The carbon dioxide (CO 2 ) capture and utilization has attracted a great attention in organic synthesis. Herein, an unpresented transient stabilization effect (TSE) of CO 2 is disclosed and well applied to the electrochemical hydrogenation of azo compounds to hydrazine derivatives. Mechanistic experiments and computational studies imply that CO 2 can capture azo radical anion intermediates to protect the hydrogenation from potential degradation reactions, and is finally released through decarboxylation. The promotion effect of CO 2 was further demonstrated to work in the preliminary study of electrochemical reductive coupling of α-ketoesters to vicinal diol derivatives. For the electrochemical reductive reactions mentioned above, CO 2 is indispensable. The presented results shed light on a different usage of CO 2 and could inspire novel experimental design by using CO 2 as a transient protecting group.

Pd-catalyzed hydrophosphorylation of alkynes with P(O)−H compounds provided atom-economical and oxidant-free access to alkenylphosphoryl compounds. Nevertheless, the applicable P(O)−H substrates were limited to those without a hydroxyl group except H 2 P(O)OH. It is also puzzling that Ph 2 P(O)OH could co-catalyze the reaction to improve Markovnikov selectivity. Herein, a computational study was conducted to elucidate the mechanistic origin of the phenomena described above. It was found that switchable mechanisms influenced by the acidity of substrates and co-catalysts operate in hydrophosphorylation. In addition, potential side reactions caused by the protonation of Pd II −alkenyl intermediates with P(O)−OH species were revealed. The regeneration of an active Pd(0) catalyst from the resulting Pd(II) complexes is remarkably slower than the hydrophosphonylation, while the downstream reactions, if possible, would lead to phosphorus 2pyrone. Further analysis indicated that the side reactions could be suppressed by utilizing bulky substrates or ligands or by decreasing the concentration of P(O)−OH species. The presented switchable mechanisms and side reactions shed light on the cotransformations of P(O)−H and P−OH compounds in the Pd-catalyzed hydrophosphorylation of alkynes, clarify the origin of the distinct performances of P(O)−H/OH compounds, and provide theoretical clues for expanding the applicable substrate scope of hydrophosphorylation and synthesizing cyclic alkenylphosphoryl compounds.

Pd-catalyzed hydroaminocarbonylation (HAC) of alkenes with CO and NH 4 Cl enables atom-economic and regiodivergent synthesis of primary amides, but the origin of regioselectivity was incorrectly interpreted in previous computational studies. A density functional theory study was performed herein to investigate the mechanism. Different from the previous proposals, both alkene insertion and aminolysis were found to be potential regioselectivity-determining stages. In the alkene insertion stage, 2,1insertion is generally faster than 1,2-insertion irrespective of neutral or cationic pathways for both P( t Bu) 3 and xantphos. Such selectivity results from the unconventional proton-like hydrogen of the Pd−H bond in alkene insertion transition states. For less bulky alkenes, aminolysis with P( t Bu) 3 shows low selectivity, while linear selectivity dominates in this stage with xantphos due to a stronger repulsion between xantphos and branched acyl ligands. It was further revealed that the less-mentioned CO concentration and solvents also influence the regioselectivity by adjusting the relative feasibilities of CO-involved steps and NH 3 release from ammonium chloride, respectively. The presented double-regiodeterminingstages mechanistic model associated with the effects of ligands, CO concentration, and solvents well reproduced the experimental selectivity to prove its validity and illuminated new perspectives for the regioselectivity control of HAC reactions.

Cu-catalyzed aerobic reactions are a powerful protocol for the synthesis of value-added chemicals based on the ideal oxidant O2. Despite the long research history, the mechanistic studies clarifying the details of the whole catalytic cycle, where Cu-O2 complexes and their derivatives directly participate in the conversion of substrates, are limited, leaving the mechanisms of emerging aerobic reactions far from understanding. Herein, a computational study on the mechanism of Cu-catalyzed aerobic aminooxygenation of alkene-tethered amides to imides is reported. It is found that the Cu(I) precursor is not the active species but can generate two types of Cu(II) complexes LCu(OAc)OH and LCu(OAc)OOR to start the aminooxygenation through the successive formation of dinuclear Cu(III) oxo complex, dinuclear Cu(II) hydroxide complex, and hetero-dinuclear Cu(II)-Cu(I) complex, followed by alkylperoxo radical capture with Cu(I) species. LCu(OAc)OH catalyzes the aminooxygenation via a mononuclear mechanism, while LCu(OAc)OOR is an active intermediate therein. In the initial catalytic stage, LCu(OAc)OH transforms alkene-tethered amides to α-amidated aldehydes through N–H activation, amide isomerization, cyclization, alkyl radical release, alkyl radical capture by O2, alkylperoxo radical capture by in situ-generated Cu(I) species to LCu(OAc)OOR, acetate-assisted proton-coupled electron transfer (PCET), and concerted PCET/O–O bond cleavage. In the second catalytic stage for the generation of imides from α-amidated aldehydes, the previously proposed aldehyde Cα–H pathway is possible, but it is more likely to generate CO2 and H2 as the byproducts. Instead, a more feasible pathway involving C(O)–H activation to acyl radical, decarbonylation, and radical capture to LCu(OAc)OOR′ was discovered. The C(O)–H activation pathway generates CO and H2O as the byproducts and is consistent with the experimental observations. The concerted PCET/O–O bond cleavage steps generating α-amidated aldehydes and imides have close energy barriers and both can be the rate-determining steps. The presented outcome revised and expanded the knowledge of Cu-catalyzed aerobic conversion of CC bonds and amide N–H bonds, highlighting the different roles of mononuclear and dinuclear copper complexes in the aerobic reactions and the in situ generation of Cu(II) catalysts, respectively.

The first copper‐catalyzed regiodivergent cyanoboration of internal allenes with B2pin2 (bis(pinacolato)diboron) and NCTS (N‐cyano‐N‐phenyl‐p‐toluenesulfonamide) derivatives is reported. The β,γ‐ and α,β‐cyanoborylated products were synthesized with high regio‐ and stereo‐selectivity. Computational studies revealed that nucleophilic addition of allylcopper or related intermediates on cyanation reagent is the regio‐ and stereo‐determining step, while transmetalation with B2pin2 is the rate‐determining step. The nucleophilic addition step proceeds via inner‐sphere mechanism in the CuI/P(o‐tol)3 and CuI/Xantphos (P(o‐tol)3=tris(o‐methylphenyl)phosphine, Xantphos=4,5‐bis(diphenylphosphino)‐9,9‐dimethylxanthene) catalytic systems and via outer‐sphere mechanism in the CuII/Xantphos catalytic system, respectively.