Masakazu Nambo

Aziridinofullerene: A Versatile Platform for Functionalized Fullerenes

An aziridine moiety on the fullerene core can serve as an acid-triggered reacting template for the controlled synthesis of a range of functionalized fullerenes that are otherwise difficult to synthesize in an efficient and selective manner. A copper-catalyzed aziridination of C(60) for the practical synthesis of aziridinofullerene 1 and acid-catalyzed reactions of 1 with mono- and bifunctional nucleophiles as well as alkynes are described. The rapid generation of structural diversity in a single chemical operation using the common platform 1 is notable.

Modular Synthesis of Triarylmethanes through Palladium-Catalyzed Sequential Arylation of Methyl Phenyl Sulfone†

Triarylmethanes, which are valuable structures in materials, sensing and pharmaceuticals, have been synthesized starting from methyl phenyl sulfone as an inexpensive and readily available template. The three aryl groups were installed through two sequential palladium-catalyzed C-H arylation reactions, followed by an arylative desulfonation. This method provides a new synthetic approach to multisubstituted triarylmethanes using readily available haloarenes and aryl boronic acids, and is also valuable for the preparation of unexplored triarylmethane-based materials and pharmaceuticals.

A bench-stable Pd catalyst for the hydroarylation of fullerene with boronic acids.

A Pd(II) catalyst for the hydroarylation of fullerene with boronic acids is presented. Treatment of C60 with an arylboronic acid in the presence of a catalytic amount of Pd(2-PyCH=NPh)(OCOC6F5)2 in H2O/1,2-Cl2C6H4 at room temperature furnishes the hydroarylation product (Ar-C60-H) in good yield with high selectivity. This complex possesses high catalytic activity paired with bench stability in the solid state.

The Concise Synthesis of Unsymmetric Triarylacetonitriles via Pd-Catalyzed Sequential Arylation: A New Synthetic Approach to Tri- and Tetraarylmethanes

The selective synthesis of multiarylated acetonitriles via sequential palladium-catalyzed arylations of chloroacetonitrile is reported. The three aryl groups are installed via a Pd-catalyzed Suzuki-Miyaura cross coupling reaction followed by back-to-back C-H arylations to afford triarylacetonitriles in three steps with no over-arylation at any step. The triarylacetonitrile products can be converted into highly functionalized species including tetraarylmethanes. This new strategy provides rapid access to a variety of unsymmetrical tri- and tetraarylmethane derivatives from simple, readily available starting materials.

Regioselective Unsymmetrical Tetraallylation of C60 through Palladium Catalysis

A Pd-catalyzed tetraallylation of C(60) that selectively occurs with an unsymmetrical addition pattern has been established. Treatment of C(60) with CH(2)=CHCH(2)Cl, CH(2)=CHCH(2)SnBu(3), and PdCl(2)[P(OPh)(3)](2) in 1,2-Cl(2)C(6)H(4) at 50 degrees C afforded the tetraallylated fullerene in 74% yield with virtually complete regioselectivity. Mechanistic investigations showed that (i) tetraallylation proceeds through consecutive nucleophilic/electrophilic allylations [likely via a bis(pi-allyl)palladium intermediate] and (ii) both steric (for the first diallylation) and electronic (for the second diallylation) factors are responsible for the high regioselectivity.

Iterative protecting group-free cross-coupling leading to chiral multiply arylated structures.

The Suzuki–Miyaura cross-coupling is one of the most often utilized reactions in the synthesis of pharmaceutical compounds and conjugated materials. In its most common form, the reaction joins two sp2-functionalized carbon atoms to make a biaryl or diene/polyene unit. These substructures are widely found in natural products and small molecules and thus the Suzuki–Miyaura cross-coupling has been proposed as the key reaction for the automated assembly of such molecules, using protecting group chemistry to affect iterative coupling. We present herein, a significant advance in this approach, in which multiply functionalized cross-coupling partners can be employed in iterative coupling without the use of protecting groups. To accomplish this, the orthogonal reactivity of different boron substituents towards the boron-to-palladium transmetalation reaction is exploited. The approach is illustrated in the preparation of chiral enantioenriched compounds, which are known to be privileged structures in active pharmaceutical compounds.

Palladium‐Catalyzed Carbon–Carbon Bond Formation and Cleavage of Organo(hydro)fullerenes

Palladium can tailor fullerenes: Palladium catalysts enable a number of C-H bond transformations of organo(hydro)fullerene. In addition to anticipated coupling reactions (C-H bond allylation and arylation), an unexpected new C-H bond dimerization reaction and C-C bond-cleavage reaction were also uncovered.

Water‐Soluble N‐Heterocyclic Carbene‐Protected Gold Nanoparticles: Size‐Controlled Synthesis, Stability, and Optical Properties

NHC-AuI complexes were used to prepare stable, water-soluble, NHC-protected gold nanoparticles. The water-soluble, charged nature of the nanoparticles permitted analysis by polyacrylamide gel electrophoresis (PAGE), which showed that the nanoparticles were highly monodisperse, with tunable core diameters between 2.0 and 3.3 nm depending on the synthesis conditions. Temporal, thermal, and chemical stability of the nanoparticles were determined to be high. Treatment with thiols caused etching of the particles after 24 h; however larger plasmonic particles showed greater resistance to thiol treatment. These water-soluble, bio-compatible nanoparticles are promising candidates for use in photoacoustic imaging, with even the smallest nanoparticles giving reliable photoacoustic signals.

Arylative Desulfonation of Diarylmethyl Phenyl Sulfone with Arenes Catalyzed by Scandium Triflate

A scandium-triflate-catalyzed arylative desulfonation of diarylmethyl phenyl sulfones with arenes and heteroarenes was established. A variety of both sulfone and arene substrates were reacted to afford symmetric and nonsymmetric triarylmethanes in good yields. Further transformations of the resulting triarylmethanes and application to the concise synthesis of a bactericidal agent analogue were also demonstrated.

Selective Introduction of Organic Groups to C60 and C70 Using Organoboron Compounds and Rhodium Catalyst: A New Synthetic Approach to Organo(hydro)fullerenes

A Rh-catalyzed reaction of C(60) and C(70) with organoboron compounds is described. This new catalytic method enables introduction of various organic groups onto C(60) and C(70). [Rh(cod)(MeCN)(2)]BF(4) proved to be the most effective catalyst in terms of productivity and selectivity. The reaction generally proceeds with a high regioselectivity and in a mono-addition selective manner. It was found that water is an essential additive to promote the reaction. By X-ray crystal structure analysis, we have confirmed the reaction site of organometallic-based hydroarylation of C(70) for the first time. Various functional fullerenes, such as fullerene-tagged amino acids and fullerene-capped π systems, can be synthesized. The X-ray crystal structure of biphenyl-attached C(60) revealed an interesting opportunity for the well-organized alignment of bucky balls by taking advantage of CH-π interactions.