Transformation of a [4+6] Salicylbisimine Cage to Chemically Robust Amide Cages

Abstract

In recent years, interest in shape‐persistent organic cage compounds has steadily increased, not least because dynamic covalent bond formation enables such structures to be made in high to excellent yields. One often used type of dynamic bond formation is the generation of an imine bond from an aldehyde and an amine. Although the reversibility of the imine bond formation is advantageous for high yields, it is disadvantageous for the chemical stability of the compounds. Amide bonds are, in contrast to imine bonds much more robust. Shape‐persistent amide cages have so far been made by irreversible amide bond formations in multiple steps, very often accompanied by low yields. Here, we present an approach to shape‐persistent amide cages by exploiting a high‐yielding reversible cage formation in the first step, and a Pinnick oxidation as a key step to access the amide cages in just three steps. These chemically robust amide cages can be further transformed by bromination or nitration to allow post‐functionalization in high yields. The impact of the substituents on the gas sorption behavior was also investigated.

Prospects and Challenges in Anion Recognition and Transport

“…For instance, it was recently demonstrated that applying a Pinnick oxidation reaction could convert a dynamic imine cage into a chemically stable amide cage. 57 This might provide a feasible method for making macrocycles or cages containing amide hydrogen-bond donors as anion receptors.…”

Porous Organic Compounds – Small Pores on the Rise

“…To increase the chemical stability of imine cages, reduction to amines was reported but is often accompanied by a higher degree of conformational freedom, leading to loss of porosity. Twelvefold Pinnick oxidation was shown to again lead to highly porous and chemically robust amide cages that are also stable over a large pH range, even allowing further post modification by means of direct bromination [16c] . All sorption data for this class of compounds is presented in Table 2.…”

“… The parent salicylbisimine Tri 4 Di 6 POC SC1 by the group of Mastalerz underwent various reactions for exo ‐functionalization. a) After post‐synthetic methylation, cage Me‐SC1 underwent Pinnick oxidation, for transformation into the chemically robust amide cage SC2 ; [16c] b) reaction of the parent POC SC1 by twelvefold Povarov reaction utilizing phenylacetylene gave quinoline POC SC3 in one step in 25 % yield; [16b] c) and d) a range of salicyldialdehydes 6 & 8 , bearing various alkyl substituents can be used to generate exo ‐functionalized salicylbisimine POCs, that allowed for successful control of the extrinsic pores in crystalline states [16e] . Hydrogen atoms and solvent molecules are omitted for clarity, space‐filling view including hydrogen atoms for exo ‐groups.…”

Chiral self-sorting and guest recognition of porous aromatic cages

“…For example, Cooper and co-workers converted the imine in CC3 to an amine, and the resulting structure can be stable over a wide pH range (pH = 1.7–12.3) 37 . Mastalerz et al reported the transformation of imine bonds in [4 + 6] salicylimine cage into chemically robust amide bonds via Pinnick oxidation 45 . Furthermore, they utilized the Povarov reaction and the subsequent oxidation to transform the salicylimine cage into a quinoline cage which is stable under harsh acidic and basic conditions 46 .…”