Collective Asymmetric Synthesis of (−)-Antofine, (−)-Cryptopleurine, (−)-Tylophorine, and (−)-Tylocrebrine with <i>tert-</i>Butanesulfinamide as a Chiral Auxiliary

A collective asymmetric synthesis of phenanthroindolizidine and phenanthroquinolizidine alkaloids (−)-antofine, (−)-cryptopleurine, (−)-tylophorine, and (−)-tylocrebrine was achieved by means of a reaction sequence involving efficient generation of chiral homoallylic amine intermediates by asymmetric allylation of the corresponding <i>tert</i>-butanesulfinyl imine. From these intermediates, the pyrrolidine and piperidine rings were constructed by means of an intramolecular S_N2 substitution reaction and a ring-closing metathesis reaction, respectively. The unusual C5-methoxy-substituted phenanthrene moiety of (−)-tylocrebrine was generated by means of an InCl₃-catalyzed cycloisomerization reaction of an <i>o</i><b>-</b>propargylbiaryl compound