COMPETITIVE 5-EXO VS 6-EXO RING-CLOSURE IN INTRAMOLECULAR AND INTERMOLECULAR GAMMA-LACTONE AND DELTA-LACTONE FORMATION

2-(2-Propenyl)-5-hexenoic acid (1) undergoes competitive intramolecula r cyclization (induced by various electrophiles) to give exclusively g amma-lactone. 3-Vinyl-5-hexenoic acid (4) has been prepared and its ki netic iodolactonization carried out, leading exclusively to the format ion of gamma-lactone. Use of these two compounds provides an ideal cas e 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 f ashion. Once again gamma-lactone formation is the major pathway.