Rh(II)-catalyzed [2,3]-sigmatropic rearrangement of sulfur ylides derived from N-tosylhydrazones and sulfides

In this paper, Rh₂(OAc)₄-catalyzed [2,3]-sigmatropic rearrangement of sulfur ylides derived from N-tosylhydrazones and sulfides is reported. A series of tosylhydrazones derived from aldehydes were successfully used for [2,3]-sigmatropic rearrangement by reaction with either allylic phenyl sulfides or propargyl phenyl sulfides. The reaction conditions were optimized and afforded the products in moderate to good yields. In addition, a novel and convenient approach for the synthesis of cyclobutenones and cyclopropanes has been developed through direct oxidation of the rearrangement products.     

Copper(II)-catalyzed [2,3]-sigmatropic rearrangement of N-methyltetrahydropyridinium ylids

A ring-contractive and highly diastereoselective [2,3]-sigmatropic rearrangement occurs when N-methyl-1,2,3,6-tetrahydropyridine is treated with sub-stoichiometric amounts of copper or rhodium salts, in the presence of ethyl diazoacetate, giving ethyl cis-N-methyl-3-ethenyl proline (4).     

Highly stereoselective [2,3]-sigmatropic rearrangement of sulfur ylide generated through Cu(I) carbene and sulfides

A highly stereoselective [2,3]-sigmatropic rearrangement of sulfur ylide generated through Cu(I) carbene and allyl and propargyl sulfides by a double asymmetric induction approach that combines a chiral camphor sultam auxiliary and Cu(I) catalyst with chiral or achiral diimine ligands has been developed.     

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.     

Asymmetric [2,3]-sigmatropic rearrangement of allylic ammonium ylides

An asymmetric Lewis acid-mediated [2,3]-sigmatropic rearrangement of allylic amines has been developed, affording the corresponding homoallylic amines in good yield and excellent enantioselectivities. The rearrangement proceeds by complexation of the chiral Lewis acid to the amine followed by deprotonation and rearrangement.     

Iron(II)-catalyzed sulfimidation and [2,3]-sigmatropic rearrangement of propargyl sulfides with tert-butoxycarbonyl azide. Access to N-allenylsulfenimides

The iron(II)-catalyzed Bach reaction of tert-butoxycarbonyl azide (BocN(3)) and allyl sulfides has been extended to include propargyl sulfides, which give N-allenylsulfenimide products. Using 10 mol % dppeFeCl(2) as catalyst the reaction proceeds at 0 degrees C with a number of different propargyl sulfides in 31-73% isolated yield. The reaction is limited by product instability toward catalyst and termination of the catalytic cycle by excess BocN(3). N-Allenylsulfenimide 2b smoothly undergoes catalytic hydrogenation and a Diels-Alder reaction with cyclopentadiene.     

Oxaziridine-mediated amination of branched allylic sulfides: stereospecific formation of allylic amine derivatives via [2,3]-sigmatropic rearrangement

Reaction of branched allylic sulfides with the N-Boc-oxaziridine 1 results in [2,3]-sigmatropic rearrangement of the intermediate allylic N-Boc-sulfimides with a high level of chirality transfer. The first example of formation of a quaternary stereocenter using this transformation is reported.     

Lewis acid mediated [2,3]-sigmatropic rearrangement of allylic alpha-amino amides

Boron trifluoride and BBr(3) mediated [2,3]-sigmatropic rearrangements of allylic alpha-amino amides have been developed affording secondary amines in good yields. (E)-Crotyl and (E)-cinnamyl alpha-amino amides 2b and 2c exhibit excellent syn-diastereoselectivity upon rearrangement with either Lewis acid. The allylic amine 2a forms upon treatment with BF(3) or BBr(3) a five-membered heterocylic complex in which a single halide anion has been displaced by the carbonyl oxygen atom. The structures of the Lewis acid-amine complexes were elucidated using NMR spectroscopy. A plausible reaction mechanism, based on DFT calculations, is presented. Thus, BF(3)- or BBr(3)-complexed allylic amines 2 are shown to preferentially proceed, after deprotonation, via an endo transition state.     

Lewis acid mediated [2,3]-sigmatropic rearrangement of allylic ammonium ylides

An investigation of the Lewis acid mediated [2,3]-sigmatropic rearrangement of allylic ammonium ylides has been conducted by employing various bases and boron Lewis acids. Using BBr₃ together with the phosphazene base 6, various allylic amines could be rearranged in good yields with low to excellent diastereoselectivity.     

Catalytic [2,3]-sigmatropic rearrangement of sulfur ylide derived from metal carbene

This paper reviews the most recent development of [2,3]-sigmatropic rearrangement of sulfur ylide generated from the reaction of sulfide with metal carbene. The metal carbene was formed from decomposition of diazo compounds catalyzed by transition metal complexes such as Cu(I) and Rh(II).     

