Monoalkyl oxalates are among the simplest half-esters, but they are versatile building blocks and therefore have been applied to the organic synthesis of various pharmaceuticals and natural products.  However, their synthesis is not trivial, and their commercial source is limited.  Among possible chemical transformations, hydrolysis or saponification reactions are simple and well-known organic reactions, but successful examples for the monohydrolysis of dialkyl oxalates are rather rare.<br/>    We have previously reported efficient and practical procedures for the selective monohydrolysis of various types of symmetric diesters.  As a part of our ongoing studies on the preparation of half-esters, we report here the synthesis of several monoalkyl oxalates by selective monohydrolysis of dialkyl oxalates in the mainly aqueous media including polar aprotic co-solvent and aqueous base.  The effects of reaction time, temperature, molar ratios of reactants, and amount of co-solvent were examined for the purpose of achieving better selectivities in the monohydrolysis.<br/>As a result, various monoalkyl oxalates were prepared in good yields with the use of THF as a co-solvent in the aqueous media.  Almost all the reactions proceeded smoothly and completed quickly, with the reaction time of up to 10 min, except for the monohydrolysis of dibutyl oxalate, which required up to 40 min due to its increased hydrophobicity. <br/>    Therefore, the procedures for the selective monohydrolysis reactions that we reported earlier appear to be effective for those of oxalate half-esters as well.

Practical Synthesis of Monoalkyl Oxalates

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