Jianbin Xu

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.

Asymmetric Ring-Opening Reactions of Aza- and Oxa-bicyclic Alkenes with Boronic Acids Using a Palladium/Zinc Co-catalytic System

The asymmetric ring opening reactions of bicyclic alkenes with boronic acids were accomplished by using a highly active palladium/zinc co-catalytic system that was suitable for both azabenzonorbornadienes and oxabenzonorbornadienes, which were transformed to the corresponding chiral hydronaphthalene products in high yields (up to 99%) and high optical purities (up to 98% ee). The reaction protocol is general and mild and displays good functional group tolerance.

Iridium-Catalyzed Anti-Stereoselective Asymmetric Ring-Opening Reactions of Azabenzonorbornadienes with Carboxylic Acids

The first anti-stereoselective asymmetric ring-opening reactions of azabenzonorbornadienes with carboxylic acids have been realized with an iridium catalyst assisted by nBu4NBr. The reaction features broad substrate scope and good functional group tolerance and allows the synthesis of chiral dihydronaphthalene derivatives with high optical purities.

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.