Synthesis of new macrocycles. Part II. Cyclic esters based on αα′-dibromo-o-xylen
Condensation of αα′-dibromo-o-xylene with the homologous series of dicarboxylic acids beginning with oxalic acid and ending with sebacic acid afforded dimeric cyclic esters ranging in ring size from sixteen to thirty-two members. By contrast, the dibromide gave only monomeric cyclic esters in reactions with maleic, citraconic, and o-phthalic acids. The influence of the ‘rigid group’ on the cyclization reaction is discussed. N.m.r. and mass spectral data for the new esters are presented and suggestions as to the likely conformations of the alicyclic rings, based largely on the n.m.r. evidence, are considered.