Thietanes desulfurization

The progress on S-C bond activation, which covers the reduction of a C-S bond to a C-H bond, cross coupling reaction of sulfides with main group organometaUic nucleophiles, ring opening reactions of thietanes and thiiranes, and desulfurization of thiols, sulfides, and thiophenes has already been reviewed elsewhere [6-10], and... 

Spectra for most thietanes contain a strong parent ion peak. The four-membered ring is usually fractured into the four possible halves. For example, the cleavage of thietane derivative (43) produces peaks at mje 240, 230, 84, and 74. The parent ion peak is absent at 35°. Similarly, spirothietane 44 splits to give fragments with m/e 162 (77%), 152 (12%), 84 (100%), and 74 (0.6%). Decomposition of the thietane nucleus is also characterized by desulfurization and retro 2-1-2 cycloaddition fragments. 

An interesting synthetic approach to thietanes is the selective desulfurization of cyclic disulfides.The treatment of dithiolanes with a diethyl-aminophosphine results in a ring contraction to thietanes, (Eq. 19). This has been demonstrated with a-lipoic acid, a coenzyme with a dithiolane structure involved in the biological oxidation of pyruvic acid. The reaction is proposed to be initiated by the electrophilic attack of the phosphorus on the ring sulfur atom, resulting in the formation of an acyclic internal phosphonium salt, which by subsequent elimination of a phosphine sulfide, closes to the four-membered ring. °... 

Paquette has used the chloroketal derivatives of thietane 1,1-dioxide as an especially well-suited model for the theoretical study of the thermally induced intramolecular six-electron ring contraction rearrangement, which is pointed out in Eq. (54) for the ketals of 2-bromocyclobutanone that give cyclopropylcarboxylates. Desulfurization of thietanes to cyclopropane did not prove too successful. ... 

Certain thietane derivatives such as (54) (67JOC2009), (55) (81JCR(M)1132) and (56) (80JOC2962) are desulfurized on treatment with triarylphosphines. These reactions probably involve initial attack by phosphorus on sulfur. 

Reaction of a carbenoid reagent with thietane has been found to lead to ring expansion to thiolane (81) (72JOC1721, 75BCJ1490). Atomic carbon desulfurizes thietanes in a stereoselective manner, perhaps via ylidic species (82) (73JA1547). 

Table 7 Desulfurization of Thietane Derivatives with Raney Nickel...

Only a limited number of examples are known of applications of thietanes in organic synthesis. Prominent among these examples would be electrophilic ring opening reactions leading to polyfunctional sulfur compounds (33)-(37), utilization of 3-thietanones (55) and metal complexes (87) derived therefrom as oxyallyl zwitterion equivalents in cycloaddition reactions, synthesis of dipeptide (63) with a /3-thiolactone, Raney nickel desulfurization of thietanes (e.g. 120 cf. Table 7) as a route to gem-dimethyl compounds, and desulfurization of thietanes (e.g. 17) in the synthesis of cyclopropanes (also see Table 7). 

A silver ion-mediated desulfurization of thiocarbonyl compounds 163 or 164 followed by condensation with benzohydroxamic acid in the presence of excess triethylamine affords, respectively, dioxazole derivatives 165 or 166 (Scheme 25) <2002H(57)143>. Other reports concern the synthesis of l,4-(oxa/thia)-2-azoles 170-173 from unusual four-atom components such as the sulfur diimides 167, the thietan sulfimide 168, and the carbimidoyl chloride 169 <1996CHEC-II(4)530>. 

Desulfurization of thietanes by Raney nickel in ethanol or methanol yields either ring-opened a synthetically useful... 

The exo-allenic thietane dioxide 407 is obtained by cycloaddition of an allenic sulfene to an enamine. Desulfurization of thiirane 406 by triphenylphosphine... 

Details of the diastereoselective synthesis of the bicyclic thietane (33) by solid-state photocyclization of an acyclic thioamide are available (94JOC3131). Photocycloaddition of 1,1-diphenyl-ethene to 4-thioazetidin-2-one gives the adduct (34) which, on desulfurization, provides a route to 4-spirocyclopropyl -lactams (93TL5951)(see 4.7). 

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