Straightforward ring expansion of pyroglutamates to perhydro-1,3-diazepine-2,4-diones.

[reaction: see text] Perhydro-1,3-diazepine-2,4-diones are rare and can only be prepared, up to now, by special methods. A new one-step protocol was developed, comprising N-carbamoylation using an isocyanate followed by intramolecular ring expansion. This new methodology provides a straightforward access to this interesting seven-membered skeleton.