Reaction of Aldonolactones with Alcohols

Reaction of Aldonolactones with Alcohols 1. Formation of Esters 

Aldono-1,5-lactones and free aldonic acids react with alcohols in the presence of hydrogen chloride to give the corresponding alkyl aldonates (84). The reaction is slower with 1,4-lactones. Because esterification takes place very slowly in the absence of an acidic catalyst, aldonic acids and their lactones may be recrystallized from boiling alcohols without appreciable esterification (85). However, in some instances, alkyl esters are formed under these conditions. For example, essentially pure ethyl L-mannonate was isolated (6.4% yield) from the mother liquors of crystallization L-man-nono-1,4-lactone, obtained by Kiliani synthesis from L-arabinose (86). Similarly, repeated recrystallization from ethanol of crude 2,3,4,6-tetra-O-acetyl-D-glucono- 1,5-lactone afforded the corresponding ethyl gluconate derivative (87). 

Ethanolysis of 2,4-di-0-benzoyl-3,6-dideoxy-L-ara mo-hexono-l,5-lactone (92) afforded ethyl 2,4-di-0-benzoyl-3,6-dideoxy-L-araW/to-hexonate (93a). On being kept, compound 93a was slowly converted into 2,5-di-O-benzoyl-3,6-dideoxy-L-ara6mo-hexono- 1,4-lactone (94). This transformation involves O-4 — 0-5 benzoyl migration, with formation of ethyl 2,5-di-0-benzoyl-3,6-dideoxy-L-araA ohexonate (93b) as an intermediate (89). 

The acid-catalyzed acetalation of aldonolactones with alkyl acetals of aldehydes or ketones takes place, in some instances, with esterification of the lactone group to give acetal derivatives of alkyl aldonates (11,22). 

Addition of alcohols to lactones results in the formation of orthoacid or orthoester derivatives. Thus, reaction of lactone 95a with potassium cyanide in ethanol led to displacement of the tosyl group by cyanide and addition of ethanol to the lactone carbonyl group, to give the orthoacid derivative 95b, which was isolated as its acetate 95c. Mild deacylation of 95c led back to 95b, but under more vigorous reaction conditions the open-chain methyl aldon-ate was obtained (90). 

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