Ryo Yamada

Synthesis of a landomycinone skeleton via Masamune–Bergmann cyclization

In this report, a synthetic study of landomycinone via Masamune–Bergmann cyclization is described. A 10-membered 1,2-dialkynylbenzene derivative was designated as a key intermediate in the formation of an angular tetracyclic core via Masamune–Bergmann cyclization. Cyclization was expected to proceed under mild heating conditions based on a DFT transition state analysis of the 10-membered enediyne. The enediyne was successfully prepared by intramolecular NHK cyclization in good yield and underwent Masamune–Bergman cyclization at 70 °C for 2 h. However, an undesired β-elimination of the secondary alcohol was involved in the cyclization. In addition, iodination at the 12 position did not occur due to the steric hindrance of two methyl groups. This methodology should be widely applicable to the synthesis of various types of highly oxy-functionalized anthraquinone derivatives as well as landomycinone, and should be a useful way to clarify structure–activity relationships.

A Circularly Arranged Sextuple Triptycene Gear Molecule

Herein we report the synthesis of a circularly arranged sextuple triptycene gear molecule, hexakis(10-dodecyloxy-9-triptycyl)ethynylbenzene, via the trimerization of the corresponding triyne with a cobalt catalyst. The six triptycene gears are closely engaged with each other as confirmed by single crystal X-ray structure analysis, and their motion in solution was established by NMR spectroscopy. Notably, when one bulky RuCp* complex was attached to one triptycene gear, the whole movement of the six gears was highly restricted via their mechanical engagement. Development of such a multigear molecule would provide a structural basis for molecular motion transmission systems with a switching function.

Diaroyl tellurides: synthesis, structure and NBO analysis of (2-MeOC6H4CO)2Te--comparison with its sulfur and selenium isologues. The first observation of [MgBr][R(C=Te)O] salts.

A series of aromatic diacyl tellurides were prepared in moderate to good yields by the reactions of sodium or potassium arenecarbotelluroates with acyl chlorides in acetonitrile. X-ray structure analyses and theoretical calculations of 2-methoxybenzoic anhydride and bis(2-methoxybenzoyl) sulfide, selenide and telluride were carried out. The two 2-MeOC6H4CO moieties of bis(2-methoxybenzoyl) telluride are nearly planar and the two methoxy oxygen atoms intramolecularly coordinate to the central tellurium atom from both side of C(11)-Te(11)-C(22) plane. In contrast, the oxygen and sulfur isologues (2-MeOC6H4CO)2E (E = O, S), show that one of the two methoxy oxygen atoms contacts with the oxygen atom of the carbonyl group connected to the same benzene ring. The structure of di(2-methoxybenzoyl) selenide which was obtained by MO calculation resembles that of tellurium isologues rather than the corresponding oxygen and sulfur isologues. The reactions of di(aroyl) tellurides with Grignard reagents lead to the formation of tellurocarboxylato magnesium complexes [MgBr][R(C=Te)O].