• 10.1002/jlac.19294700113
  • Justus Liebig's Annalen der Chemie
  • Volume 470
  • January 1929
  • pp 224-254

Über die Konstitution des Sinomenins

Blocking diazonium couplings of aromatic rings


H. Kondo and E. Ochiai Ann. Chem. 1929 470 p224 reported using the iodo group to block Pschorr diazonium cyclizations into an aromatic carbon position when making polycyclic aromatics.  This protocol was repeated by K. Goto and H. Sudzuki Bull. Chem. Soc. Jpn 1929 4 p163 to give the expected 8-bromo-3,4,5,6-tetramethoxy-9-phenanthrencarboxylic acid in a modest 27% yield.  They reported 13% coupling into the “protected” position and 6% dehalogenation of product.  We have repeated this reaction and only isolated 10% of the dehalogenated product, and mostly (20%) dienone from coupling into the “blocked” position.  The iodo blocking group was likely selected because of the easy deprotection, but only complicates the coupling of this electron-transfer mediated reaction.

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