A small bicyclic cryptand 3 bearing urea groups along the 7-atom bridges was synthesized in 22% yield by a novel tripod-tripod coupling procedure. Protonation and complexation studies are reported and compared with results with polyoxa-[2]-cryptands and [3]-cryptand 6. These show that 3 is a moderate base, a weak metal ion binder, but a two-proton binder exhibiting strong positive cooperativity (p K a2> p K a1) and fast proton exchange kinetics. ...
![1,4,6,9,12,14,19,21-octazabicyclo[7.7.7]tricosane-5,13,20-trione Structure](https://image.chemsrc.com/caspic/190/118090-03-2.png)