Reaction of 5-substituted (Z)-2-en-4-ynoic acids with iodine and NaHCO3 in CH3CN or with ICl in CH2Cl2 affords mixtures of (E)-5-(1-iodoylidene)-2 (5H)-furanones and 6-substituted 5- iodo-2 (2H)-pyranones in which these last compounds are the major products. The 5-iodo-2 (2H)-pyranones, which are easily separated chromatographically from the corresponding regioisomers, are able to undergo Stille-type reactions with a variety of organotin ...