LAUSR

The formation of meso-aryl-BODIPYs (boron dipyrrins) through the acidic condensation of 3,4-dialkylpyrroles with aromatic aldehydes, followed by 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) oxidation and BF2 complexation, has been reviewed. Surprisingly, it was found that the major products from these reactions were not the anticipated symmetric BODIPYs, but non-symmetric derivatives carrying one benzyl substituent at the BODIPY α position. The best yields and simple purification conditions were be achieved if the oxidant was not employed in the one-pot reaction sequence. Electron-rich benzaldehydes provided the best results, whereas precursors with electron-withdrawing substituents gave significant amounts of the symmetric BODIPYs as side-products. This unexpected result can be rationalized mechanistically on the basis of two reaction pathways that diverge from a common intermediate at an early step in the condensation sequence. Preliminary reactivity investigations showed chlorination to give unexpected results, but a typical substitution and coupling chemistry.