Thiete 1,1-dioxides reduction

Application of the enamine-sulfene cycloaddition allowed the synthesis of 78 and 79 from the corresponding a,/l-unsaturated amines and sulfenes. Similarly, using enamine 80, the crystalline morpholino thietane dioxides (81) were produced. Elimination via the N-oxide gave the corresponding thiete dioxide, whereas reduction by LiAlH4 yielded the thietane 82. 

Conversion of 3-chlorothietane 1,1-dioxide to the 3-(N,N-dimethylaraino) derivative followed by reduction, quaternization, and Hofmann elimination affords a convenient route to the highly reactive thiete (thiacyclobutenel... 

It is intriguing to note that this reaction scheme for the reduction of a sulphone to a sulphide leads to the same reaction stoichiometry as proposed originally by Bordwell in 1951. Which of the three reaction pathways predominates will depend on the relative activation barriers for each process in any given molecule. All are known. Process (1) is preferred in somewhat strained cyclic sulphones (equations 22 and 24), process (2) occurs in the strained naphtho[l, 8-hc]thiete 1,1-dioxide, 2, cleavage of which leads to a reasonably stabilized aryl carbanion (equation 29) and process (3) occurs in unstrained sulphones, as outlined in equations (26) to (28). Examples of other nucleophiles attacking strained sulphones are in fact known. For instance, the very strained sulphone, 2, is cleaved by hydride from LAH, by methyllithium in ether at 20°, by sodium hydroxide in refluxing aqueous dioxane, and by lithium anilide in ether/THF at room temperature. In each case, the product resulted from a nucleophilic attack at the sulphonyl sulphur atom. Other examples of this process include the attack of hydroxide ion on highly strained thiirene S, S-dioxides , and an attack on norbornadienyl sulphone by methyllithium in ice-cold THF . ... 

The thietane dioxides can be converted into thietes by successive reduction, methyla-tion and Hofmann elimination of the resulting thietane derivatives (equation 2)18. 

However, thiete 1.1-dioxide does not give thiete under these oon-ditions, and thiophenol is the only product identified fifOin the reduction of S-phenylthiotbietane 1,1-clloxide, ... 

The first thiete fused to an aromatic system 219 (and an anthracene derivative) was reported in 1965 and was prepared by reduction of a naphthothiete sulfone. An attempt to prepare benzothiete by desulfurization of benzo-l,2-dithiolane was unsuccessful. Photolysis of benzo-l,2-dithiolane 1,1-dioxide in an attempt to extrude sulfur dioxide to give benzothiete also was unsuccessful. The naphthothiete 205, however, was prepared by extrusion of sulfur dioxide from 220 and nitrogen from 221. Thiete 205 also is obtained in 6-8% yield by treatment of 1,8-dehydronaphthalene with carbon disulfide. The unstable thiolactone 211 was formed by a photochemical extrusion of benzaldehyde from 222 and from 222a at 350°C. The benzothietes 209, 223, " and 224 have been... 

No evidence could be obtained for the formation of 2ff-benzo[i>]thiet or its valence tautomer by irradiation of 3/f-l, 2-benzodithiole l,l-dioxide. Naphtho-[l,8-6c]thiet (58) has been prepared and its 5-oxide, and S -dioxide, have been obtained by oxidation with m-chloroperoxybenzoic acid. All three compounds react with lithium aluminium hydride to give ring-opened products as the result of hydride attack on sulphur. After reduction and methylation, (58) gave the methyl sulphide (59), and the 5-oxide gave bis(a-naphthyl) disulphide (75%) together with (58) (6%) and the corresponding sulphone (4%), which was the major product (85%) from the 55-dioxide (Scheme 8). Thiets are believed to be... 

---