Promoting role of Ru species on Ir-Fe/BN catalyst in 1,2-diols hydrogenolysis to secondary alcohols

Noble metal-based-bimetallic catalysts have been highly investigated and applied in wide applications including biomass transformation via regioselective C−O hydrogenolysis while further modification especially with noble metal is highly promising yet still under investigation.Herein,Ru was found as an effective modifier among the screened noble metals(Ru,Pt,Rh,Pd,Au,and Ag)for Ir-Fe/BN(Ir=5 wt%,Fe/Ir=0.25)catalyst in terminal C−O hydrogenolysis of 1,2-butanediol(1,2-BuD)to 2-butanol(2-BuOH).Only trace amount of Ru(up to 0.5 wt%)was effective in terms of high 2-BuOH selectivity(>60%)and activity(about twice).Larger amount of Ru species(3 wt%)highly enhanced the activity but gave low selectivity to 2-BuOH with by-products of terminal C−C bond scission.Optimized catalyst(Ru(0.5)-Ir-Fe/BN)was reusable at least 4 times and gave moderate 2-BuOH yield(47%)in hydrogenolysis of 1,2-BuD.The promoting effect of Ru addition(0.5 wt%)to Ir-Fe/BN on hydrogenolysis of various alcohols was also confirmed.Combining catalytic tests with various characterizations,the promotion mechanism of Ru species in trimetallic catalysts was clarified.The Ru species in Ru(0.5)-Ir-Fe/BN form alloy with Ir and are enriched at the interface with BN surface,and direct interaction between Ru and Fe was not necessary in Ru-Ir-Fe alloy.The interface of Ir and Fe on the surface of Ir-Fe alloy may work as active sites for 1,2-diols to secondary alcohols via direct C−O hydrogenolysis,in which Ru-modified Ir activates H_(2) to form hydride-like species.The activity of Ru species in C−C bond cleavage was highly suppressed due to the direct interaction with Ir species and less exposed to substrate.Larger loading amount of Ru species(3 wt%)led to the formation Ru-rich trimetallic alloy,which further works as active sites for C−C bond scission.

Stereochemical editing:Catalytic racemization of secondary alcohols and amines

Chiral alcohols and amines are important structural units widely existing in pharmaceuticals,agrochemicals,and food additives.Dynamic kinetic resolution(DKR)is an efficient strategy to deliver optically active alcohols and amines from their racemates.For the development of DKR method,racemization catalyst plays as a crucial element with the requirement of compatibility with the kinetic resolution(KR)system.In this paper,recent advance in the catalytic racemization of secondary alcohols and amines is summarized based on different types of racemizing intermediates,which are redox racemization via ketone/imine intermediates,racemization via radical intermediates,and racemization via carbocation intermediates.Enzymatic racemization of secondary alcohols and amines is also enclosed.

Salen-Mn(III)-Complex-Catalyzed Oxidations of Secondary Alcohols

Secondary alcohols were catalytically oxidized with diacetoxyiodobenzene as oxidant in the presence of salen- Mn(III) complex to afford the corresponding ketones, in up to 99% yield, using CH 2Cl 2 or water as reaction media.

Visible Light-Mediated Cobalt and Photoredox Dual-Catalyzed Asymmetric Reductive Coupling for Axially Chiral Secondary Alcohols

Secondary alcohols bearing both axial and central chirality comprise attractive biological activity and exhibit excellent chiral induction in asymmetric reactions.However,only very limited asymmetric catalytic approaches were developed for their synthesis.We herein describe visible light-mediated cobalt-catalyzed asymmetric reductive Grignard-type addition of aryl iodides with axially prochiral biaryl dialdehydes leading to the direct construction of axially chiral secondary alcohols.Preliminary mechanistic studies indicate that efficient kinetic recognition of diastereomers might occur for axially prochiral dialdehydes to improve the stereoselectivity,which might open a new avenue for the challenging cascade construction of multiple chiral elements.This protocol features excellent enantio-and diastereoselectivity,green and mild conditions,simple operation,and broad substrate scope,providing a modular platform for the synthesis of secondary axially chiral alcohols.

Base-controlled NHC-Ru-catalyzed transfer hydrogenation andα-methylation/transfer hydrogenation of ketones using methanol

Herein,we report the NHC-Ru catalyst system that realizes the chemo-selective transformation of ketones with methanol.By simply changing the base,a broad range of structurally diverse ketones,could be selectively and efficiently converted to the correspondingβ-methylated secondary alcohols or secondary alcohols.Remarkably,this catalytic system was very effective for the synthesis of bio-related molecules and deuterated alcohols,as well as the three-component coupling between methyl ketones,primary alcohols,and methanol.The reaction mechanism was further revealed by experiment and DFT mechanistic investigations.

A Concise,Practical Chiral Resolution Approach of Racemic (E)-4,4-Dimethyl-1-(4-nitrophenyl) pent-1-en-3-ol to Its both Enantiomers via Strategy of Diastereomeric Ester Formation and Crystallization Using both N-Boc-D- and N-Boc-L-phenylglycines as Chiral Auxiliaries

Chiral secondary alcohols are an important class of functionalities commonly seen in drugs and other bioactive compounds.In an ongoing drug discovery program in our laboratories,a nitro-bearing racemic allylic secondary alcohol (±)-1 was discovered as a promising drug candidate,and in the following preclinical studies,a concise,reliable,practical synthetic approach to its both enantiomers with high optical purities was greatly needed.In the present study,we developed a chiral resolution approach of (±)-1 to its both enantiomers,i.e.,(+)-1 and (-)-1,via the strategy of diastereomeric ester formation and crystallization using both N-Boc-D- and N-Boc-L-phenylglycines as chiral auxiliaries.The absolute configurations of all the four key intermediates were unambiguously determined by single-crystal X-ray diffraction,providing a solid foundation for the stereochemistry of the present study.The two enantiomers were obtained in high optical purities.This approach is characterized by scalability and practicality and is envisaged to enable the chiral resolution of other racemic secondary alcohols,especially those with labile groups,such as NO_(2);olefinic C=C bond.

Chemo-and Enantioselective Arylation and Alkenylation of Aldehydes Enabled by Nickel/N-Heterocyclic Carbene Catalysis

Herein,we report the first highly enantioselective Ni-catalyzed arylation and alkenylation of simple aldehydes using readily available and stable organoboronic esters.This protocol provides various chiral secondary alcohols in high yields and enantioselectivities(up to 97% ee)with a broad scope of substrates,functional groups,and heterocycles.The use of a bulky N-heterocyclic carbene(NHC)ligand for nickel catalyst is the key to high enantiocontrol.The competitive Ni-catalyzed transformations,including Tishchenko reaction,dehydrogenation/hydrogenation reaction,and Suzuki-Miyaura couplings,are avoided.The excellent chemoselectivity is likely due to the application of mild base CsF and η^(2)-coordination of aldehydes with nickel.