NEW CROWN ETHER-LIKE MACROCYCLES CONTAINING A NITROPHENOL UNIT - SYNTHESIS AND METAL-ION EFFECTS ON THE REACTIVITY OF THEIR ACETATES IN TRANSACYLATION REACTIONS

A series of crown ether-like macrocyclic compounds 3 containing the 2,6-dibenzyl-4-nitrophenol substructure have been prepared by cyclization reactions of disalicylideneacetone 4 with ditosylates 7 of oligoethylene glycols, followed by hydrogenation and double aldol condensation with nitromalondialdehyde. These compounds may be regarded as possessing a section of a 1,3-crowned calix[4]arene. X-ray analysis of two examples shows, however, that the three phenolic units linked via o-methylene groups adopt a conformation different to the all-cis conformation found in calix[4]arenes. The reaction of the nitrophenyl acetates derived from 3 and from suitable model compounds with ethoxide in ethanol was studied kinetically. This reaction is accelerated by the addition of SrBr2 and BaBr2 in all cases, indicating that the metal ion is bound more strongly to the transition state than to the initial state. Especially high acceleration factors (up to 700 in the case of 10e) were observed for cyclic and open-chain compounds with longer flexible oligoethylene oxide chains, which means that only in these cases do the ether oxygens contribute effectively to the binding of the metal ion in the transition state.