An original approach to 5,6-dihydroindolizines from 1-allylpyrroles by a tandem hydroformylation/cyclization/dehydration sequence

6-Methyl-5,6-dihydroindolizine and 3- or 2-ethyl derivatives were obtained via a one-pot hydroformylation/cyclization/dehydration sequence starting from 1-(2-methyl-2-propenyl)pyrroles. 7-Phenyl-5,6-dihydroindolizine and 5-methyl-5,6-dihydroidolizine were similarly synthesized. An easily occurring electrophilic aromatic substitution by the carbon atom of the carbonyl group on the alpha position of the pyrrole ring with the formation of the six-membered ring, is the key step of the process.