Our recent work on organometallic molecular devices, which should lead to development of molecular circuit, is reviewed. The initial work on organometallic molecular wires consisting of two redox-active organometallic termini connected by π-conjugated linkers has been followed by the work on higher dimensional and functional systems. The higher dimensional systems serve as junctions of molecular circuits and involve polynuclear complexes, where the redox-active centers are connected by the ethylene, benzene and hexaarylbenzene (HAB) derivatives. It is notable that the HAB system exhibits toroidal delocalization through π-π interaction among the peripheral aromatic rings. For the functional systems we have developed molecular variable resistor based on attachment/detachment of the dicobalt fragments to the alkyne-based molecular wire and molecular switch containing the photochromic dithienylethene bridges. The preparative methods of the organometallic molecular devices and the evaluation methods of their wire-like performance are also briefly described.
Arynes were found to be utilizable as unsaturated hydrocarbons in the insertion reactions into σ-bonds. Nitrogen-silicon (aminosilane), halogen-carbon (acid halide) and carbon-phosphorus bonds (phosphorylacetonitrile), as well as strain-free carbon-carbon bonds of active methylene compounds and fluorene derivatives were easily cleaved and added across arynes via electrophilic coupling of arynes with in situ-generated carbanions. Furthermore, total synthesis of cytosporone B and phomopsin C was accomplished by using the C-C bond cleavage reaction. In the presence of transition metal catalysts, arynes could also be inserted into tin-tin (distannane), boron-boron (diboron), carbon-bromine (alkynyl bromide) and carbon-hydrogen bonds (terminal alkyne).
Over a long period of time, in the field of synthetic organic chemistry, Lewis acids have been used mainly as activators for heteroatom-containing functional groups such as carbonyls, imines and halides. In contrast to the traditional approach utilizing such Lewis acid chemistry, we have been focusing on developing new catalytic reactions on the basis of activation of hydrocarbon functional groups by Lewis acids. In order to activate effectively the hydrocarbon functional groups classified into C≡C, C=C, C−C and C−H, an appropriate choice of a Lewis acid catalyst is a crucial aspect. Herein, I disclose our recent achievements based on the Lewis acid-activated hydrocarbon functional groups.
FTY720 (Fingolimod) is the first of a novel class: Sphingosine 1-phosphate (S1P) receptor modulator and has been approved in the US, Russia, Switzerland, Australia and EU as a first-line treatment for relapsing forms of multiple sclerosis (MS) so far. FTY720 was designed and synthesized by chemical modification of an immunosuppressive natural product, ISP-I (myriocin). ISP-I was isolated from the culture broth of Isaria sinclairii, a type of vegetative wasp. ISP-I is an amino acid having three successive asymmetric centers and some functionalities. We simplified the structure drastically to find a symmetric 2-substitued-2-aminopropane-1,3-diol framework for an in vivo immunosuppressive activity and finally discovered FTY720. During the lead optimization, we encountered an unexpected dramatic change of the mechanism. FTY720 is mainly phosphorylated by sphingosine kinease 2 in vivo and the phosphorylated drug (FTY720-P) acts as a potent agonist of four of the five G protein coupled receptors for S1P: S1P1, S1P3, S1P4, and S1P5. Immunomodulation by FTY720-P is based on agonism at the S1P1 receptor. FTY720 was discovered by a classical “physiology-based drug discovery” strategy, showing that such a strategy as adopted by the FTY720 program would more likely meet serendipity compared to the recent strategies such as “target-based drug discovery”.
We synthesized chiral phosphoric acids bearing 3,3'-substituents starting from (R)-BINOL and demonstrated their catalytic activity as chiral Brønsted acid. Proper choice of the 3,3'-substituents of the phosphoric acid is critical to attain excellent enantioselectivity. We wish to describe in this article the background of development of the catalyst, design of the catalyst, and application of them to a range of asymmetric reactions: (1) nucleophilic addition to aldimines, (2) cycloaddition toward aldimines, (3) Friedel-Crafts alkylation of indoles with nitroalkene, α,β-unsaturated ketone, and trifluoropyruvate, (4) kinetic resolution in the intramolecular aldol reaction, and (5) desymmetrization in the intramolecular aldol reaction. We also studied the role of the phosphoric acid and elucidated that phosphoryl oxygen played a critical role as a Lewis basic site.
Novel and efficient synthetic methodologies for nitrogen-containing heterocycles by utilizing a wide range of functionality-containing carbodiimides as vital building blocks are described. The key steps involve the iminophosphorane-mediated aza-Wittig reaction with isocyanates, followed by a variety of ring-forming reactions such as electrocyclization, Diels-Alder reaction, and various intramolecular reactions together with preliminary transformation reaction if necessary.
The C (aryl) -O bond formation was generally carried out by using transition metal-catalyzed coupling reaction between aryl halide and alcohol. Among them, Cu-mediated Ullmann reaction is a powerful method for the preparation of alkyl aryl ether from secondary alcohol. In this article, recent advances in Ullmann reaction are reviewed being categorized into two parts: ligand and aryl donor.