Regioselectively trisilylated hexopyranosides through homogeneously catalyzed silane alcoholysis

The iridium complex [Ir(COD)(PPh3)2]+ SbF6- reacts with tert-butyldimethylsilane in DMA to form [IrH2(Sol)2(PPh3)2]+ SbF6-, which is an active catalyst for the regioselective di- and trisilylation of a series of representative methyl hexopyranosides, beta-1,6-anhydrohexopyranosides and 1,3,5-O-methylidene inositol. The corresponding 2,3,6- and 2,4,6-silylated glycosides are obtained in a separable mixture of 47-89% (2,3,6-isomers) and 9-25% (2,4,6-isomers) yield in a single-pot reaction. The 2,4-disilylated derivatives of mannosan, galactosan, and 1,3,5-O-methylidene inositol as well as persilylated levoglucosan are accessible in >85% yield by this method. The homogeneous nature of the catalysts is a prerequisite for the effective di-/trisilylation, as nanoparticle colloid catalysts generated in situ from Pd2(dba)3 (approximately 1.5 nm average particle size) or Ru2Cl5(MeCN)7 (approximately 0.65 nm average particle size) result in only low yields.