and in the substituents in the aromatic rings, have the same dioxymethylene linkers. They were used as potential sodium or potassium ionophores in classic and miniature (screen-printed) ion-selective electrodes. The properties (tautomerism, acid–base equilibrium) of newly prepared o-hydroxyazobenzocrown ethers and their p-substituted analogs were studied using spectroscopic methods and compared.     

A Computational Study of Conformers of 2-Thiaoxacyclohexane (1,2-Oxathiane)

Ab initio molecular orbital theory with the 6-31G(d), 6-31G(2d), 6-31+G(d), 6-31G(d,p), 6-31+G(d,p), and 6-311G(d,p) basis sets and the hybrid density functionals B3LYP, B3P86, and B3PW91 have been used to calculate the optimized geometries and relative energies of the chair, half-chair, sofa, twist, and boat structures of 2-thiaoxacyclohexane (1,2-oxathiane). The values of the energy difference (E, kcal/mol) between the chair and 3,6-twist structures of 1,2-oxathiane were 4.92 (HF), 4.73 (MP2), and 4.66 (DFT). The HF chair–twist energy difference (G _c–t ^o) for 1,2-oxathane was 5.16 kcal/mol. Intrinsic reaction coordinate (IRC) calculations connected a transition state (TS-A) between the chair conformation and the less stable 2,5-twist form and connected two transition states (TS-B, TS-C) between the chair conformation and the more stable 3,6-twist conformer. The DFT energy differences between the chair and TS-A, TS-B, and TS-C were 11.4, 10.8, and 12.6 kcal/mol, respectively. Hyperconjugative stereoelectronic interactions were observed in the chair (n _o and ) and 3,6-twist (n _S and n _O ) conformers of 1,2-oxathiane. The chair conformation of 1,2-oxthiane is 9.6 and 10.0 kcal/mol, respectively, less stable than the chair conformations of 3-thiaoxacyclohexane (1,3-oxathiane) and 4-thiaoxacyclohexane (1,4-oxathiane, thioxane).     

Rearrangement Reactions of Tritylcarbenes: Surprising Ring Expansion and Computational Investigation

As a rule, acetylides and sulfonyl azides do not undergo electrophilic azide transfer because 1,2,3‐triazoles are usually formed. We show now that treatment of tritylethyne with butyllithium followed by exposure to 2,4,6‐triisopropylbenzenesulfonyl azide leads to products that are easily explained through the generation of short‐lived tritylethynyl azide and its secondary product cyanotritylcarbene. Furthermore, it is demonstrated that tritylcarbenes generally do not produce triphenylethenes exclusively, as was stated in the literature. Instead, these carbenes always yielded also (diphenylmethylidene)cycloheptatrienes (heptafulvenes) as side products. This result is supported by static DFT, coupled cluster, and ab initio molecular dynamics calculations. From these investigations, the fused bicyclobutane intermediate was found to be essential for heptafulvene formation. Although the bicyclobutane is also capable of rearranging to the triphenylethene product, only the heptafulvene pathway is reasonable from the energetics. The ethene is formed straight from cyanotritylcarbene.     

Theoretical Study on the Bicyclo[4.1.0]heptatriene Rearrangement in a Molecular Container

The conversion process from bicyclo[4.1.0]heptatriene （BCT） to 1,2,4,6-cycloheptatetraene （CHTE） within a molecular container was studied with AM1 method, and single point energies for all stationary points were evaluated by B3LYP and HF methods. The conversion potential barrier for the encapsulation complex became smooth when compared with that for the rearrangement in free state. The influences of the inner phase of the molecular container on the conversion process were discussed.     

Computational Study of the Release of H2 from Ammonia Borane Dimer (BH3NH3)2 and Its Ion Pair Isomers.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.     

A Formal Rearrangement of Allylic Silanols

We show that 1M aqueous HCl/THF or NaBH₄/DMF allows for demercurative ring-opening of cyclic organomercurial synthons into secondary silanol products bearing terminal alkenes. We had previously demonstrated that primary allylic silanols are readily transformed into cyclic organomercurials using Hg(OTf)₂/NaHCO₃ in THF. Overall, this amounts to a facile two-step protocol for the rearrangement of primary allylic silanol substrates. Computational investigations suggest that this rearrangement is under thermodynamic control and that the di-tert-butylsilanol protecting group is essential for product selectivity.     

