Reactions with sulphenyl derivatives

The Chemistry of Thiiranium Ions. - The chemistry of episulphonium ions and the reactions of alkenes with sulphenyl derivatives have been reviewed Stable thiiranium and thiirenium chlorides have been generated in S02. Kinetic studies for the quantitative generation of (329 R =R = Bu, X = Cl) from the ionization of (328) and the equilibrium between (330) and (331) in SO2 were followed, using n.m.r. spectrometry. Compounds (329 R = Bu, X = SbCls or BF4) have been isolated as stable salts at room temperature... 

New reactions of various phosphazenes with a wide range of electrophilic species continue to be reported. These include those of alkoxy-derivatives with dialkyl sulphates, e.g. to give (56), or with sulphenyl chlorides, e.g. the reaction that produces (57) (see Scheme 4). With pyridine, compound (56) can be converted into two isomeric products (58) and (59). 

The reactions of acetylenes with sulphenyl halides and related compounds have been reviewed. A-(Benzenesulphenyl)-/ -nitroaniline (326) reacts with 1 -pentyne in acetonitrile in the presence of boron trifluoride etherate to yield solely the 2-azabutadiene derivative 327235. 

Sulphenyl derivatives, particularly the chlorides, add to olefinic double bonds, often with great facility (Scheme 4). This reaction has been exploited recently to... 

References to addition reactions of sulphenyl halides with alkenes and alkynes are given in the Sulphides section. An incidental bonus from a study of the addition of PhSCl to adamantylideneadamantane is the formation of the 4e-chloro-derivative and PhSSPh, via an intermediate thiiranium salt. Sulphenyl and selenenyl chlorides have been used for the dehydration of aldoximes to nitriles. Whereas sulphinyl chlorides yield sulphinate esters with alkoxytri-methylsilanes, no reaction occurs with sulphenyl chlorides. ... 

The formation of unsymmetrical disulphides by the reaction of S-sulphonates with thiols is analogous to a number of other sulphenyl derivatives. In general terms the reaction may be represented as shown in eq. 7.14. A number of intermediates in addition to the sulphenyl iodides [92], sulphenyl thiocyanates [108] and sulphenyl sulfonates [175] have been utilized to advantage in the synthesis of unsymmetrical disulphides. These include the monodisulphide dioxides (RSO2—), studied in detail by Field and his colleagues [178], the disulphide monoxides (RSO—) [178, 179] and more recently the S-monothiocar-bonates (ROCS--) [180] and sulphenamides [186]. 

The photostimulated reactions of thiolate anions with 2-halo-2 -nitropropane derivatives yield both oc-nitrosulphides via an S l pathway and disulphides (equation 71a)282 284. In contrast with the case of the oxidative dimerisation products of the mono-enolates, the disulphides are formed via an ionic mechanism nucleophilic attack by the thiolate anion on the a-halogen and subsequent reaction of a second thiolate with the sulphenyl halide. As expected for such a process, disulphide formation is favoured (and thus a-nitrosulphide formation is disfavoured) the more nucleophilic the thiolate (i.e. derived from a less acidic thiol) and the easier the abstraction of the halo-substituent (i.e. I > Br > Cl). Use of the protic solvent methanol instead of the usual dipolar aprotic solvents for the reaction of equation 71a is detrimental to the yield of the S l substitution products exclusively disulphides are formed285 (equation 71b). Methanol solvation probably retards the dissociation of the radical anion intermediate in the SRN reaction, into radical and anion, and hence retards the chain reaction relative to the ionic reaction. The non-nucleophilic methylsulphinate ion gives only an S l reaction product with 2-bromo-2-nitropropane286. 

The additions of thiols and sulphenyl chlorides to alkenylphosphonic derivatives to yield (2-alkylthioethyl)phosphonic compounds are reactions which have already been noted" Dialkyl (alkylthiomethyl)phosphonates yield a-chloro derivatives when treated with ncs in CCl/° the resultant dialkyl (l-alkylthio-l-chloromethyl)phosphonates undergo Friedel-Crafts arylation with benzene, alkylbenzenes or other activated aromatics in the presence of SnCl4 or TiCl/ yields are said to be good. 

Various derivatives of sulphur may be prepared by the reaction of sulphur monochloride, sulphur dichloride or sulphenyl halides with thiolates the products depend on the reactant stoichiometry. 

A synthesis of 2-alkyl- or 2-aryl-substituted benzo[Z>]thiophens consists of the cyclization of an aryl thioether with an acetonyl or phenacyl group in the or/Ao-position (315) with 48% hydrobromic acid. In order to obtain (315 R = Ph), 2-methylthiobenzyl cyanide is treated with phenyl-magnesium bromide. The reaction of or//to-methylthiostyrene derivatives, especially cinnamic acids (316), with sulphuryl chloride followed by pyridine, probably gives the benzo[6]thiophens (318) via the sulphenyl chloride (317). ... 

Easily prepared thiocarbonyl derivatives of alcohols, such as the 5-methyl dithio-carbonates (64 Y == SMe), can be treated with soft electrophiles A-X to improve the leaving ability of the alcohol oxygen in the presence of a nucleophile and thus provide a simple mild method of hydroxy group replacement (Scheme 27). For instance, use of CH3I as the electrophile produces alkyl iodides, and sulphenyl halides PhSX can be utilized to synthesize chlorides, bromides, or iodides. Similar reactions have been described for some selenocarbonyl alcohol derivatives. ... 

Addition of positive sulphur species, RS", usually derived from sulphenyl halides, to olefins is commonly assumed to proceed by way of thiiranium ions, the reactions often showing the stereochemistry expected for trans-addition For instance, the reaction of cyclohexene with methanesulphenyl tetrafluoroborate is believed to form an intermediate thiiranium ion (73), which then reacts with nucleophiles to give trans-methylthio-derivatives, e.g. (74). Addition of thiocyanogen chloride to olefins may... 

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