19713-73-6Relevant articles and documents
Electrochemical Proton Reduction over Nickel Foam for Z-Stereoselective Semihydrogenation/deuteration of Functionalized Alkynes
Valiente, Alejandro,Martínez-Pardo, Pablo,Kaur, Gurpreet,Johansson, Magnus J.,Martín-Matute, Belén
, (2021/12/22)
Selective reduction strategies based on abundant-metal catalysts are very important in the production of chemicals. In this paper, a method for the electrochemical semihydrogenation and semideuteration of alkynes to form Z-alkenes was developed, using a simple nickel foam as catalyst and H3O+ or D3O+ as sources of hydrogen or deuterium. Good yields and excellent stereoselectivities (Z/E up to 20 : 1) were obtained under very mild reaction conditions. The reaction proceeded with terminal and nonterminal alkynes, and also with alkynes containing easily reducible functional groups, such as carbonyl groups, as well as aryl chlorides, bromides, and even iodides. The nickel-foam electrocatalyst could be recycled up to 14 times without any change in its catalytic properties.
A Straightforward, Purification-Free Procedure for the Synthesis of Ando and Still-Gennari Type Phosphonates
Janicki, Ignacy,Kie?basiński, Piotr
, p. 378 - 382 (2021/10/21)
Z-Selective Still-Gennari and Ando modifications of the typically E-selective Horner-Wadsworth-Emmons reaction are highly valuable synthetic tools in organic chemistry. These procedures are based on application of bis(2,2,2-trifluoroethyl) phosphonates or diaryl phosphonates, respectively, for the olefination of carbonyl groups. In our research, we present an improved, straightforward, purificationfree procedure for the synthesis of these reagents. The key step of our procedure is the reaction of phosphonic dichlorides with the appropriate sodium alkoxides, which results in 52-97% isolated yields of the desired products on a gram scale. The whole three-step process is performed in one pot. Most importantly, the product is obtained in over 95% purity after simple extraction, avoiding column chromatography and distillation. Moreover, we present the synthesis of a novel Still-Gennari type reagent, bis(1,1,1,3,3,3-hexafluoroisopropyl) phosphonates, which may exhibit improved Z-selectivity in Still-Gennari olefinations.
Heterogeneous Isomerization for Stereoselective Alkyne Hydrogenation to trans-Alkene Mediated by Frustrated Hydrogen Atoms
Zhang, Weijie,Qin, Ruixuan,Fu, Gang,Zheng, Nanfeng
supporting information, p. 15882 - 15890 (2021/10/02)
Stereoselective production of alkenes from the alkyne hydrogenation plays a crucial role in the chemical industry. However, for heterogeneous metal catalysts, the olefins in cis-configuration are usually dominant in the products due to the most important and common Horiuti-Polanyi mechanism involved over the metal surface. In this work, through combined theoretical and experimental investigations, we demonstrate a novel isomerization mechanism mediated by the frustrated hydrogen atoms via the H2 dissociation at the defect on solid surface, which can lead to the switch in selectivity from the cis-configuration to trans-configuration without overhydrogenation. The defective Rh2S3 with exposing facet of (110) exhibits outstanding performance as a heterogeneous metal catalyst for stereoselective production of trans-olefins. With the frustrated hydrogen atoms at spatially separated high-valence Rh sites, the isolated hydrogen mediated cis-to-trans isomerization of olefins can be effectively conducted and the overhydrogenation can be completely inhibited. Furthermore, the bifunctional Rh-S/Pd nanosheets have been synthesized through the surface modification of Pd nanosheets with rhodium and sulfide. With the selective semihydrogenation of alkynes into cis-olefins catalyzed by the small surface PdSx ensembles, the bifunctional Rh-S/Pd nanosheets exhibit excellent activity and stereoselectivity in the one-pot alkyne hydrogenation into trans-olefin, which surpasses the most reported homogeneous and heterogeneous catalysts.
