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The first sequentially combined inorganic base promoted N-addition/[2,3]-sigmatropic rearrangement reaction of α-alkylidene pyrazolinones and propargyl sulfonium salts has been reported to construct homoallyl sulfur-containing pyrazolones with moderate to excellent yields. α-Alkylidene pyrazolinones function as N-nucleophilic agents distinguished from the reported C-addition reactions. Propargyl sulfonium salts were first involved in the [2,3]-sigmatropic rearrangement protocol differentiated from the well-established annulation reactions. The excellent regioselectivity, the broad scope of substrates, gram-scale synthesis and convenient transformation embody the synthetic superiority of this cascade process.

In the presence of 2-(trimethylsilyl)aryl triflates as aryne precursors under mild conditions, a range of tertiary propargylic amines bearing electron-withdrawing groups were converted to quaternary propargylic ammonium ylides followed by a [2,3]-sigmatropic rearrangement to afford structurally diverse amino-substituted allenes or conjugated dienes, depending on their structure, in moderate to good yields.

An efficient protocol for [2,3]-sigmatropic rearrangement of allyl and propargyl thioethers is reported. The key sulfonium ylide intermediate is in situ formed via S-arylation of arynes. This transition metal-free method allows for ready access to a wide array of functionalized thioether derivatives in good to excellent yields.

The rearrangement of a range of N-benzyl-O-allylhydroxylamines to the corresponding N-allylhydroxylamines upon treatment with n-BuLi in THF, followed by reduction to the corresponding N-allylamines, is described. Mechanistic studies of the transformation are consistent with an intramolecular [2,3] sigmatropic rearrangement.

1,3,4,5,6,11a-Hexahydro-7E-2-benzothionine 5, which is a [2,3] sigmatropic rearrangement product of 2-phenyltetrahydrothiopyranium 1-methylide 8, has been synthesized by reaction of 1-methyl-2-phenyltetrahydrothiopyranium triflate 3 with sodium amide in liquid ammonia or by the fluoride ion-induced desilylation of trans-2-phenyl-1-[(trimethylsilyl)methyl]tetrahydrothiopyranium perchlorate trans-7. Compound 5 is stable at room temperature and reverts to ylide 8 by ring-opening.

The efficient synthesis of a series of 2° allylic alcohols from a vanadium-catalyzed oxidation of suitably disposed allylic selenides with tandem [2,3] sigmatropic rearrangement is outlined.

Allylic nitro compounds 1a–d undergo [2,3]-sigmatropic rearrangement in refluxing 1,2,4-trichlorobenzene, to afford rearranged alcohols 3a–d and carbonyl compounds 4a–d; the heating, under the same conditions, of a mixture of nitroalkenes 7a–c, propargyl alcohols or amine 8 and ButOK promotes a one-pot formation of allylic alcohols 3a–c.

The first enantioselective [2,3] sigmatropic rearrangement of acyclic diprop-2-ynyl ethers and alkenyl benzyl ethers is achieved by a BuLi–chiral ligand complex.

N-Alkylation of N-allyl α-amino esters and [2,3]-Stevens rearrangement occur in one pot on warming in the solvent DMF, with the bases K2CO3 and DBU; this in situ formation of the quaternary ammonium salts and rearrangement of the subsequent ylides gives N,N-dialkylated allyl glycine derivatives.

The [2,3] sigmatropic rearrangement of open-chain allylic phosphinites was found to proceed with high stereoselectivity, allowing the preparation of chiral (E) allylic phosphine oxides and aminophosphine oxides with 99% ee and a perfect transfer of the chiral information.

Preparation of the tertiary allylic alcohols 17–22, follwed by subjection of these substances to the Still–Mitra [2,3]-sigmatropic rearrangement sequence, provides the functionalised bicyclo[4.3.0]nonanes 23–26; acquisition of 26; points to a strategy for the synthesis of C-19 oxygenated cyathane-type diterpenoids.

E-Homoallylic sulfides with 1,4,5 related chiral centres have been synthesised in a stereocontrolled way. An aldol condensation sets up the stereochemistry. Lactonisation with 1,2 arylsulfanyl migration followed by reduction and sulfur-assisted dehydration converts the aldols stereospecifically into allylic sulfides with 1,2 related chiral centres. Sulfonium salts are generated from the allylic sulfides at low temperature, and are deprotonated to give sulfonium ylides which undergo [2,3] sigmatropic rearrangement in good yield to give E-homoallylic sulfides with 1,4,5 related chiral centres. The 1,4 relative stereochemistry results from stereospecific chiral transfer and is directly related to the allylic sulfide 1,2 relative stereochemistry. High 4,5 diastereoselectivity is also observed. An explanation for the observed stereoselectivity is provided.

