Aromatic molecules are undoubtedly one of the most important compounds for materials science. We recently explored unique macrocycles composed of aromatic hydrocarbons. Among various interesting findings, we wish to overview our recent contributions to materials science in this account. Macrocycles from robust synthesis have been found superior in its performances over conventional materials, which highlights importance of organic synthesis. Shaped in unique structures via elaborate synthesis, macrocycles have also paved a way to unexpected functions/devices. The importance of molecular design shall be clear from these results that have been obtained by using macrocycles composed solely of hydrogen and carbon atoms.
Described herein are the synthetic strategies toward polyketide-derived polycyclic compounds decorated by post-functionalizations. The approaches are based on two key reactions, (1) annulation via benzonitrile oxide, and (2) benzoin cyclization, providing a linear tricarbocyclic intermediate with an angular hydroxy group. Also described are the stereocontrolled introduction of angular substituents via pinacol-type 1,2-shift and N-methylation-hydroxylation to pave the way to advanced intermediates. The synthetic utility of the approach has been highlighted by successful total syntheses of some structurally complex, polycyclic natural products.
Organic light-emitting diodes (OLED) have attracted much attention from the viewpoint of application to next-generation flat panel displays and illumination devices. Phosphorescent iridium(III) and platinum(II) complexes are frequently used as the emitting materials because they are superior to fluorescent ones in terms of exciton generation. Here we report the development of phosphorescent organometallic dendrimers bearing charge carrier-transporting dendrons, especially focusing on fabrication of non-doped multilayer OLEDs. We chose our blue phosphorescent bis- and tris-cyclometalated iridium(III) complexes as the phosphorescent core. Attaching liposoluble tert-butyl groups on the periphery of the dendrons, the iridium(III) dendrimers showed good solubility in cyclohexane and insolubility in lower alcohols. The unique properties allowed us to fabricate multi-stacked, spin-coated thin films of hole-transporting poly(vinylcarbazole)/phosphorescent iridium(III) dendrimer/alcohol-soluble electron-transporting material by using an orthogonal solvent system of toluene-cyclohexane-alcohol. Thus, non-doped multilayer OLEDs were successfully obtained by solution processing. We also developed phosphorescent platinum(II) dendrimers bearing hole-transporting dendrons, where peripheral tert-butyl groups provided similar solubility to the iridium(III) dendrimers. Upon fabrication of non-doped multilayer OLEDs with the platinum(II) dendrimers, the excimer emission was tuned by steric hindrance of the ligands, and the optimized balance of blue monomer and reddish orange excimer emissions afforded white emission.
A preparative synthesis of new supramolecular phosphorus ligands that are based on a resorcinarene and flanked by two quinoxaline walls was described, including a description of complexation with Au metals that reside in the space. We explored a catalytic proclivity of the Au complexes, and found that they efficiently catalyze selective transformations that were previously unthinkable and not possible heretofore in bulk solution. In addition, we sought reasonable mechanism of the effect through a comparison with the corresponding model molecules that weakened and/or lacked the cavity compartments: comparative experiments revealed that the models exhibited much lower reactivities and selectivities. Consequently, the two quinoxaline-moieties proved to be quintessential for the catalysis and the selective production of molecules. Clearly, our progress reported herein will constitute an illustration of high potential of cavitand-driven metal catalysts because of the pivotal evidence showing the catalytic utility of quinoxaline-spanned resorcinarene which is a monumental platform in supramolecular chemistry. These results serve as intellectual basis for future catalytic cavitand chemistry.
Metal carbenoids exhibit unique reactivities towards stable chemical bonds. Such reactive species are recognized as powerful tools for direct functionalization of unactivated compounds. Meanwhile, the high and versatile reactivity of metal carbenoids sometimes become problematic in the development of chemoselective reactions, because organic molecules often include some reactive sites to metal carbenoids such as C-H bonds, multiple bonds, and heteroatoms. Therefore, considerable efforts have focused on the control of chemoselectivity of metal carbenoid-mediated reactions in recent years. We have been interested in the potential of metal carbenoids to develop an unusual reaction and succeeded in developing catalyst-controlled highly chemoselective reactions for the synthesis of complex molecules. Herein we summarized our achievements; an insertion reaction of Rh-carbenoid into an amide C-N bond and a dearomative ipso-Friedel-Crafts (DIFC) reaction mediated by chiral Ag-carbenoid species. An application of the amide insertion reaction to the natural product synthesis is also described.
Diisobutylaluminum hydride (DIBAL-H) is a common reagent in synthetic organic chemistry, and well known as a reducing agent of carbonyl groups and C-C multiple bonds. DIBAL-H is also used for modifications of alkynes. The preparation of haloalkenes via hydroalumination of alkynes and following halodemetallation of the resultant alkenylaluminums is the prime example. However, application of the alkenylaluminums to intramolecular bond formation remained largely unexplored. Recently, our attention has been focused on the reactivity and synthetic use of α-silylalkenylaluminums readly prepared from alkynylsilanes and DIBAL-H. During the course of our research, we succeeded in developing new cyclization reactions by DIBAL-H-promoted C-C and C-Si bond formation, which are valuable for regio-controlled syntheses of substituted benzenes, naphthalenes, indenes, benzosiloles, and siloles. These studies have provided not only efficient synthetic methods for carbocycles and silacycles but also novel information on the reactivity of organoaluminums.
Transition-metal catalyzed C(sp3)-H functionalization is one of the most attractive reaction because it enables straightforward and economical syntheses of organic compounds. In the past decades, C(sp3)-H functionalization approaches using directing groups have been developed, however, their stoichiometric installation and removal of directing groups limit efficiency. Recently, a “transient directing group” strategy has been emerged as the solution of this program. This review highlights recent advances in C(sp3)-H arylation using a “transient directing group”.
In nature, there are a number of natural products containing guanidine moiety. Among them, polycyclic guanidine compounds have attracted considerable attention from synthetic chemists and biologists because of their architecturally intriguing structures and potent biological activities. This short review summarizes synthetic methodologies toward batzelladines focusing on stereoselective construction of the core tricyclic guanidine skeleton.