Aryl benzyl sulfides

The relative ease with which aryl benzyl sulfoxides undergo homolytic dissociation (Rayner et al., 1966) as compared to aryl benzyl sulfides or sulfones is supportive of this idea that ArSO radicals are easier to form than ArS or ArS02 radicals. Another interesting set of observations is the following. Booms and Cram (1972) found that optically active arene-sulfinamides ArS(0)NRPh (R = H or CH3) racemize thermally very readily at room temperature and that this racemization is the result of a free radical chain reaction (160) that is initiated by the dissociation of some of the sulfinamide into an ArSO and a PhNR radical (159). While the length of the inhibition... 

Arenesulfenyl chlorides can be prepared by chlorinating cleavage of aryl benzyl sulfides by means of sulfuryl chloride,651 and thiocarbonyl chlorides similarly from dithiocarboxylic acids and thionyl chloride.652... 

The enantioselective C-silylation of allylic substrates such as (V-(terf-butoxycarbonyl)-A(-(p-methoxyphenyl)allylamines or 1,3-diphenylpropene is accomplished with butyUithium in the presence of (—)-sparteine, followed by the addition of TMSOTf (eq 47). The same procedure allows the asymmetric deprotonation-substitution of arenetricarbonyl(O) complexes, while chiral bis(oxazolines) have been the ligands of choice to perform such transformation with aryl benzyl sulfides in these reactions, different yields and enantioselectivities are reached if trimethylsilyl chloride is used as sUylating reagent, although there is a substrate dependence and no definite rules can be established. 

A chiral Ti complex formed in situ by reacting Ti(0 Pr)4, (J ,P)-diphenylethane-1,2-diol, and water was reported to be effective for asymmetric oxidation of aryl alkyl and aryl benzyl sulfides using TBHP as the oxidant to obtain optically active sulfoxides in good yields and high enantiomeric excesses [274] (Scheme 14.115). 

Steric and electronic effects have been investigated for the Cu(acac)2-catalysed asymmetric oxidation of aryl benzyl, aryl alkyl and alkyl benzyl sulfides with H2O2 in presence of hexane/MeOH and the ligand 4-chloro-2-[( )-[( 17 )-l-(hydroxymethyl)-2,2-dimethyl-propyl]iminomethyl]phenol. High enantioselectivity is dependent on the attachment of an aryl group to the sulfur and was highest, with up to 97% ee, for 2-naphthyl benzyl sulfoxide. Cu-mediated oxidation of substituted aryl benzyl sulfides shows modest steric and electronic effects. ... 

The complex (70) is the most efficient catalyst in the titaniumsalan-catalysed asymmetric oxidations of bulky aryl benzyl sulfides and small alkyl phenyl sulfides by H2O2 in CH2CI2 to corresponding sulfoxides with 77% ee. The kinetics suggest that a direct attack of the sulfide on the electrophilic active oxygen species occurs... 

A new catalytic procedure for the asymmetric oxidation of aryl alkyl and aryl benzyl sulfides to optically active sulfoxides by TBHP is mediated by a chiral titanium complex formed in situ by reacting Ti( -PrO)4, (R, / )-diphenylethane-l,2-diol, and water. The results were largely unaffected by the nature of the phenyl substituents, suggesting that the same mechanism operates in all cases. Only the / -N02 substituent on the aryl ring caused a considerable loss of enantioselectivity and this is attributed to the electron-withdrawing power of this group or, more likely, its coordinating ability. ... 

SCHEME 5.25 Preparation of diaryl sulfides from aryl benzyl sulfides. 

Cross-coupbng aryl benzyl sulfides with aryl iodides would be a good place to start [40]. An interesting approach using CSj as the sulfur source has hear used in the copper-catalyzed synthesis of diaiyl sulfides [45]... 

Various S-nucleophiles are allylated. Allylic acetates or carbonates react with thiols or trimethylsilyl sulfide (353) to give the allylic sulfide 354[222], Allyl sulfides are prepared by Pd-catalyzed allylic rearrangement of the dithio-carbonate 355 with elimination of COS under mild conditions. The benzyl alkyl sulfide 357 can be prepared from the dithiocarbonate 356 at 65 C[223,224], The allyl aryl sufide 359 is prepared by the reaction of an allylic carbonate with the aromatic thiol 358 by use of dppb under neutral condi-tions[225]. The O-allyl phosphoro- or phosphonothionate 360 undergoes the thiono thiolo allylic rearrangement (from 0-allyl to S -allyl rearrangement) to afford 361 and 362 at 130 C[226],... 

In the presence of sulfide or sulfhydryl anions, the quinonemethide is attacked and a benzyl thiol formed. The P-aryl ether linkage to the next phenylpropane unit is broken down as a result of neighboring-group attack by the sulfur, eliminating the aryloxy group which becomes reactive phenolate ion (eq. 2). If sulfide is not present, a principal reaction is the formation of the stable aryl enol ether, ArCH=CHOAr. A smaller amount of this product also forms in the presence of sulfhydryl anion. 

The reaction described is of considerable general utility for the preparation of benzoyloxy derivatives of unsaturated hydrocarbons.2"8 Reactions of 2-butyl perbenzoate with various other classes of compounds in the presence of catalytic amounts of copper ions produce benzoyloxy derivatives. Thus this reaction can also be used to effect one-step oxidation of saturated hydrocarbons,9, 10 esters,6,11 dialkyl and aryl alkyl ethers,12 14 benzylic ethers,11,15 cyclic ethers,13,16 straight-chain and benzylic sulfides,12, 17-19 cyclic sulfides,11,19 amides,11 and certain organo-silicon compounds.20... 

Good yields are generally observed, especially for methyl ethers. The combination of boron tribromide with dimethyl sulfide has been found to be particularly effective for cleaving aryl methyl ethers.87 Trimethylsilyl iodide cleaves methyl ethers in a period of a few hours at room temperature.85 Benzyl and /-butyl systems are cleaved very rapidly, whereas secondary systems require longer times. The reaction presumably proceeds via an initially formed silyl oxonium ion ... 

HEXAHYDRO - 4a,5 - DIMETHYL - 2(3H) - NAPHTHALE-NONE and 2-TRIMETHYLSILYLOXY-1,3-BUTADIENE AS A REACTIVE DIENE DIETHYL trans -4-TRIMETHYL-SILYLOXY-4-CYCLOHEXENE-1,2-DICARBOXYLATE. Sulfur substitution also continues to be of high interest, and three preparations on sulfide synthesis are included BENZYL SULFIDE DIALKYL AND ALKYL ARYL SULFIDES NEOPENTYL PHENYL SULFIDE and UNSYMMETRICAL DIALKYL DISULFIDES sec-BUTYL ISOPROPYL DISULFIDE. 

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