Ring formation, factors affecting

It is often possible to predict the reactivity of a chlorosulfonyloxy group by a consideration of the steric and polar factors affecting the formation of the transition state,27-28 as indicated in Section 11,1 (see p. 227) for nucleophilic-replacement reactions of sulfonic esters of carbohydrate derivatives. Thus, it has been found that the presence of a vicinal, axial substituent or of a (3-trans-axial substituent on a pyranoid ring inhibits replacement of a chlorosulfonyloxy group also, a chlorosulfate group at C-2 has been observed to be deactivated to nucleophilic substitution by chloride ion. 

Chapters 7 to 12 deal with factors affecting conformational equilibria and complex formation. Angyal explains the effect of calcium chloride on the anomeric equilibria of certain sugars by formation of especially stable complexes. These involve an axial-equatorial-axial sequence of three hydroxyl groups on a six-membered ring or a cis-cis sequence on a five-membered ring. Lemieux and Brewer use model compounds to study solvation effects on the orientation of the hydroxymethyl... 

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