Synthesis of the Bicyclic Welwitindolinone Core via an Alkylation/Cyclization Cascade Reaction

Synthesis of an advanced welwitindolinone intermediate via an alkylation/cyclization reaction is reported. The key step involves a one pot Lewis acid-mediated alkylation of a silylketene aminal with a furan alcohol followed by an intramolecular cyclization. The reaction is stereoselective and takes place at low temperature. The cycloadduct was highly functionalized and contains the welwitindolinone core structure.