Facile oxidation of a carbaporphyrin at the internal carbon atom: synthesis of novel benzo[18]annulene ketals†

Treatment of benzocarbaporphyrin 2 with refluxing FeCl3 in CHCl3–alcohol mixtures leads to a remarkably selective oxidation at the interior carbon atom to produce dialkoxy products 5; these species show potentially valuable long wavelength absorptions in their UV–VIS spectra.