UTILIZATION OF NEUTRAL ALUMINA AS A MILD REAGENT FOR THE SELECTIVE CLEAVAGE OF PRIMARY AND SECONDARY SILYL ETHERS

The selective cleavage of primary and secondary trimethylsilyl (TMS), triisopropylsilyl (TIPS), tert-butyldimethylsilyl (TBDMS) and tert-butyldiphenylsilyl (TBDPS) ethers with neutral alumina under very mild conditions is described. The method involves utilization of the support, previously activated by heating at 80 degrees C/0.1 torr for 16 h and later deactivated with variable amounts of water (1.5-4.5%), in 50:1 ratio with regard to the substrate and in the presence of non-polar solvents, like hexane. The deprotection rate depends on the steric bulkiness of the silicon substituents, following the order TMS > > TBDMS approximate to TIPS > TBDPS, as well as on the type of the attached carbon. The procedure can discriminate between different silyl groups located at equivalent positions of the same molecule affording the corresponding monoprotected alcohols in very good yields.