The electroreductive intramolecular coupling of phthalimides with alpha,beta-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.

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The electroreductive intramolecular coupling of phthalimides with aromatic aldehydes in the presence of chlorotrimethylsilane and triethylamine led to five-, six-, and seven-membered cyclized products (58-84%). The electroreductive cyclization was applied to the total synthesis of lennoxamine.

Electroreductive Intermolecular Coupling of Phthalimides with Aldehydes: Application to the Synthesis of Alkylideneisoindolin-1-ones. -The three-step approach is based on the electroreductive coupling of phthalimides with aldehydes followed by selective reduction of the resulting diols and dehydration. -(KISE*, N.; ISEMOTO, S.; SAKURAI, T.; Tetrahedron 68 (2012) 42, 8805-8816, http://dx.