A number of modifications of the original Grignard C-1 homologation of hexoses as examined, e.g. reactions of protected hexodialdo-1,5-pyranosides with benzyloxymethyllithium, transmetalation, precomplexation of the aldehydes. Some of the modifications, e.g. benzyloxymethyl Grignard addition in the presence of tert amines showed good to very good stereoselectivity of the heptoside formation. (C) 2002 Elsevier Science Ltd. All rights reserved.
Homologation of Protected Hexoses with Grignard C1 Reagents
hexodialdo-1,5-pyranosides were reacted with four Grignard C1 reagents: methoxymethyl-, allyloxymethyl-, benzyloxymethyl, and dimethylphenylsilylmethyl-magnesium chlorides. Two stereoisomeric heptoses were obtained in each case in a good yield. The methyl alloside-derived heptosides were accompanied by C-5 inverted products. The addition of Grignardreagents to aldehydes 5–8 has been discussed in terms