Electroreductive Coupling of Phthalimides with α,β-Unsaturated Esters: Unusual Rearrangement of Resulting Silyl Ketene Acetals

The electroreductive intramolecular coupling of phthalimides with α,β-unsaturated esters in the presence of chlorotrimethylsilane and subsequent desilylation of resulting silyl ketene acetals with TBAF gave five- and six-membered trans-cyclized products stereospecifically. The silyl ketene acetals were readily rearranged to benzoindole and tetrahydrobenzoquinoline by standing or treatment with a Lewis acid under open-air conditions. The electroreductive intermolecular coupling of N-methylphthalimide with methyl acrylate also proceeded.