Sulphides allylic, rearrangement

Sulphonium ylides are in certain cases unstable and they undergo further transformation affording useful final products. In this way allylic sulphides and selenides were used to transfer an alkylthio- or alkylseleno-group onto the a-carbon of / -dicarbonyl compounds in the form of their ylides the sequence of reactions were a transylidation followed by [2,3]-sigmatropic rearrangement. 

Sigmatropic rearrangements of allyl sulphonium allyl ylides (75) provide the basis of a repetitive one-pot ring-expansion sequence" for 2-vinyl thiocyclic compounds (Scheme 50). A paper" and a section in a review article" have described the utilization of allyl thiol dianions and allyl sulphide anions in carbonyl group umpolung . 

The allyl sulphide (223) was obtained peracid oxidation furnished the sulphoxides (224). These sulphoxides rearranged on treatment with diethylamine to give, after deprotection, 7-hydroxy ... 

A number of reports have focused interest on the synthesis of various allylic sulphur compounds. A one-pot procedure for the preparation of allylic sulphides from the corresponding alcohols involves initial rearrangement of the xanthate followed by... 

Important variants of procedure have been tested, providing wider possibilities for thio-Claisen rearrangements in synthesis like any other method for forming carbon-carbon bonds whose scope exceeds its limitations, there is the likelihood of studies of the type described in this Section being taken up in many more laboratories. Lithiation of allyl sulphides is followed by rearrangement, providing a very efficient method for the synthesis of thiols, alkyl sulphides, and hydrocarbons of the squalene type, or based upon the artemisyl skeleton. Typically, benzyl yy-dimethylallyl sulphide (65) gives (66) with four equivalents of... 

Corey has reported a novel method for the introduction of two alkyl appendages at the carbonyl carbon of ketones. Ketones react with the anion of diethyl allylthiomethylphosphonate (155) to give vinyl allyl sulphides such as (156) heating in the presence of mercury(ii) oxide induces a thio-Claisen rearrangement to yield the aldehyde (157), which can be further elaborated by various oxidation-reduction sequences to give, for example, the spiro-enone (158). 

The unsaturated ester (113) is prepared, as a mixture of E) and (Z) isomers, by the Lewis-acid-catalysed addition of allylic sulphides to methyl propiolate followed by an ionic [3.3] sigmatropic rearrangement (Scheme 68). ... 

Thus, Simonneaux and co-workers have reported treatment of methyl allyl sulphide with 2-diazoethyl acetate at 25 in the presence of (SBF>4PRuCO as catalyst (homogeneous reaction, entry 1 in Table 4), which leads to ethyl-2-(methylthio)pent-4-enoate in 88 % yield with 8 % of dimers [56]. As presented in Scheme 21, the formation of ethyl-2-(methylthio)pent-4-enoate derives from the [2,3]-sigmatropic rearrangement of the sulphur ylide and that of the dimers (di-ethylfumarate and diethylmaleate) derives from 2-diazoethyl acetate dimerization. 

The addition of nitrenes, generated from iV-aminophthalimide with lead tetraacetate, to allyl sulphides gave iV-(substituted)sulphenamides by a [2,31-sigma-tropic rearrangement of the initially formed sulphimides (55). In contrast to carbenes, photochemically generated nitrenes added to 4-t-butyIthiacyclohexane... 

Addition of thiols to diketen gives y-alkylthio-jS-butyrolactones, which suffer rearrangement, or loss of CO2 to give the allyl sulphide. Radical addition of thiophenol to the allenes (12) and (12a) gives vinyl and allyl sulphides (13) and (14), respectively." The radical pathway is normally... 

Dimethylprop-2-ynylsulphonium bromide isomerizes to the allene, which is susceptible to nucleophilic addition, giving a product mixture including the demethylation product MeSCH=CMeX (X = nucleophile). (+)-l-Adamantyl allyl ethyl sulphonium fluoroborate undergoes [2,3]-sigmatropic rearrangement to give a mixture of adamantyl ethyl and allyl sulphides and (-)-(R)-l-adamantyl pent-4-en-2-yl sulphide,i.e. with inversion at carbon chirality is transferred from S to C with at least 94% optical induction. 

Chelotropic addition of dichlorocarbene to bornadiene gave (200 X = C1) whereas with difluorocarbene the, yyn-adduct was favoured over the anh-adduct (200 X = F) (cf. Vol. 3, p. 59). A thio-Claisen rearrangement has been reported with the allylic enethiolic ether of thiocamphor. Flash thermolysis of allyl exo-2-bornyl sulphide to thiocamphor and propene has been examined. 

The formation of rearranged products during nucleophilic substitution in a-bromo-ketones probably involves enolisation, followed by allylic (5n2 ) substitution. The ready conversion of4, 5i8-epoxy-3-ketones (45) into 2a-acetoxy-or 2a-hydroxy-4-en-3-ones is similarly rationalised.When the nucleophile is dimethyl sulphoxide, the resulting 2-oxysulphonium ion (46) breaks down with elimination of dimethyl sulphide to give the 4-ene-2,3-dione (47), or its A -enolic equivalent (48). 

A tracer study of the mechanism of the rearrangement of thiolsulphinate with acetic anhydride using 13C and lsO has been carried out by Oae and coworkers194. A deuterium isotope effect study of the mechanism of the reactions of singlet oxygen with allylic and vinylic sulphides,... 

A detailed paper on the thermal rearrangements of allyl perchloro-vinyl sulphides has now appeared. Heating (32) to 100-120°(S led to mixtures of (33) and (34) in proportions indicated in the figures. The products were isolated by column chromatography and preparative gas chromatography. Diasteromeric mixtures of (33) were obtained. Treatment of (33a,c,d) with potassium t-butdxide gave (35). 

Full details have been published this year of the synthesis of allyl phenyl sulphides by acid-catalysed rearrangement of /8-phenythio-alcohols [(71)- (72)]. 

Definitive evidence for the sole intermediacy of 2-allylarenethiols was obtained from work on the rearrangements of allyl quinolyl sulphides - . For example, 3-methallylquinolyl sulphide (100), which rearranges in dimethylaniline to 101 and 102, gave in butyric anhydride quantitative yield of the butyryl derivative (103) of the Claisen product 104. Compounds 100 and 104 yielded 101 and 102 in the same proportions when heated under identical conditions. 

Similar results were observed in the thiophene series . In the rearrangement of allyl 3-thienyl sulphide (105) to 107 and 108, the intermediate 2-allylthiol 106 has been isolated for the first time directly from the reaction mixture. 

When the two ortAo-positions are blocked, no parfl-Claisen products are observed. Heating of allyl 2,6-dimethylphenyl sulphide (111) yields a cleavage product 112 and four cyclic materials (113-116) which probably result from or/Ao-rearrangement followed by 1,3- and 1,4-methyl migrations . ... 

The thio-Claisen rearrangements of allylic phenyl sulphides, allyl thienyl sulphides, addition products of acetylene derivatives and allyl mercaptan, and dimethylallyl 2-indolyl sulphonium salts have been described. Of particular interest is a recent paper reporting the quantitative formation of (62) by the thermal rearrangement of the sulphoxide (61). The second step in the mechanism (Scheme 3) proposed for this reaction... 

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