4-Methylphenyl sulfoxide

The anions derived from racemic alkyl and benzyl tert-butyl sulfoxides undergo 1,4-addition to a,/J-unsaturated esters to give adducts with high product diastereoselection (>5 1)10,11. Alkyl 4-methylphenyl sulfoxides were found to be less diastereoselective. In the case of 2-methyl-2-(methylsulfinyl)propanc the highly hindered 2,6-di-rer7-butyl-4-methylphenyl ester was required to prevent a competing acylation reaction. 

Silica gel is also the support of choice for the activation of V-halosuccinimides. The silica functions both as a proton donor which increases the electrophilic nature of the reagent, and as a support with geometrical constraints which contributes to the stereoselectivity. Alkyl and aryl sulfoxides are readily halogenated at the a position with yields of48-80%91. The reactions are carried in the solid state on the surface of TLC plates. The conversion of the optically active alkyl 4-methylphenyl sulfoxide into 1-haloalkyl 4-methylphenyl sulfoxide is accompanied by inversion of configuration at the S-atom. The stereoselectivity in these reactions is much higher than that observed in liquid-phase halogenation. 

Ethynyl 4-methylphenyl sulfoxides 33a and 33b give mixtures of two diastereomers 34 and 35 with d.r. (synjanti) 70 3O4S. 

Scheme 9. Expected oxidation intermediate for (R)-methylphenyl sulfoxide formation.

The binaphthol host 10b was found to be very effective for enantiomeric separation of some sulfoxides. When a solution of 10b and two molar equivalents of rac-me-thyl m-methylphenyl sulfoxide (85c) in benzene-hexane was kept at room temperature for 12 h, a 1 1 complex of 10b and (-i-)-85c was obtained, after one recrystallization from benzene, as colorless prisms in 77% yield. Chromatography of the complex on sihca gel gave (-i-)-85c of 100% ee in 77% yield [32]. By the same procedure, rac-85d was separated by 10b to give (-i-)-85d of 100% ee in good yield. However, rac-85a was poorly separated with 10b, giving approximately 5% ee enantiomer, while 85b and 85e did not form complexes with 10b. In order to establish why the chirality of the m-substituted derivatives 85c and 85d is so precisely recognized by 10b, the crystal structure of the complex of 10b and (-i-)-85c was studied by X-ray analysis [33]. 

Polymers, with [//] = 0.30—0.56 dl/g, containing methyl sulfonyl groups have been synthesized by copolymerization of methyl-4-vinylphenyl sulfoxide with styrene [92]. These copolymers are soluble in toluene but are insoluble in water. Their catalytic activity has been studied in Sf 2-type reactions of alkyl halides with different nucleophiles in water-toluene solutions at 100°C for 20 h. The copolymers effectively catalyze two-phase reactions of octyl bromide with KSCN, NaSCN and KI and of butyl bromide with NaOPh and NaSPh with a 11-78% yield of respective reaction products. These reactions, however, are not catalyzed by DMSO, methylphenyl-sulfoxide and benzyl methyl sulfoxide. The copolymer catalytic activity is higher than that of the monomer analogues and increases with an increment in the number of styrene units in the copolymer. These copolymeric catalysts are easily extracted from the reaction medium. The influence of the hydrophobic environment of active centers on the catalytic activity of polymeric catalysts has already been discussed. 

However, addition of (+ )-(7 )-l-methyl-4-(mcthylsulfinyl)benzene, to aldehydes and ketones proceeds with low stereoselectivity. An improvement of the 3-syn diaslereoselectivity was found with the zinc reagent obtained by transmetalation of the lithiated sulfoxide with anhydrous zinc chloride38. An improvement of the stereoselectivity was also attained by exchange of the 4-methylphenyl substituent for a 2-methoxyphenyl or 2-pyridinyl substituent. Thus, the introduction of an additional complexing site into the aromatic part of the sulfoxide reagent enhances the stereoselectivity35. 

The addition of enolate anions to (E)- and (Z)-3,3,3-trifluoro-l-[(4-methylphenyl)sulfinyl]-1 -propene has been investigated (E)- and (Z)-a,/(-unsaturated sulfoxides undergo addition in the opposite stereochemical sense3,4. In general, yields and product diastereoselection are high. When the -position of the double bond of the enolate is substituted then all four diastereomer-ic products result. 

