Ethylene-oxide ring formation

A sulfate group situated on a secondary hydroxyl group is labile to alkali only if there is an adjacent, trans, free hydroxyl group available for ethylene oxide ring formation, as, for example, in 1,6-anhydro-0-D-galactopyranose 2-sulfate (IS) which, with sodium methoxide, forms" 1,6 2,3-dianhydro-(8-D-talopyranose (16). One apparent exception to this general rule is... 

Anhydro-D-glucose results from the action of anhydrous ammonia on l-chloro-2-trichloroacetyl-D-glucose triacetate (Brigl s compound73 8) and the preferential formation of an ethylene oxide ring is undoubtedly due to the lability of the trichloroacetyl group in position 2. 

Some examples are known where the formation of alternative, anhydro-ring structures is possible, and the deformation of the molecule required in the alternative reactions is approximately the same, so that entropy changes may be largely neglected. In such cases the ethylene oxide ring is not favored. The action of bases on methyl 3,4-di-0-acetyl-2,6-di-0-tosyl-/J-D-glucopyranoside and on methyl 2,6-di-0-mesyl- -D-galactopyranoside affords predominantly the 3,6-anhydro-2-0-sulfonyl derivative in each case. 

C13-0111. Ethylene oxide forms a polyether by ring opening followed by chain formation. 

The inference is that the hydrofuranol ring of XL can never be directly formed by the saponification of a 3-tosyl ester of D-glucose, but only indirectly by the intermediate formation and scission of an anhydro ring of the ethylene oxide type. The sequence of reactions involved in the conversion of methyl 3-tosyl-jS-D-gIueoside into methyl 3,6-anhydro-n-glucoside is shown by XXXVI to XL. 

Our Form II has two uncommon features. In the first place it contains two hydroxyl groups attached to the same carbon but we have that in chloral hydrate. In the second place there is an ethylene oxide oxygen linkage. This might be called an alpha lactone with the water not split off. This formation of a ring structure is believed to account for the reversal of the sign of rotation. It is well known that the formation of the lactide from lactic acid, while not a lactone formation in the same... 

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