N,N-DIIsopropyl-N-phosphonyl imines lead to efficient asymmetric synthesis of aziridine-2-carboxylic esters

Asymmetric Reactions of N-Phosphonyl/Phosphoryl Imines

The asymmetric reactions of imines continued to attract the attention of the scientific community for decades. However, the stereoselective reactions of N-phosphonyl/phosphoryl imines remained less explored as compared to other N-substituted imines. The chiral auxiliary-based asymmetric-induction strategy with N-phosphonyl imines could effectively generate enantio- and diastereomeric amine, α,β-diamine, and other products through various reactions. On the other hand, the asymmetric approach for the generation of chirality through the utilization of optically active ligands, along with metal catalysts, could be successfully implemented on N-phosphonyl/phosphoryl imines to access numerous synthetically challenging chiral amine scaffolds. The current review critically summarizes and reveals the literature precedence of more than a decade to highlight the major achievements existing to date that can display a clear picture of advancement as well drawbacks in this area.

3-Arylaziridine-2-carboxylic Acid Derivatives and (3-Arylaziridin-2-yl)ketones: The Aziridination Approaches

Aziridination reactions represent a powerful tool in aziridine synthesis. Significant progress has been achieved in this field in the last decades, whereas highly functionalized aziridines including 3-arylated aziridine-2-carbonyl compounds play an important role in both medical and synthetic chemistry. For the reasons listed, in the current review we have focused on the ways to obtain 3-arylated aziridines and on the recent advances (mainly since the year 2000) in the methodology of the synthesis of these compounds via aziridination.

Synthesis of Structurally Diverse 3-, 4-, 5-, and 6-Membered Heterocycles from Diisopropyl Iminomalonates and Soft C-Nucleophiles

Herein, we present a general synthetic strategy for the preparation of 3-, 4-, 5-, and 6-membered heterocyclic unnatural amino acid derivatives by exploiting facile Mannich-type reactions between readily available N-alkyl- and N-aryl-substituted diisopropyl iminomalonates and a wide range of soft anionic C-nucleophiles without using any catalyst or additive. Fully substituted aziridines were obtained in a single step when enolates of α-bromo esters were employed as nucleophiles. Enantiomerically enriched azetidines, γ-lactones, and tetrahydroquinolines were obtained via a two-step catalytic asymmetric reduction and cyclization sequence from ketone enolate-derived adducts. Finally, highly substituted γ-lactams were prepared in one pot from adducts obtained using acetonitrile-derived carbanions. Overall, this work clearly demonstrates the utility of iminomalonates as highly versatile building blocks for the practical and scalable synthesis of structurally diverse heterocycles.

One-Pot Syntesis of 3-Functionalized 4-Hydroxycoumarin under Catalyst-Free Conditions

A concise and efficient one-pot synthesis of 3-functionalized 4-hydroxycoumarin derivatives via a three-component domino reaction of 4-hydroxycoumarin, phenylglyoxal and 3-arylaminocyclopent-2-enone or 4-arylaminofuran-2(5H)-one under catalyst-free and microwave irradiation conditions is described. This synthesis involves a group-assisted purification process, which avoids traditional recrystallization and chromatographic purification methods.

An efficient one-pot synthesis of functionalized chromeno[4,3-b]pyridine derivatives under catalyst-free conditions

A concise, efficient one-pot synthesis of functionalized chromeno[4,3-b]pyridine derivatives via a three-component reaction of 4-oxo-4H-chromene-3-carbaldehydes, malononitrile or cyanoacetates, and aromatic amines under catalyst-free conditions in an environmentally friendly medium (ethanol-water, 3:1 v/v) is described. This synthesis involves a group-assisted purification process, which avoids traditional recrystallization and chromatographic purification methods.

N-Phosphonyl/phosphinyl imines and group-assisted purification (GAP) chemistry/technology

Group-assisted purification (GAP) chemistry, which can provide various chiral amines and other functionalities without the use of column chromatography or recrystallization; products are consistently obtained with excellent stereocontrol.

Synthesis of chiral N-phosphinyl α-imino esters and their application in asymmetric synthesis of α-amino esters by reduction

A variety of chiral N-phosphinyl α-imino esters have been synthesized for the first time from ketoesters and phosphinylamide, which were then reduced by L-selectride to give the corresponding N-phosphinyl-protected α-amino esters. The reduction proceeded very well with excellent chemical yields (88–98%) as well as high diastereoselectivities (96:4 to 99:1). Some of these products could be obtained without column chromatography and recrystallization. The chiral phosphinyl auxiliary could be easily cleaved under acidic conditions.