Synthesis of new chiral 2,2′-bipyridyl-type ligands, their coordination to molybdenum(0), copper(II), and palladium(II), and application in asymmetric allylic substitution, allylic oxidation, and cyclopropanation

A series of chiral bipyridine-type ligands 5-12 has been:synthesized: via: a de novo construction of the pyridine nucleus. The chiral moieties of the ligands originate from the monoterpene realm, namely, pinocarvone (13 --> 6, 7, and 9), myrtenal (18 --> 5), nopinone (21 --> 8 and 10), and menthone (28 --> 11 and 12); the first three precursors can be obtained in one step from beta- and alpha -pinene, respectively. Complexes of these ligands with molybdenum(0) (38-40) and copper(II) (41) have been characterized by single-crystal X-ray crystallography. While complex 38 exhibits polymorphism (monoclinic and tetragonal forms crystallize from the same batch), 41 is characterized by a tetrahedrally distorted geometry of the metal coordination. The Mo and Pd complexes exhibit modest asymmetric induction:in allylic substitution (43 --> 44), and the Cu(I) counterpart of 41, derived from 10 (PINDY) and Cu(OTf)(2), shows promising enantioselectivity (49-75% ee) and reaction rate (greater than or equal to 30 min at room temperature) in allylic oxidation of cyclic olefins (47 --> 48). The Cu(I) complex of 11 (MINDY) proved effective in cyclopropanation (49 --> 50) with up to 72% ee.