Oximino esters, hydrogenation

Reduction of oximino esters, i.e. oximes of keto esters, is very useful for the preparation of amino esters. Reductions are very selective since the oximes are easily reduced by catalytic hydrogenation over 10% palladium on carbon in ethanol (yield 78-82%) I094, by aluminum amalgam in ether (yields 52-87%) [750, 70P5], or by zinc dust in acetic acid (yield 77-78%). None of these reagents attacks the ester group. The last mentioned reaction gives an N-acetyl derivative [1096. ... 

In ethyl 3-keto-2-oximino-3-phenylpropanoate catalytic hydrogenation over palladium on carbon reduced both the keto and oximino group, giving a 74% yield of ethyl ester of -phenylserine (ethyl 2-amino-3-hydroxy-3-phenylpropionate). The reduction is stereospecific and only the erythro dia-stereomer was obtained, probably via a cyclic intermediate 11097]. Similarly, hydrogenation over Raney nickel at 25-30° and 1-3 atm converted ethyl a-oximimoacetoacetate quantitatively to ethyl 2-amino-3-hydroxybutanoate [45]. 

The oximino group in (149) can be introduced through nitrosation on carbon if there is an active hydrogen at that carbon atom. For example, nitrosation of the acylamino half ester of malonic acid gives an intermediate (163) that can isomerize to an oxime (164) and then cyclize to a 3-ethoxycarbonyloxadiazole (165). 

The ketone carbonyl can be replaced by a substituted carbon-carbon double bond as in the p methyl cinnamic esters shown in Eqn. 14.21,6 or by an a imino (Eqn. 14.22) or oximino group (Eqn. 14.23).62 Hydrogenation of these compounds gave the corresponding chiral materials with ee s ranging from 5-35%. 

Conversion of a nitrite ester to a y-oximino alcohol by photolysis involving the homolytic cleavage of a nitrogen-oxygen bond followed by hydrogen abstraction ... 

Synthesis, Hydroxyproline is synthesized by the method of Mcllwain and Richardson (542). a-Acetyl-S-chloro-y-valerolactone, prepared from acetoacetic ester and epichlorohydrin by the method of Leuchs (497), is converted to a-oximino-8-chloro-y-valerolaetone (A) by the action of nitrosyl sulfuric acid. (A) is reduced to a-aniino-8-chIoro-r-valerolactone (B) by shaking it for 3 days with hydrogen and platinum oxide catalyst. (B) is converted to a mixture of the isomeric DL-hydroxy-prolines by treatment for 2 hours with a saturated aqueous solution of ammoma. The copper salts of the two pairs of optical isomers are pre- > see p. 360. 

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