Electroreductive intramolecular coupling of aliphatic cyclic imides with α,β-unsaturated esters and ketones: unusual methyl-alkoxy exchange in silyl ketene acetals

The electroreductive intramolecular coupling of aliphatic cyclic imides with α,β-unsaturated esters in the presence of chlorotrimethylsilane and subsequent desilylation with TBAF gave five- and six-membered cyclized esters and one-carbon elongated methyl ketones. These methyl ketones were formed by methyl-alkoxy exchange in intermediate silyl ketene acetals. The same methyl ketones were also obtained by the electroreductive intramolecular coupling of aliphatic cyclic imides with α,β-unsaturated methyl ketones. The cyclized methyl ketones were transformed to the known indolizidine and quinolizidine alkaloids, (±)-tashiromine and (±)-epilupinine.