Cobalt-Catalyzed Facial-Selective Hydroalkylation of Cyclopropenes.

Cyclopropene hydrofunctionalization has been a promising strategy for accessing multi-substituted cyclopropanes; however, cyclopropene hydroalkylation remains underdeveloped. Herein, we report a low-valent CoH-catalyzed facial-selective cyclopropene hydroalkylation to access multi-substituted cyclopropanes. This reaction exhibits a broad substrate scope of alkyl halides and cyclopropenes and tolerates many functional groups. Moderate-to-good facial-selectivity is obtained without any directing groups. Mechanism studies provide evidence that alkyl radicals are generated from alkyl halides and irreversible CoH insertion is responsible for the facial-selectivity. Our preliminary exploration demonstrates that asymmetric cyclopropene hydroalkylation can be realized without conspicuous auxiliary groups.

NiH-catalysed proximal-selective hydroalkylation of unactivated alkenes and the ligand effects on regioselectivity.

Alkene hydrocarbonation reactions have been developed to supplement traditional electrophile-nucleophile cross-coupling reactions. The branch-selective hydroalkylation method applied to a broad range of unactivated alkenes remains challenging. Herein, we report a NiH-catalysed proximal-selective hydroalkylation of unactivated alkenes to access ß- or γ-branched alkyl carboxylic acids and ß-, γ- or δ-branched alkyl amines. A broad range of alkyl iodides and bromides with different functional groups can be installed with excellent regiocontrol and availability for site-selective late-stage functionalization of biorelevant molecules. Under modified reaction conditions with NiCl2(PPh3)2 as the catalyst, migratory hydroalkylation takes place to provide ß- (rather than γ-) branched products. The keys to success are the use of aminoquinoline and picolinamide as suitable directing groups and combined experimental and computational studies of ligand effects on the regioselectivity and detailed reaction mechanisms.

Pivotal Electron Delivery Effect of the Cobalt Catalyst in Photocarboxylation of Alkynes: A DFT Calculation.

Photocarboxylation of alkyne with carbon dioxide represents a highly attractive strategy to prepare functionalized alkenes with high efficiency and atomic economy. However, the reaction mechanism, especially the sequence of elementary steps (leading to different reaction pathways), reaction modes of the H-transfer step and carboxylation step, spin and charge states of the cobalt catalyst, etc., is still an open question. Herein, density functional theory calculations are carried out to probe the mechanism of the Ir/Co-catalyzed photocarboxylation of alkynes. The overall catalytic cycle mainly consists of four steps: reductive-quenching of the Ir catalyst, hydrogen transfer (rate-determining step), outer sphere carboxylation, and the final catalyst regeneration step. Importantly, the cobalt catalyst can facilitate the H-transfer by an uncommon hydride coupled electron transfer (HCET) process. The pivotal electron delivery effect of the Co center enables a facile H-transfer to the α-C(alkyne) of the aryl group, resulting in the high regioselectivity for ß-carboxylation.

Mechanistic Study on Decarbonylative Phosphorylation of Aryl Amides by Nickel Catalysis.

The phosphorylation of amide represents an unprecedented environmentally friendly and easily achievable method to constitute C-P bonds in organic synthesis. In this study, the mechanisms for the nickel-catalyzed direct decarbonylative phosphorylation of amides recently reported by Szostak's team were systematically studied with density functional theory calculations. The reaction mainly undergoes four steps: oxidative addition (rate-determining step), phosphorylation, decarbonylation, and reductive elimination. The structures of the substrate and Na2CO3 were found to be critical for the reaction efficiency. Substrates bearing electron-withdrawing groups like carbonyl groups near the amide bond facilitate the reaction by weakening the C-N bond, and Na2CO3 can not only neutralize the H atom in the phosphate ligand as an alkali but also activate the Ni-N bond through the coordination bond with the adjacent carbonyl of the amide group.