New procedures for the selective synthesis of 2(2H)-pyranone derivatives and 3-aryl-4-iodoisocoumarins

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 iodolactonization of stereodefined methyl 2-en-4-ynoates by Method B allowed preparation in moderate yields of 2(2H)-pyranone derivatives by a one-pot sequence of iodolactonization and Stille-type reactions.