Transition-metal-catalyzed borylation has emerged as a powerful method for preparation of organoboron compounds, which are useful synthetic reagents in organic synthesis. However, chemo-, regio-, and stereoselective synthesis of the boron compounds are still highly required. Herein, we report copper(I)-catalyzed boryl substitution of allylic carbonates and ethers, monoborylation of 1,3-dienes and enynes, boryl substitution of alkyl halides, and borylative cyclization of alkenes containing an appropriate leaving group for the selective synthesis of various organoboron compounds including allyl- and allenylboronates, and optically active carbocyclic boronates. Preparation of the borylation products has been difficult with known procedures. In addition, direct enantio-convergent transformation of racemic substrates without a racemization or symmetrization process, a novel methodology for asymmetric synthesis with racemic substrates, is also reported.
omino reactions have received great attention as efficient synthetic methodologies to construct structurally complex molecules from simple materials in a single operation. Recently a new concept, “tandem catalysis” in domino reactions has been proposed. Tandem catalysis is categorized into three subclasses: Orthogonal, auto-, and assisted-tandem catalysis. Auto-tandem catalysis is defined as a process in which one catalyst promotes more than two mechanistically different reactions in a single vessel. It has been discovered by several researchers including us that triflic imide (Tf2NH) activates a variety of chemical transformations, such as Mukaiyama-aldol reaction, conjugate addition, cycloadditions and so on. This account summarizes our recent development of auto-tandem catalysis of triflic imide.
The aza-Morita-Baylis-Hillman (aza-MBH) reaction is a C-C bond-formation between enones and imines mediated by a nucleophilic Lewis base catalyst. The aza-MBH products are highly functionalized allylic amines which are proved to be valuable building blocks for pharmaceutical compounds. Organocatalyzed domino reactions are an attractive methodology because of its ability to construct complex chiral molecules from readily available substrates under mild reaction conditions in two or more steps in a single operation without using any toxic metals. However, a few reports on the domino reaction based on the MBH have been made due to the complicated MBH process involving Michael/Mannich/H-transfer/retro-Michael sequence. Herein, we report an enantioselective domino reaction based on the aza-MBH process using chiral acid-base organocatalysts. The acid-base functionalities activate the substrates and promote the complicated MBH sequence by their synergistic cooperation. The designed enantioselective MBH-type domino reactions provided highly functionalized heterocycles in up to 98% ee, some of which have a tetrasubstituted carbon stereogenic center.
Development of chemical glycosylations is crucial to achieve effective synthesis of biologically important oligosaccharides and glycoconjugates in a large amount with high purity. Although tremendous efforts have been done to synthesize complex oligosaccharides for more than several decades, numbers of reliable and versatile methods for chemical glycosylations are limited. Solid-phase synthesis does not seem to be the final answer for oligosaccharide synthesis and automated synthesizers for oligosaccharides in solution-phase are still under development. Therefore, it is particularly important to review recent progress of methodologies for chemical glycosylations carefully and figure out what is a challenge in this research field. In this review article, recent development of glycosylation methods and novel strategies for oligosaccharide synthesis is highlighted from the viewpoint of a synthetic organic chemist.
CS-0777 (4) is phosphorylated in vivo, and the phosphate of CS-0777 (CS-0777-P) (25) acts as a selective S1P1 receptor agonist, which is known as a novel mechanism of action to be able to provide a potent immunosuppressant agent. We report herein the primary synthetic route of CS-0777 and CS-0777-P using asymmetric desymmetrization of prochiral-diol precursor as a key reaction along with the biological activity of those compounds, and in the later part of the manuscript, we also describe an extensive process research effort to establish the scalable synthetic method to prepare CS-0777 at tens of kilogram scale.
Glutathione S-transferase (GST) are phase II enzymes that catalyze the nucleophilic attack of glutathione (GSH) to a wide range of hydrophobic and electrophilic compounds. GST is of high clinical interest in inflammation, pathophysiology and tumor drug resistance. In addition, GST is known to highly express in cancer cells. Therefore, we tried to develop new luminescent probes that can detect and image GST expression in living cells. Recently, we found that the electrophilic centre in the dinitrobenzenesulfonamide derivative is attacked by GSH and that this reaction is catalyzed by GST releasing the strong fluorophore. Based on this knowledge, we synthesized fluorescent probe, 19F MRI probe, and bioluminogenic probe. The fluorescent probe and kinetic parameters for purified GST were giving a rate enhancement of 106 compared with the nonenzymatic reaction. In addition, fluorescent probe successfully image GST in living cells. The fluorescent probe is potentially useful reagent for detection of GST activity in living cells. 19F MRI and bioluminogenic probes were synthesized using 4-acetyl-2-nitrobenzenesulfonyl group. 19F MRI probe exhibited a peak shift of 19F MRI signal and fluorescence enhancement in a bimodal way in response to GST activity. Bioluminogenic probe provided strong bioluminescence from GST activity. Moreover, both probes were successfully applied to the monitoring of GST expression in living E. coli cells. Successful detection of GST activity in living cells could be very useful for identifying tumor cells that overexpress GSTs.
Planar-chiral compounds have found widespread application as chiral ligands for asymmetric catalysts, or as photosensitizer for functional materials. Recently, various research groups reported catalytic asymmetric synthesis of planar-chiral compounds. In this short review, the synthesis of various planar-chiral compounds by using metal catalysts are described in a comprehensive manner.
Two-dimensional polymers comprising areal repeat unit such as graphene exhibit unique properties originating from its sheet like structure. The development of versatile routes for the two-dimensional polymers based on organic synthesis is of great interest for their broad applications. This review describes the novel topochemical two-dimensional photopolymerizations to take place within layered monomer crystals.