Competitive 5-exo vs 6-exo ring closure in intra- and intermolecular gamma and delta-lactone formation

2-(2-Propenyl)-5-hexenoic acid (1) undergoes competitive intramolecular cyclization (induced by various electrophiles) to give exclusively gamma-lactone. 3-Vinyl-5-hexenoic acid (4) has been prepared and its kinetic iodolactonization carried out, leading exclusively to the formation of gamma-lactone. Use of these two compounds provides an ideal case for assessing the relative formation of gamma versus delta-lactones, both involving exo mode of ring closure. 2-(2-Propenyl)hexanoic acid (2) and 2-(n-propyl)-5-hexenoic acid (3) have been used to assess the relative formation of gamma- and delta-lactones in an intermolecular fashion. Once again gamma-lactone formation is the major pathway.