Metal-catalyzed synthesis of cyclic imines: a versatile scaffold in organic synthesis

Photomediated One-Pot Multicomponent Cascade Reaction for the Synthesis of N-Acyl/Sulfonyl-α-Phosphonated-1,2,3,4-Tetrahydroisoquinoline via Twice Acyl/Sulfonyl Iminium Formation

N-acyl/sulfonyl-α-phosphonated 1,2,3,4-tetrahydroiso-quinolines (THIQs) are significant structural motifs in organic synthesis and drug discovery. However, the one-pot approach enabling direct difunctionalization of THIQs remains challenging. Herein we report a photomediated one-pot multicomponent cascade reaction to access N-acyl/sulfonyl-α-phosphonated THIQs via twice acyl/sulfonyl iminium. This method features air as an oxidant, high atom and step economy, and mild conditions.

Selective electrochemical acceptorless dehydrogenation reactions of tetrahydroisoquinoline derivatives

Selective dehydrogenation reactions of tetrahydroisoquinoline derivatives through electrochemical oxidation are disclosed. In the presence of nitric acid, the selective partial dehydrogenation of tetrahydroisoquinolines to form 3,4-dihydroisoquinolines was achieved via anodic oxidation. The results of CV (Cyclic Voltammograms) experiments and DFT calculations showed the 3,4-dihydroisoquinolines protonated by an external Brønsted acid to be less prone than their unprotonated counterparts to oxidation under electrochemical conditions, thus avoiding their further dehydrogenation. Moreover, a TEMPO-mediated electrochemical oxidation enabled a complete dehydrogenation to yield fully aromatized isoquinolines. Thus, tunable processes involving electrochemical dehydrogenation of tetrahydroisoquinolines could be used to selectively produce various 3,4-dihydroisoquinolines and isoquinoline derivatives.

Coupling Interrupted Fischer and Multicomponent Joullié-Ugi to Chase Chemical Diversity: from Batch to Sustainable Flow Synthesis of Peptidomimetics

The generation of peptidomimetic substructures for medicinal chemistry purposes requires effective and divergent synthetic methods. We present in this work an efficient flow process that allows quick modulation of reagents for Joullié-Ugi multicomponent reaction, using spiroindolenines as core motifs. This sterically hindered imine equivalent could successfully be diversified using various isocyanides and amino acids in generally good space-time yields. A telescoped flow process combining interrupted Fischer reaction for spiroindolenine synthesis and subsequent Joullié-Ugi-type modification resulted in product formation in very good overall yield in less than 2 hours compared to 48 hours required in batch mode. The developed protocol can be seen as a general tool for rapid and facile generation of peptidomimetic compounds. We also showcase preliminary biological assessments for the prepared compounds.

Recent Development of Bis-Cyclometalated Chiral-at-Iridium and Rhodium Complexes for Asymmetric Catalysis

The field of asymmetric catalysis has been developing to access synthetically efficacious chiral molecules from the last century. Although there are many sustainable ways to produce nonracemic molecules, simplified and unique methodologies are always appreciated. In the recent developments of asymmetric catalysis, chiral-at-metal Lewis acid catalysis has been recognized as an attractive strategy. The catalysts coordinatively activate a substrate while serving the sole source of chirality by virtue of its helical environment. These configurationally stable complexes were utilized in a large number of asymmetric transformations, ranging from asymmetric Lewis acid catalysis to photoredox and electrocatalysis. Here we provide a comprehensive review of the current advancements in asymmetric catalysis utilizing iridium and rhodium-based chiral-at-metal complexes as catalysts. First, the asymmetric transformations via LUMO and HOMO activation assisted by a chiral Lewis acid catalyst are reviewed. In the second part, visible-light-induced asymmetric catalysis is summarized. The asymmetric transformation via the electricity-driven method is discussed in the final section.

Cyclic Imines in Ugi and Ugi-Type Reactions

Ugi four-component reactions (U-4CRs) are widely recognized as being highly efficient for the synthesis of pseudopeptides. However, the products of these reactions are not so interesting as drug candidates because they are not conformationally restricted enough for a potent interaction with biological targets. One possible way to overcome this problem is to replace amine and oxo components in the U-4CRs with cyclic imines in so-called Joullié-Ugi three-component reactions (JU-3CRs). This approach provides a robust single-step route to peptide moieties connected to N-heterocyclic motifs that are found as core skeletons in many natural products and pharmaceutical compounds. JU-3CRs also provide much better diastereoselectivity than their four-component analogues. We survey here the redesign of many synthetic routes for the efficient preparation of a wide variety of three-, five-, six-, and seven-membered heterocyclic compounds connected to the peptide backbone. Additionally, in the Ugi reactions based on the cyclic imines, α-acidic isocyanides, or azides can be replaced with normal isocyanides or acids, respectively, leading to the synthesis of N-heterocycles attached to oxazoles or tetrazoles, which are of great pharmaceutical significance. This Review includes all research articles related to Ugi reactions based on the cyclic imines to the year 2020 and will be useful to chemists in designing novel synthetic routes for the synthesis of individual and combinatorial libraries of natural products and drug-like compounds.

Aminophosphonates and aminophosphonic acids with tetrasubstituted stereogenic center: diastereoselective synthesis from cyclic ketimines

New chiral tetrasubstituted aminophosphonic acid derivatives of hexahydroquinoxalin-2(1H)-one were synthesised via highly diastereoselective hydrophosphonylation of the corresponding imines with tris(trimethylsilyl) phosphite as phosphorus nucleophile. High asymmetric induction, good yields, mild reaction conditions, and ease of purification of the final products are the key advantages of the presented protocol.

Cyclic imines – preparation and application in synthesis

Cyclic imines, available from various nitrogen-containing reactants, serve as versatile synthetic intermediates for biologically active compounds.