S sulphoxide

Stereoselective oxygen transfer to the sulphur atom of alkyl aryl sulphides catalyzed by 2-flavoenzyme monooxygenases afforded optically active sulphoxides in high optical yields . For instance, with ethyl p-tolyl sulphide as substrate cyclohexanone monooxygenase from Actinetobacter produces predominantly (— )-(S)-sulphoxide with 64% e.e. In contrast, FAD-containing dimethylaniline monooxygenase purified from hog liver microsomes affords (+ )-(i )-enantiomer of this sulphoxide with 90% optical purity . ... 

Cephalosporin (Ss)-sulphoxides give 2-exomethylene derivatives under Mannich reaction conditions but the corresponding (/ s)-sulphoxides fail to react . ... 

In the presence of oxidizing agents (e.g. sodium metaperiodate, hydrogen peroxide, m-chloroperbenzoic acid, t-butyl-hypochlorite, iodobenzene dichloride, etc.) both penicillins and cephalosporins undergo facile oxidation to either sulphoxides or sulphones. The esters of penicillin sulphox-ides (4) were described in 1949 [1]. It was found later [5] that the free acids could be oxidized by periodate. When a 6(7)-/3-acylamino side-chain is present in the molecule the resulting reagent-approach control due to the N-H proton promotes the formation of the (S)-sulphoxide (4a) [6,7]. 

The oxidized derivatives possess a very much lower antibacterial activity. The activity retained by the (R)-sulphoxides (4b) and the sulphones (5) is about five times higher than that of the corresponding (S)-sulphoxides [8]. 

The 2-exomethylene derivatives [60] (24, 25) have opened a new route for the synthesis of further compounds, because the 2-exomethylene group can easily be transformed into other derivatives. The Mannich reaction providing (24) through the action of formaldehyde and amine salts on cephalosporin-(S)-sulphoxides is highly stereospecific no reaction has been observed in the case of cephalosporin-(R)-sulphoxides [63]. Scheme 8.1 shows the derivatives obtained from the exomethylene parent compound (24). For the bioassay results, see Tables 8.5, 8.6 and 8.7. 

Chromans. - 2,4-Diethoxychromans (78) (mainly cis) represent a new type of chroman and have been prepared in high yield from a phenol (but not a deactivated phenol) and malonaldehyde bis(diethyl acetal) in the presence of SnCU they are converted into the benzopyrylium salts (79), in excellent yield, by treatment with perchloric acid. A Wittig-Horner reaction of the chiral phosphoryl ( S)-sulphoxide (81) and the ketone (80) gave the chiral sulphoxide (82), which was cyclized by aqueous alkali to a mixture which contained 22% diastereoisomeric excess of (25 )-chroman (i )-sulphoxide. This was converted, in three steps, into the aldehyde (83), which is a useful synthon for a-tocopherol. ... 

The following classes of sulphur compounds occur in Solubility Groups II, III and VII sulphonic acids and derivatives, ArSO,OR sulphinic acids and derivatives, ArSOOR mercaptans, RSH thiophenols, ArSH sulphides or thioethers, RSR disulphides, RSSR sulphoxides, RR S->0 ... 

Sulphinic acids. Aromatic sulphinic acids are found in Solubility Group II. They may be detected by dissolving in cold concentrated sulphuric acid and adding one drop of phenetole or anisole when a blue colour is produced (Smiles s test), due to the formation of a para-substituted aromatic sulphoxide. Thus the reaction with benzenesulphinic acid is ... 

Again both S- and O-bonded sulphoxides are found. mer-[RuCl3(Ph2SO)3] has one S-bonded sulphoxide and two O-bonded sulphoxides (one trans to Cl, one trans to S) [112], The imidazole-substituted complexes are being studied as possible radiosensitizers and for anti-tumour activity. 

Complexes of O-donors are relatively rare, explicable by the soft nature of the divalent ions. A telling indication is that sulphoxide ligands will only bind through O if steric effects make S-bonding impractical. The most important complexes are diketonates and carboxylates (for the aqua ions see section 3.5). 

