Stereodivergent Alkyne Reduction by using Water as the Hydrogen Source

Abstract

A homogeneous Pd-catalyzed stereodivergent reduction of alkynes to Z and E alkenes by using H O as the H source is presented. Mediated by a diboron reagent, the transfer hydrogenation has been accomplished to yield the desired geometrical isomer by rational ligand selection. The switchable stereoselectivity achieved using simple phosphine ligands is generally excellent. D O has also been used as a D source for synthesizing the corresponding deuterated olefins. Supported by a gram-scale synthesis, the reaction can easily be scaled up making it an efficient way to prepare alkenes commercially as well. Mechanistic studies suggest formation of H-PdL -OAc as the crucial step leading to the presence of two pathways involving H-Pd-B(OR) and molecular H as active intermediates.

Ligand-free (Z)-selective transfer semihydrogenation of alkynes catalyzed by in situ generated oxidizable copper nanoparticles

“…Changing methanol 86 for its homologues led to lower conversions. Obtained results 87 indicate that the reaction rate decreases with the longer car-88 bon chain of alcohol which affects its acidity (Table 1, entries 89 [11][12]. In the case of aprotic solvents, like THF, DMF, or 90 MeCN, no semihydrogenation products were found in the re-91 action mixtures (Table 1, entries [13][14][15].…”

Hydrolysis of B2pin2 over Pd/C Catalyst: High Efficiency, Mechanism, and in situ Tandem Reaction

“…For example, in 2016, Pd(OAc) 2 ‐catalyzed transfer hydrogenation of N‐heteroaromatics via a combined B 2 pin 2 /H 2 O system, had been reported by Song's group (Scheme 1a) [27] . In 2016, Prabhu's group further confirmed that clean hydrogen gas is produced from water by Pd(OAc) 2 ‐catalyzed hydrolysis of B 2 pin 2 (Scheme 1b) [28,29] . In 2019, with a combined ethanol/B 2 pin 2 system as the hydrogen source, Jin and Liu's group also reported CuCl/Ligand‐catalyzed semihydro‐genation of alkynes to synthesize Z‐alkenes with excellent stereoselectivity (Scheme 1c) [30] .…”

Bis-NHC–Ag/Pd(OAc)2 Catalytic System Catalyzed Transfer Hydrogenation Reaction

“…In addition, aldehyde-bearing strong electronwithdrawing group CF3, which could afford the corresponding alcohol 8a in a 92% yield (entry 7), indicates that our reaction works for both electron-donating and electron-withdrawing substituents. Recently, numerous studies of Pd-catalyzed transfer hydrogenation using H2O as the hydrogen agent and the solvent have been reported [51][52][53][54][55][56][57][58][59]. We turned our attention to the possibility that the transfer hydrogenation of internal/terminal alkynes may also continue in the presence of the bis-NHC-Ag/Pd(OAc)2 catalytic system in aqueous media under air.…”