Alkyl aryl sulfides, from

The highly regio- and diastereoselective addition of an alkyl and an arylthio group to an olefinic double bond ( carbosulfenylation ) is achieved with arenesulfenyl chlorides and alkyl-chloro-titanium(IV) species (Reetz reagent, from R2Zn/TiCU 5 1 M. T. Reetz, 1987, 1989), Use of the more bulky 2,4,6-triisopropylbenzenesulfenyl chloride improves the yield of the highly versatile alkyl aryl sulfide products. 

Oae and coworkers oxidized several diaryl, dialkyl and alkyl aryl sulfides to their corresponding sulfoxides using purified cytochrome P-450 obtained from rabbit liver microsomes138. In agreement with expectations, this enzyme did not exhibit much stereospecificity. Some examples including the observed e.e. values are shown by 121-125. A model was proposed to account for the absolute configurations of the sulfoxides produced (126). The sulfur atom is preferentially oxidized from the direction indicated. 

This reaction is analogous to 10-16. Primary and secondary alcohols can be converted to alkyl aryl sulfides (ROH RSAr) in high yields by treatment with BU3P and an V-(arylthio)succinimide in benzene. Thioethers RSR can be prepared from an alcohol ROH and a halide R Cl by treatment with tetra-methylthiourea Me2NC(=S)NMe2 followed by NaH. ... 

Several palladium catalysts for formation of aryl sulfides from aryl halides have been investigated more recently. A combination of Pd2(dba)3 and DPEphos catalyzed the formation of a broad range of diaryl sulfides in the presence of 1 mol.% palladium and NaO-t-Bu base in toluene solvent.12,rThe highest yields of alkyl aryl sulfides were obtained from aryl triflates and n-butyl thiol catalyzed by a combination of palladium acetate and BINAP. However, these reactions contained 10 mol.% catalyst, were long, and required deactivated aryl triflates. A combination of Pd2(dba)3 and DPPF catalyzed the coupling of thiols with resin-bound aryl halides.121... 

The typical S-oxidation with BVMOs allows the formation of chiral sulfoxides from organic sulfides. This oxidation has received much interest in organic chemistry due to its use in the synthesis of enantiomerically enriched materials as chiral auxiliaries or directly as biologically active ingredients. This reaction has been studied extensively with CHMO from Adnetohacter showing high enantioselectivi-ties in the sulfoxidation of alkyl aryl sulfides, disulfides, dialkyl sulfides, and cychc and acyclic 1,3-dithioacetals [90]. CHMO also catalyzes the enantioselective oxida-hon of organic cyclic sulfites to sulfates [91]. 

Asymmetric oxidation of ArSR with H202 The chiral (salen)MnCI complexes derived from this diamine can effect asymmetric oxidation of alkyl aryl sulfides. The highest enantioselectivity is obtained with (R,R)-3. 

Formation of high-valent oxometal species from (salen)metal complexes and iodosylbenzene (PhIO) and the mechanism of the oxygen transfer from these species to alkyl aryl sulfides have been investigated in detail [22]. Fluorous salen ligands 13 and 14 were synthesized and the corresponding (salen)manganese(III) complexes Mn-13 and Mn-14 were evaluated in the oxidation of alkyl aryl sulfides with PhIO under homogeneous and FB conditions, respectively [23]. 

A systematic study of the sulfoxidation by cyclohexanone monooxygenase from Acinetobacter using as the substrates many alkyl aryl sulfides, dialkyl sulfides and dialkyl disulfides has been carried out by Carrea, Colonna, and colleagues in the presence of NADP and a NADPH-regenerating system [143,144]. Chemical yields are good (at 0.8 mmol scale), with wide variations of ee s (from 0 to 98%) according to the structure of the sulfides. 

Relationship to Electron Transfer Mechanisms. The inter-molecular reactions of dialkyl or alkyl aryl sulfides with tert-butvl perbenzoates have been shown by Pryor and Hendrickson (31) to give only a small amount (0.7 - 3.5 ) of scavengeable radical product. The rates of disappearance of the perbenzoates are strongly accelerated by addition of the sulfides. The mechanism which has been postulated involves an electron transfer from sulfur to the peroxide and kinetic isotope effect data have been presented in support of this mechanistic postulate (32). 

The screening of a metagenomic library derived from loam soil afforded a novel two-component SMO, which has been heterologously expressed in E. coli [52], This biocatalytic system was able to perform selective sulfoxidations of alkyl aryl sulfides, providing the recovered (R)-sulfoxides with good to high selectivities and moderate conversions after 16h. Ethyl phenyl sulfide was the best substrate for this enzyme, as the final sulfoxide was obtained with 92% ee. It therefore represents an interesting SMO alternative. 

Colona and coworkers oxidized a variety of alkyl aryl and heterocyclic sulfides to the sulfoxides using t-butyl hydroperoxide and a catalytic amount of a complex (97) derived from a transition metal and the imines of L-amino acids. Of the metals (M = TiO, Mo02, VO, Cu, Co, Fe), titanium gave the highest e.e. (21%), but molybdenum was the most efficient catalyst. The sulfoxides were accompanied by considerable sulfone125. 

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