Aromatic sulfoxide

CO + HF) from pentafluorophenol (CHO + F) from fluoroaldehydes Aromatic sulfoxides... 

The formation of adduct is followed by fragmentation and subsequent H-atom abstraction reaction from the sulfinic acid produced. Strong acid solutions of aromatic sulfoxides like thianthrene 5-oxide (7) or phenothiazine 5-oxide (8) gives rise to ESR signals, which... 

Electrochemically, the reduction of activated sulfoxides (unsaturated or aromatic) in protic media exhibits a specific step leading to corresponding sulfides. However, in acidic solutions of sulfoxides a hydrogen reduction wave can be seen [223, 224] because of the reduction of their pro-tonated form. On the contrary, in the absence of electrophiles (in aprotic DMF), the reduction of aromatic sulfoxides was reported to afford [225] a complex between the reduced form and the substrate (the process therefore would be analogous to... 

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... 

Among addition reactions of imines, malonate esters have been added to dihydroiso-quinolines (27) at C(l), to give the corresponding tetrahydro derivatives in high ee,74 and enantiopure aromatic sulfoxides (prepared by o-dircctcd metallation) have been added enantioselectively to imines.75... 

Analytical Properties (i-Cyclodextrin (cycloheptamylose) normal phase separation of positional isomers of substituted benzoic acids reverse phase separation of dansyl and napthyl amino acids, several aromatic drugs, steroids, alkaloids, metallocenes, binapthyl crown ethers, aromatics acids, aromatic amines, and aromatic sulfoxides this substrate has seven glucose units and has a relative molecular mass of 1135 the inside cavity has a diameter of 0.78 nm, and the substrate has a water solubility of 1.85 g/ml, although this can be increased by derivatization Reference 13-28... 

Resolution of the enantiomeric compounds, aromatic amino acids, amino acid derivatives, aromatic sulfoxides, coumarin derivatives, benzoin, and benzoin derivatives have been accomplished on the albumin columns. The a-acid glycoprotein protein column has been used to resolve 50 enantiomeric drugs [288]. The mobile-phase requirements of these sorbents have been reviewed [288]. Although the selectivity of these sorbents are often outstanding, the solute capacity is only 1 nmol per injection. 

Aromatic sulfoxide radical cations have been generated by pulse radiolysis from the parent sulfoxides (Chart 11)7 ... 

DFT calculations were carried out for aromatic sulfoxide radical cations showing that in the lowest energy conformers the S-O bond is almost coplanar with the aromatic ring. In all radical cations the major fraction of charge and spin density is localized on the -S(=0)-Me... 

When run in nonpolar solvents, the reaction is stoichiometric in the formation of both aliphatic and aromatic sulfoxides and aliphatic sulfones. 

Synthesis of aromatic sulfoxides is usually effected preparatively by one of the two following methods. First, aromatic compounds can be treated with thionyl chloride under Friedel-Crafts conditions di-p-tolyl sulfoxide has thus been obtained from toluene,232 diphenyl sulfoxide from benzene,233,234 and bis-Q -hydroxyphenyl) sulfoxide from phenol.235... 

Deoxygenation of aromatic sulfoxides. Aromatic sulfoxides are deoxy-genated by treatment with thionyl chloride at 70°. Chlorinated by-products are obtained unless cyclohexene is added to react with the chlorine formed. 

Unlike the carbonyl, the unconjugated sulfoxide is not associated with a long wavelength absorption of its own. Therefore most of what is reported herein has to do with conjugated sulfoxides. Aliphatic sulfoxides are treated separately, though there are many commonalities with aromatic sulfoxide chemistry. The aliphatic compounds have been examined by gas phase physical chemistry mediods, which also justify a separate treatment. 

By our usual definition, benzylic and allylic sulfoxides are not aromatic. Certainly, they are not conjugated to the aryl group. However, their behavior is more related to the aromatic sulfoxides than the other aliphatic compounds. Perhaps this is because the observed a-cleavage chemistry is as related to the benzyl chromophore as it is to the sulfoxide. Nonetheless, these reactions were among the first to be studied historically, and they set precedent for the thinking of authors working in conjugated systems. 

The first report of the photochemistry of a conjugated aromatic sulfoxide appears to be that of Kharasch and Khodair [32]. In a study more principally aimed at the sulfones, they showed that photolysis of diphenyl sulfoxide 5-H in benzene led to biphenyl 41 (53%), diphenyl sulfide (7%), and trace diphenyl-disulfide 45. Biphenyl was also the major product of diphenyl sulfone photolysis, and it was shown to arise from attack of the photochemically generated phenyl radical on solvent (benzene). The same mechanism was clearly implied for the sulfoxide. The disulfide presumably comes from secondary photolysis of the unobserved phenyl benzenesulfenate 42. (The formation of the sulfide is addressed below in the section of deoxygenation.) Later workers showed that pyridine could be tolylated by photolysis of di-p-tolyl sulfoxide 5-Me with a product distribution quite consistent with other radical phenylations [33]. 

A series of papers on the photochemistry of a set of aromatic sulfoxides by German and Israeli authors relied very heavily on CIDNP results. A few of the conclusions reached in these papers may be over-reaching in retrospect, perhaps because of the limitations of the CIDNP technique, some imknown-until-later triplet energies, and the lack of product analysis in some cases. Nonetheless, this work gives very good evidence for the participation of ho-molytic a-cleavage. 

The sulfoxide center is stereogenic if it has two different carbon substituents. It has long been known that aromatic sulfoxides are subject to stereomutation under photochemical conditions, though the number of studies that treat it directly is limited. However, stereomutation should be an anticipated result of photolysis of aromatic sulfoxides. When there are diastereomeric interactions that favor one isomer over the other, the reaction may have synthetic value. This has been more notably demonstrated in a few dialkyl cases vide infra). 

To date, all results of these studies have been negative. We are skeptical that hydrogen abstraction is truly a significant primary photochemical process of aromatic sulfoxides, but this remains an open question. 

The reduction of aromatic sulfoxides to sulfides is perhaps the single most interesting photochemical reaction of sulfoxides because it has no analog in... 

Deoxygenation is most commonly a minor or merely competitive reaction pathway, with 9 being one of the exceptional cases in which it is an essentially quantitative reaction. The earliest examples of aromatic sulfoxide deoxygenation were those of Shelton and Posner, both with simple systems. Shelton showed that t-butyl phenyl sulfoxide 78 produced modest quantities of the sulfide on direct photolysis [14]. Methyl phenyl sulfoxide and diphenyl sulfoxide were other prototypical early examples, and a solvent dependence was suggested [97]. 

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