Acetaldehyde: A Small Organic Molecule with Big Impact on Organocatalytic Reactions

The Cyclohexa-2,5-dienyl Group as a Placeholder for Hydrogen: Organocatalytic Michael Addition of an Acetaldehyde Surrogate

An aldehyde with a cyclohexa-2,5-dienyl group in the α-position is introduced as a storable surrogate of highly reactive acetaldehyde. The cyclohexa-2,5-dienyl unit is compatible with an enantioselective Michael addition to nitroalkenes promoted by a Hayashi-Jørgensen catalyst and can be removed by a boron Lewis acid mediated C-C bond cleavage. The robust two-step sequence does not require a large excess of the aldehyde component that is typically needed when directly using acetaldehyde.

Development of bifunctional organocatalysts and application to asymmetric total synthesis of naucleofficine I and II

The proline-type organocatalysts has been efficiently employed to catalyze a wide range of asymmetric transformations; however, there are still many synthetically useful and challenging transformations that remain unachievable in an asymmetric fashion. Herein, a chiral bifunctional organocatalyst with a spirocyclic pyrrolidine backbone-derived containing fluoro-alkyl and aryl sulfonamide functionalities, are designed, prepared, and examined in the asymmetric Mannich/acylation/Wittig reaction sequence of 3,4-dihydro-β-carboline with acetaldehyde, acyl halides, and Wittig reagents. As a result, the spirocyclic pyrrolidine trifluoromethanesulfonamide catalyst can facilitate this versatile sequence as demonstrated by 18 examples displaying excellent enantioselectivity (up to 94% ee), as well as moderate to good yields (up to 54% over 3 steps). As a practical application, the asymmetric total synthesis of naucleofficine I (1a) and II (1b) in ten steps have been accomplished.

Natural products often contain complex N-fused polycyclic structures with multiple substituents and stereocentres. Here, the authors developed a bifunctional organocatalyst that is instrumental in obtaining such structures and applied it to the total synthesis of naucleofficine I and II in 6 steps.

A practical green approach to diversified spirochromene/spiropyran scaffolds via a glucose–water synergy driven organocatalytic system

Development of a versatile, new glucose–water organocatalytic system promoted, one pot, practical green method for the synthesis of diversified spirochromenes/spiropyrans is reported.

Chiral Primary Amine Catalysis for Asymmetric Mannich Reactions of Aldehydes with Ketimines: Stereoselectivity and Reactivity

The application potential of primary amine catalysts in the context of Mannich reactions of aldehydes with ketimines is exemplified by isatin-derived ketimines and cyclic trifluoromethyl ketimines. Primary amine catalysts exhibit either unusual stereoselectivity or reactivity, which is not observable with secondary amine catalysts. Moreover, reversal of diastereofacial selectivity between primary and secondary amine catalysts is disclosed. These new reactions provide useful methods for the syntheses of chiral 3-substituted 3-amino-2-oxindoles and dihydroquinazolinones bearing a trifluoromethylated quaternary stereocenter. The synthetic utility of the reactions is demonstrated through the formal synthesis of AG-041R and DPC 083 and the total synthesis of (-)-psychotriasine.

Bioorganopromoted green Friedländer synthesis: a versatile new malic acid promoted solvent free approach to multisubstituted quinolines

An efficient new strategy for the green synthesis of a variety of polysubstituted quinolines, using the Friedländer approach is reported, employing malic acid as a catalyst in organic synthesis for the first time.

Organocatalytic domino Knöevenagel–Michael reaction in water for the regioselective synthesis of benzo[4,5]imidazo[1,2-a]pyrimidines and pyrido[2,3-d]pyrimidin-2-amines

An organocatalyzed aqueous media domino reaction is developed for the regioselective synthesis of benzo[4,5]imidazo[1,2-a]pyrimidines and pyrido[2,3-d]pyrimidin-2-amines.

Asymmetric synthesis of bicyclic dihydropyrans via organocatalytic inverse-electron-demand oxo-Diels–Alder reactions of enolizable aliphatic aldehydes

An unprecedented highly enantioselective amine catalyzed oxo-IEDDA reaction of cyclic enones with enolizable aldehydes including aqueous acetaldehyde has been developed.