K2CO3-Catalyzed (3 + 2) Cycloaddition Reaction of N-2,2,2-Trifluoroethylisatin Ketimines with Azodicarboxylates: Access to Spirooxindoles Containing Trifluoromethyl-1,2,4-triazolines

Potassium carbonate-catalyzed (3 + 2) cycloaddition reaction between N-2,2,2-trifluoroethylisatin ketimines and azodicarboxylates has been developed, constructing a series of novel N-heterocycle infused spirooxindoles in good to excellent yields (up to 98%) under milder conditions. The presence of both biologically active oxindole and trifluoromethyl-1,2,4-triazoline moieties in these novel spirocyclic compounds would provide new lead structures in the discovery of heterocyclic compounds with potential pharmaceutical activities.

Recent Advances of N-2,2,2-Trifluoroethylisatin Ketimines in Organic Synthesis

The special properties of fluorine atoms and fluorine-containing groups have led to an increasing number of applications for fluorine-containing organic compounds, which are also extremely widely used in the field of new drug development. Unfortunately, naturally fluorinated organics are rare in nature, so the selective introduction of fluorine atoms or fluorine-containing groups into organic molecules is very important for pharmaceutical/synthetic chemists. N-2,2,2-trifluoroethylisatin ketimines have received the attention of many chemists since they were first developed as fluorine-containing synthons in 2015. This paper reviews the organic synthesis reactions in which trifluoroethyl isatin ketimine has been involved in recent years, focusing on the types of reactions and the stereoselectivity of products, and also provides a prospect of its application in this field.

Stereoselective synthesis of CF3-containing spirocyclic-oxindoles using N-2,2,2-trifluoroethylisatin ketimines: an update

The introduction of fluorine-containing groups into organic molecules either changes or improves the characteristics of the target compounds. On the other hand, spirocyclic-oxindoles featuring C-3 functionalized sp3-hybridized carbon atoms of three-dimensional orthogonally shaped molecules were well recognized in the core structure of varied natural products and synthetic pharmaceutical targets. Consequently, the construction of spirooxindoles by an elegant synthetic approach with efficient stereocontrol has received tremendous interest over the past decades. In this context of the synergic combination of the features associated with fluorine-containing compounds and the synthetic and medicinal efficiency associated with spirooxindoles, the stereodivergent installation of CF3 groups embedded with spirooxindoles is of increasing academic and scientific interest. This mini-review article is dedicated to demonstrating a critical overview of the recent stereoselective synthesis of spirocyclic-oxindoles featuring trifluoromethyl groups by employing the reactivity of N-2,2,2-trifluoroethylisatin ketimines as an efficient and easily prepared synthon, and covers the literature reports from 2020 to date. Besides exploring the advancements accomplished in this area, we also investigate the limitations associated with reaction discovery, mechanistic rationalization, and future applications.

Pyridine vs DABCO vs TBAB in Annulations of δ-Acetoxy Allenoates with Thioamides Leading to Dihydrothiophene, Thiopyran, and Thiazole Scaffolds

The same δ-acetoxy allenoates and thioamides, under DABCO, pyridine, or tetra-n-butyl ammonium bromide (TBAB) catalysis, undergo distinctly different annulations giving chemoselective routes to dihydrothiophene, thiopyran, or thiazole motifs. Thus, using pyridine in [3 + 2] annulation, dihydrothiophenes are obtained as essentially single diastereomers. By contrast, under DABCO catalysis, allenoates deliver thiopyran motifs in good to high yields through 6-exo-dig cyclization. In the thiazole forming [3 + 2] annulation, tetra-n-butyl ammonium bromide (TBAB) facilitates addition-elimination and 5-exo-trig cyclization in which β- and γ-carbons of allenoates participate to deliver thiazole cores exclusively with a Z-isomeric exocyclic double bond. A possible rationale for these observations is delved into.

Ligand-dependent, palladium-catalyzed stereodivergent synthesis of chiral tetrahydroquinolines

The most fundamental tasks in asymmetric synthesis are the development of fully stereodivergent strategies to access the full complement of stereoisomers of products bearing multiple stereocenters. Although great progress has been made in the past few decades, developing general and practical strategies that allow selective generation of any diastereomer of a reaction product bearing multiple stereocentres through switching distinct chiral catalysts is a significant challenge. Here, attaining precise switching of the product stereochemistry, we develop a novel P-chirogenic ligand, i.e.YuePhos, which can be easily derived from inexpensive and commercially available starting materials in four chemical operations. Through switching of three chiral ligands, an unprecedented ligand-dependent diastereodivergent Pd-catalyzed asymmetric intermolecular [4 + 2] cycloaddition reaction of vinyl benzoxazinanone with α-arylidene succinimides was developed. This novel method provides an efficient route for the stereodivergent synthesis of six stereoisomers of pyrrolidines bearing up to three adjacent stereocenters (one quaternary center). Despite the anticipated challenges associated with controlling stereoselectivity in such a complex system, the products are obtained in enantiomeric excesses ranging up to 98% ee. In addition, the synthetic utilities of optically active hexahydrocarbazoles are also shown.

An unprecedented ligand-dependent stereodivergent Pd-catalyzed asymmetric intermolecular [4 + 2] cycloaddition reaction of vinyl benzoxazinanone with α-aryliene succinimides was developed.