Total Synthesis of Keramaphidin B and Ingenamine by Base-Catalyzed Diels-Alder Reaction Using Dynamic Regioselective Crystallization

The control of the selectivity is a central issue in the total synthesis of complex natural products. In this paper, we report the total synthesis of (±)-keramaphidin B and (±)-ingenamine. The key reaction is a DMAP-catalyzed Diels-Alder reaction in which the regioselectivity is completely controlled by dynamic crystallization. Our synthesis successfully demonstrates that dynamic crystallization can be an alternative when the selectivity is not controlled by either kinetic or thermodynamic approaches in solution.

Catalytic Efficiency of Primary α-Amino Amides as Multifunctional Organocatalysts in Recent Asymmetric Organic Transformations

Chiral primary α-amino amides, consisting of an adjacent enamine bonding site (Bronsted base site), a hydrogen bonding site (Bronsted acid site), and flexible bulky substituent groups to modify the steric factor, are proving to be extremely valuable bifunctional organocatalysts for a wide range of asymmetric organic transformations. Primary α-amino amides are less expensive alternatives to other primary amino organocatalysts, such as chiral diamines and cinchona-alkaloid-derived primary amines, as they are easy to synthesize, air-stable, and allow for the incorporation of a variety of functional groups. In recent years, we have demonstrated the catalytic use of simple primary α-amino amides and their derivatives as organocatalysts for the aldol reaction, Strecker reaction, Michael tandem reaction, allylation of aldehydes, reduction of N-Aryl mines, opening of epoxides, hydrosilylation, asymmetric hydrogen transfer, and N-specific nitrosobenzene reaction with aldehydes.

Enantiodivergent [4+2] Cycloaddition of Dienolates by Polyfunctional Lewis Acid/Zwitterion Catalysis

Diels-Alder reactions have become established as one of the most effective ways to prepare stereochemically complex six-membered rings. Different catalysis concepts have been reported, including dienophile activation by Lewis acids or H-bond donors and diene activation by bases. Herein we report a new concept, in which an acidic prodiene is acidified by a Lewis acid to facilitate deprotonation by an imidazolium-aryloxide entity within a polyfunctional catalyst. A metal dienolate is thus formed, while an imidazolium-ArOH moiety probably forms hydrogen bonds with the dienophile. The catalyst type, readily prepared in few steps in high overall yield, was applied to 3-hydroxy-2-pyrone and 3-hydroxy-2-pyridone as well as cyclopentenone prodienes. Maleimide, maleic anhydride, and nitroolefin dienophiles were employed. Kinetic, spectroscopic, and control experiments support a cooperative mode of action. High enantioselectivity was observed even with unprecedented TONs of up to 3680.

New Hybrid-type Squaramide-Fused Amino Alcohol Organocatalyst for Enantioselective Domino Michael Addition/Cyclization Reaction of Oxoindolines with Cyclic 1,3-Diketones

The new hybrid-type squaramide-fused amino alcohol containing both a Brønsted basic site and hydrogen-bonding sites in the molecule showed a high catalytic activity as an organocatalyst in the enantioselective domino Michael addition/cyclization reaction of oxoindolines with cyclic 1,3-diketones to afford the chiral spiro-conjugated oxindoles featuring 2-aminopyrans fusing with carbo-heterocyclic ring systems with excellent chemical yields (up to 98%) and enantioselectivities (up to 95% ee). The obtained chiral spiro-conjugated 2-aminopyrans bearing quaternary stereogenic carbon center could be used as synthetic precursors for several natural products that have a broad spectrum of fascinating biological activities.