Thio group migration

Scheme 26. 1,2-Ethyl (or phenyl) thio group migration for the stereospecific synthesis of 2-deoxy-P-glycosides.

The Willgerodt Reaction allows the synthesis of amides from aryl ketones under the influence of a secondary amine and a thiating agent. The mechanism involves the formation of an enamine which undergoes thiation, and the carbonyl group migrates to the end of the chain via a cascade of thio-substituted iminium-aziridinium rearrangements. 

Several thiopropargylimines 32 underwent ring-closure to the pyrroles 33 upon treatment with Cul in hot A V-dimethylacetamide (DMA). This process involves a propargyl-allenyl isomerization followed by a 1,2-migration of the thio-group in the intermediate allenes <03AG(E)98>. 

Pozsgay, V, A simple method for avoiding alkylthio group migration during the synthesis of thioglycoside 2,3-orthoesters. An improved synthesis of partially acylated 1-thio-a-L-rhamnopyrano-sides, Carbohydr. Res., 235, 295-302, 1992. 

Auzanneau, F I, Bundle, D R, Incidence and avoidance of stereospecific 1,2 ethylthio group migration during the synthesis of ethyl 1-thio-a-L-rhamnopyranoside 2,3-orthoester, Carbohydr. Res., 212, 13-24, 1991. 

In the latter case the S N allyl group migration is only efficient when Pd catalysis is employed, otherwise, at much higher temperatures, a double bond isomerization occurs first and is then followed by an S C allyl shift by means of a thio-Claisen rearrangement. As the appropriate 5-allyl thioimidates are easily prepared by alkylation of thioamides with allyl halides, the overall process is an 5n substitution of an allylic halide by an amine, a reaction which is difficult to achieve directly. 

A series of 2-alkyl(aTyl)thio-3//-quinolin-4-ones 120 were synthesized in a thermally induced cyclization <05OL5281>. Initially, the ketenimine 121 undergoes a [1,5] sigmatropic migration of the alkyl(aryl)thio group to form 122 followed by a 67t-electrocyclic ring closure resulting in the formation of 120, illustrated in Scheme 34. 

Fluorination of fi-hydroxy sulfides. Ruorination with migration of a thio group is... 

Dithiepins.—There are two new variations on the preparation of dithiepins by migration of a thio-group in 1,3-dithians. Treatment of the l,3-dithian-2-yl-methanols (164 R = C02Me or H) with methanesulphonyl chloride gave the 1,4-dithiepin (165), presumably by ring-expansion of the sulphonate ester. Another example is provided by the oxidation of the 2-ethylidene-l,3-dithian (166) with lead tetra-acetate the yields if R = alkyl or aralkyl varied between 34 and 67%, but if R = phenyl only (167) was produced, and not the thiepin enol acetate, as stated earlier by another group. ... 

Claisen rearrangement. On contrary, thioethers 226 and 227 synthesized by the reaction of the corresponding furan or thiophene with allyl mercaptane are thermally stable and no evidence of thio-Claisen rearrangement of these compounds was found. ° The fluorine atom of 2-fluoro-3-trifluoromethylfurans and thiophenes can be replaced upon nucleophilic substitution with benzyl alcohols. Compounds 228 are susceptible to [1,3]- and [l,5]-benzyl group migration. " ... 

A recent paper [44] shows that the treatment of silyl thioketones 68 with lithium diethylphosphite proceeds via a thiophiUc attack followed by a thio-phosphate mercaptophosphonate (69 70) carbanionic rearrangement and the migration of the silyl group from the carbon to the sulfur atom leading to the S-silylated sulfanylphosphonate carbanion 71. The last step represents the first example of the thia-Brook rearrangement (Scheme 18). 

In the cyclization of arylthioacetones under strong acid conditions a partial migration of the methyl group can occur, to produce mixtures of both the 2- and 3-methylbenzo[6 ]thio-phenes. For example, cyclization of (109 R = H) in PPA at 160-180°C gave a mixture composed of about 82-85% (110) and 15-18% of (111). Similar results were obtained when R in (109) was alkyl, but not when R was chlorine or bromine (68JCS(C)2733). 

Cyclodehydrations of ortho- or para-substituted (arylthio)acetones afford 7- and 5-substituted 3-methylbenzo[6]thiophenes,respectively mete-substituted (arylthio)acetones afford mixtures of 4- and 6-substituted 3-methylbenzo[6]thiophenes (see, e.g., Matsuki and Ito105). However, in these cases a partial migration of the 3-methyl group to the 2-position may be an added complication.297,306 Such isomerizations occur during the preparation of 3-methylbenzo[6]thio-phene and its 5-alkyl,297 306 but not its 5-halo 297 derivatives. A mixture of 3-methylbenzo[6]thiophene and its 5- (the expected product) and 6-JerJ-butyl derivatives is obtained on cyclization of (p-terf-butyl-... 

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