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Cyclopropanation of alkenes using t-BuSO,CHR2Li at 80°C
Alkene R2 Yield (%)“ Trans/cis ratio
Styrene Me 60 55:45
Styrene n-Bu 91 (70) 53:47
1-IIexene Me 73 51:49
]-Hexene n-Bu 92 (67) 45:55
1-Decene Me 64 52:48
1-Dodecene Me 83 (62) 51:49
MeO(CH2)9CH=CH2 n-Bu 70 50:50
"GC yield with internal standard (isolated yields given in parentheses).
4.4.4 Asymmetric synthesis with sulfur ylides
A number of attempts have been made to use optically active sulfur ylides to transfer the chirality of sulfur to carbon in the formation of epoxides and cyclopropanes. The results were somewhat disappointing. Thus, virtually no asymmetric induction was observed with the ylide (1) . With the stabilized ylides (2), e.e. values in the range 7-43% were reported . Better results were obtained with sulfonium ylides derived from Eliel oxathiane . Optically active diaryl epoxides could be prepared under PTC in high yields and good e.e. values.
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S 2 Ar-S-CH-R
Ar-Fh. p-Tol H-H, Me
Durst [478, 479] has shown that the sulfonium ylide (3) transfers its benzylidene group to some carbonyl compounds with e.e. values approaching enantiomeric purity, although the reaction was not yet amenable to synthetic utility (low overall yields, side reaction). However, an interpretation of the difference of behaviour of (3) and (4) towards PhCHO (e.e. values, respectively, 96% and less than 3%) led the authors to propose a [2 + 2] cycloaddition mechanism rather than the commonly accepted nucleophilic antiperiplanar addition for the reaction of a sulfur ylide with a carbonyl compound . Clearly, more work is needed in this area.
Syntheses of cyclopropanes and oxiranes of high optical activity could be achieved  through reactions of anions derived from optically active sulfoximines or sulfoxides, respectively, with Michael acceptors or aldehydes, separation of the diastereoisomeric adducts and conversion of these to the cyclized products.
High stereoselectivity and yield were also observed in the reaction of dimethylsulfoxonium methylide with an optically pure methyl a-(p-tolylsulfinyl) acrylate .
Cyclopropanation of methyl 3,3-diphenyl-2-(p-tolylsulfinyl)-2-propenoate
A solution of dimethyloxosulfonium methylide in DMSO (30 ml) was prepared under argon from trimethyloxosulfonium iodide (9.6 mmol) and NaH (60% dispersion in oil, 9.6 mmol) at room temperature. After stirring for 90 min (the evolution of hydrogen ceased) the solution of the ylide was added dropwise to a solution of the vinyl sulfoxide (3.2 mmol) in DMSO (25 ml) over a 30 min period. The reaction mixture was stirred at room temperature for 14h, poured into an ice water mixture, and extracted twice with ether. The ether layers were washed twice with water, dried over anhydrous MgS04 and evaporated in vacuo to give a crude cyclopropyl sulfoxide as a white solid. Flash chromatography (silica, ethyl acetate/n-hexane (25:75) gave the (Rc,Ss) isomer (1.02 g, 82%), m.p. 227-228°C and the (ScjSs) isomer (0.17g, 14%), m.p. 202-203°C.
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4.5 PERICYCLIC REACTIONS OF ORGANOSULFUR COMPOUNDS
Sigmatropic, electrocyclic, cycloaddition and cycloelimination, and cheletropic reactions have all been carried out with organosulfur compounds and often used for synthetic purposes. A chapter of Block’s monograph  is devoted to this topic, and most of the pericyclic processes include examples with sulfur compounds. The treatises by Barton and Ollis , Trost and Fleming  and Klamann  are guides to the more specialized literature. Some reviews deal with specific cases: thiocarbonyl compounds  or cycloaddition reactions .
Here, only some particular aspects of a few pericyclic reactions of
¹vSs) diastereoisomer: 82% (+ (SoSs): 14%)
organosulfur species will be discussed, criteria of choice being mainly the potentialities of synthetic utilization of the compounds available through these reactions.
The [3,3] sigmatropic rearrangement of ally! vinyl sulfides (thio-Claisen) is particularly easy; activation enthalpies can be 10 kcal mol1 lower than for the oxygen analogues , and the reaction which was pioneered by Brandsma  occurs usually at room temperature and with excellent yields.
The reaction is of great value and most of the early work in the field is quoted and discussed in  by Block. As the allyl vinyl sulfide can be metallated and submitted to electrophilic substitution prior to rearrangement and the thiocarbonyl group hydrolysed in situ to a carbonyl group in the reaction product, the process has found considerable utility. The syntheses of propylure  and m-jasmone  are early examples in which a thioaldehyde was intermediary formed (Y = H). A thioketone was involved  in the rearrangement of the allyl allenyl sulfide shown here.