Synthesis of delta-eicosanolactone and delta-docosanolactone directly frommeadowfoam oil

delta -Eicosanolactone and delta -docosanolactone were synthesized directly from the triacylglycerides of meadowfoam (Limnanthes)oil. Perchloric and s ulfuric acids were used in stoichiometric quantities (0.5-4.0 mol equiv) to cyclize triglyceride to F-lactone. When the reactions were run in the abse nce of solvent at 40 degreesC, delta -lactone yields ranged from 17-75% whe re delta/gamma ratios ranged from 6:1 to 10.4:1. Sulfuric and perchloric ac ids gave similar yields for their individually optimized reactions. Perchlo ric acid-catalyzed reactions required less acid to produce similar amounts of delta -lactone (HClO4 at 2.0 mol equiv gave 73% yield vs. H2SO4' which g ave 75% yield at 2.5 mol equiv). The use of polar nonparticipating solvents during the reaction had little impact on delta -lactone formation or delta /gamma ratio. Higher perchloric acid concentrations provided higher F-lacto ne yields with delta/gamma ratios remaining nearly constant. The effect of sulfuric acid on F-lactone yield and delta/gamma ratio was more direct; hig her acid concentration improved both. Both crystallization and short path d istillation improved delta -lactone quality, but short path distillation ga ve higher recovered yields. The blactones were converted to their correspon ding 5-hydroxy acids in the same reaction vessel, separated, and cyclized b ack to delta -laclones upon heating under vacuum. This provided a convenien t method for delta -lactone purification.