Ring-D-bridged steroid analogs—VII : Homoconjugate diels-alder addition of methyl propiolate to substituted bicyclo[2.2.1]Heptadienes

Abstract

3β-Acetoxy-20-keto-5,14,16-pregnatriene (I) reacts with hexafluorobutyne or with dimethyl acetylenedicarboxylate to form normal Diels-Alder adducts. However, reaction of I with methyl propiolate leads to the stereospecific formation both of normal Diels-Alder adduct and of a diadduct derived from homoconjugate addition of a second mole of dienophile to the monoadduct. The stereochemistry of the monoadduct was established by a correlation with 14α, 17α-ethano-16α-carbomethoxypregn-5-ene- 3β-ol-20-one acetate. The homoconjugate addition of methyl propiolate to methyl bicyclo [2.2.1]heptadiene-2-carboxylate is alsodescribed.