Lewis acid-catalyzed rearrangement of 2,2-dichloronorbornane to 1-chloronorbornane

The mechanism for the unusual AlCl(3)-catalyzed rearrangement of 2,2-dichloronorbornane to 1-chloronorbornane in pentane has been elucidated; the reaction, which also yields four isomeric dichloronorbornanes, occurs in three steps: (1). ionization to form the 2-chloro-2-norbornyl cation, which was fully characterized by two-dimensional (1)H and (13)C NMR in SbF(5)/SO(2)ClF; (2). Wagner-Meerwein shift to yield the 1-chloro-2-norbornyl cation, which was partially characterized by (1)H NMR; and (3). hydride abstraction.     

Aza-pinacol rearrangement: acid-catalyzed rearrangement of aziridines to imines

A series of di-, tri-, and tetra-substituted N-tosylaziridines [N-(toluene-p-sulfonyl)aziridines] 1, prepared by aziridination of the corresponding alkenes with N-[(tolyl-p-sulfonyl)imino]phenyliodinane (TsN = IPh), was found to undergo a BF3-catalyzed rearrangement (aza-pinacol rearrangement) under mild conditions to give the corresponding N-tosylimines 2 generally in satisfactory yields.     

Lewis acid-catalyzed rearrangement of multi-substituted arylvinylidenecyclopropanes

An interesting rearrangement of arylvinylidenecyclopropanes having three substituents at the 1- and 2-positions of the corresponding cyclopropane catalyzed by Lewis acids to give 6aH-benzo[c]fluorine derivatives via a double intramolecular Friedel-Crafts reaction or to give an indene derivative via an intramolecular Friedel-Crafts reaction is described.     

A novel acid-catalyzed rearrangement of cyclobutanols

Under acid-catalysis 7-arylbicyclo[3.2.0]hept-2-en-6-ols rearrange to diarylmethanes and cyclopenteno-annelated polycyclic aromatic hydrocarbons.     

1, 2-丙二醇酸性条件下反应机理的量子化学研究

用MNDO方法研究了1, 2-丙二醇在酸性条件下反应机理, 寻找到了反应过渡态, 并从理论上确证了它最可行的反应过程和最终产物。     

Revised structure of acid-catalyzed rearrangement product of aucubigenin

The ¹³C NMR spectrum of 6, the acid-catalyzed rearrangement product of aucubigenin, has led to a critical re-examination of its ¹HNMR data and instead of the previous structure 6a, the definitive structure of the add-catalyzed rearrangement product is 1,10-anhydro, 3,4-dihydro, 4-decarbomethoxy, -3α-hydroxygardenogenin 6b.     

Effects of substituents in acid-catalyzed Claisen amino rearrangement

A series of 4-R²-N-R¹-N-(1-methyl-2-butenyl)- and 4-R²-N-R¹-2-(1-methyl-2-butenyl)-anilines was synthesized. The rate constants of rearrangement and elimination of the hydrochlorides of the 4-R²-N-R¹-N-(-1methyl-2-butenyl)anilines in nitrobenzene were measured at 110 and 130°C. The correlation equations which describe the effect of the nature of the substituents on the reactivity of the substrate in these reactions and the selectivity of their occurrence were established. A mechanism of the processes was proposed.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2303–2308, October, 1989.     

One-pot N-dealkylation and acid-catalyzed rearrangement of morphinans into aporphines

The one-pot N-demethylation and acid-catalyzed rearrangement of morphinan-N-oxides offers a new, shorter and more efficient route to neuropharmacologically important N-substituted aporphines. An improved procedure is described for the preparation of the starting alkaloid N-oxides using Na₂WO₄ as catalyst. The transetherification during the rearrangement of codeinone into 2-O-alkyl-norapocodeines is documented.     