环丙基卡宾重排为环丁烯机理的密度泛函研究

采用 B3LYP 方法,用 6-311G(d)基组计算了环丙基卡宾重排为环丁烯的反应物、过渡态和产物的能量和振动频率,并用 IRC 计算验证了过渡态。结果表明环丙基卡宾的重排机理不同于通常碳正离子重排采用的亲核重排机理,而是一个亲电重排机理。     

A radial probability density function for analysis of canonical molecular orbitals

A one‐dimensional probability density function, analogous to the atomic radial density for the hydrogen atom, r²R_nl(r), is defined for an arbitrary three‐dimensional density. It is obtained numerically by taking the derivative of a cumulative probability distribution with respect to the cubic root of the volume enclosed by each in a series of isosurfaces. Each point in the function is associated with a unique isosurface, and the isosurface associated with the maximum of the defined function represents the most probable isosurface with respect to the putative radius. This function therefore provides an objective selection criterion for a single isosurface to represent a three‐dimensional density. This technique is applied to set of canonical molecular orbitals. The selected threshold value varies from orbital to orbital, but the enclosed probability falls in the range of 20% to 55% for the reported orbitals. In all cases, the enclosed probability is much smaller than the common choices found in the literature. The concomitant smaller volume often makes possible a more localized interpretation and helps to clarify the conventional delocalized interpretation of molecular orbitals. For example, the isosurface plots selected by this method distinguish the formally bonding orbital in He₂ from the true bonding orbital in H₂. Examples from N₂, F₂, HF, H₂O, C₂H₆, and Ni(CO)₄ are also presented. © 2000 John Wiley & Sons, Inc. J Comput Chem 21: 310–321, 2000     

ChemInform Abstract: Azidopentazole is Probably the Lowest-Energy N8 Species - A Theoretical Study.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

Computational and Theoretical Chemistry in Structure-Reactivity Studies of Organophosphorus Compounds

Computational multivariation analysis, molecular orbital calculation as well as molecular mechanics study were used for the qualitative and quantitative evaluation of the relationship between chemical structure and reactivity of organophosphorus compounds.     

Diels-Alder反应轨道作用情况研究

根据三轨道作用法重点讨论了Diels-Alder反应中反应物轨道演变成产物轨道的过程, 演变结果与轨道对称守恒原理的结果基本相同. 量子化学计算证实了演变过程的合理性, 这表明在解释D-A反应方面轨道对称守恒原理比前线轨道理论更加合理可靠.     

A DFT Study on the Binuclear Copper(I)-Catalyzed Synthesis Mechanism of 1,2,3-Triazolo[1,5-c]Pyrimidine via Interrupted Click and Ketenimine Rearrangement

In this paper, the mechanism of the full catalytic cycle for binuclear Cu(I)-catalyzed sulfonyl azide-alkyne cycloaddition reaction for the synthesis of triazolopyrimidines was rationalized by density functional theoretical (DFT) calculations. The computed reaction route consists of: (a) formation of dicopper intermediates, including C−H activation of terminal alkyne, 3+2 ring cycloaddition and ring-reducing reaction and transmetalation, (b) interrupted CuAAC reaction, including di-copper catalyzed ring-opening of 2H-azirines and C−C bond formation to generate the copper-triazoles and -ketenimines, (c) two-step C−N cross-coupling and following (d) multi-step hydrogen transfer by the hydrogen bonding chain of water to promote the C−N formation and another C−N cleavage through the removal of p-tolyl sulfonamides. Our DFT results indicate that the multi-step hydrogen transfer process is the rate-determining step along the potential energy surface profile. The explicit water model was used for systematic determination of barrier for C−C cross-coupling, C−N bond formation and cleavage, and p-tolylsulfonamide removal. A critical insight in the interrupted CuAAC reaction was proposed. Further prediction interprets H₂O hydrogen bond chain plays an important role in C−N bond formation and cleavage, and the removal of p-tolylsulfonamide. This may have fundamental guidance on the design of 1, 5-herterocyclic functionalized triazolopyrimidines via interrupted CuAAC rearrangement reaction, as well as hydrogen bond chain of water.     

Rearrangement of Ethers: A New Route to Tolterodine

Efficient methods for the syntheses of amines 6b and 9b, the major metabolites of the antidepressant drugs amitriptyline 1a and nortriptyline 1b, are described.