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25.6.6.2 Method 2: Intramolecular Formylation with Formic Esters: Lewis Acid Mediated Formylation of Phenols by Fries Rearrangement of Aryl Formates

DOI: 10.1055/sos-SD-025-00443

Schall, A.; Reiser, O.Science of Synthesis, (200725606.

Aryl formates can act as intramolecular formylating agents via a Fries rearrangement (Table 1).[‌9‌] Due to the instability of formylium cations, conditions must be chosen that sufficiently activate the aryl formate without causing its decomposition. Consequently, the choice of Lewis acid is crucial for the success of the rearrangement. As found for transformations using formyl fluoride (Section 25.6.6.3), boron Lewis acids give the best results here for the formation of 2-hydroxybenzaldehydes 4, while aluminum trichloride apparently does not give sufficiently stable Lewis acid adducts with aryl formates but more likely unstable formylium ions, resulting largely in the decomposition of the starting materials (Scheme 3).

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