Organocatalytic enantioselective Mannich reaction of isoxazol-5(4H)-ones to isatin-derived ketimines

An efficient organocatalytic asymmetric Mannich reaction between isoxazol-5(4H)-ones and isatin-derived ketimines has been developed. A bifunctional squaramide/Brønsted base organocatalyst catalyzed the enantioselective Mannich addition to afford chiral 3-aminooxindoles bearing a tetrasubstituted stereocenter at C3 decorated with an isoxazole moiety in good yields and with excellent enantioselectivities. Additionally, several synthetic transformations were described showing the versatility of the prepared compounds.

Organocatalytic enantioselective 1,6-aza-Michael addition of isoxazolin-5-ones to p-quinone methides

A thiourea-Brønsted base bifunctional catalyst allowed the enantioselective 1,6-aza-Michael addition of isoxazolin-5-ones to p-quinone methides to give isoxazolin-5-ones having a chiral diarylmethyl moiety attached to the N atom with fair to good yields and enantiomeric excesses. To the best of our knowledge this reaction represents the first example of enantioselective N-alkylation of isoxazolin-5-ones as well as the first example of enantioselective 1,6-aza-Michael reaction involving p-quinone methides.

Asymmetric Addition and Cycloaddition Reactions with Ylidene‐Five‐Membered Heterocycles

Five-membered heterocycles bearing an exocyclic double bond have been successfully used as substrates in asymmetric addition and cycloaddition reactions. Ylidene-heterocycles are attractive substrates due to their high functionalization and the presence of an electrophilic conjugated exocyclic double bound that can participate in nucleophilic addition reactions as well as cycloaddition reactions, which may be triggered by the formation of aromatic intermediates or products in many cases. During the last decades, catalytic methodologies have been developed using ylidene-heterocycles as substrates in order to synthesize useful optically active heterocyclic derivatives. 4-Ylidene-pyrazol-5-one…

Organocatalytic Enantioselective 1,6-aza -Michael Addition of Isoxazolin-5-ones to p -Quinone Methides

CCDC 1961393: Experimental Crystal Structure Determination

Related Article: Ricardo Torán, Carlos Vila, Amparo Sanz-Marco, M. Carmen Muñoz, José R. Pedro, Gonzalo Blay|2020|Eur.J.Org.Chem.|2020|627|doi:10.1002/ejoc.201901907