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°C, in the presence of Rh4(CO)I2. At all the temperatures the branched aldehyde was prevailing with respect to the linear isomer for all the substrates (a-regioselectivity). With increasing temperature, an increase of the linear aldehyde was observed to a different extent in dependence on the substrate nature. 2H 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 c~-regioselectivity with increasing temperature must be connected to a /3-hydride elimination process occurring for the branched alkyl-rhodium intermediates but not for the linear ones.