Metal‐Free Oxidative CC Bond Formation through CH Bond Functionalization

Abstract

The formation of C-C bonds embodies the core of organic chemistry because of its fundamental application in generation of molecular diversity and complexity. C-C bond-forming reactions are well-known challenges. To achieve this goal through direct functionalization of C-H bonds in both of the coupling partners represents the state-of-the-art in organic synthesis. Oxidative C-C bond formation obviates the need for prefunctionalization of both substrates. This Minireview is dedicated to the field of C-C bond-forming reactions through direct C-H bond functionalization under completely metal-free oxidative conditions. Selected important developments in this area have been summarized with representative examples and discussions on their reaction mechanisms.

The emergence of sulfoxide and iodonio-based redox arylation as a synthetic tool

“…Interestingly, iodonium O-enolate intermediates have been invoked with both classes of hypervalent reagents, and the difference, therefore, appears to reside in the preferred class of rearrangement for each type of intermediate. 23 Thus, for the diaryliodonium species a [1,2] rearrangement dominates leading to an ipso substitution, while in the present case a [3,3] rearrangement leads to ortho products (Scheme 22).…”

“…The intermediacy of the allenyl-(aryl)iodinanes was also invoked to explain the reactivity of the aryliodanes blocked at both ortho positions. In this case the [3,3] rearrangement product is unable to rearomatize, and instead undergoes a [1,2] shift leading to meta propargylation (Scheme 5B).…”

Metal-Free &alpha;-C(sp³)&ndash;H Functionalized Oxidative Cyclization of Tertiary <em>N,N</em>-Diaryl Amino Alcohols: Theoretical Approach for Mechanistic Pathway

“…[9] Based on a literature search, we could explain that the CDC reaction resulted from the tert-amino effect. [10] However, in the study, we didn't get the clear conclusion on (1) 'what is direct reactive species for the functionalization', (2) 'which kind intermediate is dominant', (3) 'how the well-known radical trapping agent, TEMPO contribute to the reaction -direct catalyst or pre-catalyst, radical trapper or radical initiator, accelerator or controller to prevent undesired side reaction'. In this study, we considered three kind pathways: (1) the aminium radical cation 3 and the SET/PCET mechanism, (2) the α-aminoalkyl radical 4 and the HAT mechanism, (3) the conventional ionic mechanism under basic condition.…”

“…[1] Even though iodine, itself is nonmetal, iodine can behave like a transition metal including ligand exchange, oxidative addition, reductive elimination, and ligand coupling. When three-center-fourelectron (3c-4e) bond (L-I-L) (hypervalent bond) is formed by the overlap of the 5p orbital on iodine atom with the orbitals on the two ligands L, the transition metal like property can be observed well.…”

Organophotocatalytic Synthesis of Phosphoramidates

“…[2] For similar reasons, cross dehydrogenative couplings (CDCs) have become a hot topic of interest for chemists. [3] CDCs present some advantages such as no requirement of prefunctionalized starting materials and typically highly efficient, atomeconomic processes, which should be an excellent way to shorten the common synthetic routes or to introduce late-functionalization for interesting scaffolds. In our research group, we are interested in the development of green organocatalytic reactions that allow us to build new atom-atom σ-bonds.…”