Total syntheses of (-)-herbertenediol, (-)-mastigophorene A, and (-)-mastigophorene B. Combined utility of chiral bicyclic lactams and chiral aryl oxazolines

A nonracemic bicyclic lactam has been used to construct a chiral cyclopenta ne containing vicinal quaternary carbon centers in optically pure form, whi ch is common to all of the title compounds. An oxazoline-mediated asymmetri c Ullmann coupling was then utilized to establish chirality about the biary l axis of mastigophorenes A and B. Through the course of this synthesis, it was clearly demonstrated that smaller chiral auxiliaries lead to higher le vels of atroposelection, a previously unknown phenomenon of the asymmetric Ullmann coupling.