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.

Rhodium(III)-Catalyzed Redox-Neutral [4 + 1]-Annulation of Unactivated Alkenes with Sulfoxonium Ylides.

A novel methodology for redox-neutral [4 + 1] annulation of unactivated alkenes with sulfoxonium ylides leads to the synthesis of a diverse library of indanone compounds. The developed annulation reaction was found to be highly versatile due to its compatibility with various unactivated alkenes functionalized with various sensitive functional groups as well as substituted sulfoxonium ylides. Further, multiple transformations such as ring-expansion, reduction, aldol condensation, and Wittig reaction were carried out with indanones. Using this way, highly useful cyclic heterocycles such as indene, dihydroisocoumarin, and 1-indanilidene were prepared in a single step. A possible reaction mechanism was supported by deuterium labeling studies, competitive studies, and kinetic isotopic studies.

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.

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

The Ir(III)-catalyzed direct allylic C-H amidation of substituted internal alkenes with substituted sulfonamides without having directing group is demonstrated. The present protocol provides substituted allylic amines in a highly atom- and step-economical manner. The reaction was compatible with symmetrical and unsymmetrical internal alkenes as well as substituted sulfonamides. It is interesting to note that, in the reaction of aryl-alkyl alkenes, the amidation selectively takes place at the alkyl-substituted allylic carbon. Meanwhile, the better selectivity was also observed in the unsymmetrical aryl-aryl alkenes having an electron-withdrawing substituent at one of the aryl groups. A possible reaction mechanism involving a π-allyl iridium intermediate was proposed and supported by the deuterium labeling studies. The deuterium labeling study clearly reveals that, in the reaction mechanism, the initial C-H activation step via the deprotonation pathway is reversible and the nucleophile prefers to attack at the more electrophilic carbon of the π-allyl iridium intermediate.

Regioselective Synthesis of Isocoumarins via Iridium(III)-Catalyzed Oxidative Cyclization of Aromatic Acids with Propargyl Alcohols.

An Ir(III)-catalyzed oxidative cyclization of benzoic acids with propargyl alcohols to give substituted isocoumarins in a highly regioselective manner is described. This protocol has a broad substrate scope with high functional group tolerance. The observed isocoumarins were converted into biologically active tetracyclic indeno[2,1- c]isocoumarins by Lewis acid-mediated cyclization. A possible reaction mechanism is proposed and strongly supported by the detailed mechanistic investigation and DFT.