Palladium-mediated N-arylation of heterocyclic diamines: insights into the origin of an unusual chemoselectivity.
The chemoselectivity of the palladium-mediated reaction of bromobenzene with various heterocyclic diamines was studied. Whatever the ligand used, 3-aminopyrrolidine underwent arylation of the secondary amine function (>82%), whereas the more flexible 3-aminoazepinine was arylated on its primary function (>70%). The ratio "arylation of primary amine versus arylation of secondary amine" of 3-aminopiperidine with bromobenzene varied from 90:10 (BINAP, electron-enriched and hindered biphenyls L2 or L3) to 32:68 with the Josiphos-type ligand L10. The same trend was observed when 4-aminopiperidine was used (82:18 with L2 and 17:83 with L10). This selectivity can be tuned by the choice of aryl halide partners having different steric and electronic properties. A cooperative effect of both nitrogens of diamines during the reaction was deduced from competitive experiments. Finally, 13C and 31P NMR experiments, carried out with 3-aminopyrrolidine at room temperature, support a fast coordination of the primary amine to the metal. Indeed, a palladium complex resulting from the unusual displacement of one phosphane group of the intermediate ArPdX(BINAP) by the primary amino group was characterized.
Cabello-Sanchez
Noemi
N
Laboratoire de Chimie Moléculaire et Thio-organique, UMR CNRS 6507, ENSICAEN, Caen Cedex, France.
Jean
Ludovic
L
Maddaluno
Jacques
J
Lasne
Marie-Claire
MC
Rouden
Jacques
J
D001969:Bromobenzenes / Q000737:chemistry; D002384:Catalysis; D003959:Diamines / Q000737:chemistry*; D006571:Heterocyclic Compounds / Q000737:chemistry*; D006841:Hydrocarbons, Aromatic / Q000737:chemistry*; D010165:Palladium / Q000737:chemistry*
D001969:Bromobenzenes; D003959:Diamines; D006571:Heterocyclic Compounds; D006841:Hydrocarbons, Aromatic; D010165:Palladium; C032036:bromobenzene