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-dihydroindolizine were similarly synthesized. An easily occurring electrophilic aromatic substitution by the carbon atom of the carbonyl group on the α-position of the pyrrole ring with the formation of the six-membered ring is the key-step of the process.