Synthesis of New Resorcinarenes Under Alkaline Conditions

Abstract

The preparation of functionalized resorcinarenes is described. Thus, 2-nitroresorcinol (= 2-nitrobenzene-1,2-diol), 2-acetylresorcinol (= 1-(2,6-dihydroxyphenyl)ethanone), and 2,6-dihydroxybenzoic acid were treated with formaldehyde in alkaline medium to give the corresponding resorcinarenes 1 -3 (Scheme 1). This method is also applicable for resorcinol (= benzene-1,3-diol) itself, but the yields are poorer. In this case, the molecule formed is the simplest resorcinarene 4 on which a number of substituents can be inserted between the two OH groups. Thus, bromation of 4 yields 5 (Scheme 2). Some properties and conformations of these new products are discussed, and the X-ray crystal structures of the nitro and bromo compounds 1 and 5, respectively, are presented.Introduction. -Resorcinarenes are well known molecules, and a number of reports appear each year on this subject [1 -4]. The particular shape of resorcinarenes is suitable for encapsulating small chemical entities such as solvent molecules or metal ions [5]. Such a compound becomes pincer-like at the nanoscale level owing to a change of conformation which is dependent on pH [6]. Cavitands and carcerands, prepared from resorcinarenes, are very interesting synthons for supramolecular chemistry [7 -11].Standard preparation of resorcinarenes is performed in alcoholic acidic medium. An aldehyde (except formaldehyde) and resorcinol (= benzene-1,3-diol) are refluxed together with hydrochloric acid for several hours to permit the formation of the most stable stereoisomer. Therefore, all resorcinarenes have an alkyl group at the C-junction of the aromatic moieties. Under these acidic conditions, formaldehyde will form a copolymer with resorcinol. With 2-methylresorcinol, however, excellent yields of resorcinarene were achieved [12].All other attempts to synthesize substituted resorcinarenes in acidic medium were unsuccessful. Thus, treatment of 2-nitroresorcinol with formaldehyde gave only dimeric compounds [8]. Reaction of 2,6-dihydroxybenzoic acid with formaldehyde gave polymeric compounds. On changing the reaction conditions, it was quickly realized that basic medium is very convenient for formaldehyde and those resorcinols that bear an electron-attracting group at position 2, such as 2-nitroresorcinol (= 2-nitrobenzene-1,2-diol), 2-acetylresorcinol (= 1-(2,b-dihydroxyphenyl)ethanone), and 2,6-dihydroxybenzoic acid. The reactions are clean and rapid with yields of ca. 50%. The only real problem of this new method is the tedious preparation of the 2-substituted resorcinols. Usually, isolation and purification of resorcinarenes (this is also true for calixarenes) are very difficult for two reasons: these products have several conformations [13] [14], and they form different supermolecular complexes with different solvents, which excludes the use of mixed solvents for crystallization. Fortunately, the new tetranitroresorcinarene 1 was not soluble in either H 2 O or in MeOH, and so it was isolated, in good purity, by simply washing with these solvents. The dry red p...

A novel, simple and effective synthesis of the hydroxybenzyl derivative of resorcinarene and the modification possibilities thereof

“…3 There are a large number of known derivatives that are obtained by functionalisation at position 2 and of the hydroxy groups. The cyclic structure of the molecule and the symmetrical arrangement of two hydroxy groups provide the molecule with unique possibilities for the formation of a series of chiral cyclic derivatives.…”

A Concise Synthesis of a Methyl Ester 2-Resorcinarene: A Chair-Conformation Macrocycle

“…Consequently, we attempted a base-catalyzed approach. Bourgeois has effected the macrocyclization of 2-nitroresorcin [4]arene using sodium hydroxide in water; [34] instead we used a solution of sodium methoxide in methanol so as not to hydrolyze the methyl ester. Upon quenching with acid and filtration, a complex mixture was observed that showed 1 H NMR signals at approximately 6.3 ppm.…”

Green Synthesis of Oligomer Calixarenes

“…The condensation reaction between formaldehyde and 2-nitroresorcinol and its analogs seems to take place in the irreversible reaction, so it is unknown whether to form a tetramer, pentamer, or hexamer [36].…”