Hironori Maeda

DNA‐Mediated Palladium Nanoparticles as an Efficient Catalyst for Hydrogenation‐ and Suzuki–Miyaura Coupling Reactions

It is well-known that heterogeneous catalysts, such as palladium on carbon (Pd/C), are used in a number of oxidationand reduction reactions because it is difficult to recycle homogeneous catalysts. However, there are issues related to the chemoselectivity of heterogeneous catalysts as well. Recently, new mediator materials have been reported that solve the problems that are commonly associated with heterogeneous catalysts. Sajiki et al. reported a Pd/C–ethylenediamine complex, [Pd/C(en)] , which was used in several chemoselective hydrogenation reactions. Akabori et al. and Sajiki et al. reported a fibroin-mediated Pd catalyst (Pd/Fib) that had unique characteristics in the chemoselective hydrogenation of olefins and acetylenes in the presence of aromatic N-Cbz (Cbz = carbobenzyloxy) protecting groups. 3] [Pd/C(en)] and Pd/Fib have different hydrogenation selectivities; the different mediating materials lead to drastic differences between their catalytic natures. There has been an ongoing search for inexpensive, highly reactive, and recyclable heterogeneous catalysts with high selectivity. Our research group has been investigating ways of using the waste DNA from discarded industrial salmon milt. Discarded salmon testes, which contain salmon DNA, are a serious industrial-waste problem in Japan; their volume reaches approximately 3 10 kg every year. 5] Therefore, the effective use of this waste DNA is important. Boersma et al. reported a new DNA-based asymmetric-catalysis concept that was based on the modular assembly of a DNA-based catalyst. Higuchi reported an artificial enzyme that consisted of platinum metal and a nucleotide polymer. Wang et al. also reported a DNAmediated metal catalyst in nanoparticulate form. The procedures for preparing these catalysts are complicated. Herein, we report the preparation of a Pd/DNA catalyst by using a method that is similar to that reported by Sajiki et al. and we show that this DNA-mediated catalyst has high activity for the selective hydrogenation of carbon carbon triple bonds, carbon carbon double bonds, and nitro groups, as well as for Suzuki–Miyaura coupling reaction. We were able to prepare the Pd/DNA catalyst by using a very simple method (Figure 1). A mixture of palladium acetate and DNA was left to stand in MeOH for 3 days at room temperature. After the solvent was removed, the resulting gray DNA residue was dried under reduced pressure. This procedure produced the catalyst in quantitative yield. TEM images of the DNA (salmon testes)-mediated Pd catalyst (1 a) are shown in Figure 2. Pd particles can be seen on the surface of the DNA strands. The average size of the Pd/DNA particles was about 5–8 nm. The Pd particles were localized on the DNA strands.

Kinetic resolution of citronellal by chiral aluminum catalysts: L-menthol synthesis from citral

A highly reactive catalytic ring-closing ene reaction is discussed. This reaction is catalyzed via novel optically active aluminum BINOL and TADDOL complexes. The kinetic resolution of the racemic analogs of citronellal was affected by these Al catalysts. The BINOL-Al catalyst afforded 68% ee of a diastereomer of isopulegol and 62% ee of citronellal at 47% conversion. The reaction mechanism proposed assumes that the optically active catalyst possesses a metal center between two parallel aromatic rings. We postulate that the edge of the aromatic rings can recognize the methyl group at the 3-position of citronellal, as the rings are oriented in a pseudoparallel orientation. We utilized the kinetic resolution for the synthesis of L-menthol from citral.

Correction: Highly selective aluminium-catalysed intramolecular Prins reaction for L-menthol synthesis

Correction for ‘Highly selective aluminium-catalysed intramolecular Prins reaction for L-menthol synthesis’ by H. Itoh et al., RSC Adv., 2014, 4, 61619–61623.

Highly selective aluminium-catalysed intramolecular Prins reaction for L-menthol synthesis

An aluminium complex bearing 2-cyclohexyl-6-phenylphenol afforded (5R)-n-isopulegol from (R)-citronellal via the intermolecular Prins reaction with an exceptionally high diastereoselectivity. Using this reaction, L-menthol was obtained with an excellent diastereoselectivity.