Studies On Iminopyridyl-type Ligand-promoted Iron/Cobalt-catalyzed Hydrofunctionalization/Cvclization Of 1,6-Enynes

Five-membered carbocyclic and heterocyclic ring systems are basic structural skeletons in many natural products,pharmaceutical molecules and functional materials.The development of efficient methods for the construction of the five-membered ring is highly desirable.Transition-metal-catalyzed hydrofunctionalization/cyclization of 1,6-enynes is an efficient strategy to construct five-membered cyclic compounds.The present studies are mainly focused on palladium and rhodium catalysts,which are limitted in the substrate scope,regioselectivity and asymmetric catalysis.Meanwhile,earth-abundant metals are low costs and biocompatible.The iminopyridyl-type ligands show redox activity,and their complexes with iron/cobalt are potentially utilized for efficient organic transformations.This dissertation mainly focuses on the synthesis optimization for highly efficient preparation of oxazoline iminopyridine ligand(OIP)and the studies for the iminopyridyl-type ligand promoted iron/cobalt-catalyzed hydrofunctionalization/cyclization of 1,6-enynes.The dissertation is arranged as following:1)Palladium-catalyzed C-2 C-H(hetero)arylation of chiral oxazolines:Diverse synthesis of chiral oxazoline ligandsUsing dppe as a ligand,a direct and practical protocol of the palladium-catalyzed C-H(hetero)arylation of 2-position of oxazolines has been developed for the efficient synthesis of OIP ligand.This method could also be applied to synthesize of other chiral oxazoline ligands.2)Reductive cyclization of 1,6-enynes catalyzed by iron complexesIron-catalyzed reductive cyclization of 1,6-enynes is demonstrated by using the OIP ligand.Alcohol,ketone,ester,ether,halide,amine,amide,imine,nitrile,silyl,and alkyne groups are tolerated under this mild reaction conditions.A speculative mechanism is proposed based on deuterium experiments.A primary enantioselective transformation is also explored.3)Cobalt-catalyzed hydrosilylation/cyclization of 1,6-enynesAn iminopyridine cobalt dichloride complex(IP·CoCl2)is synthesized and structural characterization.It is an efficient precatalyst for hydrosilylation/cyclization of 1,6-enynes to form alkyl silanes.Various functional groups such as amine,free aniline,ester,ether,nitrile,halide,trifluoromethyl group,and heterocycle are tolerable.A primary mechanism is proposed based on the analysis of side-products and deuterium experiments.4)Cobalt-catalyzed ligand-controlled regioselective hydroboration/cyclization of 1,6-enynesWith IP and OIP as the ligand,a ligand-controlled cobalt-catalyzed regioselective hydroboration/cyclization of 1,6-enynes with HBPin is developed to afford alkenylboronates and alkylboronates,respectively.Meanwhile,the products are beneficial for further derivatizations to construct five-membered cyclic compounds.A primary mechanism is proposed on the basis of controlled experiments and deuterium experiments.