Title: Convenient Synthesis of a Simple Coumarin from Salicylaldehyde and Wittig Reagent. IV: Improved Synthetic Method of Substituted Coumarins
Abstract:The reaction of salicylaldehydes (2) with Horner-Wadsworth-Emmons (HWE) or Ando-HWE reagents was attempted to afford intramolecular phosphonate derivatives (6).A new synthetic method for coumarins (1)...The reaction of salicylaldehydes (2) with Horner-Wadsworth-Emmons (HWE) or Ando-HWE reagents was attempted to afford intramolecular phosphonate derivatives (6).A new synthetic method for coumarins (1) was achieved by using protected 2.Previously, we reported a convenient method for synthesizing a coumarin (1) by the Wittig reaction of a COOEt Scheme 1We attempted Z-olefination (the Ando-HWE reaction) 2 of 2, which is known as the Z-selective Horner-Wadsworth-Emmons (HWE) reaction (Table 1).Treatment of salicylaldehyde (2a) with ethyl diphenylphosphonoacetate (5a) at 0°C in the presence of NaI gave an unexpected intramolecular † Dedicated to Professor Yuichi Kanaoka for the celebration of his 75th birthday.Read More