Sommelet oxidation benzaldehydes

The net outcome of the Sommelet reaction is the oxidation of the benzyl methylene position into the corresponding carbonyl, and in that sense, the Krbhnke reaction may be considered a close variant. The KrOhnke reaction transforms benzyl halides to benzaldehydes using pyridine and an aromatic nitroso compound 16.16,17 As shown below, quaternary pyridinium salt (15) is formed from addition of pyridine to benzyl halide 1. Oxidation of 15 with p-nitrosodimethylaniline (16) affords nitrone 17, which is then hydrolyzed to benzaldehyde 3 and hydroxylamine 18. 

The third variation of the Sommelet reaction is the oxidation of benzyl halide 1 to the corresponding benzaldehyde 3 using 19, the sodium salt of 2-nitropropane (20).18,19... 

As with heterocycles, the Sommelet reaction tolerates ester and phosphonates. For instance, benzyl bromide 38 was oxidized to benzaldehyde 39 in the presence of phosphonate functionality although the yield was not reported. 

The amidomethyl group, which is readily introduced into even deactivated rings, can be oxidized via N-bromosuccinimide and hydrolysis to give the corresponding benzaldehyde in high yield.The use of phase-transfer catalysts significantly increases the yields in Reimer-Tiemann reactions.In a recent review on the uses of hexamethylenetetramine, the scope and utility of the Duff and Sommelet reactions are discussed (ca. 30 references). ... 

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