Sulphenes Diels-Alder reactions

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). 

Schenone and coworkers have shown in a large number of papers that tertiary aminomethyleneketones react as heterodienes, e.g. with sulphene generated from aliphatic sulphonyl chlorides and triethylamine as a heterodienophile, to yield / -aminosultons in a Diels-Alder reaction. An early simple example is reported by Opitz270 (equation 199). 

The most common route to sulphenes, the elimination of hydrogen halide from a sulphonyl halide, has been the subject of a recent mechanistic and kinetic study which led to the conclusion that this reaction most probably proceeds by an El mechanism. Tsuge and Iwanami used this reaction for the generation of benzoylsulphene (130) from benzoylmethane-sulphonyl chloride. The reaction of (130) with a series of anils (131) was found to be somewhat dependent on the presence or absence of triethylamine and very dependent on the nature of R in (131). For R = alkyl, the (4 -I- 2) cycloadduct (132) is the predominant or only product, whereas for R = aryl the (2 + 2) cycloadduct (133) is the reaction product. Similar results were obtained for the reaction of (130) with carbodi-imides. The reaction of (130) with aryl cinnamylideneamines gave Diels-Alder adducts (134). ... 

Thioamide vinylogues (100) have been reported to yield Diels-Alder adducts on treatment with substituted alkenes and sulphenes/ In the former case, the heterocyclic compounds (107) and/or (108) were produced, depending on the substituents. In the latter case, the unsubstituted sulphene afforded merely (109), whereas solely the de-aminated products (110) were formed in reactions with benzylsulphene. 3-Alkylthio-l-aryl-3-arylamino-2-propene-l-thiones (41) have been converted into 3-arylamino-1,2-oxazoles, 3-arylaminopyrazoles, and the quinoline derivatives (111) by treatment with hydroxylamine, hydrazine, and sulphuric acid, respectively. " The formation of 2-imino-2H-thiopyrans by spontaneous ring-closure of -mercaptovinyl-acrylonitriles (112) has been reported recently. ... 

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