Thiete 1,1-dioxides cycloaddition with

The following compounds have been obtained from thiete 1,1-dioxide Substituted cycloheptatrienes, benzyl o-toluenethiosulfinate, pyrazoles, - naphthothiete 1,1-dioxides, and 3-subst1tuted thietane 1,1-dioxides.It is a dienophile in Diels-Alder reactions and undergoes cycloadditions with enamines, dienamines, and ynamines. Thiete 1,1-dioxide is a source of the novel intermediate, vinylsulfene (CH2=CHCH=SQ2). which undergoes cyclo-additions to strained olefinic double bonds, reacts with phenol to give allyl sulfonate derivatives or cyclizes unimolecularly to give an unsaturated sultene. - Platinum and iron complexes of thiete 1,1-dioxide have been reported. 

Based on the high dienophilicity of acyclic vinyl sulfones one should expect thiete dioxides to exhibit similar properties. Indeed, several Diels-Alder (2 +4) cycloadditions with thiete dioxide as dienophile are known. For example, 1,3-butadiene and 1,3-diphenylisobenzofuran react with 3-chloro- or 3-bromo-thiete dioxides to afford the corresponding 1 1 Diels-Alder cycloadducts255 277 (equation 105). 

As expected, 1 1 (2 + 2) cycloadducts are obtained in the reactions of thiete dioxides with some typical electron-rich olefins, e.g. enamines and ynamines, although this cycloaddition has not proven to be general190. 

The preparation and investigation of the thietane oxide system (5a) is largely associated with stereochemical and conformational studies . The investigation of the thietane dioxides (5b) is substantially related to the chemistry of sulfenes , the [2 -I- 2] cycloaddition of which with enamines is probably the method of choice for the synthesis of 5b . The study of the thiete dioxide system (6) evolved, at least in part, from the recognition that the unstable thiete system 183 can be uniquely stabilized when the sulfur in the system is transformed into the corresponding sulfone , and that the thiete dioxide system is very useful in cycloadditions and thermolytic reactions. The main interest in the dithietane oxides and dioxides (7) appears to lie in the synthetic challenge associated with their preparation, as well as in their unique structural features and chemical behavior under thermolytic conditions . ... 

Cycloadditions of nitrones, nitrile oxides or diazo compounds to thiete dioxides do not show the high stereoselectivity observed with acyclic vinyl sulfones, and mixtures of the two possible adducts are formed . The charge-transfer stabilization energy calculated according to the Klopman-Salem perturbational approach is able to account for the experimental trends of the isomer ratio in terms of the major stereochemical structural differences between the acyclic vinyl sulfones and the four-membered ring sulfones (see Section IV.B.3). 

The use of optically active enamines in [2 + 2] cycloadditions with thiocarbonyl 5.5-dioxides gives asymmetric induction in the product thiirane 1,1-dioxides. Thus, when thioformaldehyde S,S-dioxide, generated from methanesulfonyl chloride and triethylamine, is treated with optically active AM-phenylethyl-Af-methylpropanal enamine, a mixture of diastereomeric thietane 1.1-dioxides 6 is formed quantitatively. Removal of the chiral 1-phenylethyl auxiliary followed by Hoffmann elimination gives (-+ )-(5)-2-methyl-2//-thiete 1,1-dioxide (7) with 6% ee1,8. 

Diels-Alder reactions of thiete 1,1-dioxides occur readily as exemplified by the syntheses of 151 ° and 152. Adducts of thiete 1,1-dioxide with tetraphenylcyclopentadienone or a-pyrone ° are thermally unstable. Thiete 1,1-dioxides also undergo 1,3-dipolar additions with diazoalkanes, (e.g., the formation of 153 from which the strained bicyclic thietane sulfone 154 is obtained) " nitrile oxides, and cycloadditions with the MA -dimethylenamine of isobutyraldehyde (e.g., the formation of 155). ° ... 

Treatment of diethyl ketals of 3-thietanone 1,1-dioxide with bases (NaOH, phenyllithium" ) results in the elimination of ethanol to give 3-ethoxythiete 1,1-dioxides, for example, 257. 3-Methoxy-2H-thiete 1,1-dioxide is obtained by elimination of methoxytrimethylsilane from the ketal of 2-trimethylsilyl-3-thietanone 1,1-dioxide. The cycloaddition of ketene yy.,4i7,494b.495a,s93,6oo. 49sa,60i sulfenes derived from... 

The cycloaddition of sulfenes with enamines provides a good synthetic route to thiete 1, 1-dioxides (174) (see Chapter 7, p. 115) (Scheme 69).8 Thiete-1, 1-dioxides like (174) react with alkylamines by conjugate addition to yield the corresponding amino derivatives (175), and by heating in the presence of a reactive alkene, e.g. norborene (176), they form the [2+4] cycloadducts, e.g. (177) (Scheme 69). 

Electrophilic sulfenes, R2CMSO2, are recognized for their ability to react with nucleophiles and for their 2ir participation in [2 + 2] and [4 + 2] cycloadditions (Chapter 5). Less well recognized is the demonstrated 4ir participation of vinyl sulfenes in Diels-Alder reactions with a select set of dienophiles. Thermolysis of thiete 1,1-dioxides including the parent thiete 1,1-dioxide (22) in the presence of norbornenes provided the Diels-Alder products derived from 4w participation of the vinyl sulfenes [Eq. (18)].40... 

In another group of (2 + 2)-cycloaddition reactions, the heterocyclic nucleus reacts via an electron-deficient carbon-carbon or carbon-nitrogen double bond with electron-rich aminoacetylenes (ynamines). For instance, thiete 1,1-dioxides, JV-benzylmaleimide, and 2,3-bis(methoxycarbonyl)-7-oxabicyclo( 2.2.1 lhepta-2,5-diene reacted with 1-diethylamino-l-propyne and with 1 -phenyl-2-( 1 -pyrrolidinyl)-acetylene to give the (2 + 2)-cycloadducts 48, 49, and 50, respec-tively.35,37,53 The latter product was thermally rather unstable, and its structure was identified on the basis of its conversion with 2,4,6-tri-methylbenzonitrile oxide into 51.53 (2 + 2)-Cycloaddition via a carbon-nitrogen double bond has been reported to take place in the reactions of 3,3-dimethyl-3//-indoles and 3,4-dihydroisoquinoline with ynamines, e.g., l-dimethylamino-2-phenylacetylene, in the presence of boron trifluoride.54 The (2 + 2)-cycloadducts 52 and 53 were not isolated, but... 

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. ... 

Reactions.—Condensation of thiet sulphone with 2 moles of halogeno-hydrazones, RC(Cl)=NNHPh, gives isoimidazoles (113). Cycloaddition of thiet sulphone to cyclopentadiene occurs with an exofendo ratio of 0.25. 2,4-Diphenylthiet dioxide is hydrolysed to dibenzyl sulphone with base, but rearranges to the isomeric sulphinate 3,5-diphenyl-1,2-oxathiolen 2-oxide with concentrated sulphuric acid. Treatment of 4-phenyl-2i/-thiet 1,1-dioxide with KOH in ethanol gives 3-ethoxy-2-phenylthietan 1,1 -dioxide. ... 

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