Unstrained CarbonCarbon Bond Cleavage

Abstract

This Focus Review presents recent developments in the cleavage of C-C bonds in organic molecules. Significant progress in C-C activation, including the development of a variety of new synthetic strategies, has contributed to the development of this field over the past few decades. Transition-metal-mediated C-C bond cleavage has been shown to be a quite efficient process and several elegant metal-free methods have also recently been developed. Strained rings have been widely used in C-C cleavage transformations; however, unstrained C-C activation has increasingly caught the attention of organic researchers, which inspired us to clarify the developments in this field.

Copper‐Catalyzed Aerobic Oxidative Cleavage of Unstrained Carbon‐Carbon Bonds of 1,1‐Disubstituted Alkenes with Sulfonyl Hydrazides

“…Catalytic and selective cleavage of carbon‐carbon bonds, which would provide a complementarily powerful strategy to organic transformation, remains less explored and underdeveloped in organic chemistry due to the difficulties associated with discriminating the carbon‐hydrogen and carbon‐carbon bonds and thermodynamically stability of C—C σ bond in organic molecules. [ 1 ] In order to conquer the above challenges, the well‐developed C—C bond cleavage reactions usually depend on specific substrates bearing strained rings, chelation‐assisted groups or electron‐withdrawing groups to polarize the C—C bonds. [ 2 ] Thus, the development of a general and more efficient strategy for selective C—C bond cleavage remains highly desirable.…”

Breaking C–C Bonds via Electrochemically Mediated Hydrogen Atom Transfer Reactions

“…[1][2][3][4][5][6] However, the inertness of the Csp3-Csp3 linkages hinders the selective and energy-efficient bond scission in these substrates. [7][8][9] Indeed, Csp3-Csp3 bond activation is difficult due to several thermodynamic and kinetic constraints, [10][11][12][13][14] including high bond dissociation energies (BDEs) of ~90 kcal mol −1 , 10 steric inaccessibility caused by surrounding C-H bonds, and unfavorable orbital directionality towards cleavage which requires the rotation of two carbon sp 3 orbitals. 15 In some cases, C-C bond scission is facile, for example, for three-or four-membered cycloalkanes with high ring strain, for structures that introduce aromaticity upon cleavage (e.g., the elimination of a methyl group of ergosterol converts its cyclohexadiene ring into a phenyl ring), or for reactants that coordinate strongly to an active site (e.g., pincer-type compounds chelate to the catalyst metal center to direct the C-C bond cleavage).…”

Iodine‐Catalyzed Aerobic Oxidative Cleavage of C–C δ‐Bonds: Difunctionalization of Dienones

“…In conventional methodologies, the oxidative C–C bond cleavage protocol is carried out with transition metals in combination with oxidants. Although this method is still often used, it presents severe drawbacks such as the use of toxic transition metals and an excess of stoichiometric oxidants, and the generation of large amounts of by‐products To address these concerns, metal‐free methods have emerged for the direct C–C σ‐bond oxidative cleavage . The fascinating development in this direction is the metal‐free oxidative cleavage with molecular oxygen as oxidant, which include the base‐, and in situ formed enamine‐ promoted or mediated, and auto‐oxidative cleavage method .…”