单重态二溴代乙叉重排反应的量子化学研究

采用量子化学中的ＡＭ１ 方法研究了单重态二溴代乙叉重排反应的机理．结果发现, 该重排反应经过１ 个三元环过渡态．根据计算结果,详细研究了该反应的热力学及动力学函数．     

单重态Cl2N＝B：重排反应的从头算研究

采用量子化学中的从头算方法,在HF／6－311G^**水平上研究了单重态Cl2N＝B：重排反应的机理。结果发现,该重排反应经过一个面外三元环过渡态,根据计算结果,详细研究了该反应的热力学及动力学函数。     

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。     

单重态二碘代乙叉重排反应的AM1方法研究

采用量子化学中的ＡＭ１方法研究了单重态二碘代乙叉重排反应的机理。结果发现,该重排反应经过一个三元环过渡态,反应的能势为２５．８ｋＪ／ｍｏｌ。根据计算结果,详细研究了该反应的热力学及动力学函数,结果表明该反应是放热反应,放出的热量约为２５０ｋＪ／ｍｏｌ;该反应的Ａ因子稍小于１０１３ｓ－１,是典型的单分子反应。由于反应的平衡常数和速度常数都很大,故Ｉ２Ｃ＝Ｃ：一旦生成就立即转变为ＩＣ≡ＣＩ。     

Reaction of 2-propargylphenylcarbamates with diphenyliodonium salts via Meyer-Schuster rearrangement

The syntheses of 2,3-dihydro-4-quinolones from 2-propargylphenylcarbamates by one-pot tandem process that involves Meyer-Schuster rearrangement or arylative Meyer-Schuster rearrangement/Michael addition of carbamate nitrogen to the resulting vinyl ketones have been developed. Phenylcarbamates tethering tertiary propargyl alcohols underwent arylative Meyer-Schuster rearrangement/Friedel-Crafts alkylation to produce 2,3-dihydroindenones.     

单重态H_2N=B:→HNBH重排反应的理论研究

用量子化学中的从头算方法, 在MP2/6-311++G(d,p)水平上研究了单重态H_2N=B→HNBH重排反应的机理。结果表明, 该重排反应经过一个三元环过渡态。根据计算结果，初步讨论了该反应的热力学及动力学函数。     

A kinetic investigation of the thermal rearrangement of N-pyridino-2-vinyl-aziridines.

The first-order rate constants of the thermal rearrangement of several N-pyridino-2-vinyl-aziridines into the corresponding pyrido-azepines have been determined. Substituent effects on this isomerization were found to be completely analogous to the related benzenic O-Claisen rearrangement.     

Organic azides: an exploding diversity of a unique class of compounds

Since the discovery of organic azides by Peter Griess more than 140 years ago, numerous syntheses of these energy-rich molecules have been developed. In more recent times in particular, completely new perspectives have been developed for their use in peptide chemistry, combinatorial chemistry, and heterocyclic synthesis. Organic azides have assumed an important position at the interface between chemistry, biology, medicine, and materials science. In this Review, the fundamental characteristics of azide chemistry and current developments are presented. The focus will be placed on cycloadditions (Huisgen reaction), aza ylide chemistry, and the synthesis of heterocycles. Further reactions such as the aza-Wittig reaction, the Sundberg rearrangement, the Staudinger ligation, the Boyer and Boyer-Aubé rearrangements, the Curtius rearrangement, the Schmidt rearrangement, and the Hemetsberger rearrangement bear witness to the versatility of modern azide chemistry.     

Synthesis of Highly Substituted Cyclobutane Fused‐Ring Systems from N‐Vinyl β‐Lactams through a One‐Pot Domino Process

In this contribution, aminocyclobutanes, as well as eight‐membered enamide rings, have been made from N‐vinyl β‐lactams. The eight‐membered products have been formed by a [3,3]‐sigmatropic rearrangement, whereas the aminocyclobutanes have been derived from a domino [3,3]‐rearrangement/6π‐electrocyclisation process. The aminocyclobutanes have been obtained in a highly diastereoselective fashion. The cyclobutane ring system tolerates fusion even if adjacent quaternary centres are present. Systems containing up to four fused rings are readily accessible. The reaction profile has been investigated by using Gaussian 03. This study suggests that two reaction pathways for aminocyclobutane formation are possible. In one pathway the [3,3]‐sigmatropic rearrangement is the rate‐limiting step and in the second pathway the electrocyclisation is rate limiting. Taken together, these reactions should facilitate the construction of fused heterocycles.     

