Réactivité des α-halobutyrolactones à halogènes tertiaires vis-à-vis des nucléophiles faiblement basiques

Abstract

2-Methyl-4-phenylbutenolide (5) is prepared in a quantitative manner by an elimination of HBr from the corresponding bromolactones 3. This reaction, induced by halide ions at 100 °C in polar aprotic solvents (DMF, DMSO), is accompanied by a bimolecular nucleophilic substitution. In these reactions, the solvent seems able to play an active role. A polar solvent induces the necessary activation of the substrate (by a prior strong polarization of the C—Br bond). In the absence of halide ions, a solvolytic reaction takes place. As soon as the elimination reaction produces enough halide ions, the bimolecular reaction takes over. The activation of the chlorolactones 4 is much more difficult than that of the bromolactones 3; however, each elimination is of the E2ip type with some E2C type. [Journal translation]