Congyang Wang

Manganese‐Catalyzed Dehydrogenative [4+2] Annulation of NH Imines and Alkynes by CH/NH Activation

Described herein is a manganese-catalyzed dehydrogenative [4+2] annulation of NH imines and alkynes, a reaction providing highly atom-economical access to diverse isoquinolines. This transformation represents the first example of manganese-catalyzed CH activation of imines; the stoichiometric variant of the cyclomanganation was reported in 1971. The redox neutral reaction produces H2 as the major byproduct and eliminates the need for any oxidants, external ligands, or additives, thus standing out from known isoquinoline synthesis by transition-metal-catalyzed CH activation. Mechanistic studies revealed the five-membered manganacycle and manganese hydride species as key reaction intermediates in the catalytic cycle.

Manganese‐Catalyzed Direct Nucleophilic C(sp2)H Addition to Aldehydes and Nitriles

Herein, a manganese-catalyzed nucleophilic addition of inert C(sp(2))-H bonds to aldehydes and nitriles is disclosed by virtue of a dual activation strategy. The reactions feature mild reaction conditions, excellent regio- and stereoselectivity, and a wide substrate scope, which includes both aromatic and olefinic C-H bonds, as well as a large variety of aldehydes and nitriles. Moreover, mechanistic studies shed light on possible catalytic cycles.

Iron‐Carbonyl‐Catalyzed Redox‐Neutral [4+2] Annulation of N−H Imines and Internal Alkynes by C−H Bond Activation

Stoichiometric C-H bond activation of arenes mediated by iron carbonyls was reported by Pauson as early as in 1965, yet the catalytic C-H transformations have not been developed. Herein, an iron-catalyzed annulation of N-H imines and internal alkynes to furnish cis-3,4-dihydroisoquinolines is described, and represents the first iron-carbonyl-catalyzed C-H activation reaction of arenes. Remarkablely, this is also the first redox-neutral [4+2] annulation of imines and alkynes proceeding by C-H activation. The reaction also features only cis stereoselectivity and excellent atom economy as neither base, nor external ligand, nor additive is required. Experimental and theoretical studies reveal an oxidative addition mechanism for C-H bond activation to afford a dinuclear ferracycle and a synergetic diiron-promoted H-transfer to the alkyne as the turnover-determining step.

Aromatic C-H addition of ketones to imines enabled by manganese catalysis

Selectivity control of varied C–H bonds in a complex molecule is a long-standing goal and still a great challenge in C–H activation field. Most often, such selectivity is achieved by the innate reactivity of different C–H bonds. In this context, the classic Mannich reaction of acetophenone derivatives and imines is ascribed to the more reactive C(sp3)–H bonds α to the carbonyl, with the much less reactive aromatic C(sp2)–H bonds remaining intact. Herein we report an aromatic C(sp2)–H addition of ketones to imines enabled by manganese catalysis, which totally reverses the innate reactivity of C–H bonds α to the carbonyl and those on the aromatic ring. Diverse products of ortho-C–H aminoalkylated ketones, cyclized exo-olefinic isoindolines, and three-component methylated isoindolines can be successfully accessed under mild reaction conditions, which significantly expands the synthetic utilities of ketones as simple bulk chemicals.The Mannich reaction proceeds by functionalization of C(sp3)-H bonds alpha to carbonyls. Here, the authors suppress the Mannich reactivity of acetophenones in presence of a manganese catalyst and obtain valuable o-aminoalkylacetophenones and isoindolines via C(sp2)-H functionalization with imines.

Dichotomy of Manganese Catalysis via Organometallic or Radical Mechanism: Stereodivergent Hydrosilylation of Alkynes

Herein, we disclose the first manganese-catalyzed hydrosilylation of alkynes featuring diverse selectivities. The highly selective formation of E-products was achieved by using mononuclear MnBr(CO)5 with the arsenic ligand, AsPh3 . Whereas using the dinuclear catalyst Mn2 (CO)10 and LPO (dilauroyl peroxide) enabled the reversed generation of Z-products in good to excellent stereo- and regioselectivity. Such a way of controlling the reaction stereoselectivity is unprecedented. Mechanistic experiments revealed the dichotomy of manganese catalysis via organometallic and radical pathways operating in the E- and Z-selective routes, respectively.