Photoinduced reactions have received much attention as a powerful tool to access kinetically or thermodynamically prohibited reactions on the ground state. However, these reactions have been developed mainly by using electro-negative elements such as C, O, N, halogens as well as transition-metals. On the other hand, we have revealed the nature of chemical species including electro-positive main-group elements, such as boron (B), silicon (Si), and tin (Sn), on the excited state, developing the highly reactive and selective photoinduced reactions. For diboron (B-B) reagents, we designed the anionic photo-absorbing borate complex to enable a quadruple borylation reaction of terminal alkynes under ultraviolet irradiation. For stannyl (Sn) species, we revealed that the illumination of stannyl anions generates the excited triplet stannyl diradicals, which showed the orthogonality to traditional reagents (cations, anions, and radicals) to enable hydrostannylation of alkynes and defluorostannylation of fluoroarenes. For silylborane (Si-B) reagents, we developed dearomative triple elementalization (carbo-silaboration) reactions of quinolines by the excitation of silyl-borate complexes without the need for any catalyst.

Tetra- and pentacyanocyclopentadienides (TCCP and PCCP) are superacid conjugate bases stabilized by the mesomeric and inductive effects of cyano groups and the aromaticity of the cyclopentadienide ring. We have developed an efficient synthetic method for various TCCP and PCCP using tetracyanothiophene and sulfones, followed by substituent transformations. We conducted a series of application studies using our synthetic method for tetra- and pentacyanocyclopentadienides. NanoGoblin, the doll-shaped ion pair of TCCP, catalyzed methanolysis of the cyclic acetal in the anthropomorphic molecule NanoKid. The cyano groups of TCCP acted as hindrances to rotation of C_Ar-O bonds in 3,3′-BINOL esters. TCCP exhibited high lipophilicity, which was utilized in anionic phase transfer reactions and the ion-pair extraction of quaternary ammonium cations. Lastly, the weakly basic nature of PCCP was helpful in the Au/Ag-catalyzed cyclization-3-aza-Cope-Mannich cascade, enabling us to achieve the total synthesis of cephalotaxine.

Dual functionalization in organic synthesis is an elegant and powerful method for simultaneously introducing two different functional groups regio-selectively into a target molecule. We herein describe our recent work on retained dual functionalization and dehydrogenative dual functionalization via oxidation of halogen. For the dehydrogenative dual functionalization by oxidation of bromide ion, a catalytic dual functionalization of ethers through dealkylation-oxidation-bromination accompanied by C-O bond cleavage via aerobic oxidation of bromide was developed to obtain α-bromo ketones. Furthermore, a nitrite-catalyzed ring-contraction reaction of substituted tetrahydropyrans by oxidation of bromide under aerobic conditions was discovered to provide 2-acyltetrahydrofurans. We also succeeded a regio-selective C_sp2-C_sp2 bromo-amination of indole derivatives via the 1,3-migration of imides on indolyl(phenyl)iodonium imides and a remote C_sp2-C_sp3 iodo-amination of 2-methyl indole derivatives with iodinating reagents to furnish the corresponding halo-amino-indole derivatives via formation of indolyl(phenyl)iodonium imides from indole derivatives, bis(sulfonyl)imides, and (diacetoxy)iodobenzene as the retained dual functionalization using hypervalent iodine (III).

In recent years, near-infrared (NIR) dyes, exhibiting absorption in the NIR region (750-2500 nm), has been applied to various optical applications such as security marking, photovoltaic cells and chemotherapy of deep tissues in vivo. Electrochromic systems capable of switching NIR absorption are attractive from the viewpoint of applications for material and life science, and thus several examples have been reported to date. The development of organic-based materials is needed to reduce the environmental impact and improve biocompatibility. However, since the redox states of organic NIR dyes are generally unstable, the switching of NIR absorption based on quantitative redox interconversion is still a challenging issue regarding reversibility and durability during their interconversion. To construct organic electrochromic systems capable of ON/OFF switching of NIR-absorbing properties, we have focused on the non-aromatic π-conjugated para-quinodimethane (p-QD) skeleton. Herein, we have shown several studies on the synthesis and functional control of NIR electrochromic molecules based on redox-active p-QD scaffolds. We have elucidated the spectroscopic and electrochemical properties of various arylated quinodimethane derivatives and demonstrated that p-QD building blocks can be versatile components for the development of NIR switchable organic electrochromic systems.

Recently, atropisomers owing to the rotational restriction around an N-C single bond (N-C axially chiral compounds) have received much attention in the field of synthetic organic chemistry. In particular, the catalytic enantioselective synthesis of various N-C axially chiral compounds and their application to asymmetric reactions have been reported by many groups. Bioactive compounds possessing an N-C axially chiral structure have also been known. The typical example of such bioactive N-C axially chiral compounds is quinazolin-4-one derivatives bearing an ortho-substituted phenyl group at 3-position. However, the catalytic asymmetric synthesis of N-C axially chiral quinazlolin-4-one derivatives has never been reported. We succeeded in the enantioselective synthesis of 3-(2-bromophenyl)quinazolin-4-one derivatives (GABA agonist, mebroqualone derivatives) through chiral Pd-catalyzed reductive asymmetric desymmetrization with 3-(2,6-dibromophenyl)quinazolin-4-ones. Furthermore, it was found that the reaction of various alkyl halides with the enolate prepared from quinazolinone products proceeds in a highly diastereoselective manner by the asymmetric induction due to the N-C axial chirality. The self-disproportionation of enantiomers (SDE) and crystal structure (chirality-dependent halogen bond) in mebroqualone derivatives, the preparation of N-C axially chiral quinazolinones bearing an ortho-fluorophenyl group, and the creation of isotopic atropisomers based on N-C axially chiral quinazolinone scaffold are also described.

Resin glycosides are known as glycolipids isolated from plants of the Convolvulaceae families, which have been used as major constituents of traditional folk medicines. However, their isolation, structure determination, and biological activities have been hampered due to poor production because of their complicated structural diversity. In this short review, total synthesis of resin glycoside merremoside D by two research groups is described.