Branched-chain Sugars. XII. The Stereoselectivities in the Reaction of Methyl 4,6-<i>O</i>-Benzylidene-α- and -β-<scp>d</scp>-hexopyranosid-3-uloses with Diazomethane

Abstract

Abstract The stereoselectivities in the diazomethane reaction of methyl 4,6-O-benzylidene-2-O-methyl-α-d-ribo-hexopyranosid-3-ulose (2), its 2-epimer (3), β-anomer of 2 and the corresponding 2-O-Benzoyl derivative were examined, in comparison with those in the Grignard reaction and sodium borohydride reduction. The complemental stereoselectivity of diazomethane reaction in the case of 2 and 3 indicated that the electrostatic attractive effect in the transition state between diazomethyl cation and the axial methoxyl oxygen at the α-position to carbonyl function in 3 is much stronger than that at β-position which is predominat in the case of 2. In cases of β-anomers having no axial oxygen, stereoselectivies were preferentially controlled by the usual steric factors.