title: Synthesis of Polysubstituted γ-Butenolides via a Radical Pathway: Cyclization of α-Bromo Aluminium Acetals and Comparison with the Cyclization of α-Bromoesters at High Temperature.
abstract: Polysubstituted butenolides were obtained in good to high yields from α-bromoesters derived from propargyl alcohols by a one-pot reaction involving the radical cyclization of α-bromo aluminium acetals, followed by the oxidation of the resulting cyclic aluminium acetals in an Oppenauer-type process and migration of the exocyclic C=C bond into the α,β-position. Comparison with the direct cyclization of α-bromoesters at high temperature and under high dilution conditions is described. Deuterium-labelling experiments allowed us to uncover "invisible" 1,5-hydrogen atom transfers (1,5-HATs) that occur during these cyclization processes, together with the consequences of the latter in the epimerization of stereogenic centres. Compared to the classical approach, the cyclization of aluminium acetals proved to be highly chemoselective and its efficiency was illustrated by the short total syntheses of optically enriched γ-butenolides isolated from Plagiomnium undulatum and from Kyrtuhrix maculans.
authors.affiliation: CEISAM UMR 6230 - UFR des Sciences et des Techniques, Université de Nantes, 2 rue de la Houssiniere BP 92208-44322, Nantes Cedex 3 (France).
authors.forename: Romain
authors.initials: R
authors.lastname: Bénéteau
authors.affiliation: CEISAM UMR 6230 - UFR des Sciences et des Techniques, Université de Nantes, 2 rue de la Houssiniere BP 92208-44322, Nantes Cedex 3 (France).
authors.forename: Carole F
authors.initials: CF
authors.lastname: Despiau
authors.affiliation: CEISAM UMR 6230 - UFR des Sciences et des Techniques, Université de Nantes, 2 rue de la Houssiniere BP 92208-44322, Nantes Cedex 3 (France).
authors.forename: Jean-Christophe
authors.initials: JC
authors.lastname: Rouaud
authors.affiliation: CEISAM UMR 6230 - UFR des Sciences et des Techniques, Université de Nantes, 2 rue de la Houssiniere BP 92208-44322, Nantes Cedex 3 (France).|Current Address: Université du Maine and CNRS UMR 6283, Institut des Molécules et Matériaux du Mans, Faculté des Sciences et Techniques, avenue Olivier Messiaen, 72085 Le Mans Cedex 9 (France).
authors.forename: Anne
authors.initials: A
authors.lastname: Boussonnière
authors.affiliation: CEISAM UMR 6230 - UFR des Sciences et des Techniques, Université de Nantes, 2 rue de la Houssiniere BP 92208-44322, Nantes Cedex 3 (France).
authors.forename: Virginie
authors.initials: V
authors.lastname: Silvestre
authors.affiliation: CEISAM UMR 6230 - UFR des Sciences et des Techniques, Université de Nantes, 2 rue de la Houssiniere BP 92208-44322, Nantes Cedex 3 (France).
authors.forename: Jacques
authors.initials: J
authors.lastname: Lebreton
authors.affiliation: CEISAM UMR 6230 - UFR des Sciences et des Techniques, Université de Nantes, 2 rue de la Houssiniere BP 92208-44322, Nantes Cedex 3 (France). fabrice.denes@univ-nantes.fr.
authors.forename: Fabrice
authors.initials: F
authors.lastname: Dénès
keywords: butenolides; deuterium-labeling experiments; hydrogen transfer; maculalactone A; radical reactions