Structures and reactions of alkoxymethyl(alkali metals). Ethylation by methyl ethers in the presence of organometallic bases

Structures and reactions of CH3OCH2M (M = Li, Na, K) were investigated in a theoretical manner. CH3OCH2M has the acute bond angle of angleM-C-O due to a strong coordination of the oxygen to the alkali metals. The nucleophilic substitution reaction of the substrate CH3OCH2Li by the nucleophile CH3OCH 2Li is more preferred than the carbene generation by alpha -elimination and a nucleophilic substitution of CH3OCH2Li by CH3Li. The resulting 2-methoxy ethyllithium readily liberated lithium methoxide to afford ethylene, which added to the anion species to give an ethylated product. Among the CH3OCH2M (M = Li, Na, K), CH3OCH2K is the most nucleophilic, due to the high sigma (C-K) level, while CH3OCH2Li is the most nucleophilic because of the lowest sigma*(C-O) level. This supports a previously proposed mechanism for the e thylation of indole derivatives by methyl ethers in the presence of BuLi - t-BuOK.