The thio-Claisen rearrangement

The Thio-Claisen Rearrangement.—The thermal [3,3]sigmatropic rearrangement of ajS-/3 y -unsaturated sulphides, resulting in the formation of 

Tanaka, T. Katagiri, K. Takabe, and S. Takeshita, Yuki Gosei Kagaku Kyokai Shi, 1971, 29, 788. 

or W) at room temperature to give solely the product (65), which at elevated temperatures was converted completely into (66) by release of carbon monoxide. The chelating behaviour of a-alkylated monothio-j9-diketones has also been investigated, and the conclusion has been drawn 

Further recent papers concerning metal complexes of thio-analogues of j3-diketones deal with the preparation of the cobalt(n) complex of 1,3-diacetylthioacetone, the synthesis and properties of a series of metal complexes of dithioacetylacetone, the synthesis of the nickel(n) complexes of monothio- and dithio-dibenzoylmethane (67) by the nucleophilic cleavage of 1,2-dithiolium salts by hydroxide or mercaptide ions in the presence of nickel(ii) ions, the bromination of the cobalt(m) complex of monothioacetylacetone (68) with iV-bromosuccinimide to yield (69), and the application of monothiodibenzoylmethane as an analytical reagent for quantitative determination of copper.  

Reactions.—Beak and Worley have studied the reactions of thiobenzo- 

The [3,5] sigmatropic rearrangement of allyl vinyl sulfides (thio-Claisen) is particularly easy activation enthalpies can be 10 kcal mob1 lower than for the oxygen analogues [486], and the reaction which was pioneered by Brandsma [487] occurs usually at room temperature and with excellent yields. 

The reaction is of great value and most of the early work in the field is quoted and discussed in [203] by Block. As the allyl vinyl sulfide can be metallated and submitted to electrophilic substitution prior to rearrangement and the thiocarbonyl group hydrolysed in situ to a carbonyl group in the reaction product, the process has found considerable utility. The syntheses of propylurc [488] and m-jasmone [489] are early examples in which a thioaldehydc was intermediary formed (Y = H). A thioketonc was involved [490] in the rearrangement of the allyl allenyl sulfide shown here. 

The dithioester was converted into an ester by CuCl2/CuO in ethanol. 

Allylic thionesters, dithiocarbamatcs and thionocarbamates are starting materials for various synthetic purposes [203, 492,493]. General synthetic routes, from Nakai et al. [492], to a, 3-unsaturated esters and ketones via the [3,3] sigmatropic rearrangement of allylic thionocarbamates (1) are featured in the accompanying schemes. 

The thermal rearrangement of an allyl xanthate to a dithiocarbonate was used to introduce the sulfur atom on a quaternary carbon in the synthesis of agelasidine A, a natural S-containing sesquiterpene [494], 

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Similar to the well-known thio-Claisen rearrangement of allyl aryl sulfides211 and sulfonium salts212, the thio-Claisen rearrangement of allyl aryl sulfoxides has also been reported213. For example, heating of allyl 2-naphthyl sulfoxide (147) at 120 °C for 2h in dimethylformamide resulted in quantitative isomerization to the dihydronaphthothio-... 

A theoretical study of substituent effects in the thio-Claisen rearrangement (91) -> (92) has been carried out. The study has shown that 2,5-disubstimtion leads to tighter transition states and to a substantial lowering of the enthalpy of... 

Thiochroman (1 R = Ha) is a product of the thio-Claisen rearrangement of allyl phenyl sulfide, as reported in 1963 27 this reaction also produces 2,3-dihydrothiophenes as shown in Eqs. (6) and (7).28,29... 

Similar reactions were carried out on 17,29 18,30 and 19.30 The last gave thiochromans and 2,3-dihydrothiophenes from an apparent cyclization at the ortho methyl substituent, but in fact involving a variety of hydrogen and methyl shifts. The route to the two main products [Eq. (7)] of the thio-Claisen rearrangement has been suggested to be via the thiirane intermediate (20).31... 

Some applications of the thio-Claisen rearrangement to the syntheses of thiocarbonyl compounds, particularly unsaturated dithiocstcrs and thionesters, and of its stereocontrol aspects are reviewed in [120]. A particularly high stereoselectivity was observed with S-allyl derivatives of P-hydroxydithioesters syn products were obtained exclusively, according to the accompanying scheme [495,496]. 

PMR spectroscopy has found wide application in studies of unsubstituted thienothiophenes,24,60,62,63,153-168 selenophenothiophenes (Table I) I38 i69 carboxy-,24,62,63,68,170,171 formyl-,68 161,164 bromo-,165,166,172 and alkyl-50,60,63,68 thienothiophenes, and carboxy-138,169 selenophenothiophenes. The PMR method has also been used to study alkylthieno-[3,2-A]thiophene sulfones63,162 and 4,6-dihydrothieno[3,4-i]thiophene (131 )98 and to analyze the mixture of products of the thio-Claisen rearrangement in (2-propargylthio)- (36) and (3-propargylthio)- (37) thiophenes.50... 

The thio-Claisen rearrangement can also be performed with secondary thioamides, providing allylation on the nitrogen atom rather than carbon atom. An elaborate example was reported by Fuchs and Smith [183]. They introduced an allyl ammonium salt to achieve SN2 alkylation of sulfur, and the product readily rearranged to furnish the expected thiolactam. However they finally preferred to employ in the first step an allyl mesylate, which was more easily synthesised. 

The Claisen rearrangement of allyloxy heterocycles is another reaction which has been studied in some detail. Yields can be variable and mixtures of N- and C-allyl products are sometimes obtained (e.g. equation 70). In other cases the reaction can be of considerable synthetic utility e.g. equation 71). The thio-Claisen rearrangement has also been studied in many cases the intermediate thiones react further (equation 72), although they can also be trapped, for example with ethyl chloroformate. 

The thio-Claisen rearrangement has its special value when the specific reactivity of a sulfur function, e.g. its carbanion-stabilizing effect or the high nucleophilicity of S, can be utilized, as in syntheses of 7-keto aldehydes (Scheme 72) or thioamides (Scheme 73). ... 

Alternative approaches to the synthesis of thienopyrimidines by thiophene ring closure are also documented. For example, the thio-Claisen rearrangement of prop-argyl sulfide 137 (X = S) affords thienopyrimidinediones 138 the rearrangement of sulfoxide 137 (X = SO) gives the corresponding formyl derivative 138 (R2 = CHO) (1989JHC1851). 

Syntheses of natural compounds and S-heterocycles by the thio-Claisen rearrangement 03T7251. 

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