Lead oxide excess route

Buncel et a/.215 found that at a higher temperature, or in the presence of an excess of nucleophile, subsequent transformation of 173 irreversibly leads to new products (Scheme 12). A proton transfer occurs first from thes/ 3 carbon atom to the N-oxide group. The resulting intermediate 175 changes by two routes, leading to 176, presumably by an intramolecular shift of the oxide substituent similar to a Smiles rearrangement, and to anion 167 by loss of OH and subsequent MeO attachment. 

Already in the last century Hantzsch (155) observed that reaction of a-halo acids (127) with excess hydroxylamine leads to oximes of a-keto acids (31) as the result of an oxidation-reduction process (Scheme 28). This process, as a method of synthesis of (31), was later thoroughly studied by Barry and Hartung (156). The oxidation-reduction reaction is responsible for the fact that later attempts to obtain the title compounds (1) from (127) by this route were never efficient (81,100) although sometimes they were patented (157). 

---