Science of Synthesis

Kubik, S., Science of Synthesis Knowledge Updates, (2013) 3, 272.

Cyclization of carbamate-protected α-amino acid amides yields hydantoins, as shown in ‌Scheme 88‌. This reaction can be conveniently mediated by a weakly basic aqueous solution (NaHCO3) if a (4-nitrophenoxy)carbonyl group is used for the protection of the amino group.[‌219‌] The transformation is believed to involve isocyanate formation if the carbamate derives from a primary amine, and 3,5-disubstituted hydantoins are obtained. As proline also gives the corresponding hydantoin derivatives under these conditions, an alternative addition–elimination pathway seems to be feasible.

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