Studies on phenothiazines. Part 16 . Synthesis and spectral studies of substituted 1,2-dichlorophenothiazines

Synthesis of the title compounds by the Smiles rearrangement has been reported. 1,2-Dichloro-7-substituted phenothiazines have been prepared by the Smiles rearrangement of 3,4-dichloro-2-formamido-2′-nitro-4′-substituted-diphenyl sulphides. The latter were obtained by the formylation of the diphenyl sulphides obtained by the condensation of 2-amino-3,4-dichlorobenzenethiol with o-halogenonitrobenzenes. 9-Nitrophenothiazines have been prepared by the reaction of 2-amino-3,4-dichlorobenzenethiol with substituted o-halonitrobenzenes containing a nitro group at both ortho positions to the halo atom in which Smiles rearrangement occurs in situ. The ir, nmr and mass spectral studies are also included.     

Herstellung und Eigenschaften von Oximen des 4-Oxo-4,5,6,7-tetrahydroindols und ihre Umlagerung in Pyrrolo-azepine 6. Mitteilung über synthetische Indol-Verbindungen [1]

The preparation and BECKMANN rearrangement of 4-tosyloxyimino-4,5,6,7-tetrahydroindoles are described. The structures of the stereoisomeric parent oximes, their tosylates, and of the products of their BECKMANN rearrangement have been confirmed by NMR and IR spectroscopy.     

Synthesis and Aza-[2,3]-Wittig Rearrangements of Vinylaziridines: Scope and Limitations

cis- and trans-2,3-Trisubstituted vinylaziridines have been prepared from cis- and trans-epoxy alcohols, respectively, and used as substrates in the aza-[2,3]-Wittig rearrangement. Five different anion-stabilizing groups have been investigated for their efficiency to promote the rearrangement, and it was found that N-tert-butyl acetyl vinylaziridines were superior in this reaction, affording the corresponding cis-2,6-tetrahydropyridines (>90%) as single isomers when treated with LDA. Similarly, the corresponding (Z)-propenylaziridines gave trans,trans-2,3,6-trisubstituted tetrahydropyridines as the sole products while the (E)-propenylaziridines afforded the cis,cis-2,3,6-derivatives with equally high selectivity. The scope and limitations of the process have been investigated by varying the structure of the substrate, and the mechanism of the rearrangement has been probed to some extent; the mechanistic picture is more complex than assumed previously.     

Evidence for nonstatistical dynamics in the Wolff rearrangement of a carbene

Two (13)C-labeled isomers of the formal Diels-Alder adduct of acetylmethyloxirene to tetramethyl 1,2,4,5-benzenetetracarboxylate have been synthesized. Flash vacuum thermolysis of these adducts leads to various isotopic isomers of acetylmethylketene, the ratios of which have been determined by NMR. The surprising finding that the principal product comes from methylpyruvoyl carbene rather than its more stable isomer diacetylcarbene is explained by MPWB1K density functional calculations, which show that the reactant probably undergoes a unimolecular rearrangement to a norcaradiene derivative prior to its fragmentation. Coupled-cluster calculations on the methylpyruvoyl carbene show that it is capable of undergoing three unimolecular isomerizations. The fastest is 1,2-acetyl migration to give acetylmethylketene directly. The next is rearrangement via acetylmethyloxirene to diacetylcarbene and thence by Wolff rearrangement to acetylmethylketene. The least-favorable reaction is degenerate rearrangement via 1,3-dimethyl-2-oxabicyclo[1.1.0]butan-4-one (the epoxide of dimethylcyclopropenone). The combined experimental and computational results indicate that Wolff rearrangement of the diacetylcarbene occurs with a 2.5:1 ratio of the methyl groups despite the fact that they are related by a twofold axis of symmetry in the carbene. Preliminary molecular dynamics simulations are consistent with this conclusion. Taken together, the results suggest that the Wolff rearrangement is subject to the same kind of nonstatistical dynamical effects detected for other kinds of thermally generated reactive intermediates.     

The phenylcarbene rearrangement revisited

The evolution of mechanistic ideas about the phenylcarbene rearrangement has been reviewed, and three closely linked problems have been identified toward whose solution this research has been aimed: 1. Why do the ratios of the stable end products from the rearrangements of o-, m- and p-tolylmethylene differ when all three reactions have been throught to pass through a common intermediate? 2. Why does the rearrangement of 2-methylcycloheptatrienylidene lead to exclusive formation of styrene? 3. What is the mechanism of styrene formation from o-tolylmethylene? New mechanisms have been proposed in which m- and p-tolylmethylene can rearrange to styrene without necessarily being converted to o-tolylmethylene. The formation of a small amount of 2,6-dimethylstyrene from the rearrangement of 3,4,5-trimethylphenylmethylene is viewed as evidence for such a mechanism, and a set of interconverting norcaradienylidenes are believed to be the crucial intermediates. Other alternatives are considered and rejected on the basis of the rearrangement products of 3,5-dimethyl- and 3,4,5-trimethylphenylmethylene.     

