Cyclic anhydrides, reduction

Reduction of Cyclic Anhydrides to Lactones and Acid Derivatives to Alcohols... 

Reductions of anhydrides of monocarboxylic acids to alcohols are very rare but can be accomplished by complex hydrides [55, 99]. More frequent are reductions of cyclic anhydrides of dicarboxylic acids, which give lactones. Such reductions were carried out by catalytic hydrogenation, by complex hydrides and by metals. 

Results of reductions of cyclic anhydrides to lactones with sodium amalgam or with zinc are inferior to those achieved by complex hydrides [1020]. However, 95.6% yield of phthalide was obtained by reduction of phthalimide with zinc in sodium hydroxide [1021]. 

Oxidation of diols 9-41 Reduction of cyclic anhydrides 9-69 Oxidative-reductive ring closure of dialdehydes... 

For the reduction of cyclic anhydrides to lactones, see page 1677, Section 2. 

In general, the dissolving metal or electrochemical reductions of acyl halides or acyclic anhydrides are not useful for the preparation of primary alcohols. Such reductions invariably provide acyloin esters, ene-diolate diesters or related species. Cyclic anhydrides may be reduced to give lactones. For example, the reduction of phthalic anhydride at a mercury cathode has been used in the synthesis of phthalide (90%). In general, however, such reduction are not widely employed in synthesis. 

Acyclic acid anhydrides are reduced to produce primary alcohols using NaBH4 and its many deriva-tives.2 - In most cases, the reaction gives both the primary alcohol and the carboxylate salt (1 1). Whilst such monoreduction may be desirable in cyclic anhydride chemistry (vide infra), it is inefficient when acyclic anhydrides are reduced. Thus, B2H6 or LAH reductions are the preferred synthetic methods. The reductions of mixed anhydrides, for example carboxylic/diphenylphosphoric or carboxylic/car-bonic anhydrides, produce the primary alcohol from the acyl component. ... 

Anhydrides have received very little attention as substrates for cathodic reduction. Polarography of cyclic anhydrides [107] in acetonitrile and DMF displayed two, one-electron waves for the most easily reduced anhydrides (pyromellitic, dibromopyromellitic, and tetrachlorophthalic anhydride). For 10 mono- and dianhydrides of aromatic carboxylic acids, the values for reduction in acetonitrile have been measured and listed [108]. 

The cyclic anhydride was converted into the amide acid which on Hofmann rearrangement followed by lithium borohydride reduction on the ester gave a derivative of ip-amino-2a, 3a-dihydroxy-43-hydroxy-methylcyclopentane. Condensation of the amino-triol with 5-amino-4,6-dichloropyrimidine followed by ring closure with triethyl orthoformate gave the 6-chloropurine derivative which on treatment with ammonia gave 11. ... 

Reduction of cyclic anhydrides. Although acid anhydrides are reduced to only a slight extent by sodium borohydride, cyclic anhydrides are reduced to 8- and y-lactones in 51-97% yield. Hydride attack occurs principally at the carbonyl group adjacent to the more highly substituted carbon atom.7... 

Finally, the regioselection in metal-hydride reduction of unsymmetrically substituted acyclic diesters is not understood [176] here, as well as in the reactions of cyclic anhydrides and imides, the effect of steric hindrance appears to play a minor role. 

Hydrolysis of the ester functions of dimethyl 2,2-bis(4-methoxyphenyl)-277-naphtho[l,2-6]pyran-5,6-dicarboxylate and cyclisation of the resulting dicarboxylic acid yields the cyclic anhydride 51. Reduction affords a mixture of two isomeric furano-fused naphthopyrans. Treatment of the anhydride with primary amines provides a route to the corresponding pyrrole derivatives. Both types of hetero-fused naphthopyrans show a red shift relative to the starting naphthopyran diester and reduced half-lives <01 WOP32661>. 

Redttctioit of cyclic aHkydrides. Hydrogenation of unsymmetrical cyclic anhydrides with this catalyst selectively reduces the less hindered carbonyl group (equation 1). Note that reduction with sodium borohydride results in... 

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