Synthesis and properties of Calix[4]naphthalenes

LI, Zhaopeng (1996) Synthesis and properties of Calix[4]naphthalenes. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

This work describes the synthesis and some properties of a new class of cyclic formaldehyde-naphthol tetramers which are analogous to the better-known calixarenes and resorcinarenes. These new compounds are of interest for their potential supramolecular properties. The "calixnaphthalenes", their derivatives and homologues, which are the subjects of this thesis, offer some potential advantages over the calixarenes and resorcinarenes. For example, the presence of the fused second aromatic ring in each naphthalene group (the "upper" rim) can allow for the formation of many funclionalized calixnaphthalenes which could enhance potential receptor abilities. Furthermore, fixed conformations of most calixnaphthalenes are dissymmetric and have potential applications as chiral hosts, or chiral ligands. -- The prototype calixnaphthalenes 8,10 and 11 were synthesized by the direct condensation of 1-naphthol and formaldehyde under basic conditions. A limited mechanistic study indicates that formation of these compounds occurs via a "pseudocalixnaphthalene" pathway. VT 'H NMR analyses show that 8,10 and 11 are conformational^ flexible at temperatures above -60 °C. However, the corresponding tetrabenzoates 8a, 10a and 11a, and tetraacetates 8bf 10b and 11b exist preferentially in the "partial cone" and "1,3-alternate" conformations at -50 °C. The coalescence temperatures of these esters are in the temperature range -10 to 0 °C. Simple molecular modeling calculations indicate that these same two conformations are also the two lowest-energy conformations. -- A water-soluble calix[4]naphthalene (20) was synthesized from 1,8-naphthalene sultone (6) under basic conditions. Under acidic conditions, 6 formed only oxycalix[4]naphthalene (30) and linear oligomeric compounds 28 and 29. -- Synthesis of calixnaphthalene 35 was effected by a self-condensation reaction of 2-hydroxy-3-hydroxymethylnaphthalene (36) under TFA catalysis. Calixnaphthalene 35 is promising as a supramolecular building block as it shows a coalescence temperature of -20 °C, and exists in a "cone" conformation. -- Dihomocalix[4]naphthalene 46 was synthesized from 3-hydroxy-2-naphthoic acid (7a) via a convergent synthetic procedure. VT1H NMR studies suggest that in CDCI₃ solution the preferred conformation of 46 at -60 °C is "1,2-alternate". X-ray diffraction of 46 shows that it exists as a "1,2-alternate" or centrosymmetric conformation in the solid state. -- The calix[4]naphthalene 62 and dihomocalixnaphthalene 70 were both synthesized from the precursor 2,3-dihydroxynaphthalene (7b) by convergent syntheses. Both 62 and 70 have rigid conformations at ambient temperature. -- Finally, a novel naphthalene-tethered calixspherand 95 which possesses a "cone" conformation was synthesized. Attempted synthesis of other calixnaphthalenes from 1,5- and 1,3-dihydroxynaphthalene and synthesis of a functionalized calixresorcinarene were not successful.

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