Artificial photosynthesis of H2O2 from H2O and O2, as a spotless method, has aroused widespread interest. Up to date, most photocatalysts still suffer from serious salt-deactivated effects with huge consumption of photogenerated charges, which severely limit their wide application. Herein, by using a phenolic condensation approach, carbon dots, organic dye molecule procyanidins and 4-methoxybenzaldehyde are composed into a metal-free photocatalyst for the photosynthetic production of H2O2 in seawater. This catalyst exhibits high photocatalytic ability to produce H2O2 with the yield of 1776 μmol g−1h−1 (λ ≥ 420 nm; 34.8 mW cm−2) in real seawater, about 4.8 times higher than the pure polymer. Combining with in-situ photoelectrochemical and transient photovoltage analysis, the active site and the catalytic mechanism of this composite catalyst in seawater are also clearly clarified. This work opens up an avenue for a highly efficient and practical, available catalyst for H2O2 photoproduction in real seawater.
A novel
enantioselective aminomethylation reaction of diazo compound,
alcohol and α-aminomethyl ether enabled by asymmetric counteranion-directed
catalysis is disclosed that offers an efficient and convenient access
to furnish optically active α-hydroxyl-β-amino acids in
high yield with high to excellent enantioselectivities. Control experiments
and DFT calculations indicate that the transformation proceeds through
trapping the in situ generated enol intermediate with methylene iminium
ion, and the asymmetric induction was enabled by chiral pentacarboxycyclopentadiene
anion via H-bonding and electrostatic interaction.
Multicomponent reactions that involve interception of onium ylides through Aldol, Mannich, and Michael addition with corresponding bench-stable acceptors have demonstrated broad applications in synthetic chemistry. However, because of the high reactivity and transient survival of these in situ generated intermediates, the substitution-type interception process, especially the asymmetric catalytic version, remains hitherto unknown. Herein, a three-component asymmetric allylation of α-diazo carbonyl compounds with alcohols and allyl carbonates is disclosed by employing a ternary cooperative catalysis of achiral Pd-complex, Rh 2 (OAc) 4 , and chiral phosphoric acid CPA. This method represents the first example of three-component asymmetric allylic alkylation through an S N 1-type trapping process, which involves a convergent assembly of two active intermediates, Pd-allyl species, and enol derived from onium ylides, providing an expeditious access to chiral α,α-disubstituted ketones in good to high yields with high to excellent enantioselectivity. Combined experimental and computational studies have shed light on the mechanism of this novel three-component reaction, including the critical role of Xantphos ligand and the origin of enantioselectivity.
Chemical bond cleavage and reconstruction are common processes in traditional rearrangement reactions. In contrast, the process that involves bond cleavage, fragment modification and then reconstruction of the modified fragment provides an efficient way to build structurally diversified molecules. Here, we report a palladium(II)/chiral phosphoric acid catalysed three-component reaction of aryldiazoacetates, enamines and imines to afford α-amino-δ-oxo pentanoic acid derivatives in good yields with excellent diastereoselectivities and high enantioselectivities. The stereoselective reaction went through a unique process that involves cleavage of a C–N bond, modification of the resulting amino fragment and selective reassembly of the modified fragment. This innovative multi-component process represents a highly efficient way to build structurally diversified polyfunctional molecules in an atom and step economic fashion. A keto-iminium is proposed as a key intermediate and a chiral palladium/phosphate complex is proposed as an active catalyst.
Pd(II)-catalyzed three-component reactions via trapping of ammonium ylides with N-alkylquinolinium salts are reported. These reactions provided polyfunctional polycyclic tetrahydroquinolines or 4-substituted 1,4-dihydroquinolines in excellent yields (89-99% and 89-98%, respectively) with high regioselectivities and moderate to good diastereoselectivities (up to 95:5 dr) under mild reaction conditions.
An enantioselective Rh(II)/chiral phosphoric acid co-catalyzed three-component reaction via trapping of oxonium ylides with 3-hydroxyisoindolinones by a formal S1 pathway is described. This reaction allows for the efficient synthesis of isoindolinone derivatives with two contiguous quaternary stereogenic centers in high yields (up to 93%) with excellent enantioselectivities and moderate diastereoselectivities under mild reaction conditions.
An efficient strategy for the synthesis of a wide variety of coordination complexes has been developed. The synthetic protocol involves a solvothermal in situ metal-ligand reaction of picolinaldehyde, ammonium acetate, and transition-metal ions, leading to the generation of 12 coordination complexes supported by a novel class of substituted 1-pyridineimidazo[1,5-a]pyridine ligands (L1-L5). The ligands L1-L5 were afforded by metal-mediated controllable conversion of the aldehyde group of picolialdehyde into a ketone and secondary, tertiary, and quaternary carbon centers, respectively. Complexes of various nuclearities were obtained: from mono-, di-, and tetranuclear to 1D chain polymers. The structures of the in situ formed complexes could be controlled rationally via the choice of appropriate starting materials and tuning of the ratio of the starting materials. The plausible mechanisms for the formation of the ligands L1-L5 were proposed.
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