Influence of the reaction temperature on the regioselectivity in the rhodium-catalyzed hydroformylation of vinylpyrroles

The influence of the temperature on the regioselectivity in the hydroformylation of the vinylpyrrole isomers and of the corresponding N-tosylated substrates has been investigated in the range 20-100 degrees C, in the presence of Rh-4(CO)(12). Ar all the temperatures the branched aldehyde was prevailing with respect to the linear isomer for all the substrates (I cu-regioselectivity). With increasing temperature, an increase of the linear aldehyde was observed to a different extent in dependence on the substrate nature. H-2 NMR investigation of the crude reaction mixture recovered from deuterioformylation of 3-vinylpyrrole at partial substrate conversion points out that the observed depression of the alpha-regioselectivity with increasing temperature must be connected to a beta-hydride elimination process occurring for the branched alkyl-rhodium intermediates but not for the linear ones. (C) 1997 Elsevier Science S.A.