Hydrogenolysis of the 4,6-o-ketals of glucopyranosides. Configuration-dependent high regio- and stereo-selectivity of the diastereoisomeric acetophenone derivatives

Article abstract of DOI:10.1071/CH9960357

Hydrogenolysis (reductive cleavage) of the (R) isomers of the acetophenone 4,6-O-derivatives of glucopyranosides with LiAlH₄/AlCl₃ gives the 4-O-(1′-phenylethyl) ethers with (R) configuration; the corresponding (5) isomers produce the respective (R) 6-O-(1′-phenylethyl) ethers are produced. The hydrogenolysis of other 4,6-O-ketals affords O 4 ether derivatives; the two diastereoisomeric 4,6-O-s-butylidene derivatives (cyclic ketals) give O 4-ethers with the opposite absolute configuration. The stereoselectivity of these reactions is explained by the development of a four-centre transition state. The absolute configuration of the ethers has been determined by means of circular dichroism measurements.