Ketones, ethyl from carbohydrates

A number of ethyl ketones and propionate esters derived from carbohydrates have been investigated in the aldol reaction. None of the compounds studied give useful levels of stereoselection. The most selective compound from this study is ketone (201 equation 121) syn aldols (202) and (203) are produced in a ratio of 79 21. 

Carbohydrate lactones have been used as the carbonyl reagent in the Reformatsky reaction. Thus, 2,3 5,6-di-O-cyclohexylidene-D-mannono-1,4-lactone [44, obtained by oxidation of the mannofuranose derivative (49)] reacted with ethyl bromoacetate and zinc to give the protected 2-deoxy-3-octulosonic acid ethyl ester (45a) in 69% yield (50). Ketonic hydrolysis with potassium hydroxide in aqueous methanol, followed by acidification and heating, afforded the 1-deoxyheptulose derivative 45b. Similarly, starting from compound 44, the 1-C-substituted allyl and propar-gyl lactols were prepared on reaction with allyl or propaigyl bromides in the presence of zinc (51). 

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