Invertible Enantioselectivity in 6′-Deoxy-6′-acylamino-β-isocupreidine-Catalyzed Asymmetric Aza-Morita−Baylis−Hillman Reaction: Key Role of Achiral Additive

Abstract

The beta-ICD (1a) or beta-ICD-amide (1e)-catalyzed aza-Morita-Baylis-Hillman reaction between N-sulfonylimines 3 and alkyl vinyl ketones 4 produced the (R)-enriched adducts 5. By adding a catalytic amount of beta-naphthol (2a), the enantioselectivity of the same reaction was inversed leading to (S)-5 in excellent yields and enantioselectivities. Both aromatic and aliphatic imines are accepted as substrates for this reaction.

An Achiral‐Acid‐Induced Switch in the Enantioselectivity of a Chiral cis‐Diamine‐Based Organocatalyst for Asymmetric Aldol and Mannich Reactions

“…In marked contrast, an initial effort for the synthetic application of chiral organocatalysts has appeared very recently, but has not been developed to a synthetically useful level. [3] In this context, we explored the capability of an additive to induce an unexpected inversion in catalyst selectivity for certain asymmetric transformations catalyzed by a single chiral organocatalyst. Herein we present the first practical example of such a system, employing achiral, organic acids as reliable additives in asymmetric, direct aldol reactions catalyzed by a chiral, cisdiamine-based, Tf-amido organocatalyst of type 1 (Tf = trifluoromethanesulfonyl Scheme 1).…”

Asymmetric Hydrogenation of 2,4‐Disubstituted 1,5‐Benzodiazepines Using Cationic Ruthenium Diamine Catalysts: An Unusual Achiral Counteranion Induced Reversal of Enantioselectivity

“…In addition to the conventional method, in which chirality is introduced using a metal‐catalyzed transformation wherein both enantiomers of a chiral ligand are used, a number of alternative approaches have recently been developed wherein only a single enantiomer of the chiral ligand is required 7. 8 For example, the sense of asymmetric induction of a metal‐catalyzed reaction can be reversed by using different metals in the presence of the same enantiomer of ligand,7a–c the use of additives,7d,e and by changing reaction parameters such as pressure, temperature, and solvent. [7f–h] Also, the identity of the counteranion was found to play an important role in the reactivity and stereoselectivity of cationic metal catalysts in asymmetric reactions 9.…”

Enantiodivergent and γ‐Selective Asymmetric Allylic Amination

“…Metal‐catalyzed enantiodivergent asymmetric catalysis can be achieved by tuning various parameters, including additive, counter ion, temperature, pressure, and solvent, used in the reactions 7a. Few organocatalytic enantiodivergent reactions have been observed; however, several were reported for an asymmetric Baylis–Hilman reaction 7b–d. In a recent example, a guanidine/bisthiourea‐catalyzed Mannich‐type reaction achieved a reversal of enantioselectivity by utilizing different solvent conditions 8.…”