Functionalized oxirane, reaction with nitriles

Styryl carbanions readily react with carbon dioxide 31) to yield carboxy end groups. These terminal groups are also introduced by reaction with anhydrides 19) whereas the use of oxirane 23) leads to the formation of hydroxy end groups esters and nitriles are used to introduce carbonyl functions at the chain end. These reactions can be carried out at low temperature in THF solution and proceed quantitatively if no deactivation by protons occurs. 

Nitriles can react with functionalized oxiranes in a regioselective manner in a tandem epoxide-opening Ritter reaction (Scheme 39) <2005JOC7447>. 

Functionality adjacent to the epoxide can modify its reactivity. For example, 2,3-epoxy sulfides can be converted to a thiiranium species upon treatment with TMS triflate. This intermediate reacts with 0-silyl amides regiospeci-fically to form l-substituted-3-hydroxy-2-thioethers. Simple primary amines undergo polyalkylation, but imines can be used as an indirect amine equivalent <1996T3609>. Nitriles react with functionalized oxiranes in a regioselective manner in a tandem epoxide opening-Ritter reaction (Equation 17) <2005JOC7447>. 

PTC is of great effectiveness in the reaction of a-halocarbanions with aldehydes and ketones producing oxiranes (the Darzens reaction). The presence of Cl or Br substituents in a position to the functional groups of aliphatic nitriles, esters, sulfones, ketones, etc., increases their CH acidities, so the corresponding carbanions are readily generated in the presence of 50% NaOH aq and the catalyst. Since in PTC system these carbanions are continuously generated in the presence of the carbonyl compounds, they are efficiently trapped to produce anions of halohydrines, which subsequently cyclize to oxiranes. These specific features of PTC are particularly favorable for the Darzens reaction thus this is the method of choice for synthesis of substituted oxiranes (eqs. 62-64). 

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