Organocatalytic α-Addition of Isocyanides to Aldehydes

Isocyanide-based Multicomponent Reactions (IMCRs) in Water or Aqueous Biphasic Systems

BACKGROUND

Isocyanide is an intriguing one-carbon synthon that is frequently employed in a variety of carbon-carbon and carbon-heteroatom bond-forming reactions. Isocyanide-based multicomponent reactions (IMCRs) are effective synthetic tools in organic synthesis for the preparation of complex heterocyclic molecules. The IMCRs in water have become an attractive research direction, enabling simultaneous growth of both IMCRs and green solvents towards ideal organic synthesis.

OBJECTIVE

The goal of this review is to provide a general overview of IMCRs in water or biphasic aqueous systems for accessing various organic molecules, as well as an examination of their benefits and mechanistic insights.

CONCLUSION

High atom economies, mild reaction conditions, high yields, and catalyst-free processes are crucial features of these IMCRs in water or biphasic aqueous systems.

Organocatalytic multicomponent coupling to access a highly functionalised tetracyclic furoindoline: interrupted Passerini/Joullié-Ugi cascade reaction

The interrupted Passerini reaction of 3-(2-isocyanoethyl)-indole catalysed by 3,5,6-trifluoro-2-pyridone is described. The reaction diastereoselectively provided a tetracyclic furolindoline, which proved to be a good substrate for the Joullié-Ugi reaction; therefore, the sequential Passerini/Joullié-Ugi reactions were performed in one-pot to rapidly provide versatile and highly functionalised furoindolines from 3-(2-isocyanoethyl)-indole.

6-Halo-2-pyridone as an efficient organocatalyst for ester aminolysis

It was found that 6-halo-2-pyridones catalysed ester aminolysis in which not only reactive aryl esters but also relatively less reactive methyl and benzyl esters could be used as a substrate. The reaction could be performed without strictly dry and anaerobic conditions and the 6-chloro-2-pyridone catalyst could be recovered quantitatively after reaction. The method could be applied to dipeptide synthesis from methyl or benzyl esters of amino acids, where a high enantiomeric purity of the products was maintained. The mechanism involving dual activation of ester and amine substrates through hydrogen bonding between catalyst and substrates is proposed where 6-halo-2-pyridones act as a bifunctional Brønsted acid/base catalyst.

6-Halo-2-pyridones effectively catalyse ester aminolysis as bifunctional catalysts. This reaction did not require any special conditions and was operationally convenient.

One-step synthesis of N,N'-substituted 4-imidazolidinones by an isocyanide-based pseudo-five-multicomponent reaction

A pseudo-five-multicomponent reaction involving an isocyanide, a primary amine, two molecules of formaldehyde and water is reported, which gives N,N'-substituted 4-imidazolidinones when trifluoroethanol is used as the solvent. The reaction proceeds with good yields and with a wide variety of amines and isocyanides, providing an efficient new entry to these heterocycles. A preliminary study of the reaction mechanism suggests that trifluoroethanol, although acting as the solvent, is directly involved as a reagent in the reaction pathway.