2-Butene episulfide

Desaffdrizadon of episii Ues. Desulfurization of cis- and rrunr-2-butene episulfides by n-butyllithium proceeds with complete stereospeciiicity to give cis- and trans-1-butene, respectively. Trost suggests that the reaction may proceed through a sulfurane intermediate (a). 

The homogeneous, gas phase, thermal decomposition of thiiranes, ethylene episulfide, propylene episulfide, and 2-butene episulfide sheds additional light on the mechanism of the S + olefin reactions. Below ca, 250 °C the decomposition products are sulfur and the olefin. The rate of olefin formation is first order in episulfide concentration, and the reaction features an activation energy which is considerably lower than the... 

Organolithium reagents elicit fragmentation of thiiranes (87). Neureiter and Bordwell (85) showed that 2-butene episulfides undergo stereospecific desulfuration. Lithium aluminum hydride may also be used (88). 

Desulfurization of Episuifides. The reaction of cyclohexene episulfide with Fe3(CO)i2, reported by King to produce cyclohexene, has been improved 2-butene episulfides, e.g. (47) (R =R = Me, R = R = H), yield alkenes by treatment with Fe2(CO)9 in refluxing benzene (eq 29). The reaction occurs with retention of the stereochemistry in yields superior to 80%. 

Butene-1 gives butene-1 episulfide, butene-l-thiol-3 (CH2=CH—CH-(SH)CH3), and butene-l-thiol-4 (CH2=CH—CH2CH2SH) as major... 

The high stereospecificity observed in the triplet reaction demands that ring closure be an efficient process to compete favorably with rotational isomerization, while the excited episulfide initially formed in the ring closure must possess a relatively long lifetime for efficient coUisional stabilization to be obtained. The actual data show that to achieve maximum stereospecificity a total pressure of ca. 300-400 torr is required for the S( P)-cis-butene-2 reaction and a pressure exceeding 700 torr for the S( Z))-m-butene-2 system. 

The latter mechanism is preferred. The intermediate is believed to be the lowest n, a triplet state of the episulfide. This, from extended Hiickel MO calculations has been estimated to lie about 30-40 kcal.mole above the ground state for ethylene episulfide, in close agreement with the experimental activation energy. The decomposition to cis and tra j-2-butene is stereospecific. Its reverse. 

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