Lithium aluminum hydride with episulfides

Addition to Alkenes. Phthalimidosulfenyl chloride can be added to alkenes to yield a-chloro thioethers which, after treatment with lithium aluminum hydride, produce episulfides (eq 4). Sodium borohydride is unsuccessful in transforming the alkene adduct to the episulhde. The alkene addition is stereospecifically trans and proceeds through a thiiranium ion intermediate, the opening of which is governed predominantly by steric factors and usually gives a predominance of the anti-Markovnikov addition product. As in the addition of phthalimidosulfenyl chloride to alkynes, the phthalimido group can also be displaced with... 

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. 

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