Synthesis of Oxiranes

Asymmetric epoxidation, synthetic aspects of 85MI10 87YGK90. Epoxidation with hydrogen peroxide catalyzed by heteropoly acids 89YGK889. 

---

The most important oxirane syntheses are by addition of an oxygen atom to a carbon-carbon double bond, i.e. by the epoxidation of alkenes, and these are considered in Section 5.05.4.2.2. The closing, by nucleophilic attack of oxygen on carbon, of an OCCX moiety is dealt with in Section 5.05.4.2.1 (this approach often uses alkenes as starting materials). Finally, oxirane synthesis from heterocycles is considered in Section 5.05.4.3 one of these methods, thermal rearrangement of 1,4-peroxides (Section 5.05.4.3.2), has assumed some importance in recent years. The synthesis of oxiranes is reviewed in (B-73MI50500) and (64HC(19-1U). 

A -(4-Toluenesulphonyl)sulphilimines, which are useful precursors in the synthesis of oxiranes and in alkylidene transfer reactions, have been prepared under solidiliquid phase-transfer catalytic conditions from Chloramine-T [2], Comparable yields are obtained irrespective of whether the reaction is catalysed by Adogen or by benzyltriethylammonium chloride (Table 4.31). The procedure is an improvement on the liquiddiquid two-phase method [3]. 

The use of quininium salts can add to the high stereoselectivity (65-80% ee) that can be achieved under phase-transfer catalytic conditions in the synthesis of oxiranes by the Darzens reaction (Section 12.1) from chloromethylsulphones and aromatic aldehydes [6],... 

Phase transfer catalysis, or more correctly, two-phase systems, were widely applied in the synthesis of oxiranes via generation of sulfonium and sulfoxo-nium ylides and their subsequent reactions with carbonyl compounds.67... 

---