Glucopyranose trimethyl ether

Benzylidene-l-phenylthio-2,3-di-0-trimethylsilyl-/2-D-glucopyranose reacts with lithium naphthalenide to give the unstable a-lithio ether 7. This undergoes 1,3-0 ->C silyl rearrangement to afford stereoselectively (4,6-0-benzylidene-2-0-trimethylsilyl-a-D-glucopyranosyl)trimethyl-silane (8) in 61 % yield in addition to a minor product (12% yield) identified as 1,5-anhydro-... 

In this manner 6-methyl-D-glucopyranose (XXIX) and some of its derivatives were synthesized from n-glucose derivatives containing a free hydroxyl group only in the 6-position. The 6-methyl ethers of D-mannose and of methyl a-n-mannoside were obtained similarly. Haworth and coworkers synthesized 2,3,4-trimethyl-n-glucose from 6-trityl-D-glucose and used the ether for the elucidation of structural problems. 

Our next task is to determine which carbon of glucose is attached to C(l) of galactose. To address this issue, we can use a Williamson ether synthesis to methylate all free hydroxyl groups in (-l-)-lactose (Rg. 22.63). After methylation, the lactose is hydrolyzed in acid to 2,3,4,6-tetramethyl D-galactopyranose and 2,3,6-trimethyl D-glucopyranose. 

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