A study of the role of metal salts in the synthesis of macrocycles from the condensations of furan with some carbonyl compounds

The acid catalysed condensation of furan with acetone was performed in i the presence of some alkali, alkaline earth and transition metal salts.The yield of a furan-acetone cyclic tetramer, C2883204, was considerably enhanced in comparison to the reactions with non-metal salts and with no added salts. Initially, the metal ions were believed to be participating in a template capacity. This condensation system was studied by systematically changing each parameter. The action of the salts was found torelate to changes in the acidity of the reaction media rather than to a k specific template action. From the furan-acetone condensation were isolated several oligomers which were further reacted to obtain macro-cycles. Lithium perchlorate was also used in the condensation of furan with some aliphatic, alicyclic, aromatic and functional ketones as well as formaldehyde and acetaldehyde. In most cases macrocylic tetramers were isolated with much improved yields compared to reactions with no added metal salts. A furan-cyclohexanone macrocycle was prepared for the first time by a one step reaction. Similarly, some B-substituted furans were condensed with acetone but no macrocyclic products were obtained. Several reactions including formylation and bromination were carried out on the furan-acetone cyclic tetramer. Both the cyclic tetramer and hexamer were hydrogenated to give the tetrahydrofuran macrocycles. The ability of these macrocycles to complex a variety of cation were tested by n.m.r. spectroscopy. The tetrahydrofuran-acetone cyclic tetramer was found to specifically complex Li+ to the exclusion of other cation and a 1:1 complex with LiC1O4 could be isolated. The tetrahydrofuran-acetone cyclic hexamer was found to weakly complex Cs+.