Norito Takenaka

Helical chiral 2-aminopyridinium ions: A new class of hydrogen bond donor catalysts

Helical chiral 2-aminopyridinium ions were designed as a significantly more acidic (active) dual hydrogen-bonding catalyst than commonly used (thio)urea-based systems. The helicene framework was specifically utilized to position an inherently chiral barrier on the hydrogen-bonding side of the catalyst. The catalyst reactivity and enantioselectivity were successfully demonstrated in additions of 4,7-dihydroindoles to nitroalkenes (0.5-2 mol % catalyst loadings, up to 98:2 er).

Helical Chiral Pyridine N‐Oxides: A New Family of Asymmetric Catalysts

Optically active chiral alkyl chlorides are valuable compounds because of their bioactivity and versatile synthetic utility. Accordingly, the ring opening of epoxides with a chloride nucleophile stands as an important goal in asymmetric catalysis. We describe herein recent advances in the design and development of chiral pyridine N-oxide catalysts for the enantioselective synthesis of chlorohydrins.

The first catalytic enantioselective Diels–Alder reactions of 1,2-dihydropyridine: efficient syntheses of optically active 2-azabicyclo[2.2.2]octanes with chiral BINAM derived Cr(III) salen complexes

Abstract We have synthesized a new family of enantiomerically enriched BINAM-derived Schiff base Cr(III) complexes and evaluated them as catalysts for Diels–Alder reactions. These complexes effectively catalyze, for the first time, the enantioselective Diels–Alder reactions between 1,2-dihydropyridine and N -acryloyloxazolidinone to afford 2-azabicyclo[2.2.2]octanes in high yields (89–99%) and with moderate to good enantioselectivities (79–85%).

Applications of Helical‐Chiral Pyridines as Organocatalysts in Asymmetric Synthesis

A new family of chiral pyridines has been designed and synthesized for use in asymmetric organocatalysis. Thus, helical-chiral pyridines induce high enantioselectivity in a range of mechanistically unrelated, synthetically significant transformations, including Friedel-Crafts alkylation with nitroalkenes, periselective Diels-Alder reactions with nitroalkenes, the ring-opening of epoxides with a chloride nucleophile, and the propargylation of aldehydes.

Enantio- and periselective nitroalkene Diels–Alder reaction

The periselective Diels-Alder reaction of 5-substituted pentamethylcyclopentadienes and nitroethylene has been realized by helical-chiral hydrogen bond donor catalysts. To our knowledge, this represents the first asymmetric catalytic nitroalkene Diels-Alder reaction via activation of nitroalkene, and thus establishes its proof-of-principle.

Enantio- and periselective nitroalkene Diels-Alder reactions catalyzed by helical-chiral hydrogen bond donor catalysts.

Helical-chiral double hydrogen bond donor catalysts promote the nitroalkene Diels-Alder reaction in an enantio- and periselective manner. This represents the first asymmetric catalytic nitroalkene Diels-Alder reaction via LUMO-lowering catalysis. To gain an insight into this new process, the substrate scope of our catalyst was investigated by exploiting readily available 5-substituted pentamethylcyclopentadienes. The catalyst was found to tolerate dienes with different steric demands as well as dienes substituted with heteroatoms. The synthetic utility of 5-substituted pentamethylcyclopentadienes is rather limited, and thus we have developed a three-step route to 1,4,5,5-tetrasubstituted cyclopentadienes from commercially available ketones.