title: Stereocontrolled Total Synthesis of (-)-Stemaphylline.
abstract: Homologation of readily available α-boryl pyrrolidines with metal carbenoids is especially challenging even when good leaving groups (Cl-) are employed. By performing a solvent switch from Et2O to CHCl3, efficient 1,2-metalate rearrangement of the intermediate boronate occurs with both halide and ester leaving groups. The methodology was used in the total synthesis of the Stemona alkaloid (-)-stemaphylline in just 11 steps (longest linear sequence), with high stereocontrol (>20:1 d.r.) and 11 % overall yield. The synthesis also features a late-stage lithiation-borylation reaction with a tertiary amine containing carbenoid.
authors.affiliation: School of Chemistry, University of Bristol, Cantock's Close, Bristol, BS8 1TS, UK.
authors.forename: Ana
authors.initials: A
authors.lastname: Varela
authors.affiliation: School of Chemistry, University of Bristol, Cantock's Close, Bristol, BS8 1TS, UK.
authors.forename: Lennart K B
authors.initials: LK
authors.lastname: Garve
authors.affiliation: School of Chemistry, University of Manchester, Oxford Road, Manchester, M13 9PL, UK.
authors.forename: Daniele
authors.initials: D
authors.lastname: Leonori
authors.affiliation: School of Chemistry, University of Bristol, Cantock's Close, Bristol, BS8 1TS, UK.
authors.forename: Varinder K
authors.identifier: 0000-0003-0344-6430
authors.initials: VK
authors.lastname: Aggarwal
keywords: Stemona alkaloids; boronic esters; lithiation-borylation; stereocontrol; total synthesis