Yongyun Zhou

A study on the substituent effects of norbornadiene derivatives in iridium-catalyzed asymmetric [2 + 2] cycloaddition reactions

Employing a series of norbornadiene derivatives as substrates, the effects of various substituents on the Ir-catalyzed asymmetric [2 + 2] cycloaddition reactions with arylacetylenes were studied. It was found that the atom forming the short bridge chain had a great effect on the enantioselectivity of the reaction. Heteroatoms, such as oxygen and nitrogen, always resulted in excellent enantioselectivity. However, carbon atoms could decrease the enantioselective control ability of the catalyst over the reaction. The groups on the unreacted carbon-carbon double bond were found to have but a little effect on the reaction. Based on the results of the experiments, a mechanism was also hypothesized for the reaction.

Palladium/Zinc Co‐Catalyzed syn‐Stereoselectively Asymmetric Ring‐Opening Reaction of Oxabenzonorbornadienes with Phenols

A new palladium/zinc co-catalyst system associated with chiral (R)-Difluorphos for asymmetric ring-opening reaction of oxabenzonorbornadienes with phenols is reported. This catalyst system allows the formation of cis-2-aryloxy-1,2-dihydronaphthalen-1-ol products in good yields (up to 95 % yield) with excellent enantioselectivities (up to 99 % ee). The cis-configuration of the product has been confirmed by X-ray crystal structure analysis. To the best of our knowledge, it represents the first example in ring-opening reactions of bicycloalkenes with heteronucleophiles in a syn-stereoselective manner.

Rh-catalyzed highly enantioselective hydroalkynylation reaction of norbornadiene derivatives.

The complexes of various Rh precusors with ferrocenyl chiral ligand (R,S)-Cy2PF-PPh2 were found effective catalysts for the asymmetric hydroalkynylation reaction of norbornadiene derivatives. When RhCl3·3H2O was employed, good yields (up to 98%) and high enantioselectivities (up to >99.9% ee) could be obtained for the reactions of a broad scope of substrates.

Rhodium-Catalyzed Asymmetric Arylative Ring-Opening Reactions of Heterobicyclic Alkenes with Anilines

Asymmetric arylative ring-opening reactions of heterobicyclic alkenes with anilines have been reported for the first time. A wide range of heterobicyclic alkenes, including azabenzonorbornadienes and oxabenzonorbornadienes, were well tolerated in the reaction with various anilines, and they generally delivered the corresponding chiral aryltetralin derivatives in good to excellent enantioselectivities. The reaction is speculated to proceed through the Friedel-Crafts reaction pathway.

Rhodium-Catalyzed Asymmetric Cyclization/Addition Reactions of 1,6-Enynes and Oxa/Azabenzonorbornadienes

A mild, efficient, and novel rhodium catalyzed asymmetric cyclization-addition domino reaction of oxa/azabenzonorbornadienes and 1,6-enynes is documented. Through the use of a [Rh(COD)2]BF4-(R)-An-SDP catalytic system, highly enantioenriched cyclization-addition products were obtained in good yields and with excellent enantioselectivities.

Cobalt-catalyzed asymmetric reactions of heterobicyclic alkenes with in situ generated organozinc halides

A general strategy for the asymmetric allylation and benzylation of heterobicyclic alkenes is described by employing in situ generated organozinc halides. This methodology features the application of a co-catalytic system comprising chiral cobalt complex and Lewis acid, which deliver both the asymmetric ring opening products of oxabenzonorbornadienes and the asymmetric addition products of azabenzonorbornadienes, respectively.

Asymmetric ring-opening reactions of azabenzonorbornadienes through transfer hydrogenation using secondary amines as hydrogen sources: tuning of absolute configuration by acids

Reductive transfer hydrogenation of bicyclic alkenes has been developed under the co-catalytic system of palladium and silver by using secondary amines as reductants. The reaction results in the asymmetric ring-opening product. A wide range of azabenzonorbornadienes reacted well giving 1,2-dihydronaphthalen-1-amine derivatives in high yields with good enantioselectivities. The control of the absolute configuration of the product by addition of carboxylic acids has been demonstrated.

Rhodium-Catalyzed Generation of Anhydrous Hydrogen Iodide: An Effective Method for the Preparation of Iodoalkanes

The preparation of anhydrous hydrogen iodide directly from molecular hydrogen and iodine using a rhodium catalyst is reported for the first time. The anhydrous hydrogen iodide generated was proven to be highly active in the transformations of alkenes, phenyl aldehydes, alcohols, and cyclic ethers to the corresponding iodoalkanes. Therefore, the present methodology not only has provided convenient access to anhydrous hydrogen iodide but also offers a practical preparation method for various iodoalkanes in excellent atom economy.

Nickel-Catalyzed Asymmetric [2+2] Cycloaddition Reaction of Hetero-Bicyclic Alkenes with Internal Alkynes

Enantioselective [2+2] cycloaddition reaction of azabenzonorbornadienes and oxabenzonorbornadienes with internal alkynes has been enabled by a catalyst system comprising Ni(COD)2 and (R)-SIPHOS-Ph-Mor. This transformation represents the first asymmetric [2+2] cycloaddition reaction of azabenzonorbornadienes with internal alkynes, providing a straightforward method to prepare four-membered carbocycles.