Reactions hydrolytic ring cleavage

This chapter, therefore, ends the monograph with a potpourri of reactions all of which occur without a change in oxidation state. In many cases, the reaction is one of nucleophilic attack at an electrophilic C-atom. The result is often hydrolytic bond cleavage (e.g., in carbohydrate conjugates, disubstitut-ed methylene and methine groups, imines, oximes, isocyanates, and nitriles, and various ring systems) or a nucleophilic substitution (e.g., hydrolytic de-halogenation of halocarbons and chloroplatin derivatives, and cyclization reactions). The formation of multiple bonds by dehydration is a special case to be discussed separately. 

Likewise, at elevated temperatures complex 21 promotes the stoichiometric cleavage of unactivated amides (e.g., dmf) or the hydrolytic ring opening of cyclic esters (e.g., butyrolactone. Scheme 4). These reactions are not catalytic, however, since the formed carboxylate in 27 and 28 acts as a tight bridge that blocks the bimetallic active site (70). 

Ring cleavage of the enol ether (167) has been achieved by hydrolytic nitrosa-tion to give the oxime (168), which is easily converted into the corresponding ketone.Another rearrangement route to macrolides occurs in the reaction of the hydroxyketone (169) with base (Scheme 83) the macrolides (170) are obtained after removal of the benzenesulphonyl group. A related fragmentation of disubstituted cyclohexane-1,3-diones leads to macrolides but mixtures of products are sometimes obtained. ° ... 

Another synthesis reaction is the hydrolytic cleavage of a suitable heterocycHc ring, for example, an Ai-methylpyridine salt, as shown in equation 9. 

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