RESUMO
A radical/polar crossover annulation between allyl-substituted arenes and electron-deficient alkenes is described. Cobalt-catalyzed hydrogen atom transfer (HAT) facilitates tandem radical C-C bond formation that generates functionalized tetralin products in the face of potentially problematic hydrofluorination, hydroalkoxylation, hydrogenation, alkene isomerization, and radical polymerization reactions. The reactions proceed under mild conditions that tolerate many functional groups, leading to a broad substrate scope. This powerful ring-forming reaction very quickly assembles complex tetralins that are the formal products of the largely infeasible Diels-Alder cycloadditions of styrenes.
RESUMO
We offer a new biogenetic proposal for the origin of the complex alkaloid alstonlarsineâ A, through rearrangement of the Strychnos alkaloids alstolucinesâ B and F. Further, we provide evidence of the chemical feasibility of this proposal in the facile conversion of synthetic alstolucines into alstonlarsineâ A through a short, efficient sequence of N-methylation, ß-elimination, and a cascade 1,7-hydride shift/Mannich cyclization. We believe that this is the first biogenetic proposal involving the "tert-amino effect", a hydride-shift-based internal redox trigger of a Mannich cyclization. A further interesting feature of the cascade is that its stereochemical outcome most likely originates in conformational preferences during the hydride shift.