Sommelet reaction, oxidation

Campaigne et al. have used 3-thenyl bromide obtained by benzoyl peroxide-catalyzed, side-chain bromination of 3-methylthiophene with A -bromosuccinimide, as a starting material for 3-substituted thiophenes. - 22 3-Methylthiophene is now prepared commercially from itaconic acid. The reactive halogen in 3-thenyl bromide could be directly reacted with a variety of nucleophiles, such as cyanide, or malonate, to give more complex 3-substituted compounds. 3-Thenyl bromide was converted by the Sommelet reaction to 3-thio-phenealdehyde which, with silver oxide, was oxidized to 3-thio-... 

Another way to oxidize primary alkyl halides to aldehydes is by the use of hexamethylenetetramine followed by water. However, this reaction, called the Sommelet reaction. is limited to benzylic halides. The reaction is seldom useful when the R in RCH2CI is alkyl. The first part of the reaction is conversion to the amine ArCH2NH2 (0-44), which can be isolated. Reaction of the amine with excess hexamethylenetetramine gives the aldehyde. It is this last step that is the actual Sommelet reaction, though the entire process can be conducted without isolation of intermediates. Once the amine is formed, it is converted to an imine (ArCH2N=CH2) with formaldehyde liberated from the reagent. The key step then follows transfer of hydrogen from another mole of the arylamine to the imine ... 

The method Is limited to activated halides which are stable to alkoxide bases and aqueous acids. According to the discoverer,the Krdhnke oxidation is inferior to the Sommelet reaction for benzyl halides, especially those bearing electron-withdrawing groups, such as nitro. Some representative examples are shown in Scheme (P and equations As can be seen, the Krdhnke oxidation is an... 

The Hass-Bender oxidation is often competitive with other methods in equation (16) 7 Sommelet reaction gave only 20% of the aldehyde, whereas in equation (20) DMSO and sodium hydrogen carbonate failed to furnish any of the desired product. 

Formylbenzenesulfonamide has been prepared by chromic acid oxidation of -toluenesulfonamide, the Sommelet reaction on p-chloromethylbenzenesulfonamide, and by the Stephen reduction of j -cyanobenzenesulfonamide. The present method provides a general procedure for the synthesis of substituted aromatic aldehydes as illustrated in Table I. 

Sommelet reaction, 33, 93 Sorbic acid, 5-hydroxy-/3-methyl, J-lactone, 32, 57 Stannic chloride, 33, 91 Stearic acid, 34, 15 Stearone, 33, 84 cis-Stilbene, 33, 88 fraws-Stilbene, 33, 89 Stirrer, for caustic fusion, 30, 104, 105 seal for, 30, 54 Stobbe condensation, 30, 18 Styrene, 33, 72 34, 85 reaction with sulfuric acid, 35, 83 Styrene dibromide, 30, 73 Styrene oxide, 31, 3 0-Styrenesulfonyl chloride, 34, 85 Succinic acid, 34, 44 Succinic acid, < -benzhydrylidene-, a-ETHYL ESTER, 30, 18 CLNNAMYL-, 31, 85 DIPHENYL ESTER, 34, 44 HEPTANOYL-, DIETHYL ESTER, 34, 51 PHENYL-, 30, 83 Succinic anhydride, 34, 40 SUCCINONITRILE, a, -DIPHENYL-, 32, 63 Sulfide, methyl 2-thienyl, 35, 85 Sulfonation of styrene, 34, 85 Sulfonyl chloride, from sodium sulfonate, 34, 85... 

The Sommelet reaction, also known as the Sommelet oxidation, is the oxidation of benzyl halides (1) to the corresponding aldehydes (3) using hexamethylenetetramine (HMTA) followed by hydrolysis of the hexaminium salt 2.1-3 This reaction is closely related to the Delepine amine synthesis, the Duff aldehyde synthesis, and the Krtihnke reaction (see Section 7.10.3). 

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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