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
A Short Intramolecular Diels-Alder Route to Himbacine Derivatives.-Substrate (VII) is prepared in a convergent manner and subjected to cycloaddition. The inseparable mixture of adducts thus obtained is directly reduced to give (VIII)-(X) as the major isomers. These lactones are further transformed to precursors of himbacine (XV) and its diastereomers following the 4-step sequence presented for (X). -(HOFMAN, SVEN; GAO, LING-JIE; VAN DINGENEN, HILDE; HOSTEN, NOEL G. C.; VAN HAVER, DIRK; DE CLERCQ, PIERRE J.; MILANESIO, MARCO; VITERBO, DAVIDE; Eur. J.
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