Dication ethers. 7. Dication ether salts from cyclic bisureas

The bicyclic bisureas 2 react with triflic anhydride to give the dication ether salts 4 . Further transformation of the remaining carbonyl groups of 4 into bis-carbenium ether linkages was not possible. The monocyclic bisurea 8 yields the dicationic heterocycle 9 in an intramolecular fashion. The structure of 9 , which is the first dication ether salt with an endocyclic ether linkage, was established by independent synthesis from 10 as well as by its hydrolysis to give the hemi-protonated bisurea 11 .