Isocyanurates with Planar Chirality: Design, Optical Resolution, and Isomerization

Abstract

Designs and syntheses of isocyanurates (1-3) are described on the basis of a novel concept that two enantiotopic faces of C(s) -symmetric, prochiral planar molecules are differentiated with a location of groups at the top or bottom of the planar skeleton using a rigid linker. Such isocyanurates are atropisomeric. The planar-chiral structures of 1 and 2(anti) (anti-conformer of 2) were confirmed by single-crystal X-ray analyses, and the space groups were P1 (for 1) and P2(1)/c (for 2(anti)), resulting that the crystals were racemates. Optical resolutions of 1-3 were successfully accomplished by using chiral high-performance liquid chromatography technique in combination with circular dichroism, absorption, and nuclear magnetic resonance spectroscopies and mass spectrometry. Furthermore, the rotational barriers (ΔG(‡)s) related to isomerizations of 1-3 were estimated to be 27.2 (for 1 at 50 °C), 27.6 (for 2(anti) at 50 °C), and 40.6 (for 3(syn) at 150 °C) kcal/mol. The ΔG(‡)s of 2 and 3 were higher than that of 1 and, in particular, that of 3 was highest among them. This result indicates that an introduction of bulky substituents and an intramolecular bridging are effective for inhibitions of the isomerizations.

Ruthenium-Catalyzed Regioselective C–H Alkenylation Directed by a Free Amino Group

“…Indeed, under similar conditions using acetic acid, the alkenylation of 2-aminobiphenyls was found to take place smoothly via a C–H bond cleavage at the 2′-position with the aid of their free-amino group to produce the corresponding 2-amino-2′-alkenylbiphenyls selectively. It should be noted that 2-aminobiphenyl frameworks are included in a wide range of functional molecules such as bioactive reagents, fluorescent probes for bioimaging, conductive polymers, inclusion compounds, porous materials, and ligands . Therefore, various methods for their precise synthesis and modification are desired in such broad fields.…”