Olah et al.466 observed immediate formation of protonated benzenesulfinic acid upon addition of SO2 to benzenium ion formed in H SO3F-Sb I 5-SO2C11 solution at —78°C. Based upon this observation, Laali and Nagvekar467 developed a method for the synthesis of aromatic sulfoxides [Eq. (5.169)]. Product formation was interpreted in terms of dehydration of protonated benzenesulfinic acid followed by nucleophilic attack by the aromatic to the formed arenesulfinyl cation. Mixed sulfoxides (4-fluorophenyl-4-methylphenyl and 4-fluorophenyl-3-trifluoromethyl sulfoxides) were also prepared by sequential addition of the two aromatics. The direct synthesis of symmetric diaryl sulfoxides in high yields (room temperature, 2—48 h, 50-95%) has been reported through the electrophilic activation of thionyl chloride with triflic acid.468... 

The addition of piperidine to (+)-l-methyl-4-[(l-methylethenyl)sulfinyl]benzene (17) is very slow, in accordance to the reactivity of the corresponding sulfone towards amines50. Furthermore, the yield of the adduct obtained from reactions in ethanol at 80 °C for 1 week is only 55%. The remainder is unchanged sulfoxide, together with optically inactive compounds which are not sulfoxides. H-NMR spectroscopy of the l-[2-(4-methylphenyl-sulfinyl)propyl]piperidine 18 showed a d.r. of64 36, corresponding to an optical purity of 29 %. This figure is tentative because of the modest yield of adduct obtained, as well as the lack of information on whether there is any selectivity between diastereomers in the formation of byproducts. 

It is apparent that the ( )- and (Z)-vinyl sulfoxides adopt different reactive conformations in their reactions with amines. Studies on the conformational preference of vinyl sulfoxides bearing dipolar substituents suggest that the (/ . )- and (Z)-vinyl sulfoxides favor the s-cis-25 (S = 0 and C = Ci>v -coplanar) and the s-trans-25 (S = 0 and C = C ann -coplanar) conformations, respectively, in solution. The stereochemical outcome of the reactions in ethanol can be readily accounted for by inferring nucleophilic attack by amine on the s-cis and s-trans conformations of the chiral ( )- and (Z)-vinyl sulfoxides, respectively, from the least hindered rc-face (i.e., anti to the 4-methylphenyl group)96. 

OXIRANES (Dimethylamino)phenyl-oxosulfonium methylide. Dimethyl-sulfonium methylide. (Dimethyl sulfoxide, derived reagent (b)). Methylene bromide-Lithium. Methylphenyl-N-p-tohienesulfonylsulfoximine. 

The auxiliary-controlled, noncatalyzed [4 + 2] cycloaddition of homodienophiles has been thoroughly studied and the results are often compared with Lewis acid catalyzed reactions (see Section 1.6.1,1.1.2.2.2.). A very interesting version of dienophiles bearing a chiral auxiliary are chiral vinylic sulfoxides in which the chirality results from the dissymmetric sulfur atom. The first example studied is the Diels-Alder reaction of ( + )-(/ )-4-methylphenyl vinyl sulfoxide (1) with cyclopentadiene (2), in which four possible diastereomers 3-6 are obtained in an endojexo ratio of (5 + 6)/(3 + 4) 64 36. The diastereomers are further separated the (2 /J)-isomers (3 and 5) being favored. Desulfuration produces pure ( + )- or (-)-dehydronorcamphor. 

Another common oxidizing agent is sodium m-periodate (NaI04). Leonard used sodium periodate to oxidize methylphenyl sulfide to the sulfoxide in near-quantitative yield. l In that report, many methods were summarized for oxidizing sulfides, including nitric acid, hydrogen peroxide, chromic acid, ozone, peroxyacids. 

Phenyl vinyl sulfoxide (8) shows a high anionic polymerizability, similar to that of (meth)acrylates and N,N-dialkylacrylamides [158-160]. Hogen-Esch first reported that 8 underwent anionic polymerization in TH F at — 78 °C to afford polymers with relatively narrow molecular weight distributions (Mw/M = 1.1-1.5) [158]. AnAB diblock copolymer, PS-b-poly(8), was also synthesized by the sequential addition of styrene, followed by 8. Subsequently, the anionic polymerization was improved by using 4-methylphenyl vinyl sulfoxide (9) with l,l-diphenyl-3-methylpentyllithium in the presence of a 20-fold excess of liCl in THF at —78°C [161]. In this way. 

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