title: Concise and enantioselective total synthesis of (-)-mehranine, (-)-methylenebismehranine, and related Aspidosperma alkaloids.
abstract: We report an efficient and highly stereoselective strategy for the synthesis of Aspidosperma alkaloids based on the transannular cyclization of a chiral lactam precursor. Three new stereocenters are formed in this key step with excellent diastereoselectivity due to the conformational bias of the cyclization precursor, leading to a versatile pentacyclic intermediate. A subsequent stereoselective epoxidation followed by a mild formamide reduction enabled the first total synthesis of the Aspidosperma alkaloids (-)-mehranine and (+)-(6S,7S)-dihydroxy-N-methylaspidospermidine. A late-stage dimerization of (-)-mehranine mediated by scandium trifluoromethanesulfonate completed the first total synthesis of (-)-methylenebismehranine.
authors.affiliation: Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139 (USA) http://web.mit.edu/movassag/www/index.htm.
authors.forename: Marius
authors.initials: M
authors.lastname: Mewald
authors.forename: Jonathan William
authors.initials: JW
authors.lastname: Medley
authors.forename: Mohammad
authors.initials: M
authors.lastname: Movassaghi
mesh_terms: D000470:Alkaloids / Q000138:chemical synthesis*; D030009:Aspidosperma / Q000737:chemistry*; D003500:Cyclization; D013237:Stereoisomerism
chemical_list: D000470:Alkaloids
keywords: alkaloids; dimerization; epoxidation; indole; total synthesis