Methoxymercuration, of glycals

In accordance with expectations, methoxymercuration of glycals and their acetates has been found, by two independent groups working concurrently, to give rise to methyl glycosides having C-2-mercury bonds, and it is considered that the mechanism of the addition involves the formation of 1,2-mercm-inium ions which are attacked at C-1 hy the solvent. 

The methoxymercuration of 4,6-0-benzylidene-D-allal yielded isomeric acetoxy-mercurial adducts having the -D-allo (439) and a-D-altro (440) configurations. Demercuration of (439) with sodium borohydride gave methyl 4,6-0-benzylidene-2-deoxy-P-D-ri6o-hexopyranoside (72%), the ot,p-unsaturated aldehyde (441) (8.3 %), and a trace of the original glycal, while demercuration of (440) gave methyl 4,6-0-benzylidene-2-deoxy-a-D-r/6o-hexopyranoside (40%), (442) (23.5%), and traces of other products. 

A further example has been given of the synthesis of a 2-deoxy-aldose by the addition of water to a glycal, but, as this reaction is known to be accompanied by competing eliminations,1 it is being replaced in synthetic work by more-specific addition procedures, for example, methoxymercuration (see p. 210). From the 4-deoxy derivative of D-glucal, prepared by standard procedures from 2,3,6-tri-O-acetyl-4-deoxy-D-xy/o-hexopyranosyl bromide, 2,4-dideoxy-D-threo-hexose was obtained.35... 

Syntheses Involving additions to glycal derivatives have included the following 2,6-dldeoxy-L-lyxo-hexose from di- -acetyl-L-fucal by addition of acetic acid or by methoxymercuration 2-... 

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