RESUMO
The first approach to hyperireflexolide A, based on the synthesis of γ-lactone-fused cyclopentane 5, a functionalized key intermediate, is presented. Compound 5 is involved in hydrolysis, α-allylation at C-8 and α-methylation at C-10 stereoselectively from the convex face. Then it is subjected to cross metathesis to give α,ß-unsaturated ketone 11 as precursor in the total synthesis of hyperireflexolide A.
RESUMO
An unusual route for the synthesis of functionalized cyclobutane derivatives starting from functionalized norbornane derivatives is reported. Base-induced fragmentation of an oxetanol-type moiety embedded in a tetracyclic norbornyl ketal leads to a cyclobutane-fused derivative as the major or exclusive product. The fragmentation reaction for bridgehead-bromine-substituted derivatives was much faster than for the corresponding chlorine-substituted substrates. The functionalized cyclobutane product was formed exclusively in high yield in the former case, while the latter furnished a minor uncyclized side product in varying yields.
RESUMO
[reaction: see text] Unprecedented molecular rearrangements during diazomethane-mediated reaction of norbornyl alpha-ketohemiketals leading to novel molecular entities are presented. A dramatic change in the reaction outcome was noted for five- and six-membered alpha-ketohemiketals: the former predominantly furnished rearranged bicyclic products involving migration of the gamma-alkoxy group, and the latter furnished the oxetane derivative as the major product. Interestingly, six-membered O-methyl-ketal yielded a product arising from the migration of the vicinal alkoxy group.