Toshiyuki Saiki

Structures of bridged calix[6]arenes bearing a bromide functionality in the cavity

Abstract The structures of bridged calix[6]arenes 1a and 1b were investigated. Whereas 1a was found to take a structure where the bridging unit lies below the calix[6]arene macroring with a cone conformation, its tetramethyl ether 1b adopts the 1,2,3-alternate conformation with the central bromide functionality pointing into the cavity, as revealed by X-ray crystallographic analysis.

Synthesis of redox active large macrocyclic hosts and the recognition of secondary ammonium salts

Abstract Interconvertible macrocyclic hosts containing thiol groups or a disulfide linkage in the binding cavity have been synthesized. The binding affinities of the reduced and oxidized forms toward benzylammoium derivatives are completely reverse. Formation of pseudorotaxane is suggested upon the host–guest complexation.

Syntheses and structures of novel m-xylylene-bridged calix(6)arenes: stabilization of a sulfenic acid in the cavity of calix(6)arene

Abstract The syntheses and structures of novel bridged calix[6]arenes 1 with inwardly directed functional groups in the cavity, and application of the bicyclic framework to the stabilization of a sulfenic acid are described. It was found that, unlike their precursors 2, the tetramethoxy compounds 1 have a tendency to adopt the 1,2,3-alternate conformation at least in the crystalline state, except when the central functionality has a large steric demand. Thermolysis of sulfoxide 1g at 80°C in toluene afforded the stable sulfenic acid 1h almost quantitatively; the structure was determined by X-ray analysis. The SOH group was found to be directed into the cavity and surrounded by the calix[6]arene macrocycle with the 1,2,3-alternate conformation, being protected from self-condensation leading to the corresponding thiosulfinate. The high stability of 1h demonstrates that the framework of the bridged calix[6]arene can effectively regulate the reactivity of the functional group fixed in the cavity.

Synthesis, Structure, and Reactions of Stable Selenenic Acids Bearing Novel Bridged Calix[6]Arene Frameworks

Isolable selenenic acids were synthesized for the first time by taking advantage of the bridged calix[6]arene frameworks. X-ray crystallographic analysis established the structure of the compound with a cone conformation, where the SeOH functionality is deeply buried in the cavity of the p-tert-butylcalix[6]arene macrocycle. Its thermal stability was so remarkable that no decomposition was observed even after heating at 120 °C for 5 h in CDCl2CDCl2.

Abnormal reaction of an aryl azide confined in a calix[6]arene skeleton

Photolysis of an aryl azide embedded in a m-phenylene-bridged p-tert-butylcalix[6]arene 2 results in the formation of unusual reaction products 3 and 4via the transannular addition reaction of an initially formed nitrene intermediate; the molecular structure of 4 was determined by X-ray crystallographic analysis.

A Hydrogen-Bonded Organic Network with Appended Chiral Metal Complexes

Abstract Treatment of anthracenebisresorcinol (1·4H) with La(OiPr)3 and binaphthol (BN·2H) as a chiral ligand affords an amorphous and insoluble 1:2:2 adduct (chiral La host) formulated as (1·2H)2-·2(LaBN)+. This formulation suggests that chiral La3+-binaphthoxide moieties are attached to the half-deprotonated hydrogen-bonded network of the host. The chiral La host catalyzes the Michael reaction of dimethyl malonate with cyclohexenone with ee ≡ 70%. The analogous chiral Al host (1·2H)2-·2(AlBN)+ obtained from Al(CH3)3 catalyzes the Diels-Alder reaction between N-crotonoyl-1,3-oxazolidin-2-one and cyclopentadiene with an ee of ∼75% for the minor exo product.