Use of alkali- and alkaline-earth-metal ions in the template synthesis of 12-crown-4, 15-crown-5, and 18-crown-6

Abstract

The synthesis of 15-crown-5 and 18-crown-6 from bis(2-chloroethyl) ether and the appropriate polyethylene glycol has been investigated using alkali- and alkaline-earth-metal hydroxides as ‘template’ agents in comparison to tetra-n-butylammonium hydroxide. A classical template effect is observed for the alkali metals, giving optimum yields for Na and K in the synthesis of 15-crown-5 and 18-crown-6 respectively, but the action of the alkaline-earth metals is more complex, particularly for Mg and Ca where involvement with the counter ion prevents a good yield. The importance of base strength in the synthesis of 15-crown-5 and 12-crown-4 is demonstrated, e.g. in the synthesis of 15-crown-5 the most effective base is found to be sodium methoxide. A novel synthesis of 12-crown-4, utilising lithium hydride as the base, gives a 24% yield, the highest yield so far reported.