Asymmetric hydrogenation of furans and benzofurans with iridium-pyridine-phosphinite catalysts.
Enantioselective hydrogenation of furans and benzofurans remains a challenging task. We report the hydrogenation of 2- and 3-substituted furans by using iridium catalysts that bear bicyclic pyridine-phosphinite ligands. Excellent enantioselectivities and high conversions were obtained for monosubstituted furans with a 3-alkyl or 3-aryl group. Furans substituted at the 2-position and 2,4-disubstituted furans proved to be more difficult substrates. The best results (80-97% conversion, 65-82% enantiomeric excess) were obtained with monosubstituted 2-alkylfurans and 2-[4-(trifluoromethyl)phenyl]furan. Benzofurans with an alkyl substituent at the 2- or 3-position also gave high conversions and enantioselectivity, whereas 2-aryl derivatives showed essentially no reactivity. The asymmetric hydrogenation of a 3-methylbenzofuran derivative was used as a key step in the formal total synthesis of the cytotoxic naphthoquinone natural product (-)-thespesone.
Department of Chemistry, University of Basel, St. Johanns-Ring 19, CH-4056 Basel, Switzerland, Fax: (+41) 61-267-1103.
Larissa
L
Pauli
René
R
Tannert
Robin
R
Scheil
Andreas
A
Pfaltz
D001572:Benzofurans / Q000737:chemistry*; D002384:Catalysis; D005663:Furans / Q000737:chemistry*; D006865:Hydrogenation; D007495:Iridium / Q000737:chemistry*; D009943:Organophosphorus Compounds / Q000737:chemistry; D011725:Pyridines / Q000737:chemistry*; D013237:Stereoisomerism
D001572:Benzofurans; D005663:Furans; D009943:Organophosphorus Compounds; D011725:Pyridines; D007495:Iridium; C023666:pyridine
N,P ligands; asymmetric catalysis; benzofurans; furans; iridium