Efficient isonitrile hydration through encapsulation within a hexameric self-assembled capsule and selective inhibition by a photo-controllable competitive guest

Abstract

Catalytic hydration of neutral isonitriles to yield the corresponding N-formylamides was achieved by reversible encapsulation in a self-assembled hexameric resorcin[4]arene capsule. Encapsulation of a photochromic dithienylethene bis-cation provides different levels of competitive inhibition depending on the geometry assumed by the cationic inhibitor.

Supramolecular Catalysis in the Synthesis of Substituted 1 H‐Tetrazoles from Isonitriles by a Self‐Assembled Hexameric Capsule

“…All of these control experiments clearly indicates the activation of the reaction occurs by encapsulation of the reagents, [16] and the possible stabilization by the electron-rich surface of the cavity rather than activation by hydrogen bonding between the reagents and the hydroxyl groups of 1. It is also notable that in all experiments, only trace amounts of the corresponding formamides-the products of isonitrile hydration [16] -were observed, which are instead formed when TMSN 3 is present in the reaction mixture. This demonstrates that the 1H-tetrazole synthesis is chemoselective in the presence of the capsule.…”

“…The first of these is the selective hydrolysis of acetals, [15] and the second is the hydration of isonitriles to formamides driven by encapsulation of the substrates, which was recently disclosed by our group. [16] Herein we present an example of an efficient, supramolecular, catalytic synthesis of aliphatic and aromatic 1-substituted 1H-tetrazoles by addition of trimethylsilyl azide (TMSN 3 ) to isonitriles, mediated by the hexameric capsule 1 6 ·8 H 2 O (Scheme 1). The reaction is rapid and efficient, showing inhibition of the catalytic activity in the presence of competitive guests, which is a typical feature reminiscent of enzymatic catalysis.…”

“…It is likely that with resorcinol, hydrogen-bonding activation of the reaction takes place, however the activation effect is much smaller compared to the self-assembled capsule based on the resorcin[4]arene 1. As it is known from previous studies that isonitriles are good guests for the hexamer, [16] we performed another experiment, repeating the reaction between TMSN 3 and 2 a in the presence of capsule and 10 equivalents of tetraethylammonium tetrafluoroborate as a competitive guest [7] for the capsule (Table 1, entry 5). Under these experimental conditions the catalytic activity decreased markedly, indicating the importance for the catalytic activation of the reaction of having a capsule with an accessible cavity.…”

The Hexameric Resorcinarene Capsule at Work: Supramolecular Catalysis in Confined Spaces

“…In the presenceo fCR 6 ,t he neutral isonitriles were encapsulated inside its hydrophobic cavity where they were hydrolyzed with as ubstrate-dependent efficiency.F or 42 a,c,d (Scheme 13), quantitative hydrolysis was observed within 18 hi nt he presence of CR 6 ,whereas lower conversionswere detected for substrates 42 b,e. [33] The ability of CR 6 to encapsulate isonitrile derivatives has been exploited for the synthesis of substituted 1H-tetrazoles from trimethylsilyl azide. [34] Thus, if 42 d (133 mm) and TMSN 3 (133 mm)w ere mixed in the absence of CR 6 ,t hen the reaction did not take place, even after 5h at 60 8C.…”

“…Hydration reaction of isonitriles inside the hexameric capsule CR 6 . [33] Scheme14. Example of the inhibition of the catalytic activity of hexameric capsule CR 6 by acompetitive tetraethylammonium guest.…”