The zwitterion-accelerated [3,3]-sigmatropic rearrangement of allyl vinyl sulfoxided to sulfines. A specific class of charge-accelerated rearrangement

Conversion of allyl vinyl gulf oxides 5 and 8 to γ, δ-unsaturated sul fines 6 and 9, respectively, under neutral conditions shows that the accelerating effects of the charges in a zwitterionic moiety do not cancel, instead the sulfoxide functionality significantly facilitates the rearrangement.     

Effect of the substituent in the thiophene ring on the [3,3]-sigmatropic rearrangement of allyl thienyl sulfides

The thio Claisen rearrangement of a number of 5-substituted allyl 2-thienyl sulfides was studied. On the basis of kinetic data it is shown that substituents that decrease the aromatic character of the transition state decrease the reactivity of the sulfide.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1195–1197, September, 1982.     

[3,3]-Sigmatropic rearrangement of chloro-substituted allyl thienyl sulfides

The kinetics of the rearrangement of allyl 5-chloro-2-thienyl sulfide and -chloroallyl 2-thienyl sulfide to, respectively, 5-chloro-3-allyl-2-thiophenethiol and 3-(-chloroallyl)-2-thiophenethiol were investigated. It is shown that an acceptor substituent in the allyl group decreases the reactivity of the sulfide significantly, whereas an acceptor in the heterocyclic ring does not have an appreciable effect on it.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 181–183, February, 1982.     

Total synthesis of pancratistatin relying on the [3,3]-sigmatropic rearrangement

A new total synthesis of the antitumor alkaloid, pancratistatin (1), has been accomplished from readily available starting materials. Claisen rearrangement of the racemic dihydropyranethylene 17 was employed to construct the A and C rings with the appropriate stereochemistry. In addition, the Ireland-Claisen rearrangement of the enantiomerically pure 9 followed by ring-closing metathesis provided the important intermediate 24, thus implying that our approach could yield the enantioselective synthesis of (+)-pancratistatin. With the appropriately functionalized cyclohexene 24, stereo- and regiocontrolled functional group interchanges, such as iodolactonization, dihydroxylations, and a cyclic sulfate elimination reaction, facilitated the production of the target natural product.     

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).     

[3,3]-Sigmatropic rearrangement of allyl and 2-butenyl 1-naphthyl sulfides

The [3,3]-sigmatropic rearrangement of alkenyl 1-naphthyl sulfides in solutions with various polarities was investigated at 138–190 °C. The reaction proceeds through the formation of 2-alkenyl-1-naphthalene thiols, which subsequently undergo cyclization to compounds of the 2,3-dihydronaphtho[1,2-b]thiophene and naphtho[1,2-b]dihydrothiopyran series. 2-Butenyl 1-naphthyl sulfide, in addition to its passing directly through a [3,3]-sigmatropic rearrangement, to a considerable extent undergoes a prior [1,3]-sigmatropic rearrangement, which ultimately leads to the formation of four cyclic products. The kinetic parameters of the rearrangement of the sulfides were determined. The more negative entropies of activation constitute evidence for the high symmetry of the transition state.Translated from Khimiya Geterotskilicheskikh Soedinenii, No. 5, pp. 611–614, May, 1981.     

A [3,3]-sigmatropic process catalysed by acetate. The decarboxylative Claisen rearrangement

Allylic tosylacetates and tosylmalonates undergo acetate-catalysed decarboxylative Claisen rearrangement in the presence of N,O-bis(trimethylsilyl)acetamide. The homoallylic sulfones formed in these transformations correspond to the products of regiospecific allylation of sulfone-stabilised carbanions. A mechanistic rationale is proposed.     

EPR support for the ketyl radical-anion "triggered" [3,3]-sigmatropic rearrangement

New physical evidence to support a ketyl radical-anion mechanism for the [3,3]-sigmatropic rearrangement is presented. With use of EPR spectroscopy, spectra are observed that can be attributed to 8, an acyl radical-anion species resulting from a [3,3]-rearrangement; this also functions as a key intermediate in the process. The spectrum of an additional paramagnetic species resulting from further addition of tin-centered radicals to the reaction product was also observed.     

Synthesis and regioselectivity of the [3,3]-sigmatropic rearrangement of substituted 2-allylthio- and 2-allylseleno-1,4-dihydropyridines

The reaction of 3-cyano-1,4-dihydropyridine-2-thiolates and the corresponding selenolates with allyl bromide gave 2-allylthio- and 2-allylseleno-3-cyano-1,4-dihydropyridines, which, upon heating in various solvents or in the solid state, undergo [3,3]-sigmatropic rearrangement to give 3-cyano-3-allyl-1,2,3,4-tetrahydropyridine-2-thiones and the corresponding selenones. The resultant pyridinethiones are alkylated by alkyl halides at the sulfur atom and are oxidized by iodine to give disulfides.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1888–1895, August, 1991.     

