Synthesis of Tetrahydroisoquinoline Alkaloids and Related Compounds through the Alkylation of Anodically Prepared α-Amino Nitriles

J Org Chem. 2016 Aug 5;81(15):6721-39. doi: 10.1021/acs.joc.6b01419. Epub 2016 Jul 26.

Abstract

α-Amino nitrile 2a was conveniently prepared in two individual steps from chiral hexafluorophosphate salt isoquinolinium (-)-8b including anodic cyanation as an efficient means to activate the sp(3) C1-H bond of the THIQ nucleus. The lithiation of 2a was carried out in THF at -80 °C in the presence of LDA to produce a stable α-amino carbanion which was condensed on a large variety of alkyl halides. The resulting quaternary α-amino nitriles were subjected to a stereoselective reductive decyanation in ethanol in the presence of NaBH4 as the hydride donor to yield N-Boc-1-alkyl-THIQs (+)-10a-g in up to 97:3 er's after removal of the chiral auxiliary group. Examination of the ORTEP view of THIQ (+)-1f revealed that the newly created stereogenic center had an absolute S configuration. Likewise, (-)-xylopinine was synthesized in four workup steps in an overall 63% yield from α-amino nitrile (+)-2b. In this process, crystallization of an enantioenriched mixture (90:10) of (-)-norlaudanosine with 1 equiv of (-)-N-acetyl-l-leucine afforded the leucinate salt (+)-13 (99:1 dr). Similarly, (+)-salsolidine was displaced from its (-)-DBTA salt (-)-12 in 99:1 er, which was determined by proton and carbon NMR spectroscopy in the presence of thiophosphinic acid (+)-14 as the chiral solvating agent.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alkaloids / chemistry*
  • Alkylation
  • Carbon / chemistry
  • Catalysis
  • Crystallography, X-Ray
  • Electrodes
  • Isoquinolines / chemistry
  • Leucine / analogs & derivatives
  • Leucine / chemistry
  • Magnetic Resonance Spectroscopy
  • Molecular Structure
  • Nitriles / chemistry*
  • Oxidation-Reduction
  • Salsoline Alkaloids
  • Solvents
  • Stereoisomerism
  • Tetrahydroisoquinolines / chemistry*

Substances

  • Alkaloids
  • Isoquinolines
  • Nitriles
  • Salsoline Alkaloids
  • Solvents
  • Tetrahydroisoquinolines
  • 1,2,3,4-tetrahydroisoquinoline
  • Carbon
  • Leucine
  • acetylleucine
  • salsolidine