A reactive lactonic dienophile - 3-carbethoxy-5,5-dimethyl-2(5H)-furanone. Application to the synthesis of a monoterpenoid lactone

Article abstract of DOI:10.1139/v82-138

In contrast to the low dienophilicity generally observed for α,β-unsaturated lactones, the title compound 2 is shown to be a reactive dienophile.Under stannic chloride catalysis, it undergoes Diels-Alder reaction regio- and stereoselectively with a variety of dienes at room temperature.The synthesis of (+/-)-o-mentha-1,3-dien-1->8-olide (20) has been achieved by a two-step sequence using lactone ester 2.Addition of 2 to 1-acetoxy-1,3-butadiene afforded epimeric acetoxy lactones 12 and 13 which were converted to the monoterpenoid lactone 20 by treatment with lithium iodide dihydrate in collidine.