Efficient synthesis of indoles using [3,3]-sigmatropic rearrangement of N-trifluoroacetyl enehydrazines

[3,3]-Sigmatropic rearrangement of N-trifluoroacetyl enehydrazines provides a novel method for the construction of indoles. N-Trifluoroacetyl enehydrazine having a cyclopentene ring smoothly underwent [3,3]-sigmatropic rearrangement followed by cyclization to give indolines in excellent yield. On the other hand, both cyclohexenyl N-trifluoroacetyl enehydrazine and acyclic N-trifluoroacetyl enehydrazine gave indoles in good yield. Additionally, the substituent effect on the benzene ring was also studied. The rearrangement of N-trifluoroacetyl enehydrazines proceeded smoothly even under either aqueous or solvent-free conditions.     

Stereoselective [3,3]-sigmatropic rearrangement promoted by the metal [1,3]-shift of binuclear Fischer carbene complexes

Reaction of chiral homobinuclear Fischer chromium carbene complexes with allyl alcohol in the presence of NaH and the following oxidative demetalation gave alpha-allyl esters in up to 97% ee via [3,3]-sigmatropic rearrangement reaction promoted by the metal 1,3-shift. On the other hand, chiral heterobinuclear tungsten carbene complexes with arene chromium complexes afforded alpha-allyl-beta-hydroxy esters as a major product in up to 92/8 dr by the same reaction sequence.     

Double diastereoselective [3,3]-sigmatropic aza-Claisen rearrangements

Asymmetric [3,3]-sigmatropic aza-Claisen rearrangement of the (Z)-N-allyl-N,O-silylketene aminal of (3S,4E,alphaR)-1-benzyloxy-3-(N-propionyl-N-alpha-methylbenzylamino)hex-4-ene furnishes (2S,3R,4E,alphaR)-N-alpha-methylbenzyl-2,3-dimethyl-7-benzyloxyhept-4-enamide in > 92% d.e.; rearrangement of the diastereomeric (3R,4E,alphaR)-(Z)-N,O-silylketene aminal proceeds with low diastereoselectivity.     

Retention of optical activity in the [3,3]-sigmatropic rearrangement of a vinyl furfuryl ether

(–)-1-(2-Furyl)ethyl 2-propenyl ether undergoes a [3,3]-sigmatropic rearrangement with the formation of (+)-2-(2-ethyl-3-furyl)propanol, which indicates an at least partially concerted reaction mechanism.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 27–29, January, 1989.     

A new approach to the synthesis of trifluoromethylated products of the [3,3]-sigmatropic rearrangement

CH-acids of general formula CF₃CH(X)CF₃ (X = CF₃, CO₂R) react with 2,3-unsaturated alcohols in the presence of bases to give trifluoromethylated products of the [3,3]-sigmatropic rearrangement. These reactions provide a convenient method for the synthesis of 2-alkenyl-2-trifluoromethylmalonates.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1273–1277, July, 1994.     

Synthesis of heterocyclic systems involving [3,3]-sigmatropic rearrangements

Russian Chemical Bulletin - The review summarizes the data on the synthesis of heterocyclic compounds by means of [3,3]-sigmatropic transformations, which include the Fischer, Claisen, and Cope...     

Preparation of 8-Amido-2-dimethylamino-1,2,3,4-tetrahydro-2-dibenzofurans and several fluorinated derivatives via [3,3]-sigmatropic rearrangement of O-aryloximes

Methodology to prepare 8-amido-2-amino-1,2,3,4-tetrahydro-2-dibenzofurans, analogues with a fluorine substituent incorporated in the 6-, 7-, and 9-positions, and a difluorinated analogue with fluorines in the 6- and 9-positions is described. The tetrahydrodibenzofuran ring systems are prepared by acid-catalyzed [3,3]-sigmatropic rearrangement of O-aryloximes. Regioselective reactions to prepare the requisite O-aryloxime intermediates from commercially available fluorobenzene derivatives are discussed.     

Efficient [3,3]-sigmatropic rearrangement accelerated by a trifluoroacetyl group: synthesis of benzofurans under mild conditions

The [3,3]-sigmatropic rearrangement took place smoothly during the course of trifluoroacetylation of O-phenyloxime at below room temperature to give the dihydrobenzofuran or benzofuran as a result of concomitant cyclization.     

An oxidative [2,3]-sigmatropic rearrangement of allylic hydrazides

The development of an efficient oxidative [2,3]-sigmatropic rearrangement of allylic hydrazides, via singlet N-nitrene intermediates, is reported. The requisite allylic hydrazide precursors are readily prepared and undergo smooth sigmatropic rearrangement upon exposure to iodosobenzene. The products of this novel transformation are shown to be useful precursors to a variety of compounds.     

Regioselective [5,5]-sigmatropic rearrangement reactions of aryl hydrazides

[reaction: see text] N,N'-Aryl hydrazides with substituents at the ortho or meta positions undergo highly regioselective [5,5]-sigmatropic rearrangement reactions to furnish benzidines in good to excellent isolated yields. The presence of single substituent at either the ortho or meta position provides sufficient bias, effectively suppressing the formation of diphenylene, the major byproduct of the conventional benzidine rearrangement reaction.