Methyl p-tolyl sulfide

Methyl p-tolyl sulfide Sulfide, methyl p-tolyl (8) Benzene, l-raethyl-4-(methylthio)- (9) (623-13-2)... 

Methyl-p-tolyl sulfide Methyl-p-tolyl sulfone S [99]... 

Imamoto and Koto131 prepared some interesting chiral oxidants (104) by the reaction of iodosyl benzene with tartaric anhydride. Methyl p-tolyl sulfide (105) was oxidized by 104c to the sulfoxide in 80% yield with 40% e.e. Methyl p-tolyl, o-tolyl and o-anisyl sulfides (105-107) were oxidized by 104a to their sulfoxides with the enantiomeric purities shown. 

The crude product (10 g) is diluted with 4 mL of a solvent mixture (ethyl acetate/cyclohexane = 9 1). This solution is poured onto a column (75-mm diameter) filled with 120 g of silica gel (Merck 230-400 mesh) for flash chromatography. Elution is performed under gravity and requires 200 mL of the above solvent system, followed by 200 mL of ethyl acetate. 2-Phenyl-2-propanol mixed with methyl p-tolyl sulfide is eluted in the first fraction ( 150 mL, monitored by TLC). The subsequent fractions are collected ( 300 mL)... 

Methyl p-tolyl sulfide, available from Aldrich Chemical Company, Inc., was distilled (bp 95°C, 18 mm) before use. 

S. H. Zhao, 0. Samuel, and H. B. Kagan 49 ENANTIOSELECTIVE OXIDATION OF A SULFIDE (S)-(-)-METHYL p-TOLYL SULFOXIDE... 

Little work has been done in this area with Ru catalysts. CM-A-[Ru(0)(py)(bpy)3] V water-CH3CN was used for the stoicheiometric oxidation of methyl-p-tolyl sulfide to (R)-methyl-p-tolyl sulfoxide with an e.e. of ca 15% [121],... 

RuCyaq. Na(lO )/CH3CN-CCiy0°C (D-mannitol-1,2 5,6-diacetonide-2,3-cyclic sulfite (6 g) to the sulfate) [116], and stoich. RuOyCCl (ca. 5 g methyl-p-tolyl, meth-ylbenzyl and triphenyl-methyl phenyl and diphenyl sulfides to the sulfones) [99,122],... 

In 1997, Chmielewski and coworkers investigated the oxidation of methyl phenyl sulfide and methyl p-tolyl sulfide with chiral carbohydrate hydroperoxides, which have been... 

In Studying asymmetric oxidation of methyl p-tolyl sulfide, employing Ti(OPr-/)4 as catalyst and optically active alkyl hydroperoxides as oxidants, Adam and coworkers collected experimental evidence on the occurrence of the coordination of the sulfoxide to the metal center. Therefore, also in this case the incursion of the nucleophilic oxygen transfer as a mechanism can be invoked. The authors also used thianthrene 5-oxide as a mechanistic probe to prove the nucleophilic character of the oxidant. 

Enantioselective Oxidation of Sulfides Synthesis of (-)-(S(-Methyl p-Tolyl Sulfoxide... 

The Orsay group found serendipitously that methyl p-tolyl sulfide was oxidized to methyl p-toly 1 sulfoxide with high enantiomeric purity (80-90% ee) when the Sharpless reagent was modified by addition of 1 mole equiv. of water [16,17]. The story of this discovery was described in a review [19], Sharpless conditions gave racemic sulfoxide and sulfone. Careful optimization of the stoichiometry of the titanium complex in the oxidation of p-tolyl sulfide led to the selection of Ti(0iPr)4/(7 ,7 )-DET/H20 (1 2 1) combination as the standard system [ 17]. In the beginning of their investigations, the standard conditions implied a stoichiometric amount of the chiral titanium complex with respect to the prochiral sulfide [16,17,20-23]. Later, proper conditions were found, which decreased the amount of the titanium complex without too much alteration of the enantioselectivity [24,25],... 

Enantioselectivity is highly dependent on the solvent employed. A screening of appropriate solvents for the oxidation of methyl p-tolyl sulfide showed a dramatic solvent effect (Table 6C.4) [22], The best solvents were dichloromethane and 1,2-dichloroethane, which have similar dielectric constants, that is, 1.6 and 1.44, respectively. 

As is often found in asymmetric synthesis, temperature is an experimental parameter that can increase enantioselectivity. Here, however, a decrease in the reaction temperature does not always increase the enantioselectivity. An optimum temperature was found to be -20°C to -25°C for the oxidation of methyl p-tolyl sulfide [17], and this temperature range was retained for the standard oxidations. In the case of the monooxidation of dithianes, the maximum enantioselectivity was obtained at ca. —40°C [29] (Scheme 6C.1). 

TABLE 6C.4. Enantioselectivity in Asymmetric Oxidation of Methyl p-Tolyl Sulfide by Various Hydroperoxides in the Presence of Ti(0-i-Pr)4/(R,/f)-DET/H20 in a Ratio of 1 2 1 in Various Solvents... 

Diethyl tartrate is the best tartaric acid derivative for enantioselective oxidation of thioethers. This finding was established for the asymmetric oxidation of methyl p-tolyl sulfide with cumene hydroperoxide, that is, 96% ee (DET) 87% ee (diisopropyl tartrate) 62% ee (dimethyl tartrate) [24] and 1.5% ee (bis A, V-dimethy I tart rami de, r-BuOOH as the oxidant) [17]. 

An interesting behavior of the Padua reagent (Ti(0-i-Pr)4/(/ ,i )-DET = 1 4) was described by Scretti et al. [42,43], who used racemic furylhydroperoxides 1 instead of cumyl hydroperoxide as oxidant. The enantioselectivities in the oxidation of methyl aryl sulfides are very good. For example, methyl p-tolyl sulfoxide was obtained in 75% yield and >95% ee together with about 15% of sulfone by using hydroperoxide 1(R =OEt,R = /-PrandR3 = Me) Simultaneously there is a kinetic resolution of the racemic hydroperoxide takes place is used in excess (2 mol equiv. with respect to sulfide). Thus in the example mentioned above, the enantiopurity of the residual hydroperoxide was 81% ee. It has also been established that some kinetic resolution of... 

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