Steric crowding increases as bigger alkyl groups are introduced so that [Pt[(Me2CHCH2CH2)2S0]4](C104)2 has only O-bonded sulphoxides (IR). IR spectra can be used to distinguish between S- and O-bonded sulphoxide ... 

In addition to nitration, oxidation of the S atom also takes place, resulting in the formation of the sulphoxide (Ref 5). It was used in Ger during WWII as a component of a non-fusible expl compn known under the name of Pressling (qv) (Refs 2 4)... 

Table 10 and Figure 17 carry all the necessary information. Since the only experimental geometry available is that for the sulphoxide, the ring geometry was kept constant in all three compounds, while OCS and OSO angles and S—O distances were taken from the analogous dimethyl derivatives. 

What has been reported in the previous subsections does not amount to an exhaustive review of the existing literature on MO calculations for sulphones and sulphoxides— which is, anyway, not particularly rich. It must be said that the treatment of the S—O bond poses special problems, and is therefore less attractive for the theoretical chemist. A search was nevertheless conducted, and what follows provides nearly all the existing entry points to the theoretical literature of sulphone and sulphoxide compounds. 

TABLE 14. Group volumes (V in A3) and surfaces (S in A2) for fragments a to sulphur, and for sulphoxide and sulphone groups... 

FIGURE 20. The free surface on the sulphur atom, S, (A2), as a function of ring strain for sulphide, sulphoxide and sulphone molecules. 

Methyl-2,5-dihydrothiophene was converted into the corresponding S-oxide 4 in 57% yield after treatment with 30% excess of hydrogen peroxide for 60 h. By the same procedure the sulphoxides 5 derived from thiophene and its a-substituted analogues were also prepared18. 

Oxidation of a thiiraneradialene with equimolar amounts of MCPBA in CH2C12 at about 0°C gave the corresponding thiiraneradialene S-oxide 26 in a quantitative yield47 (equation 11). 5-Membered heterocyclic sulphoxides such as 1,3-benzoxathiolane sulphoxide 27, 1,3-benzdithiolane sulphoxide 28 and 1,3-dithiolane sulphoxide 29 were readily obtained from their sulphide precursors by oxidation with MCPBA in dich-loromethane solution48. 

It was proposed that an initially formed S-nitrosulphonium ion 33 rearranges into the S-nitritosulphonium ion 34, which is then stabilized by loss of NO+ ion to give the corresponding sulphoxide (equation 13). 

It was reported earlier that even dialkyl sulphides are efficiently oxidized to sulphoxides without a concomitant C—S bond cleavage by NBS or N-chlorosuccinimide (NCS) when the reaction is performed in anhydrous methanol at low temperature103. iV-Chloro-Nylon-6,6 in methanol-water or dioxane-water104 and iV-bromo- -caprolactam in water or alcohols105 were also used successfully for oxidation of sulphides. 

Sulphides are quickly and efficiently converted into sulphoxides by 1-chlorobenzo-triazole (NCBT) in methanol at —78°106. However, this. reagent cannot be used for the oxidation of t-butyl sulphide and dibenzyl sulphide since C—S bond cleavage takes place. 

In the reaction between chloramine B and di-(2-chloroethyl)sulphide in aqueous solvents simultaneous formation of di(2-chloroethyl)sulphoxide and the corresponding sulphimide, PhS02N=S(CH2CH2Cl), was observed107. The amount of sulphoxide increased on increasing the concentration of water in the reaction mixture. 

Due to the presence of a heterocumulene unit, sulphines may be considered as a group of compounds which are able to undergo cycloaddition reactions. Reaction of sulphines with enamines and phosphorus ylides reported by Sheppard217 and Trippett218 and their coworkers may be considered formally as an example of [2 + 2] cycloaddition. In fact, Sheppard and Dickman217 obtained a 1 1 adduct from thiofluorenone S-oxide and 1-morpholinocyclohexene to which they assigned the dipolar sulphoxide structure 168. 

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