Solvent-free Wittig olefination with stabilized phosphoranes - Scope and limitations
Neat mixtures of arene/hetarenecarbaldehydes, alkanals as well as alkenals with alkyl (triphenylphosphoranylidene)acetates react exothermally to furnish the corresponding alkenes. In certain cases, heating has to be provided externally. Reaction times are short and yields are generally very high. Neat mixtures of ketones and alkyl (triphenylphosphoranylidene)acetates react preferentially under microwave irradiation. The better stabilized phosphoranes do not react in the solid state with aldehydes or ketones under conventional heating, but necessitate microwave irradiation, although not all of the phosphoranes have been found to be stable under microwave irradiation at 500 W (2450 MHz).
Convenient synthesis of a simple coumarin from salicylaldehyde and wittig reagent. IV: Improved synthetic method of substituted coumarins
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.