Comprehensive Summary,We herein report a simple ether-directed iridium-catalyzed site-and enantioselective C(sp^(2))-H borylation of benzhydryl ethers for the first time.Various chiral benzhydryl ethers were obtained with high enantioselectivities in the presence of a tailor-made chiral bidentate boryl ligand.We found that the kinetic resolution relay significantly amplified the enantioselectivity.The synthetic utility of the current method was demonstrated by gram-scale C—H borylation and C—B bond transformations.
A highly enantioselective gold-catalyzed intermolecular[3+2]cycloaddition of N-allenamides with nitrones was realized by the application of Ming-Phos M6 as a chiral ligand.Both enantiomers of the cycloadducts with opposite configuration could be obtained in high yields with high regio-and enantioselectivity by the employment of either diastereomer of the chiral ligand.The acidic N—H bond(hydrogen bonding)of sulfinamide moiety of Ming-Phos and pentaflurophenyl substituent(fluorine effect)may play important roles in enhancement of enantioselectivity,that is,Ming-Phos is a multifunctional ligand in this transformation.
The search for new methodologies to tune and control the enantioselectivities of molecular catalysts is of great importance in the field of asymmetric catalysis.Here,we have illustrated that chiral molecular catalysts can be boosted from very low enantioselectivity to high enantioselectivity when installed in supramolecular metal-organic cages.By deliberately designing two optically active 1,1′-spirobiindane-7,7′-diol(SPINOL)-based dipyridine linkers,we synthesized two chiral Pd_(3)L_(6) cages featuring chiral dihydroxyl or dimethoxymethyl auxiliaries in the nanosized cavities.After treatment with metal ions,the cage featuring dihydroxyl groups could serve as efficient catalysts for asymmetric conjugate addition of styrylboronic acids toα,β-enones to produce γ,δ-unsaturated ketone and the asymmetric addition of diethylzinc to aldehydes to afford secondary alcohols.While the molecular SPINOL display very low enantioselectivity,restriction of its freedom in the cages led to 91−99.6% and 80−99.9% enantiomeric excess(ee)of products,respectively,which were increased by up to 35% and 78% ee,compared with the molecular control.Thus,our present work paves a way of utilizing supramolecular porous assemblies to manipulate the enantioselectivities of molecular catalysts.
Dandan ChuWei GongHong JiangXianhui TangYong CuiYan Liu
A chiral cobalt pincer complex,when combined with an achiral electron-rich mono-phosphine ligand,catalyzes efficient asymmetric hydrogenation of a wide range of aryl ketones,affording chiral alcohols with high yields and moderate to excellent enantioselectivities(29 examples,up to 93%ee).Notably,the achiral mono-phosphine ligand shows a remarkable effect on the enantioselectivity of the reaction.
The C-C bond activation and recyclization of benzocyclobutenone to poly-fused rings catalyzed by the[Rh(R,S-L)]+complex producing the R,S-,S,R-,R,R-and S,S-product were investigated systematically at the BP86/6-31G(d,p)level in gas phase and THF,and the R,S-and S,R-reaction pathways were revisited at the M062X/6-31G(d,p)level in THF.The computational results reveal that THF only marginally alters the free-energy barriers,but elevates the relative energies of all species.The BP86 functional testifies that in both gas phase and THF,the activation of strained C-C bonds bears relatively low free-energy barriers,and the rate-determining steps of S,R-and R,R-channels are different from those of R,S-and S,S-channels.The BP86 functional also predicts that the R,S-channel is energetically most favorable in gas phase,but the S,R-product is dominant in THF.The change of NPA charges can mirror the variation of molecular structures to elucidate reaction mechanisms.
