Science of Synthesis

Kubik, S., Science of Synthesis Knowledge Updates, (2013) 3, 269.

Hydantoins can be obtained by reacting 1,2-dicarbonyl compounds with unsubstituted or substituted urea derivatives in basic aqueous media. As ‌Scheme 81‌ shows, reaction between benzil and urea yields 5,5-diphenylhydantoin (‌49‌) under these conditions indicating that the reaction involves the 1,2-shift of one aromatic ring. A complication arises from the fact that glycolurils are usually formed as side products. The ratio of hydantoin and glycoluril depends on various factors. For example, glycoluril formation becomes more pronounced when an excess of urea is used in the reaction. The solvent also plays a role, with dimethyl sulfoxide suppressing glycoluril formation to some extent.[‌222‌] By using an excess of urea and working in acidic media, glycolurils become the major products. These conditions are therefore usually employed if preparation of a glycoluril derivative is the goal.

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