Deoxygenation of tertiary and secondary alcohols ROH by thiol-catalysed radical-chain redox decomposition of derivatives ROCH2X to give RH and XCHO

Abstract

Compounds of the type ROCH₂X, in which the substituent X is an electron-donating alkoxy, aryl or amido group, undergo thiol-catalysed radical-chain decomposition to give RH and XCHO. This reaction has been applied for the deoxygenation of representative tertiary and secondary alcohols ROH under metal-free conditions that require no stoichiometric co-reactant. Of the derivatives investigated, methoxymethyl (MOM) ethers and 1-alkoxymethylpyrrolidin-2-ones (PYRM ethers) proved to be the most generally successful and typical conditions for the redox decomposition to give RH involve heating under reflux in octane solvent in the presence of a peroxide initiator and tri-tert-butoxysilanethiol [(Bu^tO)₃SiSH] as a protic polarity-reversal catalyst. Conversions to RH were negligible in the absence of thiol. Several different types of tertiary alcohol, including steroidal and carbohydrate examples, were deoxygenated as their MOM and PYRM ethers to give very good isolated yields of RH. Although the MOM and PYRM ethers derived from many types of secondary alcohol also afforded good yields of RH, the MOM ether of diacetone D-glucose gave the 3-deoxy sugar in poor yield and the yield from the corresponding PYRM ether was still only moderate.