It is well-known that ynamides can be oxidized at the α-position in the presence of pyridine-N-oxides or sulfoxides as oxidants. In contrast, with mCPBA as an oxidant, we observed the formation of N,O-acetals, which is thought to form via β-oxidation of ynamides (Eq. 1). These N,O-acetals are bench stable and can be stored at room temperature for several months. Furthermore, by employing chiral phosphoric acids, they can function as a precursor of forming enantio-enriched N,O-acetals (Eq. 2). Our approach to the optically active N,O-acetals are unique in that most known methods rely on the protonation of imines, or previous transacetalization protocols have been limited to intramolecular cases. The enantioenriched N,O-acetals were configurationally stable and could transformed into optically active tertiary α-hydroxy aldehydes in high diastereoselectivity without any racemization (Eq. 3).

β-Oxidation of Ynamides into N,O-Acetals by mCPBA: Application in enantioselective intermolecular trans-acetalization

ACS Spring Meeting 2021

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