Imines Vilsmeier-Haack reaction

There are several methods for the direct introduction of an aldehyde group into an aromatic compound. In the Vilsmeier-Haack reaction, activated aromatic systems such as aryl ethers and dialkylanilines are formylated by a mixture of dimethylformamide, HCONMe2, and phosphorus oxychloride, POCL, (Scheme 6.4). The process involves elec-trophilic attack by a chloroiminium ion, Me2N=CHCl, formed by interaction of dimethylformamide and phosphorus oxychloride. Hydrolysis of the dimethyl imine completes the synthesis. 

In a related reaction, the Gattermann aldehyde synthesis, the carbon monoxide of the previous reaction is replaced by hydrogen cyanide (Scheme 6.6). This reaction gives poor yields with benzene itself, but is successful with activated species such as aryl ethers and phenols. The reaction proceeds via an aryl imine and the mechanism is not dissimilar to that of the Vilsmeier-Haack reaction. 

TL5981>. The proposed mechanism involves the oxidation of the amine to an imine, tautomerization to an enamine, and a sequence of nucleophilic attacks on the pyridazine rings followed by oxidation steps. The oxidant of choice is (bispyridine)silver permanganate <1982TL1847>, which is easily prepared, mild in action, and is soluble in organic media. If R1 = H in the product 77, electrophilic substitution (e.g., bromination, nitration, Mannich, and Vilsmeier-Haack-Arnold reactions) occurs at this position. 

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