Electrochemical reduction lactones

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. 

Diazene 19 was synthesized in the manner portrayed below. Thus, treatment of anhydride 20 with sodium borohydride selectively reduces one carbonyl to a methylene unit. Reduction of the resulting lactone with DIBAL followed by a Wittig reaction and oxidation with PCC afforded aldehyde 22. When treated with cyclopentadiene in the presence of diethylamine in methanol, 22 undergoes a smooth and efficient conversion to fulvene 23. Diels-Alder cycloaddition to the azodicarboxylate 24 proceeded rapidly, a characteristic of reactions with this electron deficient chlorinated dienophile [8]. Selective reduction of the endocyclic n bond using diimide generated in situ, followed by the electrochemical reductive cleavage of the biscarbamate led to diazene 19 [6]. 

Methyl trichloroacetate reacts with olefins in the presence of transition-metal catalysts to give mixtures of the corresponding butyrate and y-butyrol-actone. Substituted y-butyrolactones are produced in the radiation-induced addition of alcohols or the electrochemical reductive addition of acetone to a/3-unsaturated esters. Acetylenic Grignard reagents react with y-lactones to give products of double addition, whereas the analogous lithium salts react only once. The products observed in the pyrolysis of y-lactone toluene-/ -sulphonylhydrazone sodium salts can be accounted for by the intermediacy of an oxycarbene. ... 

Polarographic (168) and electrochemical (169) procedures for the reduction of D-ribono-1,4-lactone have been developed, and the latter has been applied on a pilot-plant scale. 

A wide variety of reactions other than substitutions and hydrolyses have been performed in microemulsions. Examples include alkylations [29], Knoevenagel condensations [13], oxidations [30,31], reductions [32], formation and decomposition of Meisenheimer complexes [33], aromatic substitution reactions such as nitration and bromination [34-36], nitrosation [37] and lactone formation, i.e. esterification [38-40]. Microemulsions have also been used for photochemical and electrochemical reactions [41-45]. 

Although lactones may be reduced electrochemically or via Bouveault-Blanc reactions to produce diols, such reactions are more frequently used to prepare lactols. Both cathodic (Hg or Pb) and Na/Hg reduction are useful in the preparation of alditols from aldonic acid y-lactones. The reductions may be easily stopped at the intermediate aldose stage. ... 

The presence of other cathodic and anodic peaks points to electrochemical activity on other oxygen species existing on the carbon surface (see Table 4). Additionally, they may be overlapped by a significant capacitive current [153]. However, it should be remembered that the real chemical structure of an oxidized carbon surface [101] depends on the hydrolysis of lactone-, ester- or ether-like anhydrous systems and the ionization of some functionalities at extreme pH values (acidic or basic environments) [91]. These phenomena influence the surface density of species that can take part in charge-transfer processes, which explains the observed differences in height of reduction peak in different environments (see Fig. 18). These relationships can account for the reactions, e.g. [7,14,148],... 

The reaction of lactone (459) with p-tolylsulfonylmethylmagnesium iodide, followed by reduction of the keto sulfone to the 3-hydroxy sulfone has been studi. ° In this paper, the 3-hydroxy sulfone was reduced to the alkene (460) electrochemically (equation 106). The me c was applied to a wide variety of esters and lactones. The yield of the reduction to the methylene derivative was 70-87%. 

Deoxy-sugars can be synthesized from aldonolactones via -elimination or bromlnatlon procedures. 3-Deoxy-D-arablno-hexono-1,5-lactone, readily available from D-glucono-1,5-lactone by sequential acetylation, B-eliminatlon, hydrogenation, and deprotection, has been converted to 2-deoxy-D-erythro-pentose In 92)J yield by Indirect electrochemical oxidation. 3-Deoxy-D-arablno-hexose, which exists as a 53 30j 17 mixture o-f the o- and B-pyranose, and a-furanose forms In aqueous solution, has been synthesized by reduction of the 2,U,6-trl-0-benzoyl derivative of... 

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