Template Effects. 2.¹ Convenient Syntheses of Crown Ethers Promoted by Ba⁺⁺ Ion in Aqueous Solution

Abstract

The current interest in the preparation of crown ethers is due to their extensive application in many different areas.² Published synthetic procedures³ that have appeared since Pedersen's first report⁴ are based mostly on the reaction promoted by strong base between two polyoxaethylene units of varying length, one of which bears two terminal OH groups, and the other two leaving groups. We now report a different approach, based on the action of hydroxide ion on polyethylene-glycol dibromides BrCH₂(CH₂OCH₂)_x-1 CH₂Br, with X = 5, 6, and 7, in highly concentrated water solution in the presence of Ba⁺⁺ ion. The most significant feature of the present method is that it requires only one building block, bearing one less oxygen atom than the crown ether to be formed.⁵ The last oxygen