Iminium Ions as Dienophiles in Aza‐Diels–Alder Reactions: A Closer Look

Abstract

This review highlights the state of the art of the use of iminium ions as dienophiles in Aza-Diels-Alder (ADA) cycloadditions. An historical survey spanning the very first discovery of the reaction to modern developments, mechanistic studies and synthetic applications of the iminium variant of the ADA (iADA) reaction are presented. The discussion is focused on the intermolecular and intramolecular versions of the iADA reactions that are conducted in aqueous solutions to generate, in situ, the reactive dienophile from an amine hydrochloride and either aliphatic or aromatic aldehydes in the presence of a variety of dienes. The retro-ADA reaction is also presented as an interesting method for the protection of amines. The use of Lewis acid catalysis in these reactions was thoroughly studied by the reactions of different amines and aldehydes conducted in the presence of lanthanide(III) complexes.

Simple descriptors for assessing the outcome of aza-Diels–Alder reactions

“…Likewise, the natural charge of C (3) ranges from +0.189e (I13-Im) to +0.216e (I4-Im). In summary, the effective atomic charges of N (2) and C (3) vary along a narrow range of about 0.03e, and, although being apparently sensitive to Ta's constants s* and E S , their small variation hinders the development of a linear model similar to the one established for u.…”

Computational Insight to Improve the Thermal Isomerisation Performance of Overcrowded Alkene‐Based Molecular Motors through Structural Redesign

“…In this regard, TS3 and TS6 can be described as being highly asynchronous. This description is reminiscent of the way that organic pericyclic reactions oftentimes occur in a perfectly concerted fashion (i.e., without intermediates), despite that the corresponding TSs are asynchronous with respect to how far the bond formation processes mediated by the TSs have progressed . Notwithstanding, in TS3/TS6, the stator substituents are no longer co‐planar with the olefinic bond, as they are in the initial species (e.g., for 2 a , the δ dihedral angle changes from 9° in ( P )‐unstable‐ Z to 75° in TS3, see Table S3).…”

Phosphine-catalyzed [4+2] annulations of α-aminonitriles with allenoates: Synthesis of functionalized tetrahydropyridines

“…Thereinto, six-membered azaheterocycles such as substituted tetrahydropyridines and piperidines have received considerable attention due to their frequent occurrence in biologically active natural products and synthetic pharmaceuticals [4][5][6][7] . [4+2] Cycloaddition reaction constitutes one of the most versatile and efficient methods to prepare this type of azaheterocycles [8][9][10][11][12] . Among them, phosphine catalyzed dipolar cycloaddition has recently emerged as a powerful approach to prepare a range of carbo-and heterocyclic motifs [13][14][15][16][17][18][19][20][21] , since Lu's pioneering work [22,23] on phosphine-catalyzed [3+2] cycloadditions of allenoate with aldimines in particular.…”