Ruthenium porphyrin catalyzed tandem sulfonium/ammonium ylide formation and [2,3]-sigmatropic rearrangement. A concise synthesis of (+/-)-platynecine

meso-Tetrakis(p-tolyl)porphyrinatoruthenium(II) carbonyl, [Ru(II)(TTP)(CO)], can effect intermolecular sulfonium and ammonium ylide formation by catalytic decomposition of diazo compounds such as ethyl diazoacetate (EDA) in the presence of allyl sulfides and amines. Exclusive formation of [2,3]-sigmatropic rearrangement products (70-80% yields) was observed without [1,2]-rearrangement products being detected. The Ru-catalyzed reaction of EDA with disubstituted allyl sulfides such as crotyl sulfide produced an equimolar mixture of anti- and syn-2-(ethylthio)-3-methyl-4-pentenoic acid ethyl ester. The analogous "EDA + N,N-dimethylcrotylamine" reaction afforded a mixture of anti- and syn-2-(N,N-dimethylamino)-3-methyl-4-pentenoic acid ethyl esters with a diastereoselectivity of 3:1. The observed catalytic activity of [Ru(II)(TTP)(CO)] for the ylide [2,3]-sigmatropic rearrangement is comparable to the reported examples involving [Rh(2)(CH(3)CO(2))(4)] and [Cu(acac)(2)] as catalyst. Similarly, cyclic sulfonium and ammonium ylides can be produced by intramolecular reaction of a diazo group tethered to allyl sulfides and amines under the [Ru(II)(TTP)(CO)]-catalyzed reaction conditions. The subsequent [2,3]-sigmatropic rearrangement of the cyclic ylides furnished 2-allyl-substituted sulfur and nitrogen heterocycles in good yields (>90%). By employing [Ru(II)(TTP)(CO)] as catalyst, the cyclic ammonium ylide [2,3]-sigmatropic rearrangement reaction was successfully applied for the total synthesis of (+/-)-platynecine starting from cis-2-butenediol.     

Lending a hand to asymmetric trifluoromethylthiolation:enantioselective [2,3]-sigmatropic rearrangement of sulfonium ylides

正The introduction of a trifluoromethanesulfenyl group(SCF3)into organic molecules can,in principle,significantly enhance the cell-membrane permeability,metabolic stability and bioavailability because of its high lipophilicity and intrinsic electron-withdrawing properties.As a consequence,tremendous efforts have been made to develop diverse trifluoromethylthiolation protocols by using either electrophilic     

Highly stereoselective C-C bond formation by rhodium-catalyzed tandem ylide formation/[2,3]-sigmatropic rearrangement between donor/acceptor carbenoids and chiral allylic alcohols

The tandem ylide formation/[2,3]-sigmatropic rearrangement between donor/acceptor rhodium carbenoids and chiral allyl alcohols is a convergent C-C bond forming process, which generates two vicinal stereogenic centers. Any of the four possible stereoisomers can be selectively synthesized by appropriate combination of the chiral catalyst Rh(2)(DOSP)(4) and the chiral alcohol.     

Catalytic asymmetric [2,3]-sigmatropic rearrangement of sulfur ylides generated from copper(I) carbenoids and allyl sulfides

Catalytic asymmetric sulfur ylide [2,3]-sigmatropic rearrangement of carbenoids generated from aryldiazoacetates has been investigated with a number of chiral Rh(II) and Cu(I) catalysts, and moderately high enantioselectivity (52-78% ee) can be achieved with Cu(MeCN)(4)PF(6)/2,2'-isopropylidenebis[(4S)-4-tert-butyl-2-oxazoline].     

Lewis acid mediated asymmetric [2,3]-sigmatropic rearrangement of allylic amines. Scope and mechanistic investigation

The first asymmetric [2,3]-sigmatropic rearrangement of achiral allylic amines has been realized by quaternization of the amines with an enantiomerically pure diazaborolidine and subsequent treatment with Et3N. The resultant homoallylic amines were obtained in good yields and excellent ee's. The observed diastereo- and enantioselectivities were rationalized by invoking a kinetically controlled process, and support for this model was obtained from an NMR spectroscopic investigation of the chiral Lewis acid-substrate complex. The structure of the Lewis acid-product complex was established by X-ray crystallographic analysis and supported the proposed mechanism.     

(NHC)AuI]-catalyzed rearrangement of allylic acetates

[(NHC)AuCl] complexes (NHC = N-heterocyclic carbene), in conjunction with a silver salt, were found to efficiently catalyze the rearrangement of allylic acetates under both conventional and microwave-assisted heating. The optimization of several reaction parameters (solvent, silver salt, and ligand) as well as a study of the reaction scope are reported. The steric hindrance of the ligand bound to gold was found crucial for the outcome of the reaction as only extremely bulky ligands permitted the isomerization.     

Amination and [2,3]-sigmatropic rearrangement of propargylic sulfides using a ketomalonate-derived oxaziridine: synthesis of N-allenylsulfenimides

Amination of propargylic sulfides with a ketomalonate-derived oxaziridine under metal free conditions gives N-Boc-N-allenylsulfenimides via [2,3]-sigmatropic rearrangement.     

Efficient amination of sulfides with a ketomalonate-derived oxaziridine: application to [2,3]-sigmatropic rearrangements of allylic sulfimides

A novel N-Boc-oxaziridine is reported, derived from diethyl ketomalonate, which effects efficient amination of sulfides to sulfimides. The reagent is applied to the [2,3]-sigmatropic rearrangement of allylic sulfimides.