In chain-growth polymerization, (co)polymerization abilities of monomers are heavily dependent on the element or functional group attaching to vinyl moiety, resulting in the limitation of accessible polymers. The replacement of the element on the polymer main chain could lead to access new class of polymers with overcoming the synthetic limitations. Herein, we describe the usability of alkenylboronic acid derivatives as the monomers for radical polymerization and post-polymerization transformation through carbon-boron bond-cleaving side-chain replacement. The key for radical polymerization ability of alkenyl boronate was vacant p-orbital of boron for moderate stabilization of chain growth radical. The alkenyl boronate monomers are usable for copolymerization with common monomers as well as for RAFT polymerization. The C-B bond transformation allows syntheses of conventionally inaccessible polymers, such as poly(α-methyl vinyl alcohol), poly(α-methyl vinyl amine), styrene-vinyl alcohol copolymer, and ethylene-acrylate copolymer. Boron on the polymer main chain was also used as the trigger for stimuli-responsive backbone degradation of methacrylate polymer through C-B bond homolysis and β-scission. Thus, alkenyl boronate monomers have an impact on not only breakthrough of the limitation in polymer synthesis but also development of novel polymer functions.

Catalytic asymmetric synthesis is one of the most efficient methods for the preparation of chiral compounds with high optical purity. Although a variety of robust chiral scaffolds have been developed to achieve efficient chiral catalysts which show high catalytic activities and stereoselectivities, use of dynamic chiral scaffold is desired for the development of advanced chiral catalysts featuring stimuli-responsive properties such as chirality-switching and asymmetric amplification. We have developed chirality-switchable helical polymer ligands bearing monodentate phosphine pendants, which exhibit high enantioselectivities based on solvent-dependent dynamic screw-sense control of poly(quinoxaline-2,3-diyl)s (PQXs) having chiral side chains. However, the application has been limited to palladium-catalyzed asymmetric reactions. This article describes the development of helically chiral polymer catalysts based on post-polymerization modification of bornyl pendants (-B(OH)₂) attached to the PQXs. Introduction of 2,2′-bipyridine pendants to chiral PQXs through Suzuki-Miyaura coupling at the boronyl pendants led to the development of chirality-switchable helical polymer ligands for copper-catalyzed asymmetric reactions. In addition, introduction of 4-aminopyridine pendants into the chiral PQXs provided chirality-switchable efficient asymmetric nucleophilic catalysts for kinetic resolution of secondary alcohols and asymmetric Steglich-type acyl rearrangements. Furthermore, by using the boronyl pendants as molecular recognition sites for screw-sense induction to achiral PQXs, a chiral-guest-responsive helical polymer ligand bearing monodentate phosphine pendants was developed for the palladium-catalyzed asymmetric reaction. Using an amino alcohol as a chiral additive, the screw-sense induction proceeded with asymmetric amplification, giving the corresponding product with higher optical purity than that of the chiral additive.

Environmentally-friendly chemical syntheses are desired for creating a sustainable society. In the field of catalysis development, organocatalysts have emerged as green catalysts and great progress in their use has been made over the past two decades. Phosphonium ylides-the cationic site is composed of a phosphonium ion and the negatively charged atom directly attached to the phosphorus center-are a specific type of zwitterion as well as phosphorus(V) compounds. Taking account of the nucleophilicity of the anionic carbon, versatile transformations have been accomplished. Despite being attractive chemical species, however, their catalytic ability has remained elusive and there are no reports on phosphonium ylide catalysts that enable multiple transformations. Hence the development of phosphonium ylide catalysis is of formidable challenge and can open a new frontier for the field of ylide chemistry. Our group focused on carbonyl-stabilized phosphonium ylides, which are synthesized from bifunctional tetraarylphosphonium salts, and has been exploring their catalytic functions as multifunctional organocatalysts. We herein describe the design of novel phosphonium ylide catalysts and the reactions using phosphonium ylides as a nucleophilic catalyst, photoredox catalyst, and Lewis base catalyst. Bifunctional tetraarylphosphonium salts-catalyzed [3+2] reactions between epoxides and heteroallenes such as carbon dioxide and isocyanates are also reported.

Highly polar compounds are generally heated by absorbing microwave energy. Since 1986, microwave irradiation has been applied to various organic syntheses as an efficient heating method. On the other hand, an additional effect called “microwave specific effect”, that cannot be explained by the simple heating effect, has been observed. In a solvent that absorbs less microwave, microwave energy can be directly provided to the reaction substrate, and microwave-specific effects can be expected. Some microwave-assisted asymmetric synthetic reactions have been observed to accelerate while maintaining enantioselectivity. Based on this working hypothesis, we experimentally confirmed the microwave-specific effect in several organic synthetic reactions.

Molecular sieves are type A zeolites with specific sized pores and are commonly used in organic synthesis to capture small molecules such as water. In addition to their trapping effect, they also have acidic and basic active sites and are used as solid acid-base catalysts. Usually, heat-drying treatments are performed prior to use, but the heat treatment methods, such as microwave ovens or heat guns, are not standardized, which could cause problems in reproducibility of reactions. Particularly, for reactions requiring acid/base sites of molecular sieves, these treatment methods are considered more sensitive because the structure of the active sites changes upon heating. In this article, we propose new methods of activation when using molecular sieves and their application to continuous-flow reactions.

Many useful organic reactions have been developed by taking advantage of the high affinity of phosphorus atoms with some heteroatoms such as oxygen and sulfur atoms. Although the reactions proceed via phosphorus ylides, phosphonium salts and phosphoranyl radicals as active species, the reactions via phosphoranyl radicals are only a few reports. In this short review, the three reactions via phosphoranyl radicals reported recently are described.