Catalytic asymmetric synthesis of R207910

J Am Chem Soc. 2010 Jun 16;132(23):7905-7. doi: 10.1021/ja103183r.

Abstract

The first asymmetric synthesis of a very promising antituberculosis drug candidate, R207910, was achieved by developing two novel catalytic transformations; a catalytic enantioselective proton migration and a catalytic diastereoselective allylation of an intermediate alpha-chiral ketone. Using 2.5 mol % of a Y-catalyst derived from Y(HMDS)(3) and the new chiral ligand 9, 1.25 mol % of p-methoxypyridine N-oxide (MEPO), and 0.5 mol % of Bu(4)NCl, alpha-chiral ketone 3 was produced from enone 4 with 88% ee. This reaction proceeded through a catalytic chiral Y-dienolate generation via deprotonation at the gamma-position of 4, followed by regio- and enantioselective protonation at the alpha-position of the resulting dienolate. Preliminary mechanistic studies suggested that a Y: 9: MEPO = 2: 3: 1 ternary complex was the active catalyst. Bu(4)NCl markedly accelerated the reaction without affecting enantioselectivity. Enantiomerically pure 3 was obtained through a single recrystallization. The second key catalytic allylation of ketone 3 was promoted by CuF.3PPh(3).2EtOH (10 mol %) in the presence of KO(t)Bu (15 mol %), ZnCl(2) (1 equiv), and Bu(4)PBF(4) (1 equiv), giving the desired diastereomer 2 in quantitative yield with a 14: 1 ratio without any epimerization at the alpha-stereocenter. It is noteworthy that conventional organometallic addition reactions did not produce the desired products due to the high steric demand and a fairly acidic alpha-proton in substrate ketone 3. This first catalytic asymmetric synthesis of R207910 includes 12 longest linear steps from commercially available compounds with an overall yield of 5%.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antitubercular Agents / chemical synthesis*
  • Antitubercular Agents / chemistry
  • Catalysis
  • Diarylquinolines
  • Protons
  • Quinolines / chemical synthesis*
  • Quinolines / chemistry
  • Stereoisomerism
  • Substrate Specificity

Substances

  • Antitubercular Agents
  • Diarylquinolines
  • Protons
  • Quinolines
  • bedaquiline