5-Iodo-2 (2H)-pyranone derivatives have been selectively synthesized by reaction of stereodefined methyl 2-en-4-ynoates with iodine in MeCN, CH2Cl2 or C6H6 at 20° C (Method C) or by treatment of these esters with ICl in CH2Cl2 at 20° C (Method B). Methods B and C proved also to be suitable for the preparation of 3-aryl-4-iodoisocoumarins from the corresponding methyl 2-(arylethynyl) benzoates. Interestingly, the high selectivity of ...