Synthesis and reactions of large-ring spirodienone calixarene derivatives

The isomerism of the polyspirodienone derivatives of the large-ring p-fertbutylcalix[n]arenes (n=5,6,8) is analyzed. Monoand polyspirodienone calix[n]arene derivatives were prepared by mild oxidation of the respective calix[n]arenes and the obtained products were characterized. Reactions of the monospirodienone derivatives with hydrazines and their rearrangements to xanthenocalixarenes are described. Introduction. Extensive synthetic efforts have been invested in the last years in developing synthetic methodologies for the selective functionalization of the calix[n]arenes (1,2). Oxidation of p-tertbutylcalix[4]arene (la) with a mild oxidizing agent (such as tetrabutylammonium uibromide or K3Fe(CN)6) in the presence of base results in the formation of bis(spirodienone) calixarene derivatives (3-5). Three bis( spirodienone) derivatives (2a-2c) were obtained which were separated by chromatography and characterized by X-ray crystallography (4). This reaction is notable because in one step the four OH groups of the calixarene are converted into ether and carbonyl groups, and two stereocenters are introduced into the macrocycle. The isomer which is more stable thermodynamically is a meso compound with an altemant arrangement of carbonyl and ether groups and opposite configurations of the two stereocenters (the spiro carbons). However, the cavity defined by the four oxygens in the bis(spirodien0ne) calixarene derivatives is too small for the inclusion of a metal atom. Spirodienone systems derived from larger calixarenes should be of interest since they should be capable of completely enveloping a cation or a small organic molecule. In addition, these compounds may serve as potential synthetic intermediates for the preparation of selectively fuctionalized large-ring calixarenes. t-Bu Q \ O H H O \ BU-t t-aBu-t 0 0 t-@Bu-t t B@; HO O H \ ’ \ / \ O H c / \ / \ t-Bu ’ t-Bu / 1-BU Bu-t t-Bu 1-BU n 3a n=l 2a (RS) 2c (RS) l a n=l 2 b (RR/SS) Ib n=2 3b n=2 l c n=3 3c n=3 Id n=5 3d n=5 Monospirodienone calixarene derivatives. The preparation of the monospirodienone derivatives of the large calixarenes is rather straightforward. OxiQation of an excess of the p-tea-butylcalix[n]arenes la-d with phenyltrimethylammonium tribromide in the presence of a weak base (aq. NaHCO3) at low temperatures results in the formation of the corresponding monospirodienone derivatives (3a-d) in good yields (6,7). Due to the presence of a single stereocenter, these systems are chiral. The structures of the monospirodienone derivatives 3a and 3b were determined by X-ray crystallography, which indicates that the compounds adopt different conformations (6,7). Polyspirodienone derivatives of large calixarenes. (a) Bis(spirodienone) culix[5]urene derivatives. The most convenient way for analyzing the isomerism of the polyspirodienone derivatives of the calixarenes is to envision the systems as possessing two independent stereogenic elements: the spiro stereocenters and the directionality of each spirodienone moiety (8). Six isomeric forms (two enantiomeric pairs and two meso forms) exist for bis(spirodien0ne) derivatives of l a (4) but the number of isomeric forms becomes larger with the increase in number of rings in the macrocycle.