Thiepin 1,1 dioxide

Treatment of cis- or ira x-3,4-dibromo-2,3,4,7-tetrahydrothiepin 1,1-dioxide with 2 equivalents of triethylamine in benzene solution at 25 CC gives, after chromatography of the benzene-soluble products, thiepin 1,1-dioxide.15... 

Treatment of ethyl 2,7-di-/ert-butylthiepin-4-carboxylate (24) with 3-chloroperoxybenzoic acid at — 78 °C results in the benzene derivative 25 only, and no sulfur-oxidized products 80 however, the stable 2,7-di-ter/-butylthiepin (26) can be oxidized with 0-benzyl 00-hydrogen monoper-oxycarbonate at — 78 °C to give the corresponding S-oxide 27, which was monitored by HNMR spectroscopy at — 40°C. At —15 C, sulfoxide 27 was converted, via extrusion of sulfur monoxide, with a half-life of 5.5 hours to the benzene derivative 28.87 The oxidation reaction of 26 with excess of the monoperoxycarbonate did not proceed to the S,S-dioxide, even though the parent thiepin 1,1-dioxide is known to be stable at room temperature.15... 

Thiepin-1,1-dioxide undergoes a number of chromium(0) mediated [6jt + 4jt] cycloaddition reactions with a range of 1,3-dienes. The intermediate adduct undergoes a Ramberg-Backlund rearrangement to form new benzannulated products <96JOC7644>. 

The thiepin 1-oxide (126)641 and thiepin 1,1-dioxides, such as 4965 and 127 together with thieno[3,4-rfJthiepin (13, X = S)67) and its dioxide 128 67) have also been analyzed by X-ray analysis. The X-ray structures are shown in Figs. 3-7. 

The first synthesis of thiepin 1,1-dioxide (131) was performed by Mock in 1967 75>. With exess bromine in chloroform 2,7-dihydrothiepin 1,1-dioxide (129), prepared by 1,6-addition of sulfur dioxide to m-hexatriene, gave a dibromide 130 which, on treatment with two equivalents of triethylamine, afforded 131. Upon catalytic reduction, 131 rapidly absorbed three molar equivalents of hydrogen to yield hexahydrothiepin 1,1-dioxide (132). The 1,1-dioxide 131 is a fairly stable compound ... 

Several derivatives of thiepin 1,1-dioxide including the parent benzo[6]thiepin 1,1-dioxide have been synthesized l3, i7-77-78-79-80). in all cases, the thermal stability of there dioxides is greatly enhanced and, as a result, some of the unstable thiepins can be characterized by oxidation to their 1,1-dioxides. For example, benzo[b]thiepin decomposes at 47 °C with a half-life of 84 min whereas its dioxide is stable even in refluxing ethanol81). 

Unlike thiepin 1,1-dioxides, thiepin 1-oxides are very labile compounds. Treatment of the stable thieno[3,4-d thiepin (13 X = S) with m-chloroperbenzoic acid in chloroform gave stable thieno[3,4-djthiepin 1,1-dioxide (135) 54). When the oxidation of 13 was carried out at 0 °C under carefully defined conditions, there was isolated in 90% yield the unstable crystalline thiepin 1-oxide 136 which decomposed on standing54). 

An alternative synthesis of thiepin 1,1-dioxide (131) has also been reported (Paquette, L. A., Maiorana, S. J. Chem. Soc. Chem. Commun. 1971, 313). Thus, the reaction of vinyldiazomethane with sulfur dioxide yields 4,5-dihydrothiepin 1,1-dioxide which was converted to 131 by bromination (NBS) and dehydrobromina-tion (Et3N) sequence. 

Rigby and coworkers305,309 also performed metal mediated [6 + 4] cycloadditions of heterocyclic trienes and tropones with various dienes. In concurrence with the all-carbon trienes, the electronic nature of the diene partners generally had little influence on the cycloaddition efficiency. The only reported exceptions are the reactions of thiepin-1,1-dioxides. Lower yields were observed in the reactions involving electron-deficient dienes in comparison with the reactions with electron-rich dienes. The reaction of complex 514... 

Thus by analogy it is anticipated that the molecular dimensions for thiepin (44) will be almost identical to those of thiepin 1,1-dioxide (45). Bond localization in the thiepin ring is evident from the X-ray structural data where both carbon-carbon single and double bonds and carbon-sulfur single bonds showed little change from normal values. 

Thermal extrusion of a sulfur atom is the most common thermal reaction of a thiepin. The mechanism of this thermal process involves two orbital symmetry controlled reactions (69CC1167). The initial concerted step involving a reversible disrotatory electrocyclic rearrangement is followed by a concerted cheleotropic elimination of sulfur (Scheme 29). Similar aromatization reactions occur with thiepin 1-oxides and thiepin 1,1-dioxides, accompanied by the extrusion of sulfur monoxide and sulfur dioxide respectively. Since only a summary of the major factors influencing the thermal stability of thiepins was given in Section... 

Thiepin 1,1-dioxide (240) has been obtained by the reaction of a six-membered cyclic sulfone with diphenylacetylene in the presence of UV light (equation 76). No mechanism has been proposed for this rather unusual ring expansion (74JOC103). 

Thiepin 1,1-dioxide (4). When sulfur dioxide is passed into a cold ethereal solution of vinyldiazomethanc (1), nitrogen is evolved, and the sulfone 4.5-dihydrothiepin 1.1 -dioxide (3) is obtained in 29 % yield. The t fj-divinyl episulfone (2), which can under-... 

An example of the degree of complexity that may be unraveled and the precision of the analysis is given in Figure 1 and Table 1, where experimental and calculated spectra for the compound thiepin-1,1-dioxide are reproduced, as obtained by Williamson, Mock, and Castellano.9... 

FIGURE 1 Experimental (upper section) and calculated Gower section) 100-MHz proton NMR spectrum of thiepin 1,1-dioxide. Frequencies (hertz) are referred to tetramethyl silane (TMS) used as an internal standard. 

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