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We disclose an iridium(III)-catalyzed regioselective B(4)–H allenylation of o-carboranes from o-carborane acids and propargyl carbonates under ball-milling conditions. This study sheds light on a novel method to accomplish regioselective B(4)-allenylation of o-carborane that cannot be realized through conventional solution-based reactions. Control experiments, including solution, neat, microwave, and high-temperature reactions, reveal that the B(4)–H allenylation of o-carborane is unique for ball-milling conditions.

An iridium(III)-catalyzed regioselective acylmethylation of the cage B(4)–H bond in o-carborane acids with sulfoxonium ylides is demonstrated through B(4)–H activation in ethanol under very mild conditions, affording a number of B(4)-acylmethylated o-carboranes. Additionally, the selective sequential B(4)- and B(6)-acylmethylation reactions finally gave B(3,5)-diacylmethylated o-carboranes in one pot.

A direct B(4)–H monoacyloxylation via a Pd-catalyzed regioselective B(4)–H activation of o-carborane acids with phenyliodonium dicarboxylates was developed, and a series of B(4)–H monoacyloxylated o-carboranes decorated with active groups were synthesized with moderate to good yields as well as excellent selectivity. In addition, a direct B(4,5)–H diacetoxylation from o-carborane acids with phenyliodonium diacetate was demonstrated.

Mechanochemistry was successfully applied to the functionalization of carboranes. The mechanochemical iridium(III)-catalyzed regioselective B(3)- and B(4)-amidation of unsubstituted o-carboranes with dioxazolones was developed. In addition, the mechanochemical iridium(III)-catalyzed regioselective B(4)-amidation of substituted o-carboranes was demonstrated. Because mechanochemical B-amidation proceeds smoothly without organic solvents or external heating, the present method is regarded as a sustainable and environmentally friendly surrogate for typical solvent-based reactions.

Described is the Ir-catalyzed cage B(4)-amidation of o-carboranes with dioxazolones by carboxylic acid-assisted B(4)–H bond activation under extremely mild conditions, affording amidated o-carboranes and amidated and methoxycarbonylated nido-carboranes through sequential B(4)-amidation, O-methylation, and B(3)-deboronation in one pot. Carboxylic acid used as a directing group after the cage B(4)-amidation is efficiently trapped by trimethylsilyldiazomethane instead of undergoing decarboxylation. Mechanism studies demonstrated that the O-methylation through trapping of acid occurred first, followed by the B(3)-deboronation.

Described herein is the first iridium-catalyzed cyclative indenylation through sequential B(4)–C and intramolecular C–C bond formation from o-carboranes and propargyl alcohols, leading to the formation of B(4)-indenylated o-carboranes with excellent regioselectivity via direct B–H activation. Moreover, the iridium-catalyzed regioselective 1,3-dienylation has been accessed through sequential B–H activation, dehydration, and decarboxylation, producing B(4)-dienylated o-carboranes.

Rhodium-catalyzed oxidative [4 + 2] cyclization reactions through the C–H activation of azulene carboxylic acids as nonbenzenoid aromatic compounds with symmetrical and unsymmetrical alkynes were developed under aerobic conditions, which produced azulenolactone derivatives with a wide substrate scope and excellent functional group tolerance. Interestingly, azulenic acids in reaction with alkynes underwent iridium-catalyzed [2 + 2 + 2] cyclization accompanied by decarboxylation to afford tetra(aryl)-substituted benzoazulene derivatives. The reactivity order for C–H activation reaction is greater toward azulene-6-carboxylic acid, azulene-1-carboxylic acid, and azulene-2-carboxylic acid. For the first time, the expansion of azulenes having directing group as nonbenzenoid aromatic compounds for C–H activation was successful, indicating that nonbenzenoid aromatic compounds can be used as good substrates for the C–H activation reaction. Therefore, the research area of C–H activation will certainly expand to nonbenzenoid aromatic compounds in future.

A synthetic method for ethyl 4‐(alkyl or arylsulfonamido)‐2‐naphthoates from ethyl (E)‐α‐ethynyl‐β‐aryl‐α,β‐unsaturated esters (1) and N‐sulfonyl azides (2) in the presence of 2,6‐lutidine in THF at 60 °C for 3 h was developed in one step, in which a copper(I)‐catalyzed 1,3‐dipolar cycloaddition, ketenimine formation, and 6π‐electrocyclization followed by [1,3]‐H shift tandem reaction took place. This method enabled efficient synthesis of a wide range of 1‐aminonaphthalene and 3‐aminobenzofuran and 3‐aminobenzothiophene derivatives with the release of molecular nitrogen. Copper(I)‐catalyzed cyclization reactions of ethyl (E)‐α‐ethynyl‐β‐aryl‐α,β‐unsaturated esters with N‐sulfonyl azides for the synthesis of 1‐aminonaphthalenes, 3‐aminobenzofurans, and 3‐aminothiobenzofurans

Iridium(III)-catalyzed regioselective B(4)–H amination is developed from the reaction of o-carborane acids with sulfilimines without any oxidants under mild conditions, which leads to a wide range of B(4)–H aminated o-carboranes in good yields with a broad substrate scope. Moreover, the selective B(3,6)-diamination reaction of the o-carborane acid was achieved. The present reaction is attractive from a practical point of view because dibenzothiophene is quantitatively recovered and reused.

Iridium(III)-catalyzed C–H cyclization of sulfoximines with diazo Meldrum’s acid provided cyclic sulfoximines with a carbonyl group in good to excellent yields. These compounds were easily converted into unsubstituted and arylated sulfoximines. Moreover, the vinyl triflates obtained from the cyclic sulfoximines underwent palladium(II)-catalyzed cross-coupling reactions with a variety of aryl, arylalkynyl, and heteroatom (N and S) nucleophiles, affording a wide range of monosubstituted sulfoximines in high yields.

Transition-metal-free synthetic method for o-carborane-fused pyrazoles as a new scaffold has been developed from the reaction of B(4)-acylmethyl or B(3,5)-diacylmethyl o-carborane with 2-azido-1,3-dimethylimidazolinium hexafluorophosphate (ADMP) in the presence of DBU in acetonitrile through sequential diazotization and cyclization reaction in one pot, consequently allowing twofold C–N bond formation under extremely mild conditions and high functional group tolerance.