Efficient radical addition of tertiary amines to alkenes using photochemical electron transfer*
Norbert Hoffmann, Samuel Bertrand, Siniša Marinković, and Jens Pesch
Laboratoire des Réactions Sélectives et Applications, UMR 6519 CNRS et Université de Reims Champagne-Ardenne, UFR Sciences, B.P. 1039, F-51687 Reims, Cedex 02, France
Abstract: An efficient photoinduced radical addition of tertiary amine, mainly cyclic derivatives, to electron-deficient alkenes was developed. The reaction was applied to the asymmetric synthesis of the pyrrolizidine alkaloids laburnine and isoretronecanol. The method was then optimized for the addition of a larger variety of tertiary amines, in particular acyclic ones. Radical tandem addition cyclization reactions with unsaturated tertiary amines have also been investigated. A detailed mechanistic study using isotopic labeling enabled the optimization of a corresponding reaction with N,N-dialkylaniline derivatives. The origin of the high reaction stereoselectivity achieved with menthyloxyfuranone was elucidated. The radical addition of tertiary amines was also performed with heterogeneous photocatalysis using inorganic semiconductors as sensitizers.
Keywords: photochemistry; radical reactions; electron transfer; heterocycles; stereoselectivity.
*Paper based on a presentation at the XXIst Symposium on Photochemistry, 2-7 April 2006, Kyoto, Japan. Other presentations are published in this issue, pp. 2193-2359.