title: Synthesis of Carbazole Alkaloids by Ring-Closing Metathesis and Ring Rearrangement-Aromatization.
abstract: Aprocess for the assembly of carbazole alkaloids has been developed on the basis of ring-closing metathesis (RCM) and ringrearrangement-aromatization (RRA) as the key steps. This method is based on allyl Grignard addition to isatin derivatives to provide smooth access to 2,2-diallyl 3-oxindole derivatives through a 1,2-allyl shift. The diallyl derivatives were used as RCM precursors to afford a novel class of spirocyclopentene-3-oxindole derivatives, which underwent a novel RRA reaction to afford carbazole derivatives. The synthetic sequence to carbazoles was shortened by combining the RCM and RRA steps in an orthogonal tandem catalytic process. The utility of this methodology was further demonstrated by the straightforward synthesis of carbazole alkaloids, including amukonal derivative, girinimbilol, heptaphylline, and bis(2-hydroxy-3-methylcarbazole).
authors.affiliation: Department of Organic Chemistry, Indian Association for the Cultivation of Science, Jadavpur, Kolkata-700032 (India).
authors.forename: Kalyan
authors.initials: K
authors.lastname: Dhara
authors.affiliation: Department of Organic Chemistry, Indian Association for the Cultivation of Science, Jadavpur, Kolkata-700032 (India).
authors.forename: Tirtha
authors.initials: T
authors.lastname: Mandal
authors.affiliation: Department of Organic Chemistry, Indian Association for the Cultivation of Science, Jadavpur, Kolkata-700032 (India).
authors.forename: Joydeb
authors.initials: J
authors.lastname: Das
authors.affiliation: Department of Organic Chemistry, Indian Association for the Cultivation of Science, Jadavpur, Kolkata-700032 (India). ocjd@iacs.res.in.
authors.forename: Jyotirmayee
authors.initials: J
authors.lastname: Dash
mesh_terms: D000470:Alkaloids / Q000138:chemical synthesis*; D002227:Carbazoles / Q000138:chemical synthesis*; D003500:Cyclization
chemical_list: D000470:Alkaloids; D002227:Carbazoles
keywords: allylation; carbazole alkaloids; rearrangement; ring-closing metathesis; tandem catalysis