Allylic Strain as a Stereocontrol Element in the Hydrogenation of 3-Hydroxymethyl-cyclohex-3-en-1,2,5-triol Derivatives. Synthesis of the Carbasugar Pseudo-2-deoxy-α-D-glucopyranose.

By adaptation of a literature method developed in the glucose series and standard protecting group manipulations a 2-deoxy-D-glucose derivative is converted to a series of 1R,2R,5R-3-hydroxymethyl-cyclohexen-1,2,5-triol derivatives whose reduction to the corresponding diastereomeric D-gluco and L-ido-2-deoxy carbasugars is studied. When the hydroxymethyl group is tied up in a cyclic isopropylidene acetal with the adjacent 6-hydroxy group the cis-fused products with the ido-configuration are formed preferentially whereas protection of the hydroxymethyl group as a methoxymethyl ether results in the formation of the D-gluco isomer on hydrogenation over Raney nickel. This result is rationalized in terms of the minimization of allylic strain in the course of the reduction, enables the preparation of the carbasugar pseudo-2-deoxy-α-D-glucopyranose, and suggests that the conformation of the side chain is an important control element in the chemistry of the pseudosugars as it is in the sugars themselves.