The synthesis and catalytic activity of several classes of NHC-Ni(0) pre-catalysts stabilized by electron-withdrawing alkenes are described. Variations in the structure of fumarate and acrylate ligands modulate the reactivity and stability of the NHC-Ni(0) pre-catalysts and lead to practical and versatile catalysts for a variety of transformations. The catalytic activity and efficiency of representative members of this class of catalysts have been evaluated in reductive couplings of aldehydes and alkynes and in -arylations of aryl chlorides.
Various allylic alcohols were carboxylated in the presence of a catalytic amount of PdCl2 and PPh3 using ZnEt2 as a stoichiometric transmetalation agent under a CO2 atmosphere (1 atm). This carboxylation proceeded in a highly regioselective manner to afford branched carboxylic acids predominantly. The β,γ-unsaturated carboxylic acid thus obtained was successfully converted into an optically active γ-butyrolactone, a known intermediate of (R)-baclofen.
Metallic Li deposited
on the anode is known to induce short circuiting
and degradation of the charge capacity of Li-ion batteries. However,
no reliable technique is currently available to observe such Li metal
without removing the case of the battery. An elemental analysis using
muonic X-rays is proposed here because of its unique properties of
nondestructive measurement, high sensitivity to light elements, and
depth resolution. We demonstrated that this technique can be applied
to detection of Li deposited on the surface of an anode containing
Li ions, using a fully charged anode with Li deposited due to overcharge
in an Al-laminated plastic pouch. The basis for the detection method
is the difference in the atomic Coulomb capture ratio of the negative
muons between the Li metal and ions. We have found, as a result, that
the intensity of the muonic X-rays from metallic Li was approximately
50 times higher than that from Li ions. Consequently, the Li metal
on the anode was clearly distinguishable from the intercalated Li
ions in the anode. Furthermore, measurements of two overcharged anodes
with 1.3 and 2.7 mg of metallic Li deposition, respectively, indicated
that this technique is suitable for quantitative analysis. Distribution
analysis is also possible, as shown by a preliminary observation on
an overcharged anode from the back side. Therefore, this technique
offers a new approach to the analysis of Li deposited on the anode
of a Li-ion pouch battery.
α-Amino acids are essential resources for human life and are highly useful as building blocks for organic synthesis. The core framework of an α-amino acid can be divided into three basic components: an aldehyde, an amine, and carbon dioxide (CO(2)). We report herein that a one-step synthesis of α-amino acids has been successfully achieved from these three basic and inexpensive chemicals with a single operation, in which the mixture of an aldehyde, a sulfonamide, and gaseous CO(2) was heated at 100 °C in the presence of Bu(3)Sn-SnBu(3) and CsF. In this one-pot sequential protocol, two important intermediates (imine and α-amino stannane) are involved and the stannyl anion generated in situ plays a crucial role, particularly for the efficient stannylation of the imine in the presence of proton sources and for promoting retrostannylation of the undesired α-alkoxy stannane owing to its high stability and tolerance of the presence of proton sources. This methodology enabled the synthesis of a wide range of racemic arylglycine derivatives in high yields.
Arylative carboxylation of allenes proceeded in an intramolecular manner to afford the corresponding β,γ-unsaturated carboxylic acids in high yields using PdCl/PAr (Ar = CH-p-CF) and ZnEt under 1 atm of CO. The intermediate of the cyclization/carboxylation sequence is thought to be a nucleophilic η-allylethylpalladium, which reacts with CO at the γ-position of palladium. The products obtained could be efficiently converted into 3-substituted indole-2-carboxylate derivatives. One-pot synthesis of strychnocarpine, a β-carboline alkaloid, from the carboxylated product was also demonstrated.
In the presence of CsF, a wide range of α-substituted α-siloxy silanes were carboxylated under a CO2 atmosphere (1 atm) via Brook rearrangement. A variety of α-substituents including aryl, alkenyl, and alkyl groups were tolerated to afford α-hydroxy acids in moderate-to-high yields. One-pot synthesis from aldehydes using PhMe2SiLi and CO2 was also possible, providing α-hydroxy acids without the isolation of an α-hydroxy silane.
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