Thiiranes, 2,2-disubstituted

S-methyl dithiocarbonate (76S413). Stereoselective isomerization of 1,2-disubstituted alkenes may be achieved by a sequence such as the following fr<2n5-alkene bromo-hydrin -> /3-hydroxythiocyanate -> cw-thiirane -> cw-alkene (75TL2709). 

In the presence of a suitably disposed /i-hydrogen—as in alkyl-substituted thiirane oxides such as 16c—an alternative, more facile pathway for thermal fragmentation is available . In such cases the thiirene oxides are thermally rearranged to the allylic sulfenic acid, 37, similarly to the thermolysis of larger cyclic and acyclic sulfoxides (see equation 9). In sharp contrast to this type of thiirane oxide, mono- and cis-disubstituted ones have no available hydrogen for abstraction and afford on thermolysis only olefins and sulfur monoxide . However, rapid thermolysis of thiirane oxides of type 16c at high temperatures (200-340 °C), rather than at room temperature or lower, afforded mixtures of cis- and trans-olefins with the concomitant extrusion of sulfur monoxide . The rationale proposed for all these observations is that thiirane oxides may thermally... 

Treatment of bis(trimethylsilyl)sulfide (8) with bromine in anhydrous dichloromethane at - 78°C followed by addition of 1,2-disubstituted alkenes (9) to the reaction mixture at the same temperature gave the thiiranes (10) in about 30% yields (Scheme 5) (88TL4177). This synthesis is (i) highly selective, since only 1,2-disubstituted alkenes undergo the transformation to thiiranes and (ii) stereospecific since the stereochemistry of the alkene is retained in the thiirane. The nature of the reagents suggests that the silyl subsituted sulfenyl bromide (11), formed by attack of bromine on (8), is an intermediate. 

Thiiranes can be formed directly and stereospecifically from 1,2-disubstituted alkenes by addition of trimethylsilylsulfenyl bromide, formed at -78 C from reaction of bromine with bis(trimethylsilyl) sulfide (Scheme 7).12 A two-step synthesis of thiiranes can be achieved by addition of succinimide-A/-sulfe-nyl chloride or phthalimide-A -sulfenyl chloride to alkenes followed by lithium aluminum hydride cleavage of the adducts (Scheme 8).13 Thiaheterocycles can also be formed by intramolecular electrophilic addition of sulfenyl chlorides to alkenes, e.g. as seen in Schemes 914 and 10.13 Related examples involving sulfur dichloride are shown in Schemes 1116 and 12.17 In the former case addition of sulfur dichloride to 1,5-cyclooctadiene affords a bicyclic dichloro sulfide via regio- and stereo-specific intramolecular addition of an intermediate sulfenyl chloride. Removal of chlorine by lithium aluminum hydride reduction affords 9-thiabicyclo[3.3.1]nonane, which can be further transformed into bicyclo[3.3.0]oct-1,5-ene.16... 

Reduction of thiiranes to alkenes. P2I4 (DMF, 80°) converts a variety of episulfides into the corresponding alkenes (65-95% yield). With a,p-disubstituted episulfides the stereochemistry is retained. A number of other reagents, including Raney Ni in ethanol... 

These systems are of little synthetic value, however, because extensive chain transfer to polymer leads to cyclization and formation of branched sulfonium ions even for mono- and disubstituted thiiranes [156]. 

Mono- and 2,2-disubstituted thiiranes reacted with alkylthiols, in the presence of zeolites or triethylamine in methanol (lower yields of product were obtained when other solvents were used) at room temperature, to give alkylthioethanethiols as major products (Scheme 51) <1998JP22441>. 

Thiiranes are very useful starting materials for synthesis of 1-mono- and 1,1-disubstituted taurines <200582122, 2006S315>. Reaction of thiiranes 220 with silver nitrate and ammonia in methanol at room temperature for 30 min gave 221. After reaction of 221 with hydrogen sulfide for 6h to form 222, oxidation of the latter with performic acid gave the corresponding mono- or disubstituted taurines 223 (Scheme 58). 

Primary sulfonyl chlorides RCH2S02C1 (R = alkyl or aryl) (202) react with triethylamine in acetonitrile at — 40 °C to give mixtures of cis- and trans-2,3-disubstituted thiirane 1,1-dioxides (203) (Equation (30) and Table 36) <89TL3i3i, 90CB1989). The reaction mechanism is shown in Scheme 73. The stereochemistry is influenced by the amine base (B) in the ring closure reaction and partially by epimerization of the episulfones (203). 

Homologation of aldehydes and ketones to thiiranes (3) and 1-alkenes (4). 2,2-Disubstituted thiiranes and 1-alkenes can be prepared from the hthio salt of (1) as formulated. This synthesis is not general for 2,3-disubstituted thiiranes or... 

Tetrathianes. Ru-catalyzed disproportionation reaction of a disubstituted thiirane (Equation 27) (monosub-stituted thiiranes give trithiolanes). 

A convenient and stereoselective, synthetic route was reported for the preparation of 3,7-disubstituted-l,2,5-trithiepanes 209 by the reaction of thiiranes with bis(trimethylsilyl)sulfide (HMDST) followed by intramolecular oxidative cyclization (14HAC678). In the reaction of substituted etha-nolamines with formaldehyde, the desired bis(oxazolidin-3-yl)methanes were prepared as a mixture of products, the ratio of the isomeric 3,8-dioxa-l,6-diazabicyclo[4.4.1]undecane 210 product present was dependent on the substituent on the ethanolamine (14CHE726). Whether the bis(oxazolidin-3-yl)methanes were isolated or the mixtures were taken on for further reaction, the subsequent product was formed exclusively. 

We have demonstrated in the case o few thiiranes, oxiranes and recently for a,a disubstituted 3 propiolactones (36) that the type of the choice (homosteric or antisteric) is depending only on the x/y ratio i.e. the ratio of alkylalkoxide species over dialkoxide species. 

The stereoselective isomerization of disubstituted olefins via thiirans has been reported. 0-Alkyl 5 -jS-keto-alkyl dithiocarbonates (5) eliminate sulphur on... 

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