There are many glycosides with 1,2-cis-O-glycosidic linkages (1,2-cis glycosides) in biologically active natural products and drugs. The development of new lead compounds for drugs by elucidating the mechanisms of their biological activities and developing their structures has attracted attention. However, the stereoselective synthesis of 1,2-cis-glycosides is still a challenging task due to the lack of general methods corresponding to the neighboring group participation method for the 1,2-trans-stereoselective glycosylation. In this context, we have developed organoboron-catalyzed regio- and 1,2-cis-stereoselective glycosylation method, namely, boron-mediated aglycon delivery (BMAD). This review article describes the recent progress in the BMAD method since our review article published in this journal in 2020, including (1) diastereoselective desymmetric BMAD reaction of meso-diols, (2) BMAD reaction of trans-1,2-diols using a diboron catalyst, (3) total synthesis of terpioside B using BMAD reaction, (4) β-arabinofuranosylation using BMAD reaction, and (5) chemical-biological studies using late-stage BMAD reaction.

In the past decades, synthetic organic electrolysis has attracted much attention as an excellent tool for organic synthesis due to its potent and irreversible electron transfer between electrodes and organic compounds. While developing new reactions using organic electrolysis, we are investigating the concept of catalyst-supported organic electrolysis. The first strategy is the generation of bromenium ions (Br⁺) via anodic oxidation and the oxidative transformation of indole compounds. We found that the semi-pinacol rearrangement of tetrahydrocarbolines proceeded with Br⁺ generated by the anodic oxidation. The anodic oxidation of tetrahydrocarbazole did not give spiro compounds under similar conditions, but instead the aromatization proceeded to afford carbazoles. This transformation required both the bromide and the lithium-ion. The second strategy is organic electrolysis promoted by the catalytic amount of electricity. The reactions that are completed by the catalytic amount of electricity can be categorized as hole- or electron-catalyzed transformations. Moreover, these reactions can be achieved using an electrochemical flow reactor, which enables efficient processes. The numerical parameters in the electrochemical flow system, such as the current values and the flow rate, were optimized using the Gaussian process regression. This machine-learning method suggested better reaction conditions with a small number of experiments.

Hexahydroindane scaffold can be found in the oxy-functionalized terpenoids such as cardiotonic steroids and picrotoxane sesquiterpenoids as a privileged structure for their biological activities. To clarify their novel functions, we have synthesized cardiotonic steroids, a pheromonal steroid, and picrotoxane sesquiterpenoid. In this publication, details of the synthetic studies on these naturally occurring products and related analogues are described, starting from tricyclic lactone as a new chiral building block.

This review focuses on the recent advancements in the Metal-Hydride Hydrogen Atom Transfer (MHAT) mechanism for alkene transformation, particularly emphasizing the novel applications and methodologies developed in our research over the past decade. Our work has significantly expanded the scope of MHAT by introducing the Radical-Polar Crossover (RPC) concept, thereby enabling a wide range of selective functionalizations and complex molecule constructions that were previously challenging. We have successfully applied MHAT/RPC mechanisms to construct oxygen-containing heterocycles, such as ethers and lactones, integral to numerous bioactive natural products and pharmaceuticals. This has included the development of methods for the efficient synthesis of five- and six-membered rings, as well as challenging medium-sized rings, highlighting the method’s versatility and effectiveness. Furthermore, our research has pioneered the synthesis of nitrogen-containing heterocycles through MHAT, opening new avenues for the creation of cyclic guanidines and azetidines, compounds with significant biological activity. The introduction of asymmetry into the MHAT mechanism has also been a cornerstone of our work, leading to the development of enantioselective transformations that provide access to chiral molecules. Through a combination of experimental and computational studies, we have elucidated the underlying mechanistic pathways of MHAT, offering insights into the reaction dynamics and factors influencing selectivity and efficiency. Our contributions not only demonstrate the broad applicability of the MHAT mechanism in organic synthesis but also pave the way for future innovations in the field, with the potential for developing new strategies for complex molecule synthesis.

Small molecules and polymers with conjugated structures are expected to serve as materials for organic electronic devices and are presently under development. These materials have traditionally been synthesized using cross-coupling reactions. In recent years, there have been developments in more straightforward synthesis methods for organic electronic device materials. These methods involve direct functionalization of C-H bonds, such as direct arylation, C-H/C-X coupling (where X is a halogen or pseudo-halogen), and cross dehydrogenation coupling, C-H/C-H cross-coupling. Although these methods are convenient for short-step synthesis, it is essential to achieve high C-H bond regioselectivity and suppress undesired homocoupling side reactions. This review presents pioneering examples of the synthesis of conjugated materials using two types of the direct C-H functionalization reactions and our recent research activities. In particular, we discuss the reaction mechanism that achieves high C-H bond regioselectivity and suppresses undesired homocoupling side reactions through the control of reductive elimination.

Thiophene-fused reactions (thienannulations) to the π-electron system are essential for the development of high-performance (high-mobility) organic semiconductors in terms of enhancing intermolecular interactions and charge delocalization. In the conventional thienannulations of ethynylated π-electron system, elemental sulfur and sodium sulfide are frequently used as sulfur sources. Meanwhile, the trisulfur radical anion (S₃^•−) has recently attracted attention as a new sulfur source that enables the development of unexplored organic semiconductors that are difficult to access based on the conventional method. This review highlights thienannulation based on S₃^•− for the synthesis of highly π-extended and unsymmetrical thienoacenes.