Synthesis of 2,9-dihydropyrano[2,3-b]-indoles via intramolecular oxa-6π-electrocyclization reaction from synthesized 3-allylideneindolin-2-one intermediates
摘要
Intramolecular oxa-6π-electrocyclization reaction are described for 3-allylideneindolin-2-one derivatives in the presence of easily prepared B(HSO4)3 catalyst and their conversion to 2,9-dihydropyrano[2,3-b]-indoles in up to 72% yield under mild condition. 3-allylideneindolin-2-one has been obtained from the reaction of isatin and 1,3-dichloropropene. Comfortable synthetic conversions of the products readily lead to pharmacologically interesting numerous functional groups.