The introduction of fluorine-containing carbon functional groups into organic compounds is one of the key processes to synthesize biological valuable organofluorine compounds. While the reaction of organolithium, magnesium and zinc reagents with appropriate carbon electrophiles is reliable method to form carbon-carbon bonds, there were few reports concerning the reaction of these organometallic reagents with electrophilic fluoroalkylating reagents. Recently, we have developed several fluoroalkylations using these organometallic reagents and electrophilic fluoroalkylating reagents. In this paper, we account the fluoroalkylation of aromatic lithium, magnesium, and zinc reagents including our developed bromodifluoromethylation of aryl Grignard reagents with CF2Br2 and dibromofluoromethylation of aryl Grignard reagents with CF2Br2 in the presence of LiBr. In addition, the (ethoxycarbonyl)difluoromethylation of arylzinc reagents with ethyl bromodifluoroacetate in the presence of cobalt catalysts is also discussed.
Synthesis of cyclic germylene-ethynylene materials, germa[N]pericyclynes, and their characterization are described in this account. With the growing attention and importance of “element blocks” for functional materials, skipped polyynes are of particular interest among polyyne materials. Although they consist of non-conjugated alkyne units interrupted by linker atoms, those are expected to enhance the through-bond and through-space interactions. Thus, use of group 14 elements such as germanium would be a preferable sp3 unit due to the hypercoordination abilities of heavy atoms and strong covalent bonds with the sp-carbon atom units. Moreover, germa[N]pericyclynes of cyclic skipped polyynes are expected to fix their conformation and reinforce the orbital interaction by ring-strain-promoted reduced vertex angles.
Germa[N]pericyclynes were initially obtained by shot-gun synthesis, and later, the product yields were improved by stepwise synthesis. Extended germa[N]pericyclynes composed of butadiynes as alkyne units were also synthesized by coupling with acetylides and germanium chlorides. The obtained pericylcynes were characterized by X-ray crystallography, UV-vis, and fluorescence and phosphorescence emission spectroscopy. The molecular orbitals are estimated by DFT calculations. A unique fluorescence emission was observed for the large germa- and pericyclynes compared to the appropriate acyclic germanium polymers. Additionally, these germanium cyclic polymers showed phosphorescence emission without transition metal components.
A series of 2-(2’-hydroxyphenyl)imidazo[1,2-a]pyridine (HPIP) derivatives that show bright solid-state luminescence with variety of emission color are synthesized, and their solid-state photophysical properties are studied. Largely Stokes-shifted excited-state intramolecular proton-transfer (ESIPT) luminescence of HPIP derivatives is markedly increased in the solid state. This emission enhancement is ascribed to the conformational fixation in the solid state, which suppresses torsional motion-coupled radiationless energy dissipation at the ESIPT state. Some of the HPIP derivatives show crystal polymorphism, and color of their luminescence is found to be polymorph-dependent. Effect of their crystal structure on the emission properties is analyzed and discussed by using X-ray crystallography and quantum chemical method. Furthermore, external stimuli-triggered phase transition between the polymorphic crystals allows reliable and reproducible switching of the ESIPT luminescence. These results indicate that tuning and switching of solid-state ESIPT luminescence by altering mode of molecular packing (supramolecular approach) is a promising concept for designing tunable solid-state organic luminescent materials.
In this review we report our recent studies on the synthesis of N-heterocyclic compounds from aziridines and azetidines. The ring expansion reactions of these strained N-heterocycles with various unsaturated compounds such as electron-deficient isocyanates, allenes, and arynes gave five to eight-membered N-heterocyclic compounds efficiently. We also studied the structure as well as the reactivity of some new N-heterocyclic compounds and disclosed their interesting properties.
Natural products and their derivatives have been very useful in the search for biologically active compounds and for the development of new drugs because of their structural diversity. However, to retain their usefulness in the future, new approaches to increase the chemical diversity of such natural products must be developed. Diversity-oriented synthesis has recently emerged as an efficient methodology to construct complex and diverse compounds from simple and similar precursors. Thus, through the combination of natural products chemistry and diversity-oriented synthesis, we propose a new approach, diversity-enhanced extracts, for increasing the diversity of natural product-like compounds. Diversity-enhanced extracts are prepared from chemical reactions that remodel molecular scaffolds directly on extracts of natural resources. The subsequent isolation of each compound produced from such reactions affords a diverse natural product-like library. We applied this method of diversification on several medicinal plants. From diversity-enhanced extracts of the medicinal plants, we obtained new and diverse sesquiterpenoids, indole alkaloids, meroterpenoids, and biaryls with some containing new molecular skeletons.
Carborane acid is the strongest Brönsted acid presently known, possessing unusually high acidity greater than fluorosulfuric acid. Protonation by a carborane acid have proceeded effectively towards the weakest bases such as benzene, fullerene, alkanes, and even carbon dioxide, producing corresponding reactive cations as salts with the least coordinating carborane anion. This short-review highlights recent reports on structural elucidations of several important cations using a carborane acid.
Metal free reactions by using organocatalysts were interested in the view point of green chemistry. On the other hand, a lot of Frustrated Lewis Pairs (FLPs) catalyzed reactions were reported because of its powerful potential to activate hydrogen molecule reversible. Recently, metal free C-H borylation reactions were achieved by application of amine-borane type of FLP catalysts. These methods should be alternative functionalization reactions to synthesize useful building blocks and drug derivatives.