New sulfur-phosphine ligands derived from sugars: synthesis and application in palladium-catalyzed allylic alkylation and in rhodium asymmetric hydrogenation

Abstract

An efficient route to mixed phosphine / thioglycoside ligands type IV starting from glucose pentaacetate is reported. In only five steps the key epoxide 6 has been obtained in high yield and its structure determined by X-ray analysis. The ring opening of the tert-butyl 4,6-O-benzylidene- 2,3-anhydro-1-thio-β-D-allopyranoside 6 with diphenylphosphinyl lithium afforded the desired ligand as a single diastereoisomer. The prepared compounds act as a bidentate ligands as shown by X-ray analysis of the Rh(I)-complex 12. Preliminary results on the behaviour of these ligands in Pd(0)-catalyzed allylic alkylation, and in Rh(I)-catalyzed enamide hydrogenation are also reported.