Transformation of a spirobarbituric acid via aminobarbituric acid‐hydantoin rearrangement

A successful application of the aminobarbituric acid‐hydantoin rearrangement to produce a bicyclic carbamoylhydantoin from an intermediate spirobarbituric acid is reported. 7a‐Phenylcarbamoyl‐tetrahydro‐1 H ‐pyrrolo[1,2‐ c ]imidazole‐1,3(2 H )‐dione ( 8 ) was obtained in a one‐pot multistep reaction of 1‐acetyl‐2,2‐bis(ethoxycarbonyl)pyrrolidine ( 5 ) and phenylurea in the presence of sodium ethoxide. Under less severe conditions, 5 and phenylurea were reacted to afford 1‐acetyl‐7‐phenyl‐triaza[4,5]decane‐6,8,10‐trione ( 6 ). The structural elucidation of the bicyclic hydantoin 8 and the spirobarbituric acid 6 was based on relevant nmr signals in accordance with those of reference compounds, i.e. monocyclic hydantoins 4a,b and acetamidobarbituric acids 2a‐c. The latter compounds were newly prepared from diethyl acetamidomalonates 1 and phenylurea.