The straightforward syntheses of C3v symmetrical calix[6]trisureas and -thiourea have been achieved. NMR studies have shown that these flexible compounds possess a major cone conformation. While these neutral hosts can strongly bind anions such as AcO(-) or HSO4(-) through induced fit processes, they can also behave as unique heteroditopic receptors for organic ion pairs with a remarkable positive cooperativity in the complexation process, the anion acting as an allosteric effector.

Intramolecular and intermolecular alkylations of carbocation precursors of limited ionization ability, principally N,O-acetals, without the use of an exogenous reagent have been developed. The reactions are carried out in 1,1,2,2-tetrachloroethane (TCE) and take advantage of the ability of this solvent to continuously release small amounts of HCl by thermolytic elimination. A study of the reaction led to several improved protocols such as (1) preheated TCE, (2) microwave-assisted reactions, and (3) flow or sealed-tube conditions, which allow significant reaction rate enhancements and made possible some challenging reactions such as the α-amidoalkylation of ketones. Studies using flow chemistry confirmed not only that very low concentrations of HCl generated from the solvent were responsible for the reactivity but also that TCE had additional beneficial properties in comparison to other chlorinated solvents such as dichloroethane. The method can easily be extended to the alkylation using proelectrophiles such as π-activated alcohols, which are normally unreactive toward HCl catalysis. This work represents the first successful use of HCl, the simplest strong Brønsted acid, as an efficient alkylation catalyst.

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Calixarenes O 0450 Calix[6]tris(thio)ureas: Heteroditopic Receptors for the Cooperative Binding of Organic Ion Pairs. -(HAMON, M.; MENAND, M.; LE GAC, S.; LUHMER, M.; DALLA*, V.; JABIN, I.; J. Org. Chem. 73 (2008) 18, 7067-7071; URCOM, Univ. Le Havre, F-76058 Le Havre, Fr.; Eng.) -Lindner 51-051