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.

An efficient synthetic route to a wide range of trisubstituted pyrazines is developed from Rh-catalyzed reaction of 2H-azirines with N-sulfonyl-1,2,3-triazoles through the elimination of nitrogen molecule and arylsulfinic acid. The present reaction proceeds through formation of in situ generated dihydropyrazines.

Dicobalt octacarbonyl-catalyzed carbonylative cyclization of pyridinyl diazoacetates is developed for the synthesis of pyridoisoquinolinones under mild conditions (room temperature) in a carbon monoxide atmosphere. Moreover, a synthetic method for various pyridoisoquinolinones from ethylpyridinyl aryl acetates is demonstrated through diazotization using TsN3 and DBU followed by Co-catalyzed carbonylation to generate ketene intermediates, which can subsequently undergo intramolecular cyclization under mild conditions in a carbon monoxide atmosphere in a semi-one-pot fashion.

An efficient, one-pot synthetic method for producing functionalized indolizine derivatives was developed via a Rh-catalyzed [2 + 1]-cyclopropanation, Pd-catalyzed ring expansion, and subsequent oxidation using manganese dioxide from pyridotriazoles and 1,3-dienes.

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.