HYDROGENOLYSIS OF THE 4,6-O-KETALS OF GLUCOPYRANOSIDES - CONFIGURATION-DEPENDENT HIGH REGIOSELECTIVITY AND STEREOSELECTIVITY OF THE DIASTEREOISOMERIC ACETOPHENONE DERIVATIVES

Hydrogenolysis (reductive cleavage) of the (R) isomers of the acetophe none 4,6-O-derivatives of glucopyranosides with LiAlH4/AlCl3 gives' th e 4-O-(1'-phenylethyl) ethers with (R) configuration; the correspondin g (S) isomers produce the respective (R) 6-O-(1'-phenylethyl) ethers a re produced. The hydrogenolysis of other 4,6-O-ketals affords O 4 ethe r derivatives; the two diastereoisomeric 4,6-O-s-butylidene derivative s (cyclic ketals) give O 4-ethers with the opposite absolute configura tion. The stereoselectivity of these reactions is explained by the dev elopment of a four-centre transition state. The absolute configuration of the et;hers has been determined by means of circular dichroism mea surements.