Stereoselective Total Synthesis of Copa and Ylango Sesquiterpenoids: Preparation of (−)-(1S,4S,5R,7R)-1,7-Dimethyl-4-isopropylbicyclo[3.2.1]octa-6,8-dione and(+)-(1R,4S,5S,7S)-1,7-Dimethyl-4-isopropylbicyclo[3.2.1]octa-6,8-dione

Abstract

Can. J. Chem. 53,2827. The efficient, stereoselective syntheses of two diastereomeric bicyclo[3.2.1]octadiones (23 and 24) are described and the potential use of these materials for the synthesis of the copa (1-5) and the ylango (7-11) sesquiterpenoids, respectively, is outlined. Conversion of (+)-carvomenthone (26) into the corresponding n-butylthiomethylene derivative 28, followed by alkylation of the latter with ethyl 2-iodopropionate, gave compound 29. Removal of the blocking group from the latter was accompanied by ester hydrolysis and afforded keto acid 30. An efficient intramolecular Claisen condensation of the corresponding ester 31 yielded ( On a transform6 I'octalone connue 39 en cCto-aldehyde 41 par des techniques standards. Le traitement de 41 par du dimethylcuprate de lithium suivi par le piCgeage de I'anion Cnolate qui en rCsulte par du chlorure d'acetyle conduit au compost 42 qui par ozonolyse oxydante fournit le cCto-acide 43. L'estkrification de ce dernier suivie par une conduisation de Claisen intramo-

Synthesis of Functionalized Bicyclo[3.2.1]octanes and Their Multiple Uses in Organic Chemistry

“…Following this cyclodehydration, new synthetic approaches based on Claisen-type, carbocyclizations appeared in the literature. The synthesis and the cyclization of chiral keto ester 99 , derived from (+)-carvomenthone, was extensively studied by Piers and collaborators . Their strategy involves the formation of bicyclo[3.2.1]octane-1,3-dione 100 which serves as key starting synthon for the stereoselective total synthesis of copa and ylando sesquiterpenoids.…”

Stereoselective Construction of Copaborneol and Longiborneol Frameworks by Intramolecular Double Michael Reaction

“…There are many sesquiterpenes characterized by the presence of a bicyclo[2.2.1]heptane system with an additional three or four carbon bridge, e.g., (+)-copaborneol (the antipode of 1 ) or (+)-logiborneol ( 2 ) . Although most synthetic approaches to these natural products are composed of the stepwise constructions of three rings, the routes utilizing the intramolecular Diels−Alder reaction (IDA) seem to be attractive since two rings are assembled in one step.…”