A facile synthesis of aryldihydropyrans using a Sonogashira–selenoetherification strategy

A high yielding and convenient synthesis of 2-aryl-2,5-dihydro-2H-pyrans is reported. Sonogashira coupling of 4-pentyn-1-ol and 5-hexyn-2-ol with a range of phenyl and naphthyl bromides affords the appropriate aryl acetylenic alcohols which then undergo ready reduction to the corresponding (E)-1-aryl-5-hydroxyalkenes. Subsequent selenoetherification of the (E)-5-hydroxyalkenes proceeds via a 6-endo-trig pathway cleanly affording the trans-2-aryl-3-phenylselenyltetrahydropyrans. Finally oxidative elimination of the selenides afforded the 2-aryl-2,5-dihydro-2H-pyrans which are convenient intermediates for the synthesis of C-aryl glycosides in that they contain a double bond which is available for further oxygenation.