6-exo versus 7-endo iodolactonizations of 2-(alkynyl)phenylacetic acids

Exposure of 2-alkynylphenylacetic acids to excess iodine in acetonitrile containing anhydrous potassium carbonate delivers good yields, either of the corresponding isochroman-3-ones or benzod]oxepin-2(1H)-ones, depending upon the alkyne substituent: when this is alkyl, the former 6-exo products dominate, otherwise the 7-endo products are formed largely or, more often, exclusively.