Reaction of I (collidine) 2” CIO4 'with unsaturated alcohols and carboxylic acids in diehlorornethane at ambient temperature has afforded three-to seven-membered-ring iodoethers and four-to seven-mernbered-ring iodolactones, respectively, in moderate yields and generally with high regioselectivity. The reaction is of particular utility for synthesis of 2-(l- iodoalkyl) 0xiranes and-oxetanes.