In the presence of a catalytic amount of chiral copper(I) or rhodium(II) compounds the enantioselective addition of a carbenoid, derived from ethyl diazoacetate, to chalcogen atoms of aryl cinnamyl chalcogenides affords a diastereoisomeric mixture of ethyl 2-arylchalcogeno-3-phenylpent-4-enoates via[2,3]sigmatropic rearrangement of the intermediate chalcogen ylide with up to 41% ee.

Rhodium(II) acetate-catalysed cyclisation of methyl 2-diazo-5-[2-methoxy-5-(2-phenylsulfanyl-ethylidene)tetrahydro-2H-pyran-4-yl]-3-oxopentanoate 4 proceeded in a stereoselective fashion to provide in a high yield cis-2-oxa-9-vinyldecalin derivative 5, the basic AB ring skeleton of vernolepin, by a [2,3]sigmatropic rearrangement via a nine-membered cyclic allyl sulfonium ylide.

The imination of chiral cinnamyl 2-(1-dimethylaminoethyl)ferrocenyl selenides with [N-(toluene-p-sulfonyl)imino]-phenyliodinane and chloramine-T affords the corresponding chiral allylic amines via[2,3]sigmatropic rearrangement of the selenimide intermediates with up to 87% ee, highly diastereoselective imination of selenides and highly stereospecific [2,3]sigmatropic rearrangement being shown.

The rhodium(II)-catalysed cyclisation of acyclic α-diazomalonate 1b and α-diazo-β-keto esters 1c, d give stereoselectively the highly substituted δ-lactone 3b and cyclohexanones 3c, d, respectively, by [2,3]sigmatropic rearrangement via the stereocontrolled nine-membered allylsulfonium ylides 2b–d.

A spiroannulation reaction using the [2,3]sigmatropic rearrangement via a cyclic allylsulfonium ylide was developed and applied to the synthesis of (+)-acorenone B starting from (–)-perillaldehyde.

High oxophilicity of metal carbenes formed in rhodium(II) perfluorobutyrate catalysed decomposition of diazo carbonyl compounds allows selective ylide generation from methyl prop-2-yn-1-yl ethers with resulting allene production through the [2,3]-sigmatropic rearrangement.

When γ-chloroallyl sulphides and N-alkyl anilines are oxidized with m-chloropehbenzoic acid, the resultant S- and N-oxides rapidly undergo [2,3] sigmatropic isomerization to labile products that decompose internally with selective formation of conjugated enones.

S-Methyl-S-(3,3-dimethylallyl)carbene, generated by Bamford–Stevens reaction of the corresponding toluene-p-sulphonylhydrazone, undergoes a 2,3-sigmatropic rearrangement to a dithiocarboxylic acid ester, thereby providing a new carbon–carbon bond synthesis.

ortho-Alkylphenols have been prepared from phenol and dialkyl sulphoxides via[2,3]sigmatropic rearrangement, using thionyl chloride or phenyl chlorosulphinate as an activator of sulphoxides. In the same manner, ortho-phenylthiomethylphenol has been prepared in good yield. When ethyl phenyl sulphoxide, diallyl sulphoxide, and methyl methylsulphinylacetate were used as sulphoxides, none of the expected products were obtained. Salicylaldehyde has been prepared in moderate yield, when methyl methylthiomethyl sulphoxide was used as a sulphoxide. 3-(2-Hydroxyphenyl)propionic acid derivatives, which were obtained from substituted phenols and dimethyl 3,3′-sulphinyldipropionate, have been cyclized to give the corresponding coumarins in good yields.

Pentafluorophenol reacted with the reagent dimethyl sulphoxide–dicyclohexylcarbodi-imide–orthophosphoric acid below room temperature to give the ether (1), the [2,3]-rearrangement product (2), and (3) a derivative of (2). Under similar conditions, 2,3,5,6-tetrafluorophenol gave (7) and (8), and 1,3,4,5,6,7,8-heptafluoro-2-naphthol gave (12) and (13). Reaction of polyfluoroarenols with dimethyl sulphoxide–trifluoroacetic anhydride at low temperatures followed by deprotonation with triethylamine resulted in more efficient rearrangement reactions; 4-bromo-3,5,6-trifluoropyridin-2-ol gave the ether (14) and the products of rearrangement both to carbon and nitrogen, (15)(after hydrolysis) and (16) respectively; 2,4,5,6-tetrafluoropyridin-3-ol resulted in the overall replacement of the 2-fluorine by CHO (17) and by CH(SMe)2(18); and with 2,5,6-trifluoropyrimidin-4-ol and 5-fluoro-4,6-dimethoxypyrimidine-2-ol, simple rearrangement products (21) and (22) were obtained. Hydrolysis of (21) gave the 5-fluorouracil derivative (23). Sodium borohydride reduction and Raney nickel desulphurisations of some of the rearrangement compounds gave phenolic products. Reaction of the sulphone from (13) with base (DBU) effected the overall efficient replacement of the 1-fluorine in the 2-naphthol by CHO (35) and by CH(SO2Me)2(36).