Abstract

The stereoselectivities in the reaction with diazomethane of methyl 4,6- O benzylidene-3- O-methyl-α- d- arabino-hexopyranosid-2-ulose ( 2), its 3-epimer ( 3), its β anomer ( 5), and the corresponding 3- O-benzoyl derivative ( 4) have been examined in comparison with those in the Grignard reaction and in reduction with sodium borohydride. The opposite stereoselectivity of the diazomethane reaction, with equatorial attack on α anomers ( 2 and 3) and axial attack on β anomers ( 4 and 5), to that of the other reactions, is explained by an attractive, electrostatic interaction in the transition state between the diazomethyl cation and either the axial O-1 of the methoxyl group or lone-pair electrons of O-5.

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