Dehydrative Beckmann rearrangement and the following cascade reactions

The Beckmann rearrangement has been predominantly studied for the synthesis of amide and lactam.By strategically using the in situ generated Appel’s salt or Mitsunobu’s zwitterionic adduct as the dehydrating agent, a series of Beckmann rearrangement and following cascade reactions have been developed herein. The protocol allows the conversion of various ketoximes into amide, thioamide, tetrazole and imide products in modular procedures. The generality and tolerance of functionalities of this met...     

γ-Lactones from malonic acid derivatives

The acid catalyzed cyclization of isopropylidene malonate derivatives of ketones to form α-earboxy-γ-lactones has been shown to occur with boron trifluoride etherate or p-toluenesulfonic acid, as well as with concentrated sulfuric or polyphosphoric acids. A similar cyclization of a diethyl ylidenemalonate to a lactone ester, in relatively poor yield, has also been accomplished. Acid catalyzed cyclization of the ylidenemalononitrile derived from pinacolone to form an α-carbamoyl-γ-lactone has been shown to occur with rearrangement. However, that derived from 2,2-dimethyleyclohexanone cyclized to the secondary carbon of the ring without rearrangement. The isopropylidene malonate derivatives of several ring-substituted and bridged ketones have been converted to α-earboxy-γ-laetones without rearrangement.     

Theoretical Study on the Transition State of N-nitropyrazoles Rearrangement Reaction

Theoretical studies on the rearrangement reactions of nitropyrazoles have been investigated. In order to gain a better understanding of the intermediate process of rearrangement reactions, the transition states of the rearrangement reactions were obtained by TS method at the B3 LYP/6-311 G(d, p) level of theory. The natural bond orbital charge, electrostatic potential and frontier molecular orbital of the molecules in the process of rearrangement were analyzed, and the solvent effect was also discussed. The rearrangement of nitropyrazoles involves two transition states and one intermediate, and the nitro group and hydrogen atom are two transfer groups for rearrangement reactions. The migration of these two groups leads to the change of charge distribution and molecular structure. The structural changes of the molecules in different solvents are not significant, but the dipole moment of the molecule has obvious change.     

The photorearrangement mechanism of α-allenic compounds: its specific character

The α-allenic compounds liquid-phase rearrangement to 1,3-dienes involves a free-radical, photoinduced rate-determining step. Several inhibiting effects have been observed and interpreted. The bimolecular rearrangement mechanism accounts quantitatively for experimental data, from very dilute to highly concentrated solutions; it rules out the existence of a mesomeric intermediate.     

The effect of ring substitution on the O-neophyl rearrangement of 1,1-diarylalkoxyl radicals. A product and time-resolved kinetic study

[reaction: see text] A product and time-resolved kinetic study of the effect of ring substitution on the reactivity of 1,1-diarylalkoxyl radicals has been carried out. The radicals undergo an O-neophyl shift to give the isomeric 1-aryl-1-aryloxyalkyl radicals from which the corresponding aromatic ketones are formed. The rearrangement rate constants are influenced by ring substitution, increasing in the presence of electron-withdrawing substituents and decreasing in the presence of electron-donating ones. From the results of product and kinetic studies, the following migratory aptitudes have been obtained: 4-trifluoromethylphenyl > phenyl approximately = 4-methylphenyl > 4-methoxyphenyl. Excellent Hammett-type correlations between the sigma+ substituent constants and both the visible absorption band maxima and the rearrangement rate constants have been obtained. The experimental results indicate that the rearrangement is governed by electronic effects in the starting 1,1-diarylalkoxyl radicals, whereas the stability of the rearranged carbon-centered radical plays a minor role, in line with a reactant-like transition state, strongly supporting the hypothesis that the O-neophyl rearrangement of 1,1-diarylalkoxyl radicals proceeds through a concerted mechanism.     

Stereoselective synthesis of allylic sulfones via the oxonia-Cope rearrangement of homoallylic alcohols containing a homoallylic sulfone moiety

The homoallylic alcohols 3 that can be prepared by the indium-mediated addition of haloallylic sulfones 1 to aldehydes 2 undergo the oxonia-Cope rearrangement with aldehydes 2 to give rise to the allylic sulfones 4 containing a conjugated diene moiety in a highly stereoselective manner. Electron-rich aldehydes preferentially participate in this oxonia-Cope rearrangement with the homoallylic alcohols 3. Excellent correlations of the stereochemistry (anti-3 to trans-allylic sulfone 4 and syn-3 to cis-allylic sulfone 4) have been observed in the oxonia-Cope rearrangement.