Structure‐Reactivity Relationships of Methylated Tetrahydrofurans with Lithium

Tetrahydrofurans methylated in the α‐position manifest remarkable chemical and electrochemical stability toward Li. While tetrahydrofuran (THF) distilled off benzophenone ketyl and stored with Li at 71°C reacts in two days, 2‐methyltetrahydrofuran (2‐Me‐THF) treated similarly was stable for over 10 months. Electrolytes comprising either 2‐Me‐THF or 2,5‐dimethyltetrahydrofuran (2,5‐di‐Me‐THF) were subjected to cycling studies in half‐cell configurations. Average Li on Li cycling efficiencies exceeded 96% for . Unlike the α‐methylated ethers, 3‐methyltetrahydrofuran (3‐Me‐THF) was as reactive towards Li as THF. Thus, the position of the methyl substituent with respect to the cyclic ether's oxygen atom is critically important, and several mechanisms are considered.