Manganese(I)‐Catalyzed C−H Activation: The Key Role of a 7‐Membered Manganacycle in H‐Transfer and Reductive Elimination

Abstract

Manganese‐catalyzed C−H bond activation chemistry is emerging as a powerful and complementary method for molecular functionalization. A highly reactive seven‐membered MnI intermediate is detected and characterized that is effective for H‐transfer or reductive elimination to deliver alkenylated or pyridinium products, respectively. The two pathways are determined at MnI by judicious choice of an electron‐deficient 2‐pyrone substrate containing a 2‐pyridyl directing group, which undergoes regioselective C−H bond activation, serving as a valuable system for probing the mechanistic features of Mn C−H bond activation chemistry.

Polycyclization Enabled by Relay Catalysis: One‐Pot Manganese‐Catalyzed C−H Allylation and Silver‐Catalyzed Povarov Reaction

“…On the basis of the above results and preceding reports, a mechanistic scenario was proposed to rationalize the reaction outcome (Scheme ). Initially, an imine‐assisted C−H activation takes place to yield intermediate B .…”

Manganese‐Catalyzed C−H Alkynylation: Expedient Peptide Synthesis and Modification

“…[4] While most C À Ht ransformations were thus far accomplished with the aid of precious transition metals,t he use of earth-abundant base metal catalysts has gained recent momentum, [5] with considerable progress accomplished by less toxic manganese catalysts. [6] However,d espite recent advances by the groups of Wang, Kuninobu, Fairlamb,a nd Ackermann, among others, [7][8][9][10][11] the organometallic manganese C À Hactivation regime is severely limited to addition reactions onto multiple CÀHet or CÀC bonds.I ndeed, in stark contrast to other [12] transition metals, [13] manganese-catalyzed substitutive CÀHa ctivation with organic halides have proven to be elusive.W ithin our program on sustainable C À Ha ctivation, [14] we have now established the first manganese-catalyzed C À Hfunctionalization with organic halides,o nw hich we report herein. In addition to the conceptual advance,n otable features of our approach include 1) versatile CÀHa lkynylations by manganese(I) catalysis with silyl, aryl, and alkyl haloalkynes, 2) as ignificant rate acceleration through as ynergistic catalysis manifold, and 3) robust C À Ha lkynylations for the latestage modification of peptides,thereby 4) setting the stage for versatile syntheses and modifications [15] of densely decorated acyclica nd cyclic peptides (Figure 1).…”

Manganese‐Catalyzed C−H Olefination Reactions

“…The coordination of alkyne to Mn-1 followed by insertion delivered sevenmembered manganacycle Mn-3, whose key role in the catalytic cycle was confirmed by Fairlamb, Lynam and coworkers. [14] After Mn-3 reacted with the second alkyne, the CÀ Mn bond of the resulting Mn-4 was quenched through a ligand-to-ligand hydrogen transfer pathway, giving the formation of Mn-5. It next underwent ligand exchange with 2-phenylpyridine to generate the olefinated product and liberate alkynylmanganese Mn-6.…”