CARBAMOYLOXA-BRIDGED CYCLOPHANES - MACROCYCLIZATION BY DOUBLE TRANSESTERIFICATION OF DIMETHYL M-XYLYLENEDICARBAMATE WITH ALPHA,OMEGA-DIHYDROXY COMPOUNDS

A series of macro-sized (16-24-membered) carbamoyloxa-bridged cyclopha nes 3a-k was prepared by sequential inter- and intramolecular transest erifications of dimethyl m-xylylenedicarbamate with alpha,omega-dihydr oxy compounds 2a-k in good yields (15-74 %) without the use of high-di lution techniques. Precursor 4 with lower reactivity cyclized selectiv ely to the desired 1:1 coupling products catalyzed by SnCl2. The confo rmationally rigid m-xylylene template restricted the location of the t wo carbamoyloxa-bridges, which resulted in moderate binding affinities to the potassium cation. The binding ability of these carbamoyloxa-br idged cyclophanes was evaluated by the extraction study of aqueous alk ali metal picrates, (log K-a = 3.6-4.0) with the formation of a 1:1 co mplex.