Iridium(III)-Catalyzed Intermolecular Allylic C–H Amidation of Internal Alkenes with Sulfonamides

Rhodium-Catalyzed Allylic C-H Functionalization of Unactivated Alkenes with α-Diazocarbonyl Compounds

A redox-neutral mild methodology for the allylic C-H alkylation of unactivated alkenes with diazo compounds is demonstrated. The developed protocol is able to bypass the possibility of the cyclopropanation of an alkene upon its reaction with the acceptor-acceptor diazo compounds. The protocol is highly accomplished due to its compatibility with various unactivated alkenes functionalized with different sensitive functional groups. A rhodacycle π-allyl intermediate has been synthesized and proved to be the active intermediate. Additional mechanistic investigations aided the elucidation of the plausible reaction mechanism.

Comprehensive Theoretical Study of Cp*IrIII-Catalyzed Intermolecular Enantioselective Allylic C-H Amidation: Reaction Mechanism, Electronic Processes, and Regioselectivity

Density functional theory was used to elucidate the reaction mechanism of Cp*Ir^III-catalyzed intermolecular regioselective C(sp³)-H amidation of alkenes with methyl dioxazolones. All substrates, intermediates, and transition states were fully optimized at the ωB97XD/6-31G(d,p) level (LANL2DZ(f) for Ir). The computational results revealed that this amidation occurred through the Ir^III/Ir^V catalytic cycle, involving four important elementary steps: C-H bond activation, oxidative addition of methyl dioxazolone, reductive elimination, and proto-demetalation, and the first was the rate-determining step. The C-H bond activation showed good α- and branch-regioselectivity, decided by the distortion energy of 2-pentene and the interaction energy of the transition state, respectively. The oxidative addition of dioxazolone occurred in one elementary step with CO₂ disassociation. The reductive elimination showed good branch-regioselectivity determined by the distorted energy of the allyl group. In the proto-demetalation, hydrogen directly transferred from the oxygen atom to the nitrogen atom. Moreover, to clarify the effect of the substituted groups, selected 12 substrates were also discussed in this text.

Looking deep into C-H functionalization: the synthesis and application of cyclopentadienyl and related metal catalysts

Metal catalyzed C-H functionalization offers a versatile platform for methodology development and a wide variety of reactions now exist for the chemo- and site-selective functionalization of organic molecules. Cyclopentadienyl-metal (CpM) complexes of transition metals and their correlative analogues have found widespread application in this area, and herein we highlight several key applications of commonly used transition-metal Cp-type catalysts. In addition, an understanding of transition metal Cp-type catalyst synthesis is important, particularly where modifications to the catalyst structure are required for different applications, and a summary of this aspect is given.

A New Dioxazolone for the Synthesis of 1,2-Aminoalcohols via Iridium(III)-Catalyzed C(sp3 )-H Amidation

Vicinal aminoalcohols are widespread structural motifs in bioactive molecules. We report the development of a new dioxazolone reagent containing a p-nitrophenyldifluoromethyl group, which 1. displays a good safety profile; 2. shows a remarkably high reactivity in the oxime-directed iridium(III)-catalyzed amidation of unactivated C(sp3 )-H bonds; 3. leads to amide products which can be hydrolyzed under mild conditions. The amidation reaction is mild, general and compatible with both primary C-H bonds of tertiary and secondary alcohols, as well as secondary C-H bonds of cyclic secondary alcohols. This method provides an easy access to free 1,2-aminoalcohols after efficient and mild cleavage of the oxime directing group and activated amide.

Rh(III)-Catalyzed allylic C-H amidation of unactivated alkenes with in situ generated iminoiodinanes

Rh(iii)-catalyzed allylic C-H amidation of substituted alkenes with in situ generated iminoiodinanes is demonstrated. The presented protocol is compatible with differently functionalized unactivated terminal alkenes and internal alkenes. In terminal alkenes, branch selectivity was observed exclusively. Based on the detailed mechanistic investigation, a possible reaction mechanism involving the in situ generated π-allyl as well as metal-nitrene intermediates has been proposed.

Electro-oxidative Intermolecular Allylic C(sp3)-H Aminations

The oxidative intermolecular nitrogenation of C(sp³)-H bonds represents one of the most straightforward strategies to construct nitrogen-containing molecules. However, a sacrificial chemical oxidant is generally required. Herein, we describe electrochemical oxidative intermolecular allylic C(sp³)-H aminations in an undivided cell by electric current. The cross-dehydrogenative amination proceeded efficiently with ample scope under metal- and chemical oxidant-free reaction conditions, giving molecular H₂ as the only byproduct.

Mechanistic studies of Cp*Ir(III)/Cp*Rh(III)-catalyzed branch-selective allylic C-H amidation: why is Cp*Ir(III) superior to Cp*Rh(III)?

Density functional theory calculations have revealed the mechanism and origins of the reactivity and regioselectivity of the Cp*Ir(iii)/Cp*Rh(iii)-catalyzed allylic C-H amidation of alkenes and dioxazolones. Generally, the catalytic cycle consists of alkene coordination, C(sp3)-H activation, dioxazolone oxidative addition, reductive elimination and proto-demetallation to give the final amidation product. The C-H activation is found to be the rate-determining step, and it controls the reactivity of the reaction. For the Cp*Ir(iii)-catalyzed system, the C-H activation undergoes an Ir(iii)-assisted proton transfer process with a low energy barrier, elucidating its high reactivity. In contrast, the C-H activation step is more like a direct deprotonation in the Cp*Rh(iii)-catalyzed system, which is responsible for its higher barrier and lower reactivity. The branched-selectivity arises from the electronic effect of the alkyl group on the charge distribution over the allylic moiety. Herein, iridium(v) polarizes the allylic group greater than that of the rhodium(v) system, which accounts for its good regioselectivity. The mechanistic insights will be useful for the further development of transition metal-catalyzed selective C-H amination reactions.

Recent advances in oxidative allylic C-H functionalization via group IX-metal catalysis

Allylic substitution, pioneered by the work of Tsuji and Trost, has been an invaluable tool in the synthesis of complex molecules for decades. An attractive alternative to allylic substitution is the direct functionalization of allylic C-H bonds of unactivated alkenes, thereby avoiding the need for prefunctionalization. Significant early advances in allylic C-H functionalization were made using palladium catalysis. However, Pd-catalyzed reactions are generally limited to the functionalization of terminal olefins with stabilized nucleophiles. Insights from Li, Cossy, and Tanaka demonstrated the utility of RhCp^x catalysts for allylic functionalization. Since these initial reports, a number of key intermolecular Co-, Rh-, and Ir-catalyzed allylic C-H functionalization reactions have been reported, offering significant complementarity to the Pd-catalyzed reactions. Herein, we report a summary of recent advances in intermolecular allylic C-H functionalization via group IX-metal π-allyl complexes. Mechanism-driven development of new catalysts is highlighted, and the potential for future developments is discussed.

Allylic C–H functionalization via group 9 π-allyl intermediates

This perspective presents an analysis of how reagent choice impacts mechanism and regioselectivity in group 9-catalysed allylic C–H functionalization.