Oxime derivatives of 5-oxoalkanenitriles (Ce chain or longer) were cyclized in most cases with a combination of AcCl and AczO, or AcgO and HC1 to 6-substituted 2-(N-acetylamino)pyridines. Alkaline hydrolysis gave the corresponding 2-aminopyridines in overall yields of 40-65%, with the éxception of pyridine 3e. Oxime derivatives of 5-oxopentanenitriles did not cyclize but gave glutaronitriles instead. In some experiments with 5-oximinohexanenitrile (la), 2,4-dimethyl-5-(2-cyanoethyl)oxazole ( 9) was detected in addition to the main product, 2-(IV-acetylamino)-6-methylpyridine (2a). Formation of these compounds can be explained on the basis of a common intermediate 7 formed through rearrangement of the O-acetylated 5-oximinohexanenitrile (4).

5-Hydroxypiperidin-2-one is a versatile building block for the preparation of potentially biologically active compounds. We detail an enantioselective biocatalytic approach towards its synthesis using (S)-hydroxynitrile lyase (HNL)-mediated cyanohydrin formation, followed by hydrogenation. By adjusting the conditions of the latter step, we were able to obtain 5-hydroxypiperidinonederived (bicyclic) N,N-acetals via an unprecedented reductive amination of the nitrile group, as well as form N-alkylated 5-hydroxypiperidinone in a single step from the same cyanohydrin intermediate.

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