1. Crown Ethers

2. structure cyclic polyethers derived from repeating —OCH 2 CH 2 — units properties form stable complexes with metal ions applications synthetic reactions involving anions Crown Ethers

3. 18-Crown-6 negative charge concentrated in cavity inside the molecule O OO O O O

4. 18-Crown-6 O OO O O O

5. O OO O O O 18-Crown-6 forms stable Lewis acid/Lewis base complex with K + K+K+

6. O OO O O O 18-Crown-6 K+K+

7. not soluble in benzene Ion-Complexing and Solubility K+F–K+F–K+F–K+F–

8. O OO O O O K+F–K+F–K+F–K+F– add 18-crown-6 benzene

9. Ion-Complexing and Solubility O OO O O O O OO O O O K+K+ 18-crown-6 complex of K + dissolves in benzene benzene F – F –

10. Ion-Complexing and Solubility O OO O O O + F–F–F–F– O OO O O O K+K+ F – carried into benzene to preserve electroneutrality benzene

11. Application to organic synthesis Complexaton of K + by 18-crown-6 "solubilizes" salt in benzene Anion of salt is in a relatively unsolvated state in benzene (sometimes referred to as a "naked anion") Unsolvated anion is very reactive Only catalytic quantities of 18-crown-6 are needed

12. Polyether Antibiotics

13. Example CH 3 (CH 2 ) 6 CH 2 Br KFKFKFKF 18-crown-6 benzene CH 3 (CH 2 ) 6 CH 2 F (92%)

14. Polyether Antibiotics Monensin

16. Monensin