Nucleophilic substitution sulphur compounds

Thermal decomposition of / -substituted sulphoxides of the type (426) leads to olefins by nucleophilic attack of phosphorus on sulphur. Compound (426) is conveniently prepared from lithiomethylsulphinyl carbanion and a non-enolizable carbonyl compound followed by treatment with phosphorochlorid-ite. A similar elimination takes place using phenylthiomethyl-lithium, PhSCHgLi, instead of (427).  

Steric rate enhancement due to hindered rotation was found to be present in ortho-substituted compounds in this series . The relatively low temperature required results from increased nucleophilicity of the sulphur, since the polarization is assisted by the dialkylamino group, towards the zwitterionic form 80. 

A series of 7-substituted norbornadienes have been synthesized by quenching the 7-norbornadienyl cation with various nucleophiles of sulphur (SMOj), arsenic (AsPhj), and antimony (SbPhg). 7-t-Butylnorbornadiene, prepared by reaction of t-butyl-lithium with 7-t-butoxynorbornadiene, has been transformed to, inter alia, (128) and (129). By a similar route, (20) and related compounds, required for study of their photoelectron spectra, were prepared (Scheme 5). Propenylidene-norbornadienes were accessible by the routes shown in Scheme 6. They provide a novel photochemical synthesis of dihydro-azulenes, azulenes, and of vinylogous heptafulvenes. 

There have been a number of reports on the photochemical reaction between diazo-compounds and sulphides to form either stable or transient ylides. lllger et al. reported the isolation of a series of ylides from the reaction of dimethyl sulphide with substituted diazomethanes, such substituents being carbonyl, sulphonyl, or phosphoryl groups. Ando et of. described the reaction of diazo dimethyhnalonate with a series of sulphides but found that the yields of ylides varied considerably, much more so than for the thermal reaction, with the nucleophilicity of the sulphide. For example, dimethyl sulphide afforded an 88% yield of ylide (6a) while diphenyl sulphide afforded a 12% yield of ylide (6b). Repetition of the reaction with dimethyl sulphide but in the presence of cyclohexene indicated that the sulphide was about six times as reactive as the olefin toward the photochemically generated carbene. These reactions aU were assumed to occur by conversion of the diazo-compound into a singlet carbene, which attacked sulphur. However, it was found that (6a) also could 

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