Stereocontrol in N-Directed Hydroboration: Synthesis of Amino Alcohols Related to the Piperidine Alkaloids

摘要

Treatment of 2-(2′-alkenyl)-piperidine boranes with iodine or triflic acid induces internal hydroboration with high regiocontrol, even with a terminal alkene (R= H). Good stereocontrol is possible for the N-benzyl substrates. Comparisons with acyclic model structures show that the source of regiocontrol with the terminal alkene is due to a steric effect of the axial piperidine C(3,5) hydrogens that destabilize the competing bridged bicyclic transition state.