Photochemical type II reaction of atropchiral benzoylformamides to point chiral oxazolidin-4-ones. Axial chiral memory leading to enantiomeric resolution of photoproducts.

Atropisomeric maleimides were synthesized and employed for stereospecific [2 + 2] photocycloaddition. Efficient reaction was observed under direct irradiation, triplet-sensitized UV irradiation, and non-metal catalyzed visible-light irradiation, leading to two regioisomeric (exo/endo) photoproducts with complete chemoselectivity (exclusive [2 + 2] photoproduct). High enantioselectivity (ee > 98%) and diastereoselectivity (dr > 99:1%) were observed under the employed reaction conditions and were largely dependent on the substituent on the maleimide double bond but minimally affected by the substituents on the alkenyl tether. On the basis of detailed photophysical studies, the triplet energies of the maleimides were estimated. The triplet lifetimes appeared to be relatively short at room temperature as a result of fast [2 + 2] photocycloaddition. For the visible-light mediated reaction, triplet energy transfer occurred with a rate constant close to the diffusion-limited value. The mechanism was established ...

Tailoring atropisomeric maleimides for stereospecific [2 + 2] photocycloaddition--photochemical and photophysical investigations leading to visible-light photocatalysis.

Alpha-oxoamides 1 with o-tert-butyl substitution on the N-phenyl moiety were found to be stable axially chiral atropisomers. These axially chiral alpha-oxoamides undergo enantiospecific photochemical gamma-Hydrogen abstraction in CHCl(3) to yield beta-lactams with high enantioselectivity (e.r. approximately 90:10) in solution. The extent of enantioselectivity was found to be dependent on the reaction temperature.

Enantiospecific Photochemical Norrish/Yang Type II Reaction of Nonbiaryl Atropchiral α-Oxoamides in Solution—Axial to Point Chirality Transfer

Amidate ligands have been used as a modular ligand set for early transition-metal complexes, and have been found to exhibit high reactivity in the catalytic hydroamination of alkynes, allenes, and alkenes. This microreview focuses on coordination metal complexes containing amidate functionality including their bonding, structure and reactivity trends. The synthesis and characterization of a number of different group-4 metal complexes is presented, and their applications in both hydroamination and organic synthesis are discussed.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Ayako Honda

Papers

Atropisomeric amides: Achiral ligands with chiral conformations.