Synthesis and evaluation in asymmetric hydrogenation of carbohydrate-derived 1,3-bisphosphines

Abstract

1,3-Bisphosphines and 1,3-phosphine sulfides have been prepared from 1,6-anhydro-β-d-glucopyranose in view of their application as bidentate ligands in transition-metal-catalyzed asymmetric hydrogenation. Reaction of 1,6:3,4-dianhydro-2-O-(p-toluenesulfonyl)-β-d-galactopyranose (1) with Ph2PH in the presence of AlMe3 gave 1,6:2,3-dianhydro-4-deoxy-4-(diphenylphosphino)-β-d-mannopyranose (6) which, upon treatment with LiPPh2, led to 1,6-anhydro-2,4-dideoxy-2,4-bis(diphenylphosphino)-β-d-glucopyranose (9). Esterification of 9 with 1-naphthoyl chloride yielded the naphthoate 11. Upon exposure to air, 9 and 11 were oxidized to the corresponding bisphosphine dioxides 10 and 12. Treatment of 6 with PhSH and DBU led to 1,6-anhydro-2,4-dideoxy-4-(diphenylphosphino)-2-phenylthio-β-d-glucopyranose (13) and, after oxidation with air, to the corresponding phosphine oxide 14. Similarly, 1 was transformed into 1,6-anhydro-2,4-dideoxy-2-(diphenylphosphino)-4-phenylthio-β-d-glucopyranose (16) and its oxide 17. Attempted ring opening of 1 by Ph2PH/KOH or by Ph2PH/AlMe3 and oxidative work-up gave 1,6-anhydro-3,4-dideoxy-4-(diphenylphosphoryl)-β-d-threo-hex-3-enopyranose (3). In the presence of HCl, both 3 and 7 (obtained by air oxidation of 6) were transformed into 1,6-anhydro-2-chloro-2,4-dideoxy-4-(diphenylphosphoryl)-β-d-glucopyranose (8). The structure of 8 was established by an X-ray analysis. 1H-, 13C-, and 31P-n.m.r. spectroscopy showed that the phosphines (9, 11, 13, and 16) prefer a 1C4 and the phosphine oxides (8, 10, 12, 14 and 17) a B3,O conformation. The results of the rhodium- or ruthenium-catalyzed asymmetric hydrogenation with the phosphines 9, 11, 13, and 16 ligands are presented. In the hydrogenation of olefins (geraniol or the α-acetamidoacrylic acid 19), low enantioselectively is observed. Better enantiomeric excesses were obtained in the hydrogenation of α- and β-ketoesters (ketopantolactone, e.e. < 48%; methyl 3-oxotetradecanoate, e.e. < 55%).