Dithiines reactions

Diene moieties, reactive in [2 + 4] additions, can be formed from benzazetines by ring opening to azaxylylenes (Section 5.09.4.2.3). 3,4-Bis(trifluoromethyl)-l,2-dithietene is in equilibrium with hexafluorobutane-2,3-dithione, which adds alkenes to form 2,3-bis-(trifluoromethyl)-l,4-dithiins (Scheme 17 Section 5.15.2.4.6). Systems with more than two conjugated double bonds can react by [6ir + 2ir] processes, which in azepines can compete with the [47t + 27t] reaction (Scheme 18 Section 5.16.3.8.1). Oxepins prefer to react as 47t components, through their oxanorcaradiene isomer, in which the 47r-system is nearly planar (Section 5.17.2.2.5). Thiepins behave similarly (Section 5.17.2.4.4). Nonaromatic heteronins also react in orbital symmetry-controlled [4 + 2] and [8 + 2] cycloadditions (Scheme 19 Section 5.20.3.2.2). 

Tile preparation of beiizo-l,2-dithiete (264) had been claimed by oxidation of 1,2-benzenedithiol (25JIC318). However, later work has shown that the reaction product was probably a polymeric mixture (61JOC4782). Subsequently, compound 265 was irradiated to give a mixture of CO, sulfur, and dithiin and thiophene derivatives, which could, at least in part, be explained by the formation of 266 (72JHC707). Results of the thermolysis of 267 were also rationalized in terms of the intermediacy of o-dithiobenzo-quinone (the tautomer of 264) (78JOC2084). 

The results are critically dependent on the level of theory. However, a stepwise mechanism with closed shell structures along the reaction path was found to be lower in energy than a concerted reaction. An all-cw conformer of 172 is reported to be a transition state rather than an intermediate. Similarities of the conformational isomers of the intermediate 2-butenedithial 172 with the dinitrosoethylenes discussed in Section IV,c are evident. 3,6-Diamino-substituted dithiins are predicted to be more stable in the open-chain bisthioamide structure [95JST51]. The... 

The photochemical behavior of a number of substituted derivatives of thiochroman-4-one 1-oxides has been examined by Still and coworkers192-194. These authors also report that rearrangement to cyclic sulfenates, with subsequent reaction by homolysis of the S—O bond, appears to be a particularly favorable process. For example, ultraviolet irradiation of a solution of 8-methylthiochroman-4-one 1-oxide (133) in benzene for 24h afforded a single crystalline product which was assigned the disulfide structure 134 (equation 54). More recently, Kobayashi and Mutai195 have also suggested a sulfoxide-sulfenate rearrangement for the photochemical conversion of 2,5-diphenyl-l,4-dithiin 1-oxide (135) to the 1,3-dithiole derivatives 136 and 137 (equation 55). 

Lithiation of the dibromodithienyl compound 464 and reaction with sulfur and subsequent oxidation yielded the tetramethyl substituted dithieno[3,Z-c.Z, 3 - ][l,2]dithiin 465 (Equation 126) <1997T7509>. 

However, the yield for the unsubstituted analogue was only 19%, due to competing lithiation reactions. Le Coustumer and Catel have recently demonstrated a high-yielding route to the unsubstituted dithieno[l,2]dithiin 467 via the dithiolate (Equation 127) <2006PS( 181) 191 >. 

Other heterocyclic systems prepared by a thionyl chloride reaction include fused thiazoles,71 thiatriazoles,72 oxathiins,73 and dithiins 74 some further examples are given in reviews.53... 

The chemistry of pentathiepins has been extended to the pyrrolo-fused derivative 155. Reaction of 155 with dimethyl acetylenedicarboxylate (DMAD) and triphenylphosphine at room temperature gave the fused 1,4-dithiin derivative 156 in high yield <06OL4529>. 

The synthesis of 1,4-dithiines from arenes and heteroarenes has been known for more than 100 years. The reaction of quinoline and sulfur monochloride gave dithiodiquinoline 152 (R = R = H) (1896JPR340). The structure of such compounds has been correctly identified only recently (1976PJC785, 1997JCR(S)435 Scheme 80). 

Only two examples of the 1,2-dithiine synthesis from biphenyls are known (1996NJC1031), although this transformation is the expected one. Dibenzodithiin 155 was formed in a reaction of 3,3, 4,4, 5,5 -hexamethylbiphenyl 154 with sulfur monochloride at low (0-5 °C) temperature. At room temperature the main product was bis[l,2]dithiine 156. Surprisingly, monodithiine 155 did not convert to bisdithiine 156 after treatment with S2CI2, and this probably implies that the addition of two sulfur monochloride molecules to biphenyl 154 took place simultaneously (Scheme 82). 

Krespan and McKusick have studied the addition reaction of dithietenes to various oleflnes and acetylenes. Thus, the reaction of 3,4-bis(trifluoromethyl)-l,2-dithiete (378) with DMAD gives a dithiin derivative (379), which loses sulfur on heating to give 2,5-dicarbomethoxy-4,5-bis(trifluoromethyl)thiophene (380) [Eq. (57)]. 

Reactions of cyclopentadienyl- and (pentmethylcyclopentadienyl)iron dicarbonyl 2-alkynyl complexes as well as cyclopentadienylmolybdenum tricarbonyl 2-alkynyl complexes with 4,5-diphenyl-3,6-dihydro-l,2-dithiin 1-oxide 111 were shown to yield transition metal-substituted five-membered ring thiosulfinate esters 112 in moderate to excellent yields (Scheme 27) <19910M2936, 1989JA8268>. These reactions are formal [3-1-2] cycloadditions. When... 

Simple side-chain reactions of 1,2-dithiin diols have been conducted. Besides the formation of esters, ethers (R = Me, Et, 7-Pr, cyclopropyl, Ph, pyridyl, cyclopentyl), and thioethers (R = H, TBDMS R = 4 -(4-hydroxyphenyl)-l//-tetrazole-5-thiol), selective oxidation of the primary alcohol groups in the presence of the 1,2-dithiin heterocycle could be readily achieved (Scheme 36) <1995JME2628, 1994SL201>. Additionally, amides, ureas, and carbamates of the dithiin diol were synthesized <1995JME2628>. 

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