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 β- and α-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 (≥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.