various arylboronicacids bearing electron-donating and -withdrawing groups in the presence of palladium acetate and 1,10-phenanthroline. These reactions provided synthetically useful C-1 aryl enones in good yields. Many sensitive functional groups as well as protecting groups present in arylboronicacids and enones, respectively, remained intact under optimized conditions. The stereoselective hydrogenation
Simple oxidation of 3-O-silylated glycals: application in deblocking 3-O-protected glycals
作者:Andreas Kirschning、Ulrike Hary、Claus Plumeier、Monika Ries、Lars Rose
DOI:10.1039/a807479h
日期:——
A high yielding allylic oxidation of 3-O-silylated glycals 5–10 with the reagent system PhI(OAc)2–TMSN3 is presented. The iodine(III) species generated under these conditions is a lot more effective for generating carbohydrate-derived 3-trialkylsiloxy-2,3-dihydro-4H-pyran-4-ones 11–15 than is [hydroxy(tosyloxy)iodo]benzene, the Koser reagent. Even disaccharide 9 containing the oxidation-labile phenylseleno group is smoothly oxidized to the corresponding enone 15. The hypervalent azido iodine reagent is complementary to the Koser reagent, because 3-O-benzylated or -acylated glycals cannot be oxidized. When the iodine(III)-mediated oxidation of 3-O-silylated or -benzylated glycals is followed by a reduction step, the formal 3-O-deblocking of glycals is achieved. In particular, the Luche reduction of enones obtained from the oxidation of lyxo-configured glycals 24 and 26 is highly selective and exclusively affords the corresponding lyxo-configured glycals 28 and 30. In some cases, these products can be transformed under Mitsunobu conditions into glycals with inverted configuration at C-3 in moderate yield.