Dithiin production

Dimethipin. 2,3-Dihydro-5,6-dimethyl-l,4-dithiin-l,l,4,4-tetraoxide [55290-64-7] (dimethipin, oxidimetbiin, UBI-N252, Harvard) (25) is used as a cotton defoHant and has been used as an experimental desiccant in potato vines. In addition, it defoHates nursery stock, grapes, dry beans, and natural mbber and is used as a desiccant for seed of canola, flax (l lnum usitatlssimum), rice, and sunflower (He/lanthus annuus) (10). The product has been available since the mid-1970s and the experimental work was first reported in 1974 (44). 

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 possibility of electrocyclic valent tautomerism of the dithiins 55 with the product of their ring opening, but-2-ene-l,4-dithione (56), has been considered (85KGS1443 96T12677). However, all the experimental data provide evidence for the dithiyne form 55 (85KGS1443 96T12677). 

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). 

During the thioketalization and distillation, thermal extrusion of HCI and isomerization to 2,3-dihydro-1,4-dithiin is observed2 and the product of Step A typically contains ca. 10% of this impurity. 

In wet acetonitrile, the oxidation of diaryldisuUrdes [119] and dialkyl disulfides (Aik 7 f-Bu) [120] affords the corresponding aryl and alkylthiosulfonates in good synthetic yields (Eq. 15). Thus, the oxidation of a cyclic disulfide, dibenzo(c,e)-1,2-dithiin (1,1) does not affect the S—S bond and results in a corresponding thiosulfonate, dibenzo(c,e)-l,2-dithiin-l,l-dioxide(Scheme 27) [121]. Such oxidized products can form in wet acetonitrile as well as in a dry solvent, but in the latter case this is probably a result of disproportionation of the primarily... 

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). 

Finally, an unorthodox pathway to the dithiin systems has been reported Tetracyanoethylene 214 combines with two molecules of thiobenzophenone in refluxing benzene to give the tetrasubstituted 1,2-dithiins 215. However, these were obtained only in addition to the corresponding thiophenes 216 as the main reaction products (Scheme 59) <1985TL1849, 1997LA1677>. 

Substituted 4,5-dihydro-l,2-dithiins were obtained as by-products in the copper-catalyzed ring expansion of vinyl... 

There are few examples of the preparations of heterocyclic compounds containing two or more heteroatoms which involve cyclization with formation of a bond between two heteroatoms. The best known instances of this type of reaction, all of which are [6 + 0] reactions, are the preparations of benzocinnolines as outlined in equations (l)-(4). A similar type of approach to that outlined in equation (4) has been used for the direct preparation of the di-N-oxide (2) from the dioxime (1 equation 5). The naphthotriazine betaine (4) is obtained as one of the products of the thermal decomposition of the azidoazo compound (3 equation 6). 1,2-Dithiins and their dibenzo derivatives have been prepared by oxidation of appropriate dithiols and related starting materials as outlined in equation (7). All of these reactions are, however, somewhat specialized and there has been essentially no systematic study of the preparation of six-membered heterocycles via formation of a bond between two heteroatoms. 

Thieno[2,3-r 1-l,2,3-thiadiazoles 40a-f heated with CS2 in a double compartment autoclave produced thieno[2,3-rfl-l,3-dithiol-2-thiones 41a-f <2001MOL145>. In addition to the thermolysis product 41e, thieno[2,3- / -l,2,3-thia-diazoles 40e also produced bisthieno[2,3-/ 2, 3 -< ][l,4]dithiine 42 in 36% yield (Equation 3). 

Reaction of various aldehydes with hydrogen sulfide leads to substituted thiophenes, dihydrothiophenes, dithiolanes and trithiolane, as well as to six-membered ring thiopyran derivatives and dithiins. Ledl (33) obtained 2,4-dimethylthiophene (1, R Me) as a product of the reaction of propionaldehyde with hydrogen sulfide in the presence of ammonia. Sultan (29) reported the formation of 2,4-diethylthiophene (1, R - Et), 2,4-dibutyl-thiophene (1, R - Bu), and their dehydro derivatives from the reaction of ammonium sulfide with butyraldehyde and caproaldehyde (hexanal), respectively. The mechanism suggested for their formation is depicted in Scheme 1. Space limitations do not allow us to discuss the mechanism here in detail (for additional information, see ref. 29). 

Dairy products, conjugated dienoic derivatives of linoleic acid, 263,266r Decyl D-glucopyranoside, 221,222r Defensin, characteristics, 308r Deterioration of flavor, 79 Dienoic derivatives of linoleic acid, 262-270 Diet-cancer risk relationship, 262 Dioxathianes, formation, 38,43,44r Disjoining pressure, definitions, 233-237 1,3,5-Dithiazines, 43,46t,47 Dithiins, formation, 4U,43 Dithiolenes, formation, 38,39r... 

Dioxin and 1,4-dithiin both undergo easy electrophilic addition reactions, e.g. of halogens to the double bonds. Alcohols under acid catalysis form ketal addition products. 

Substitution products can be obtained from some 1,4-dithiins. Thus, 2,5-diphenyldithiin is formylated under Vilsmeier conditions, and mono- or di-nitrated and brominated in the heterocyclic ring. 1,4-Benzodithiin shows similar properties (see Scheme 51). 

Dithieno[2,3-6 3, 2 -e]-l,4-dithiin (421) has been obtained as a by-product in the reaction of 2-iodothiophene with sulfur whereas dithieno[3,4-6 3, 4 -e]-l,4-dithiin (422) is formed when a mixture of 3-bromothiophene-4-thiol, potassium hydroxide and copper oxide is... 

A [5 - 2 + 2 + 1] fragmentation followed by cyclization forming a new five-membered ring was observed by FVP studies of 2-propenyl-l,3-dithiolan 1,1-dioxide (79) (95H1967). The reaction mixture consists of four products thiophene (26%), 2,5-dihydrothiophene (80,34%), 4-methyl-2-propenyI-4//-l,3-dithiine (20%), and 2,6-dimethyl-2//,6//-l,5-dithiocine (20%). The last two compounds are formed by [4 + 2] or [4 + 4] dimerization of the intermediate 2-butenethial. Formation of 80 involves a 1,5-H shift of the as-butenethial, followed by cyclization. 

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