Thiirane oxides reactions

Reactions of thiirane oxides with metal salts.424... 

In contrast to thiirane oxides, the electrophilic oxidation of thiirene oxides to thiirene dioxides is feasible, probably because both the starting material and the end product can survive the reaction conditions (equation 21). 

There are several reactions in which the sulfoxy oxygen exhibits its nucleophilicity, the most noticeable being the thermal rearrangement of thiirane oxides (in the presence of a suitable disposed /J-hydrogen) to allylic sulfenic acids2,63,105 (see equation 9 in Section III.C.l). 

To date, several well-established methods are available for the convenient preparation of thiirane oxides, the two main ones being the controlled oxidation of thiiranes63a and the reaction of sulfenes with diazoalkanes636. 

The above reaction is a convincing example of an intermolecular hydrogen abstraction leading essentially to the same result as obtained in the pyrolysis of alkyl-substituted thiirane oxides through an intramolecular /(-elimination of hydrogen. 

The above explains the key roles of (a) the nucleophilicity of the nucleophile (b) the substituent(s) (c) the polarity of the reaction medium and (d) the the bulkiness of the nucleophile, in determining the regio- and stereo-specificity of the reaction. The reaction of alkyl chloromethyl ethers with thiirane oxides to give sulfenic esters128 appears to be mechanistically analogous. 

Whereas acyclic sulfoxides form complexes with various metal salts, thiirane oxides react with copper(II) chloride or bromide163 in benzene at room temperature to give the thiolsulfonate 146a. In alcoholic solution below 0 °C the major products are sulfinates (149). Similar results are obtained in the reaction of thiirane oxides with ethanesulfinyl chloride163 as summarized in equation 60. 

Thus the reaction of the three geometrical isomers of 2,4-hexadiene with thiirane oxide afforded the three related 3-thiolene 5-oxides 154 depicted in equation 62104... 

It has been generally assumed that thermal decomposition of thiirane oxides proceeds stereospecifically to the corresponding olefins by elimination of sulfur monoxide, possibly through a concerted nonlinear chelatropic reaction with retention of configuration of the liberated olefin. 

A mechanism analogous in many ways to that of the acid-catalyzed ring opening reaction was advanced for the reaction of the thiirane oxide with alkyl chloromethyl ethers S . The first step is the displacement of the chloride by the sulfoxy oxygen (equation 24). In view of the above mechanistic interpretation, it is quite surprising that the parent thiirane oxide (16a) was found to be protonated on sulfur and not at oxygen in FSOjH-SbFfi at — 78 °C, according to NMR studies s . 

The mechanistic interpretation of the acid-catalyzed ring opening reaction of thiirane oxides is based on the push-pull mechanism with a transition state in which the bonded hydrogen atom plays a major role (see equation 59). 

A reaction of this type would resemble the well known thermal extrusion of sulfur monoxide from thiirane oxides ... 

Anhydrous RuCb catalyzes the reaction of epoxides with acetone (in acetone under reflux, 1.5-5 h) to give 1,3-dioxolanes [64]. The same catalyst, in the presence of ammonium thiocyanate, converts epoxides into thiiranes. The reaction takes place with inversion of configuration (R)-(-r)-styrene oxide was converted into (5)-(-)-sty-rene sulfide of 78 % optical purity [65]. This transformation is also mediated by catalytic amounts (2 %) of an Fe(III) pentafluorophenylporphyrin complex [66]. Chloro-hydrins are formed on treatment of epoxides with stoichiometric amounts of FeCl3 in ether [67]. 

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