Episulfides, reactions

The [S + C=C] route is illustrated by reaction of disulfur dichloride or sulfur dichloride with alkynes (Scheme 9), or by episulfidation of alkenes by sulfur atom donors in the presence of molybdenum oxocomplexes (Scheme 10) . 2-Phenylthiirane is the most efficient sulfur donor in the molybdenum-catalyzed episulfidation and the reaction proceeds stereoselectively as yy/z-addition e.g., the episulfidation reaction of trans-cyclooctene affords /r my-epithiocyclooctane (Scheme 10) <2003JA3871>. 

The problem of the synthesis of highly substituted olefins from ketones according to this principle was solved by D.H.R. Barton. The ketones are first connected to azines by hydrazine and secondly treated with hydrogen sulfide to yield 1,3,4-thiadiazolidines. In this heterocycle the substituents of the prospective olefin are too far from each other to produce problems. Mild oxidation of the hydrazine nitrogens produces d -l,3,4-thiadiazolines. The decisive step of carbon-carbon bond formation is achieved in a thermal reaction a nitrogen molecule is cleaved off and the biradical formed recombines immediately since its two reactive centers are hold together by the sulfur atom. The thiirane (episulfide) can be finally desulfurized by phosphines or phosphites, and the desired olefin is formed. With very large substituents the 1,3,4-thiadiazolidines do not form with hydrazine. In such cases, however, direct thiadiazoline formation from thiones and diazo compounds is often possible, or a thermal reaction between alkylideneazinophosphoranes and thiones may be successful (D.H.R. Barton, 1972, 1974, 1975). 

Primary and secondary amines also react with epoxides (or in situ produced episulfides )r aziridines)to /J-hydroxyamines (or /J-mercaptoamines or 1,2-diamines). The Michael type iddition of amines to activated C—C double bonds is also a useful synthetic reaction. Rnally unines react readily with. carbonyl compounds to form imines and enamines and with carbo-tylic acid chlorides or esters to give amides which can be reduced to amines with LiAlH (p. Ilf.). All these reactions are often applied in synthesis to produce polycyclic alkaloids with itrogen bridgeheads (J.W. Huffman, 1967) G. Stork, 1963 S.S. Klioze, 1975). 

Phosgene reacts exothermically with thiirane in two steps (Scheme 36) (77MI50602). 3,5-Dinitrobenzoyl chloride and benzoyl fluoride initiate polymerization of thiirane. A novel reaction of benzoyl isocyanate or trichloroacetyl isocyanate, which yields ethylenethiol derivatives from epithiochlorohydrin (2-chloromethylthiirane), 2-methylthiirane or cyclohexene episulfide, has been reported (Scheme 37) (71BAU2432). 

Treatment of thiiranes with lithium aluminum hydride gives a thiolate ion formed by attack of hydride ion on the least hindered carbon atoms (76RCR25), The mechanism is 5n2, inversion occurring at the site of attack. Polymerization initiated by the thiolate ion is a side reaction and may even be the predominant reaction, e.g. with 2-phenoxymethylthiirane. Use of THF instead of ether as solvent is said to favor polymerization. Tetrahydroborates do not reduce the thiirane ring under mild conditions and can be used to reduce other functional groups in the presence of the episulfide. Sodium in ammonia reduces norbornene episulfide to the exo thiol. 

Thermolysis of trithiane (69) or carbonate (70) at reduced pressure yields methylene-thiirane which is stable in cold, dilute solution (Scheme 152) (78JA7436, 78RTC214). A novel acenaphthylene episulfide is obtained by treatment of the six-membered sulfoxide (71) with acetic anhydride (Scheme 153) (68JA1676), and photolysis of (72) gives a low yield of episulfide (73 Scheme 154) (72JA521). Low yields may be due to the desulfurization of the thiiranes under the reaction conditions. 

Benzenediazonium fluoroborate, 2-carboxy-xanthone synthesis from, 3, 838 Benzenediazonium ions phenyl azide formation from, 5, 839 Benzenediazonium salts, o-(imidazol-l-yl)-intramolecular diazo coupling, 5, 404 Benzene-1,2-disulfonimides N-substituted reactions, 6, 930 Benzene episulfide formation, 7, 577 Benzeneimine... 

A solution of the acylated thiocyanatohydrin in a minimal amount of 5% potassium hydroxide in diglyme (other solvents such as methanol, ethanol or tetrahydrofuran have also been used) is stirred for 2 days at room temperature. Water is added to the reaction mixture to precipitate the product which is filtered or extracted with ether (or chloroform). The ether extract is washed several times with water, dried (Na2S04), and concentrated under vacuum. The thiirane usually can be crystallized from an appropriate solvent pair. Chromatography over alumina has been used for the purification of episulfides. 

Episulfides, which can be generated in situ in various ways, react similarly to give P-amino thiols, and aziridines give 1,2-diamines. Triphenylphosphine similarly reacts with epoxides to give an intermediate that undergoes elimination to give alkenes (see the Wittig reaction, 16-47). 

Thiadisiliranes are also formed in high yield in the reaction of disilenes with episulfides. Thus 1 with cyclohexene sulfide gave 5084 and the reac-... 

From X-ray crystal structures of the products, the reactions of these stereoisomeric disilenes with episulfides, and with sulfur, were shown to proceed with retention of configuration at silicon. These findings suggest that the reaction proceeds in a concerted fashion, through intermediates or transition states involving tetracoordination for the sulfur atom being transferred (Scheme 13). Similar intermediates are believed to occur in other sulfur-transfer reactions.86... 

Secondly, in view of the generally accepted mechanism for the sulfur extrusion reaction, which involves valence isomerization of the thiepin ring to its corresponding thianorcaradiene (benzene episulfide) isomer followed by irreversible loss of sulfur,... 

A quite different use of a thiocyanate salt is the conversion of an epoxide (oxirane) to an episulfide (thiirane) this normally heterogeneous reaction is markedly accelerated by the use of silica gel coated with, or finely ground with, potassium thiocyanate, rather than with the thiocyanate salt alone.17... 

Thiiranes (episulfides) have been suggested as intermediates in the reaction of thionyl chloride with various substrates including ketones and carboxylic acids.54 However, apart from one claim, later corrected, no such compounds have been isolated.55,56... 

Ethylene and propylene episulfides polymerize in THE at 0-70°C in the presence of sodium naphthalene, and (importantly) the polymer contains no naphthalene residues. The reaction involves one-electron transfer followed by dimerization of the resulting radical to give a dithiolate ion. This ion then polymerizes an episulfide by anionic mechanism (Boileau et al. 1967 Scheme 7.14). 

Ring closure to an episulfide is a feasible reaction for thiocarbonyl ylides. In most cases, the sulfur is further extruded under the reaction conditions to afford an olefin as the final product. This cascade transformation has been utilized by Danishefsky and co-workers in their total synthesis of ( )-indolizomycin (Scheme 16)." In the Danishefsky s approach, diazo ketone 137 is treated with a catalytic amount of Rh2(OAc)4 to generate thiocarbonyl ylide 138, which cyclizes to give episulfide 139. This episulfide isomerizes to mercaptan 140, which is then desulfurized by partially deactivated W-2 Raney nickel. 

This section describes that the first example of photoenhanced copolymerizability of epoxide and episulfide in a reaction using the zinc complex of M-substi-tuted porphyrin (NMTPP)ZnSPr (17,X=SPr) as initiator. 

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