Development of a new Lewis acid-catalyzed [3,3]-sigmatropic rearrangement: the allenoate-Claisen rearrangement

A new Lewis acid-catalyzed Claisen rearrangement has been developed that allows the stereoselective construction of beta-amino-alpha,beta,epsilon,zeta-unsaturated-gamma,delta-disubstituted esters from simple allylic amines and allenoate esters. This reaction, which is contingent upon the use of Lewis acid, can be conducted with a range of metal salts (Yb(OTf)3, AlCl3, Sn(OTf)2, Cu(OTf)2, MgBr2.Et2O, FeCl3, Zn(OTf)2) with catalyst loadings as low as 5 mol %. This catalytic process provides access to a diverse range of beta-amino-alpha,beta,epsilon,zeta-unsaturated-gamma,delta-disubstituted esters in high yield and with excellent levels of diastereoselectivity for a series of allyl pyrrolidines (R1 = H, Me, i-Pr, Ph, NR2 = pyrrolidine, piperidine, NMe2; >/=81% yield, >/=94:6 syn:anti) and allenoate esters (R2 = H, Me, i-Pr, Ph, allyl, NPht, Cl; >/=75% yield, >/=91:9 syn:anti). The capacity of this new Claisen rearrangement to provide catalytic access to elusive structural motifs has also been demonstrated in the stereospecific formation of quaternary carbon bearing frameworks arising from geranyl- and neryl pyrrolidine (>/=93% yield, >98:2 dr).     

Iridoids—XXIII : Isolation of aucubigenin and its acid-catalyzed rearrangement

Aucubigenin 3, the unstable aglycone of aucubin 2, has been successfully isolated. In acidic medium 3 is converted into the acetal 6 whose structure resulted to be 1,10-anhydro-6-desoxy-7,8-dihydro-7,8-dihydroxyaucubigenin.     

Lewis acid-catalyzed oxidative rearrangement of tertiary allylic alcohols mediated by TEMPO

Two methods for the oxidative rearrangement of tertiary allylic alcohols have been developed. Most of tertiary allylic alcohols studied were oxidized to their corresponding transposed carbonyl derivatives in excellent to fair yields by reaction with TEMPO in combination with PhIO and Bi(OTf)₃ or copper (II) chloride in the presence or not of oxygen. Other primary oxidants of TEMPO such as PhI(OAc)₂, mCPBA, and Oxone^® were unsatisfactory giving the enone in modest to low yields.     

Novel acid-catalyzed rearrangement of tetrahydro-1,2,3,4-tetrazines: unexpected formation of glycosazones

The present contribution discloses a simple and unexpected acid-catalyzed cleavage of tetrahydrotetrazines leading to 1,2-bis(hydrazones). Incorporation of a chiral fragment derived from carbohydrates enables the rapid preparation of glycosazones, a family of compounds employed by Emil Fischer to elucidate the configuration of sugars. In addition, a mechanistic proposal accounts for experimental observations.     

Chemistry of O-arylhydroxylamines. A novel acid-catalyzed rearrangement of O-aryl-N-acetoacetylhydroxylamines to benzofurans

Acid-catalyzed rearangement of O-aryl-N-acetoacetylhydroxylamines (1) affords 2-methylbenzofuran-3-carboxamides. Some abnormal rearrangements of the title compounds are also described.     

Synthesis of N,N-disubstituted phosphoramidates via a Lewis acid-catalyzed phosphorimidate rearrangement

A Lewis acid-catalyzed rearrangement of phosphorimidates allows a direct, high-yielding transformation of azides with commercially available phosphites into secondary phosphoramidates.     

A mild thermal and acid-catalyzed rearrangement of O-aryl ethers into ortho-hydroxy arenes

[reaction: see text] An unusual rearrangement of an O-aryl ether to an ortho-hydroxyaryl system was discovered during our studies on the synthesis of diazonamide A. We discuss the exploration of this rearrangement under mild thermal and both Br?nsted and Lewis acid-catalyzed conditions.     

The 1-AZA-cope rearrangement

N-Acyl-1-aza-1,5-dienes participate in the Cope rearrangement.     

Benzylation of morphinandienes and new aspects of their acid-catalyzed rearrangement to new aporphines

The benzylation of thebaine and 6-demethoxythebaine resulted in different product mixtures. Explanations were given for both the observed differences in the ratio of 5β- versus 7-benzyl products and the deviation of the electronic structure of ring C of 7-benzyl products. The acid-catalyzed rearrangement of morphinan-5,8-dienes, 5,6- and 6,7-disubstituted morphinan-6,8-dienes was achieved and mechanistic interpretations for the formation of new, potentially dopamine-active aporphines were provided.