17668-66-5Relevant articles and documents
C1-symmetric diphosphite ligands derived from carbohydrates: Influence of structural modifications on the rhodium-catalyzed asymmetric hydroformylation of styrene
Gual, Aitor,Godard, Cyril,Claver, Carmen,Castillon, Sergio
experimental part, p. 1191 - 1201 (2009/07/11)
New 3,5-diphosphite-substituted xylofuranoside (1b, 25a,b, and 26a,b) and glucofuranoside (3a, 7a, 8a,b) ligands with C1 symmetry have been prepared and used in the Rh-catalyzed asymmetric hydroformylation of styrene. The main structural features of these ligands are a) the presence of a 6-O-isopropyl group in ligands with a gluco configuration, b) the absence of 1,2-O-isopropylidene, a common group in many ligands with a furanoside skeleton, c) the presence of an alkyl chain bound to the 2-OH, and d) modification of the diol in the phosphite moiety. Modification of the carbohydrate backbone and diphosphite bridge affects the activity and selectivity of the reaction. Catalytic systems with ligands 1b and 8b were not active at 40 °C, although the formation of the expected hydride species [RhH(CO)2(1b)] was demonstrated by NMR spectroscopy. The highest enantioselectivity (83%) was obtained with the catalytic system Rh/8a. The complex [RhH(CO)2(8a)] was characterized by NMR spectroscopy using high-pressure techniques and was shown to exist in solution as two isomers in equilibrium; the two isomers adopt an equatorial-equatorial (eq-eq) configuration. Wiley-VCH Verlag GmbH & Co. KGaA, 2009.
Chiral diphosphites derived from D-glucose: New ligands for the asymmetric catalytic hydroformylation of vinyl arenes
Dieguez, Montserrat,Pamies, Oscar,Ruiz, Aurora,Castillon, Sergio,Claver, Carmen
, p. 3086 - 3094 (2007/10/03)
A series of novel diphosphite ligands derived from readily available D-(+)-glucose has been synthesized. These ligands have been applied to the Rh-catalyzed hydroformylation of vinyl arenes. Both excellent enantioselectivities (up to 91%) and regioselectivities (up to 98.8%) were achieved under mild conditions. The advantage of these ligands is that their modular natures allow facile, systematic variation in the configurations at the stereocenters [C(3), C(5)] at the ligand bridge and in the biphenyl substituents, enabling their effects on the stereoselectivity to be studied. Results show that the absolute configuration of the product is governed by the configuration at the stereogenic center C(3), while the level of the enantioselectivity is influenced by a cooperative effect between stereocenters C(3) and C(5). Replacement of the tert-butyl substituent by methoxy substituents at the para positions of the biphenyl moieties improved the enantioselectivities. We have characterized the rhodium complexes formed under CO/H2 by NMR techniques and in situ IR spectroscopy and have observed that there is a relationship between the structure of the [HRh(CO)2(PP)] species and their enantiodiscriminating performance in hydroformylation. Enantio-selectivities were highest with ligands with a strong bis-equatorial coordination preference, while an equilibrium of species with bis-equatorial and equatorial-axial coordination modes considerably reduced the ee's.
THE SYNTHESIS OF (-)-ANAMARINE
Valverde, S.,Hernandez, A.,Herradon, B.,Rabanal, R. M.,Martin-Lomas, M.
, p. 3499 - 3504 (2007/10/02)
The enantiospecific total synthesis of (-)-anamarine, starting from D-glucose, has been carried out.
