[65218-74-8] · C17H12NNaO2 · Sodium 4,6-Diphenyl-1-oxido-2-pyridone · (MW 285.29)
(nonhydrolytic conversion of alkyl and benzyl halides to aldehydes and ketones)
Alternate Name: pyridona.
Physical Data: white solid, mp 299-301 °C.
Solubility: sol methanol, DMF, ethanol.
Preparative Methods: the reagent is not commercially available. It can be synthesized by treatment of ethyl benzoylacetate with Sulfuric Acid to give 4,6-diphenyl-2-pyrone,1 which is converted by reaction with Hydroxylamine followed by base to the title compound (eq 1).2,3
Purification: the salt is used without purification. The N-hydroxy precursor, mp 162 °C, is recrystallized from benzene light petroleum.
Analysis of Reagent Purity: 1H NMR (DMSO-d6) d (ppm) 6.4 (1H, s), 6.5 (1H, s), 7.5 (10H, m).
Handling, Storage, and Precautions: store protected from moisture.
A disadvantage of most of the methods of accomplishing this transformation4 (e.g. the Kröhnke and Kornblum oxidations) is the need for strongly hydrolytic conditions which may be deleterious to sensitive functionality. Furthermore, many of these alternative methods are limited to activated (allylic or benzylic) halides. The reaction employing pyridona developed by Katritzky et al. avoids these problems.3,5-7 This oxidation takes place in two steps. First, the halide and title reagent are allowed to react together in a solvent (usually DMF but also MeOH and EtOH), giving the N-alkoxy-2-pyridone derivative. On thermolysis or photolysis, this compound then undergoes homolytic decomposition to the carbonyl compound and the 2-pyridone (eq 2).
As can be seen from Table 1, the reaction proceeds very smoothly for benzylic halides. For certain aliphatic halides a significant amount of the alcohol is produced as a byproduct in the second step.
The thermolysis is usually performed neat, and the carbonyl compound is obtained as it is formed by distillation from the reaction mixture. The alternative photolysis procedure is conducted with a medium-pressure mercury lamp through a pyrex filter, usually in ethyl acetate or benzene (eq 3). A limitation of the method is the further fragmentation of certain substrates.6
The oxidation may be performed with comparable results with the alternative reagents (1) and (2).8
S. Nicholas Kilényi
Sanofi Research, Brussels, Belgium