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An intramolecular rhodium-catalyzed transannulation of readily available cyanothiadiazoles containing an ester, amide, or ether as a linker is described. It provides a wide range of bicyclic isothiazoles in good to excellent yields together with the release of molecular nitrogen. These results indicate that the carbon atom in the α-thiavinyl carbene is nucleophilic and that the sulfur atom is electrophilic.

An efficient synthetic method for the selective preparation of dihydrophosphaisocoumarins and their derivatives was developed through a palladium-catalyzed oxidative cyclization reaction of a wide range of arylphosphonic acid monoethyl esters with activated and unactivated 1,3-dienes, including 1-aryl-substituted 1,3-dienes and 1-alkyl-substituted 1,3-dienes, thus opening a new avenue for the synthesis of phosphaheterocyclic compounds.

A synthetic method for obtaining a wide variety of isothiazoles by the Rh-catalyzed transannulation of 1,2,3-thiadiazoles with alkyl, aryl, and heteroaryl nitriles, which proceeds via an α-thiavinyl Rh-carbenoid intermediate, was developed. The results suggest that during its reaction with nitriles, the α-thiavinyl carbene acts as an umpolung 1,3-dipole equivalent, in contrast to its behavior during its reaction with alkynes. The developed method was successfully employed to synthesize pentaoligomeric arylene compounds consisting of three benzene and two isothiazole rings.

Sequential copper-catalyzed [3+2] cycloaddition, rhodium-catalyzed OH insertion, intramolecular 1,8-addition, and rearrangement starting from 1-alkynes, N-sulfonyl azides, and tropolones is demonstrated for the synthesis of the 2-functionalized aminotropones in one pot. These results indicate that sequential functionalization of OH and C(sp2)O bonds smoothly occurs in the C(sp2)OH bonds of tropolone

Alkenylation of phosphacoumarins is developed from the reaction of phosphacoumarins with a variety of activated as well as nonactivated alkenes via aerobic oxidative Heck reactions. In addition, 3-alkenylphosphacoumarins undergo an inverse electron demand Diels-Alder reaction (IEDDA) with enamines in situ generated from ketone and pyrrolidine followed by 1,2-elimination and a dehydrogenation, producing fluorescent benzophosphacoumarins.

An efficient synthetic method of fluorenes having an enamine moiety at C-9 methylene bridge is developed from N-sulfonyl-4-biaryl-1,2,3-triazole derivatives via Rh-catalyzed denitrogenative cyclization in a 5-exo mode. Rh-catalyzed denitrogenative cyclization followed by catalytic hydrogenation produces N-tosylaminomethyl-substituted fluorenes in one pot. Moreover, fluorenes are synthesized via tandem Cu-catalyzed [3 + 2] cycloaddition and Rh-catalyzed denitrogenative cyclization in a 5-exo mode starting from 2-ethynylbiaryls and N-sulfonyl azides in one pot.

The Cu-catalyzed, formal aza-[3 + 2] cycloaddition reaction of pyridine derivatives with α-diazo oxime ethers in trifluoroethanol was used to synthesize imidazopyridines via the release of molecular nitrogen and elimination of alcohol. These methods enabled modular synthesis of a wide range of N-heterobicyclic compounds such as imidazopyridazines, imidazopyrimidines, and imidazopyrazines with an α-imino Cu-carbenoid generated from the α-diazo oxime ethers and copper.

Diethyl bromoalkylphosphonates are coupled with a broad variety of aryl iodides via intermediate alkylindium species to give the corresponding arylalkylphosphonates in moderate to good yields.

Phosphoryl alkylindium reagents are generated in situ from the direct insertion of indium with bromoalkyl phosphonates in the presence of CuCl, and their synthetic application to arylalkyl phosphonates is reported via a Pd-catalyzed cross-coupling reaction with tolerance of a diversity of functional groups including ester, ketone, aldehyde, nitrile, nitro, trifluoromethyl, chloride, methoxy, hydroxy, and amino.

A method for synthesis of substituted pyrroles has been developed. 1-Sulfonyl-1,2,3-triazoles generated from terminal alkynes gave α-imino rhodium carbene complexes, which when reacted with alkenyl alkyl ethers afforded substituted pyrroles. The method can be efficiently applied to a one-pot sequential reaction starting from terminal alkynes.

A tyrosinase inhibitor was isolated from the whole plant of Barbarea orthocerus Led. (Brassicaceae) by activity-guided fractionation, and identified as (R)-5-phenyl-2-oxazolidinethione (barbarin) by structural analysis followed by comparison with reported spectral data. The compound exhibited significant inhibitory effects on mushroom and murine tyrosinases at more than 1.6 × 10 -5 M. Barbarin exhibited IC 50 values of 4.2 × 10 -5 M on mushroom tyrosinase and of 4.8 × 10 -5 M on murine tyrosinase. Kojic acid as a positive control exhibited IC 50 values of 3.4 × 10 -5 M and 6.0 × 10 -5 M on mushroom and murine tyrosinases, respectively. Therefore, barbarin exhibited a similar level of inhibitory potency with kojic acid used as a positive control. In a kinetic study with various concentrations of L-dopa as the substrate, barbarin was identified as an uncompetitive inhibitor and kojic acid as a mixed inhibitor of both mushroom and murine tyrosinases. Barbarin exhibited K EIS values of 3.3 × 10 -5 M and 3.6 × 10 -5 M on mushroom and murine tyrosinases, respectively. Kojic acid exhibited K EIS and K EI values of 2.4 × 10 -5 M and 2.2 × 10 -5 M on mushroom tyrosinase and those of 8.9 × 10 -5 M and 7.2 × 10 -5 M on murine tyrosinase, respectively.