Taku Kitanosono

Traditional organic synthesis relies heavily on organic solvents for a multitude of tasks, including dissolving the components and facilitating chemical reactions, because many reagents and reactive species are incompatible or immiscible with water. Given that they are used in vast quantities as compared to reactants, solvents have been the focus of environmental concerns. Along with reducing the environmental impact of organic synthesis, the use of water as a reaction medium also benefits chemi

Abstract Ever‐evolving catalyst advances in synthetic protocols using water as a reaction medium have enriched the understanding of sustainable organic chemistry. Because conventional classification and definitions were ambivalent, it is proposed here that catalytic reactions using water be collectively called to be “in water”, with further classification into seven types. When accelerated in water as heterogeneous mixtures, the reactions can be regarded as following an “on‐water” mechanism. The

Acicular purplish crystals were obtained from Cu(acac)2 and a chiral bipyridine ligand. Although the crystals were not soluble, they nevertheless catalyzed asymmetric silyl conjugate addition of lipophilic substrates in water. Indeed, the reactions proceeded efficiently only in water; they did not proceed well either in organic solvents or in mixed water/organic solvents in which the catalyst/substrates were soluble. This is in pronounced contrast to conventional organic reactions wherein the ca

Mukaiyama aldol reactions in aqueous media have been surveyed. While the original Mukaiyama aldol reactions entailed stoichiometric use of Lewis acids in organic solvents under strictly anhydrous conditions, Mukaiyama aldol reactions in aqueous media are not only suitable for green sustainable chemistry but are found to produce singular phenomena. These findings led to the discovery of a series of water-compatible Lewis acids such as lanthanide triflates in 1991. Our understanding on these benef

Asymmetric Michael reactions and enantioselective protonations between enones and thiols were catalyzed by a Sc(OTf)(3)-chiral 2,2'-bipyridine complex in water. The remarkable governing of the enantioselectivity for simple introduction of protons despite their abnormally high mobility in water may provide us with new synthetic opportunities as well as significant chemical advances.

It was proved that a judicious choice of counteranion played a prominent role in Cu(II) catalysis for enantioselective boron conjugate additions in water; the use of Cu(OH)2 renders heterogeneous catalysis, whereas Cu(OAc)2 renders homogeneous catalysis; cyclic dienones underwent a remarkable switch of regioselectivity between 1,4- and 1,6-modes of the additions through these catalyses.

The development of highly reactive and stereoselective catalytic systems is required not only to improve existing synthetic methods but also to invent distinct chemical reactions. Herein, a homogenized combination of nickel-based Lewis acid-surfactant-combined catalysts and single-walled carbon nanotubes is shown to exhibit substantial activity in water. In addition to the enhanced reactivity, stereoselective performance and long-term stability were demonstrated in asymmetric conjugate addition

We have developed Cu(II)-catalyzed enantioselective conjugate-addition reactions of boron to α,β-unsaturated carbonyl compounds and α,β,γ,δ-unsaturated carbonyl compounds in water. In contrast to the previously reported Cu(I) catalysis that required organic solvents, chiral Cu(II) catalysis was found to proceed efficiently in water. Three catalyst systems have been exploited: cat. 1: Cu(OH)2 with chiral ligand L1; cat. 2: Cu(OH)2 and acetic acid with ligand L1; and cat. 3: Cu(OAc)2 with ligand L

We have developed asymmetric Mukaiyama aldol reactions of silicon enolates with aldehydes catalyzed by chiral Fe(II) and Bi(III) complexes. Although previous reactions often required relatively harsh conditions, such as strictly anhydrous conditions, very low temperatures (-78 °C), etc., the reactions reported herein proceeded in the presence of water at 0 °C. To find appropriate chiral water-compatible Lewis acids for the Mukaiyama aldol reaction, many Lewis acids were screened in combination w

There is a growing awareness of the underlying power of catalytic reactions in water that is not limited to innate sustainability alone. Some Type III reactions are catalytically accelerated without dissolution of reactants and are occasionally highly selective, as shown by comparison with the corresponding reactions run in organic solvents or under solvent-free conditions. Such catalysts are highly diversified, including hydrophilic, lipophilic, and even solid catalysts. In this Outlook, we hig

Enantioselective conjugate addition of bis(pinacolato)diboron to α,β-unsaturated imines proceeds smoothly in water in the presence of a chiral copper(II) complex consisting of Cu(OAc)2 and chiral 2,2'-bipyridine. The corresponding β-boryl imines, which were oxidized to β-hydroxy imines, further leading to γ-amino alcohols, were obtained in high yields and high enantioselectivities.

Abstract The use of copper(0) powder in water enables chiral induction as well as high catalytic activity. Water plays a prominent role to determine both the catalytic activity and enantioselection. Elevated temperature is indispensable for the regular reaction pathway, and an active species tends to aggregate after the completion of the reaction. Selective deuteration implies enantiofacial differentiation of the deuteron toward an O ‐enolate intermediate. Strict substrate specificity suggests t

Abstract Metal‐bound water molecules have recently been recognized as a new facet of soft Lewis acid catalysis. Herein, a chiral palladium aqua complex was constructed that enables carbon–hydrogen bonds of indoles to be functionalized efficiently. We embraced a chiral 2,2′‐bipyridine as both ligand and hydrogen‐bond donor to configure a robust, yet highly Lewis acidic, chiral aqua complex in water. Whereas the enantioselectivity could not be controlled in organic solvents or under solvent‐free c

The electrophilic palladation of indoles through C–H bond functionalization with the aid of surfactant was achieved in water in a highly enantioselective manner. The system displayed attractive features that are reminiscent of both precious-metal catalysis and micellar catalysis. The palladium(II) catalyst entangled with a surfactant did not respond to commonly recognized phosphine-based ligand but to 2,2′-bipyridine L1. The insights gained from this unique set of palladium(II) catalysts demonst

Enzymes exhibit overwhelmingly superior catalysis compared with artificial catalysts. Current strategies to rival enzymatic catalysis require unmodified or minimally modified structures of active sites, gigantic molecular weight, and sometimes the use of harsh conditions such as extremely low temperatures in organic solvents. Herein, we describe a design of small molecules that act as the simplest metalloenzyme-like catalysts that can function in water, without mimicking enzyme structures. These