A Short Intramolecular Diels−Alder Route to Himbacine Derivatives

The intramolecular cycloaddition of 5 yields the unsaturated lactones 17a, 17b, and 17c as three major isomeric adducts. These were further reduced to the corresponding derivatives 21a, 21b, and 21c, which are intermediates for the synthesis of (+)-himbacine and stereoisomers thereof. Precursor 5 was obtained in a short convergent way using Sonogashira and Stille coupling reactions as the main C−C bond construction reactions.