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Sulfur–Sulfur-Based Ligands Derived from D-Sugars: Synthesis of PdII Complexes, Application in Palladium-Catalyzed Allylic Alkylation for the Synthesis of Both Members of Enantiomer Pairs, and Structural Studies

AuthorsKhiar el Wahabi, Noureddine ; Serrano Araújo, Cristina; Suárez Jiménez, Belén; Fernández Fernández, Inmaculada
KeywordsAsymmetric catalysis
S-S ligands
Exo-Anomeric effect
Issue Date3-Feb-2006
CitationEuropean Journal of Organic Chemistry (7): 1685-1700 (2006)
AbstractA divergent synthetic approach for the synthesis of optically pure bis(thioglycosides) of type I is reported. A common chiral intermediate with up to eight free hydroxy groups is obtained in only two steps, and from this common intermediate a large number of ligands can be synthesized. A strategy resembling positional scanning enabled the rapid discovery of an efficient catalyst for the palladium-catalyzed asymmetric allylation of malonate. Both enantiomers of the allylated product could be obtained in up to 90 % ee values through the use of natural D-sugars as catalyst precursors, thanks to the structural similarity of α-D-arabinose and β-L-galactose. Treatment of several C2-symmetric bis(thioglycosides) with [PdCl2(CH3CN)2] always resulted in single diastereomeric PdII complexes. Dynamic NMR studies of various PdII complexes have shown that there is efficient stereochemical control over the sulfur configuration upon coordination to the palladium, as a consequence of the exo-anomeric effect. An explanatory model for the observed enantioselectivity based on NMR studies is discussed.
Description16 páginas, 12 figuras, 4 tablas, 8 esquemas.
Publisher version (URL)http://dx.doi.org/10.1002/ejoc.200500651
Appears in Collections:(IIQ) Artículos
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