Sulphenes cycloaddition

For a recent discussion on the stereochemical aspects of the Diels-Alder reaction with vinyl sulphoxides see References 662, 663. It should be pointed out that vinyl sulphoxides can be considered in [2 + 4]-cycloadditions as acetylene synthons since the sulphinyl moiety may be removed from the product by sulphenic acid elimination. Paquette and coworkers took advantage of this fact in the synthesis of properly substituted anthracenes 562664, (equation 360). 

Due to the amino group, enaminones are more electron-rich than 1-oxabutadiene and are well reactive in cycloadditions with electrophilic dienophiles as sulphene, ketene and electron-deficient alkenes. 

The 4 + 2-cycloaddition of enaminones could be extended to many tertiary alicyclic derivatives and by using benzylsulphonyl chlorides271 as sulphene precursors. The resulting 4-amino-3-phenyl-l,2-benzoxathiin-2,2-dioxides are a mixture of cis- and fra/w-isomers (equation 200). 

Sulphenes have been shown to undergo both [2 + 2] and [4 + 2] cycloaddition to dienamines61-63. Other methods of forming four-membered heterocyclic rings, such as 1,2-cycloaddition of isocyanates64 and TV-sulphonylimines65, do not seem to have been applied to dienamines. 

One special case is that of the reactive intermediates, the sulphenes (252), and the isolable compounds, the sulphines (253). In the first place, cycloadditions of these species... 

The thieten 1,1-dioxide (48) has been prepared by cycloaddition of an enamine and sulphene at 0°C. Mild thermolysis causes a ready retrocyclo-addition to occur. Additional stable 3-sultines have been isolated, by the reaction of the anion of a sulphoxide with a ketone and cyclization of the resulting j3-hydroxy-sulphoxide with sulphuryl chloride. Treatment of 2-methylthietan (49) with alumina at 150-350 °C results in the formation of tetrahydrothiophen and but-3-enethiol. ... 

Reactions of Vinylthiophens and Related Compounds. - 2-Aroyl-5-vinyl-thiophens react with triphenylphosphine, palladium chloride, and carbon monoxide to give 2-(5-aroyl-2-thienyl)propionic acid. Cycloaddition of sulphene, from methanesulphonyl chloride and triethylamine, to 2-(a-dimethylaminovinyl)thiophen gave (160). The synthesis of some substituted 3-(2-thienyl)acryloylamino-acids has been described. Some reactions of 3-chloro-j8-(2-thienyl)vinylphosphonic acid dichlorides have been studied, ... 

Cycloaddition of diphenylisobenzofurans to (101), to sulphenes, to 2-phenyl-3-spirocyclopropylazirines, and to o-benzoquinonedi-imines have been reported. The preparation and trapping of 1-methoxy- and 1-benzyl-isobenzofuran have been described and a high degree of regio-and stereo-specificity is observed in the reactions of a range of 1-substituted isobenzofurans with quinone acetals, for example in the formation of... 

It also participates in dipolar cycloaddition reactions, for example with diazo-compounds [221], nitrile oxides [222], nitril-imines [223] and sulphenes [224]. A mixture of products may be isolated including rearrangement products from the original adducts. 

By Cycloadditions involving Sulphenes. The cycloaddition of sulphenes to electron-rich olefins remains a convenient method of preparing compounds with the thietan ring system. In their preparation of 3-substituted thietans,... 

Siegl and Johnson formed 3-substituted-3-iV-morpholinothietan 1,1-dioxides by cycloaddition of sulphene to the appropriate 1-substituted-... 

Formation.—Preparation of thietan oxides by oxidation of thietans is covered in the previous section. Cycloaddition of sulphenes to electron-rich alkenes, the other important method of preparation of episulphones, has been further used for the preparation of a-chloro- and /S-amino-, cf-sila- and -amino-, and cf-alkoxycarbonyl- and -amino-thietan dioxides. The sulphonyl enamine (96) can be converted into the thietan dioxide (97) by treatment with acid, a procedure that usually hydrolyses enamines to ketones. Regeneration of (96) from (97) occurs on heating in alcoholic base. Thiet sulphone cyclo-adds to cyclopentadiene to give the Diels-Alder adducts with an exo/endo ratio of 0.25. ... 

Sultenes, Sultines, and Sultones.—Further reports have appeared on the formation of sultones from SO3 and dienes and from the cycloaddition of c-amino-methylene-ketones and sulphene. Unusual sultone formations occurred during the reaction of a ketose derivative with mesyl chloride and during the rearrangements of bicyclic ketones that were induced by sulphuric acid, respectively. The kinetics of reactions of sultones (181) with nucleophiles and the enthalpy changes accompanying their alkaline hydrolysis," which allow an estimation of differences in ring strain between the five- and six-membered sultones, have been studied. 

Several sultams have been prepared by cycloaddition reactions similar to those applied to the synthesis of sultones. Thus, the generation of sulphene in the presence of pyridine gave the sultam (186). Activated dienes reacted with simple iV-sulphonylamines, e.g. MeN=S02, to give unsaturated sultams such as (187), and thione S-imides reacted smoothly as 1,3-dipoles to give cyclic sulphenamides (188), or as dienophiles, with the formation of A -dihydrothiopyran l-imides. ... 

A combination of [4 + 2] cycloaddition and [2,3]-sigmatropic rearrangement has been used with effect in the synthesis of hasubanan derivatives. Thus the 1-butadienyl phenyl sulphoxide (456) reacts with the enamine (457) to yield (458) as a mixture of diastereoisomeric sulphoxides. Heating (458) in the presence of a thiophilic species drives the equilibrium over to the sulphenate ([2,3]-sigmatropic shift) as the latter is converted into the amino-alcohol (459). This annelation sequence may also be used with electron-deficient dienophiles by employing 1-butadienyl phenyl sulphide (460). ... 

The perhalogenoketones(CF2Cl) CX>, (CFCl2)2CO, and(CF a)(CFCl,)CO undergo cycloaddition with sulphene, generated in situ from methane-sulphonyl chloride and triethylamine, to yield jS-sultones in 60—81% yield. However, under comparable conditions the alkyl perfiuoroalkyl ketones MeCO CF, and EtCO CQF yield vinyl sulphonates, - e.g. 

Thioacylketen dithioacetals participate with alkenes and sulphenes in 1,4-cycloaddition reactions. Thio-Claisen rearrangement of 1-allylthio-l-aminoalkenes to thioamides or isothiocyanates, and of 5 -allyl-5 -methyl-keten mercaptals to dithioesters, has been described. 

Tbiadiazolo[3,4-a]isoquinolines.—l,3-Dipolar cycloaddition of sulphenes to the highly reactive azomethine imines of the 3,4-dihydroisoquinoline type gives this new ring system (see Chapter 3, Section 2). 

Some of these 3-aminothietan 1,1-dioxide derivatives have been claimed to be useful as anti-inflammatory ents and as sedatives. Cycloadditions of sulphenes with a/3-unsaturated sulphides also yield thietan sulphones. ° Aryl propargyl sulphones eliminate sulphur dioxide under electron impact. oftho-Substituents reduce the amount of sulphur dioxide, and a substituted thietan 1,1-dioxide intermediate was suggested. ... 

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