Symbiodinolide is a polyol marine natural product isolated from dinoflagellate Symbiodinium sp. This natural product exhibits voltage-dependent N-type Ca2+ channel-opening activity at 7 nM and COX-1 inhibition activity at 2 µM. The planar structure of symbiodinolide was elucidated by the detailed 2D NMR analysis. However, the huge and complex molecular structure of this molecule featuring a molecular weight of 2,860 and the presence of 61 chiral centers has hampered the complete stereochemical determination. Herein, we report our synthetic study of symbiodinolide toward the structural elucidation.
2-Azido-1,3-dimethylimidazolinium chloride (ADMC) and its corresponding hexafluorophosphate (ADMP) were found to be safe and efficient diazo-transfer reagents to various organic compounds. ADMC was prepared by the reaction of 2-chloro-1,3-dimethylimidazolinium chloride (DMC) and sodium azide. ADMP was isolated as a crystal having thermal stability and low explosibility. ADMC and ADMP reacted with 1,3-dicarbonyl compounds under mild basic conditions to give 2-diazo-1,3-dicarbonyl compounds in high yields, which are easily isolated because the by-products are highly soluble in water. Naphthols also reacted with ADMC to give corresponding diazonaphthoquinones in good to high yields. Furthermore, ADMP shows efficient diazo-transfer ability to primary amines even without the aid of a metal salt such as Cu(II). Using this diazotization approach, various alkyl/aryl azides were obtained directly from corresponding primary amines in high yields. In addition, ADMC/ADMP could be used as azide-transfer and amidation reagents.
Buckybowls are bowl-shaped aromatic hydrocarbons corresponding to a partial fullerene structure or a cap structure of carbon nanotubes. Since the discovery of C60 fullerene in 1985, buckybowls have attracted much attention due to their physical properties, not only as model compounds for fullerenes, but also as unique bowl-shaped aromatic compounds. We have achieved first enantioselective synthesis of chiral buckybowl, trimethylsumanene, and chiral azabuckybowl, triazasumanene. To achieve the synthesis, we have developed Pd-catalyzed syn-selective cyclotrimerization of enantiopure iodonorbornene derivatives, giving enantiopure C3 symmetric syn-tris(norborneno)benzenes. By using syn-tris(norborneno)benzene derivatives as synthetic intermediates, trimethylsumanene and triazasumanene were synthesized featuring tandem ring-opening/closing metathesis reaction or amide recombination reaction and oxidative aromatization. From the racemization experiments, the bowl inversion/racemization energies of trimethylsumanene and triazasumanene were determined to be 21.6 kcal/mol and 42.2 kcal/mol, respectively.
The functional group manipulation is fundamental in synthetic organic chemistry. Hence, the development of chemoselective hydrogenation methods using a heterogeneous catalyst has been a topic of sustained interest in a synthetic organic chemistry. While many applications to achieve a chemoselective catalyst system have been evaluated, only a few studies such as Lindlar catalyst and Rosenmund’s reaction have been accepted as general chemoselective methodologies. We have successfully developed useful heterogeneous catalysts such as a combination of Pd/C and a nitrogen-containing base, Pd/C-ethylenediamine complex [Pd/C(en)], Pd/C-diphenyl sulfide complex [Pd/C(Ph2S)], Pd-fibroin complex [Pd/Fib], Pd-molecular sieves complex (Pd/MS), Pd-boron nitride complex (Pd/BN), Pd-polyethyleneimine complex (Pd/PEI), and a combination of Pd/BN and a nitrogen-containing base, possessing specific characteristics and suppressed catalyst activities to enable the reliable and chemoselective hydrogenation among various reducible functionalities. This review provides a brief overview of each of the catalyst systems with a focus on specific features and catalyst activities in a comprehensive manner.
A highly sensitive photopolymerization system by using violet laser, 405 nm, was investigated. The photopolymerization composition which contained an initiator and a high fluorescent dye showed efficient sensitization of the system. The photosensitization mechanism seemed to have a singlet energy transfer process. A key molecular design of the dye getting the higher photosensitization efficiency is a repression of thermal relaxation from the excitation state. The photopolymerization system was applied to the computer to plate (CTP) technology, a digital printing plate, to develop our i-Presso P-NV for the violet laser. As compared with a system using a conventional FD-YAG laser, the P-NV system revealed the advantage of high productivity on plate making and also handling under a brighter safelight.
Helicenes are polycyclic aromatic compounds with nonplanar screw-shaped skeletons formed by ortho-fused benzene or other aromatic rings. Since the first synthesis of helicenes was reported in 1903, helicene chemistry including their synthetic methodologies and applications has been greatly exerted. Especially in recent years, the helicence synthesis accompanied by the development of new synthetic reactions, have made such a remarkable progress. In this review, I would like to introduce the recent development of helicene synthesis.
Supramolecular approaches to engineering chiral transition metal complexes for asymmetric catalysis have the advantages through the expeditious construction of catalyst libraries with structural modularity and diversity. Catalyst optimization by non-covalent binding of the building blocks can reduce the synthetic effort for chiral ligands and the time for the screening studies. These strategies promote streamlining of discovery of enantioselective catalysts not only for established reactions but also for new reactions.
Enantiopure sulfoxides are recognized as useful and versatile chiral auxiliaries in asymmetric synthesis. In contrast, much less explored is the use of chiral sulfoxide as ligands for late transition metal catalysts which favorably make sulfur coordination. This article provides a brief overview of the development of such ligands bearing chiral sulfoxide moiety. In 2008, Dorta introduced the highly efficient axially chiral bis-sulfoxide ligands (BINASO) for Rh-catalyzed enantioselective 1,4-addition of arylboronic acids to α,β-unsaturated ketones. After this seminal report, several novel chiral sulfoxide ligands appeared to work for Pd- or Rh-catalyzed asymmetric transformations.
(−)-Actumine A is a tetracyclic alkaloid isolated from the roots of Sinomenium acutum. (−)-Actumine A possesses selective T-cell cytotoxicity, antiamnesic activity, and characteristic aza-propellane core and spirocycle structure. In this review, total syntheses of (−)-actumine A are described, focusing on the construction of above-mentioned structure.
This article summarizes how “blog” media, which is complementary to traditional media (newspaper, television, academic journal etc.), is affecting and changing scientific communication processes especially in synthetic organic chemistry, through reviewing recent representative examples.