Synthesis of pyrrole derivatives through functionalization of 3,4-bis(lithiomethyl)dihydropyrroles

Bis(2-lithioallyl)amines 2, substituted at the double bonds, undergo intramolecular carbolithiation of a lithiated double bond in different solvents to afford dilithiated dihydropyrroles 3. Treatment of these dianions with electrophiles allows the preparation of functionalized pyrrole derivatives 5 and 6. Interestingly, treatment of these dianions with carboxylic esters selectively affords either keto or hydroxy compounds (9 or 10), depending on the conditions. Several experiments have been carried out in order to clarify the mechanism of this selective transformation. Finally, dilithiated dihydropyrrole 3a could be transformed in a three-step procedure into the corresponding 3,4-bis(bromomethyl) derivative 31, which can easily be converted into bicyclic pyrrole compounds 32-33 by treatment with different nucleophiles.