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

A nonracemic bicyclic lactam was employed to produce a chiral cyclopentane vicinal quaternary carbon centers in optically pure form, which is common to (-)-herbertenediol, (-)-mastigophorene A, and (-)-mastigophorene B. An oxazoline-mediated asymmetric Ullmann coupling was then used to establish chirality about the biaryl axis of mastigophorenes A and B. It was observed that smaller chiral auxiliaries lead to higher levels of atroposelection.