General access to tacamine and vinca-eburna alkaloids through tandem non-biomimetic oxidation of dihydropyridines/Zn-mediated radical addition processes - Unexpected facial selectivity of flattened cyclohexyl-type radicals
R. Lavilla et al., General access to tacamine and vinca-eburna alkaloids through tandem non-biomimetic oxidation of dihydropyridines/Zn-mediated radical addition processes - Unexpected facial selectivity of flattened cyclohexyl-type radicals, EUR J ORG C, (19), 2001, pp. 3719-3729
A general route to the eburnamine-vincamine and tacamine indole alkaloid gr
oups has been developed. The key features of the synthetic strategy are the
halocyclization of a dihydropyridine (a non-biomimetic oxidation of these
compounds) and the radical addition of the resulting halo derivative to act
ivated alkenes. The latter process shows an unusual stereos electivity, fav
ouring the generation of a cis stereochemistry in a 1,2-disubstituted 6-mem
bered ring. Theoretical calculations suggest conformational control at the
intermediate radical level, and a preferential face selectivity producing t
he observed products.