Naphthalene Gattermann-Koch reaction

In the di-substituted benzene series o- and m-xylene give the expected products. However, p-xylene undergoes isomerisation to furnish 2,4-dimethylbenzaldehyde. The tri-substituted benzene series i.e. mesitylene and pseudo-cumene yield normal formylation products. Tetralin and di-isopropyltetralin in the naphthalene series are reported to undergo Gattermann-Koch formylation whereas naphthalene itself is formylated in the modified reaction using HF and BF3 as catalyst. 

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