Iridium-Catalyzed Asymmetric Ring-Opening of Azabicyclic Alkenes with Phenols

Catalytic asymmetric transformations of oxa- and azabicyclic alkenes

This review provides an overview of the fundamental concepts and recent developments in a wide range of enantioselective transformations involving oxa- and azabicyclic alkenes.

Palladium-Catalyzed syn-Stereocontrolled Ring Opening of Oxabicyclic Alkenes with Arylsulfonyl Hydrazides

A novel palladium-catalyzed ring-opening reaction of oxabicyclic alkenes with arylsulfonyl hydrazides was first developed. In this work, we provide an efficient one-pot reaction to afford the corresponding cis-2-aryl-1,2-dihydronaphthalen-1-ols and 2-aryl-naphthalenes in moderate to excellent yields (up to 95%) under an open-air condition. Various types of functional groups attached to the substrates were tolerated well in this method. Among them, the cis-1,2-configuration of product 3ag was confirmed by X-ray crystallographic analysis. In addition, a plausible mechanism for ring opening was also proposed.

Desymmetrization of Achiral Heterobicyclic Alkenes through Catalytic Asymmetric Hydrophosphination

Asymmetric addition of diarylphosphines to oxa- and azabicyclic alkenes proceeded in the presence of a chiral phosphapalladacycle catalyst and a mild acid at room temperature to give exclusively the enantioenriched addition products in excellent yields and good selectivities. Three new chiral carbon centers were generated stereoselectively by the catalytic hydrophosphination reaction.

Platinum-catalyzed syn-stereocontrolled ring-opening of oxabicyclic alkenes with sodium arylsulfinates

A new efficient platinum-catalyzed ring-opening reaction of oxabicyclic alkenes with a wide range of sodium arylsulfinates was developed.

Iridium/Copper Co-catalyzed Anti-Stereoselective Ring Opening of Oxabenzonorbornadienes with Grignard Reagents

Cooperative catalysis has been widely considered as one of the most powerful strategies to improve synthetic efficiency. A new iridium/copper cocatalyst was developed for the ring-opening reaction of oxabenzonorbornadienes with a wide variety of Grignard reagents, which afforded the corresponding anti-2-substituted 1,2-dihydronaphthalen-1-ols in high yields (up to 99% yield) under mild conditions. The effects of catalyst loading, Lewis acid, Grignard reagent loading, and reaction temperature on the yield were investigated. To the best of our knowledge, it represents the first example of ring-opening reactions of oxabicyclic alkenes with Grignard reagent nucleophiles in a trans-stereoselective manner.

Iridium-Catalyzed Asymmetric Ring-Opening of Oxabenzonorbornadienes with N-Substituted Piperazine Nucleophiles

Iridium-catalyzed asymmetric ring-opening of oxabenzonorbornadienes with N-substituted piperazines was described. The reaction afforded the corresponding ring-opening products in high yields and moderate enantioselectivities in the presence of 2.5 mol % [Ir(COD)Cl]₂ and 5.0 mol % (S)-p-Tol-BINAP. The effects of various chiral bidentate ligands, catalyst loading, solvent, and temperature on the yield and enantioselectivity were also investigated. A plausible mechanism was proposed to account for the formation of the corresponding trans-ring opened products based on the X-ray structure of product 2i.

Nickel-catalyzed asymmetric ring opening of oxabenzonorbornadienes with arylboronic acids

A new, versatile, and highly efficient nickel-catalyzed asymmetric ring-opening (ARO) reaction of oxabenzonorbornadienes with a wide variety of arylboronic acids has been developed, yielding cis-2-aryl-1,2-dihydronaphthalen-1-ols in high yields (up to 99%) with good to excellent enantioselectivities (up to 99% ee) under very mild conditions. The effects of various nickel precursors, chiral bidentate ligands, catalyst loadings, bases, solvents, and temperatures on the yield and enantioselectivity of the reaction were also investigated. A plausible mechanism was proposed to account for the formation of the corresponding cis-ring-opened products based on the X-ray structure of product 4b.

Platinum-catalyzed anti-stereocontrolled ring-opening of oxabicyclic alkenes with Grignard reagents

A new platinum-catalyzed anti-stereocontrolled ring-opening of oxabicyclic alkenes with various Grignard reagents was reported, which afforded the corresponding anti-2-substituted-1,2-dihydronaphthalen-1-ol products with moderate to good yields in the presence of a catalytic amount of Pt(PPh3)4 (2.5 mol%) under mild conditions. The effects of catalyst loading, solvent and temperature on the yield were also investigated. Furthermore, the trans-configuration of the product 5i was confirmed by X-ray diffraction analysis.

Iridium-catalyzed intramolecular [4 + 2] cycloadditions of alkynyl halides

Iridium-catalyzed intramolecular [4 + 2] cycloadditions of diene-tethered alkynyl halides were investigated by using [IrCl(cod)]₂ as catalyst, and dppe was found to be the most suitable phosphine ligand for the reaction. No oxidative insertion of the iridium into the carbon–halide bond was observed, and the reactions proceeded to provide the halogenated cycloadducts in good yield (75–94%). These results are the first examples of cycloadditions of alkynyl halides using an iridium catalyst.