Chiral Aminoalcohol-Derived d-Lactams Provide Easy Access to Piperidines and Acyclic Five-Carbon Building Blocks Bearing a Tertiary and a Quaternary Stereocenter

A procedure for the synthesis of enantiopure piperidines and acyclic building blocks (5-aminopentanols, O-protected 5-hydroxypentanenitriles) containing a tertiary and a quaternary stereocenter has been developed. Starting from a phenylglycinol- or aminoindanol-derived d-lactam bearing an alkyl substituent at the a-position of the N,O-acetal carbon, easily accessible by a cyclocondensation reaction, the stereoselective dialkylation at the carbonyl a-position generates the quaternary stereocenter and the subsequent two-step reductive removal of the chiral inductor provides enantiopure 3,3,5-trisubstituted piperidines. Alternatively, the simultaneous reductive opening of the oxazolidine and piperidone rings of the dialkylated lactams followed by reductive or oxidative cleavage of the chiral inductor opens access to chiral 2,2,4-trisubstituted 5-amino-1-pentanols or 2,4,4-trisubstituted 5-hydroxypentanenitriles.