Aldol condensation ethyl oxalate

Condensations with alkyl nitrites and nitrates, however, are not so generally applicable as the true ethyl acetoacetate reaction, and the possibility is not excluded that they proceed in another way compounds with mobile hydrogen might first he added to the inorganic part of the ester by means of an aldol condensation. The fact that fluorene, which contains no active double bond at all, combines with ethyl nitrate (as well as with ethyl oxalate) and sodium ethoxide in the same way, yielding oci-nitrofluorene, seems to support this second theory (W. Wislicenus). 

Reactivity of the C-5 methyl group in (120) is exhibited in aldol-type condensations, e.g. benzaldehyde with an acid catalyst to give (121) or ethyl oxalate with a strong base to give (122). The greater reactivity of a methyl group at C-5 is also shown in the results of lithiation... 

Among other reactions proceeding through aldol-like intermediates, the formation of 2 hydroxymethylene-3-ketones (20) and similar derivatives deserves comment. The condensation occurs when ethyl formate reacts with the A2>4 enolate anion (ig), the product separating from non-polar solvents as an enolate salt (21) [xg6]. Similar condensations occur with ethyl oxalate [igy] 5a-3-Ketones naturally react at C 2>, through their stable enolates, but A -g-ketones and 5j5-3 ... 

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