Cyclometalated N-Heterocyclic Carbene-Platinum Catalysts for the Enantioselective Cycloisomerization of Nitrogen-Tethered 1,6-Enynes

Platinum(II) complexes which combine six‐membered N‐heterocyclic carbene‐containing metallacyclic units and monodentate chiral phosphines have been prepared. The key step of their synthesis is the intramolecular oxidative addition of N‐2‐iodobenzylimidazolylidene‐platinum(0)‐diene complexes in the p...

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Veröffentlicht in:Advanced synthesis & catalysis 2011-05, Vol.353 (7), p.1109-1124
Hauptverfasser: Jullien, Hélène, Brissy, Delphine, Sylvain, Rémy, Retailleau, Pascal, Naubron, Jean-Valère, Gladiali, Serafino, Marinetti, Angela
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Sprache:eng
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Zusammenfassung:Platinum(II) complexes which combine six‐membered N‐heterocyclic carbene‐containing metallacyclic units and monodentate chiral phosphines have been prepared. The key step of their synthesis is the intramolecular oxidative addition of N‐2‐iodobenzylimidazolylidene‐platinum(0)‐diene complexes in the presence of the chiral phosphorus ligands. The platinum(II) metallacycles have been used as well‐defined pre‐catalysts for the enantioselective cycloisomerization of nitrogen‐tethered 1,6‐enynes into 3‐azabicyclo[4.1.0]hept‐4‐enes. High enantiomeric excesses have been obtained with either Monophos or phenyl‐Binepine based catalysts (ees=82–96%), although phenyl‐Binepine outperforms Monophos in these reactions. The absolute configuration of the final 3‐azabicyclo[4.1.0.]heptenes has been established by X‐ray diffraction studies. The method has been extended then to the cycloisomerization of dienynes with enantiotopic vinyl groups. An (S)‐phenyl‐Binepine‐platinum(II) complex allows total diastereoselectivity and high enantioselectivity levels to be attained in these reactions (ees up to 95%) which represent the first enantioselective desymetrizations achieved via enyne cycloisomerizations.
ISSN:1615-4150
1615-4169
1615-4169
DOI:10.1002/adsc.201000904