Collective asymmetric synthesis of (-)-antofine, (-)-cryptopleurine, (-)-tylophorine, and (-)-tylocrebrine with tert-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 tert-butanesulfinyl imine. From these intermediates, the pyrrolidine and piperidine rings were constructed by means of an intramolecular SN2 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 o-propargylbiaryl compound.