Vinylogous Umpolung with Nitrosobenzene

Significance

A one-pot procedure to N-PMP-protected β-amino acid esters by a NHC-catalyzed reaction of enals and nitrosobenzene, followed by an acid-catalyzed esterification and a Bamberger-like rearrangement of the intermediate N-phenylisoxazolidin-5-ones is reported. Several aryl- and alkyl-substituted α,β-unsaturated aldehydes were tested. Substrates with different functional groups are also suitable for this transformation. This new methodology was applied to the synthesis of N-PMP-protected β-DOPA. Furthermore a preliminary study of an enantioselective modification of this protocol is presented.