Enantioselective rhodium-catalyzed hydrogenation of enol carbamates in the presence of monodentate phosphines
摘要:
The rhodium-catalyzed asymmetric hydrogenation of different acyclic and cyclic enol carbarnates to give optically active carbarnates has been examined in the presence of chiral monodentate ligands based on a 4,5-dihydro-3H-dinaphthophosphepine motif 4. The enantioselectivity is largely dependent upon the reaction conditions, the nature of substituents on the phosphorus ligand and structure of the enol carbamate. By applying the optimized reaction conditions, enantioselectivities of up to 96% ee have been achieved. (c) 2007 Elsevier Ltd. All rights reserved.
合成了17种具有4,5-二氢-3 H-二萘并[2,1 - c ; 1',2'- e ]磷平结构结构的单齿磷平配体,并在各种β-酮酯的不对称氢化中进行了测试。通过改变磷原子上芳基的取代基,可以精细调节催化体系的选择性。使用4-(4-甲氧基苯基)氢化乙酰乙酸甲酯(7a),3-氧代戊酸甲酯(7b)和4-苯基-3-氧代丙酸乙酯(7d)进行氢化时,定量收率和对映选择性高达95%ee )-4,5-dihydro-3 H -dinaphtho- [2,1-c; 1',2'- e ] phosphepine(4g)作为配体。在相对较高的温度(100–120°C)下可获得最佳对映选择性,其优点是提高了反应速率。
The rhodium-catalyzedasymmetrichydrogenation of various β-dehydroamino acid derivatives to give optically active β-amino acids has been examined. Chiral monodentate 4,5-dihydro-3H-dinaphthophosphepines, which are easily tuned and accessible in a multi-10-g scale, have been used as ligands. The enantioselectivity is largely dependent on the nature of the substituent at the phosphorous atom and on
novel class of bidentate (P,N) ligands is presented, the structures of which are characterized by three distinct elements of chirality. The stereoselective installation of the elements of central chirality (at the benzylic carbon and the phosphorus atom) depends on the size of the phosphorus substituent. Thermal inversion of the phosphorus center has been studied experimentally and further correlated
A general synthesis of chiral monodentate 4,5-dihydro-3H-dinaphthophosphepines 4 and a detailed study of the catalytic performance of the resulting ligands 4a-n in benchmark hydrogenation reactions is presented. Hydrogenation of methyl alpha-acetamidocinnamate 11 and methyl alpha-acetamidoacrylate 13 proceeded with enantioselectivities up to 95% and 94%, respectively. The best enantioselectivity for the rhodium-catalyzed hydrogenation of dimethyl itaconate 15 was 88%. (C) 2004 Elsevier Ltd. All rights reserved.
NEUE CHIRALE LIGANDEN UND DEREN ÜBERGANGSMETALLKOMPLEXE SOWIE DEREN KATALYTISCHE ANWENDUNG