title: Studies in sigmatropic rearrangements of N-prenylindole derivatives--a formal enantiomerically pure synthesis of tryprostatin B.
abstract: Rearrangement of N(a)-prenyl-N(b)-acetyltryptamine, induced by BF3.Et2O at low temperature, leads to a 2-prenyl derivative, and thence to the tricyclic tryptamine 7 and the indoline 8. Similarly, N(a)-prenyl-N(b)-phthaloyl-l-tryptophan methyl ester furnished the corresponding 2-prenyl derivative 16, a known advanced precursor of tryprostatin B. Density functional (B3LYP) calculations for the putative rearrangement transition state for N-prenylskatole show that prior coordination of BF3 to the indolic nitrogen changes the character of the subsequent sigmatropic pericyclic shifts from being entirely covalent to acquiring a significant degree of ionic character. The shifting prenyl group favours the endo over the exo mode of the transition state by 4.1 kcal mol(-1).
authors.affiliation: Chemistry Department, REQUIMTE/CQFB, Faculty of Sciences and Technology, New University of Lisbon, 2829-516, Monte de Caparica, Portugal.
authors.forename: A Sofia P
authors.initials: AS
authors.lastname: Cardoso
authors.forename: M Manuel B
authors.initials: MM
authors.lastname: Marques
authors.forename: Natarajan
authors.initials: N
authors.lastname: Srinivasan
authors.forename: Sundaresan
authors.initials: S
authors.lastname: Prabhakar
authors.forename: Ana M
authors.initials: AM
authors.lastname: Lobo
authors.forename: Henry S
authors.initials: HS
authors.lastname: Rzepa
mesh_terms: D002384:Catalysis; D026121:Indole Alkaloids / Q000138:chemical synthesis* / Q000737:chemistry; D007211:Indoles / Q000737:chemistry*; D008958:Models, Molecular; D010879:Piperazines / Q000138:chemical synthesis* / Q000737:chemistry; D013237:Stereoisomerism; D013816:Thermodynamics
chemical_list: D026121:Indole Alkaloids; D007211:Indoles; D010879:Piperazines; C097859:tryprostatin B