Synthesis of Stereodefined Piperidines from Aziridines and Their Transformation into Conformationally Constrained Amino Acids, Amino Alcohols and 2,7-Diazabicyclo[3.3.1]nonanes

2-(2-Cyano-2-phenylethyl)aziridines were converted into novel <i>cis</i>- and <i>trans-</i>2-chloromethyl-4-phenylpiperidine-4-carbonitriles <i>via</i> alkylation with 1-bromo-2-chloroethane followed by microwave-assisted 6-<i>exo-tet</i> cyclization and regiospecific ring opening. The latter piperidines were used as eligible substrates for the synthesis of stereodefined 2-chloromethyl-, 2-hydroxymethyl-, and 2-carboxymethyl-4-phenylpiperidine-4-carboxylic acids, 2-hydroxymethyl-4-phenylpiperidine-4-carbonitriles, 3-hydroxy-5-phenylazepane-5-carbonitriles, and 5-phenyl-2,7-diazabicyclo[3.3.1]nonanes.