title: Synthesis and Conformational Characteristics of Inherently Chiral Monoalkyl Ethers of p-tert-Butyldihomooxacalix[4]arene.
abstract: The synthesis of four inherently chiral monoalkyl ethers (methyl, ethyl, allyl, and benzyl), derived from p-tert-butyldihomooxacalix[4]arene, is described. Their conformational features were studied by variable temperature (1)H NMR spectroscopy in solvents with different polarity, such as chloroform (or CDCl(2)CDCl(2)), acetone, DMSO, and pyridine. Coalescence temperatures and DeltaG() were determined in CDCl(2)CDCl(2) and pyridine solutions. Monomethyl ether has a T(c) of 86 degrees C in CDCl(2)CDCl(2) and of -8 degrees C in pyridine, and the other derivatives are conformationally immobilized (DeltaG() >> 20 kcal mol(-1) in both solvents). The cone conformation, obtained for all monoethers, was confirmed by (13)C and NOESY spectra and also from a series of NOE 1D experiments. Complete assignment of both proton and carbon NMR spectra was achieved for the monomethyl ether by a combination of COSY, HMQC, and selective INEPT experiments, in chloroform at room temperature. Inherent chirality for all compounds was demonstrated by the addition of Pirkle's reagent to CDCl(3) solutions of monoethers derivatives, causing duplication of the NMR proton signals.
authors.affiliation: Faculdade de Farmácia de Lisboa and Departamento de Química, Faculdade de Ciências de Lisboa, Rua da Escola Politécnica, 58, 1250 Lisboa, Portugal, Instituto Superior Técnico, Complexo I, Av. Rovisco Pais, 1096 Lisboa Codex, Portugal, Université Claude Bernard Lyon-I, Lab. Chimie Industrielle, 43, Bd du 11 Novembre 1918, 69622 Villeurbanne Cedex, France, and Centro de Ciência e Tecnologia dos Materiais, Faculdade de Ciências de Lisboa, 1700 Lisboa, Portugal.
authors.forename: Paula M.
authors.initials: PM
authors.lastname: Marcos
authors.forename: José R.
authors.initials: JR
authors.lastname: Ascenso
authors.forename: Roger
authors.initials: R
authors.lastname: Lamartine
authors.forename: J. L. C.
authors.initials: JL
authors.lastname: Pereira