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Enantiomerically pure 4-piperidones, prepared by asymmetric [4 + 2] Diels−Alder cycloadditon of chiral 2-aminodienes with imines, have been used as starting materials for the synthesis of several derivatives of pipecolic acid. The α-amino acid moiety is obtained after the oxidation of a hydroxy group or a furan ring of a conveniently protected 2-aryl-6-(hydroxymethyl)-4-piperidone. Depending on the starting piperidone and the synthetic strategy, it is possible to obtain d- or l-functionalized pipecolic acid derivatives by a short synthetic procedure. Moreover, a stereoselective epimerization of the α-carbon atom of a particular pipecolate allows for the preparation of both cis- and trans- 6-(hydroxymethyl)pipecolic acids, structures related with dipeptide isosteres.

Chiral2-amino-I ,3-butadienes 1 derived from commercially available (S)-2-methoxymethylpyrrolidine react with aromatic N-trimethylsilylaldimines and Nphenylaldimines in the presence of ZnC1, to give, after the reaction workup, 4-piperidones 4 and 6, respectively, with moderate to very high enantiomeric excesses. In addition, the absolute configurations of derivatives of 4 a and 4g were determined by circular dichroism and NMR spectroscopy on the Mosher ester, respectively. asymmetric

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2-Amino-1,3-butadienes bearing commercially available S-(+)-2-(methoxymethyl)pyrrolidine as chiral auxiliary undergo a [4 + 2] cycloaddition reaction with nitroalkenes to furnish 4-nitrocyclohexanones upon hydrolysis of the resulting enamine. The cycloadducts are obtained with good yields and very high enantiomeric excesses. The reaction has been performed with aromatic and aliphatic conjugated nitroalkenes. Moreover, a 2-amino diene which features a (Z) double bond undergoes a Michael addition reaction with nitroalkenes, which gives rise to open chain compounds with high enantioselectivity. After acidic hydrolysis, the open chain compounds cyclize to form chiral substituted furans.