The syntheses of the bicyclic 2, 4-oxazolidinedione la and the bicyclic hydantoin lb were attempted from several new N-acvlearbamates patterned after known precursors to monocyclic 2, 4-oxazolidinediones. Heating 3-chloro-l-(ethoxyca:rbonyl)-3-phenyl-2-piperidinone (13) resulted in ester pyrolysis, and the reaction of 3-hydroxy-3-phenyl-2-piperidinone (22) with ClCO2Et and K2CO3 yielded l-(ethoxycarbonyl)-3-hydroxy-3-phenyl-2-piperidinone (24). The monocyclic analogue 31 rapidly cyclized at room temperature to yield 5-ethyl-3-methyl-5-phenyl-2, 4-oxazolidinedione (32), potentially representing a new, mild, neutral method for the synthesis of 2, 4-oxazolidinediones. However, heating 24 resulted in decomposition or polymer formation, and the reaction of 24 with NaH resulted in an intramolecular ethoxycarbonyl migration to give 3-(ethoxycarbonvloxy)-3-phenyl-2-piperidinone (35). An analogous approach to the bicyclic hydantoin lb utilized 3-amino-l-(ethoxycarbonyl)-3-phenyl-2-piperidinone (26), butwas also unsuccessful. © 1979, American Chemical Society. All rights reserved.