How to Shrink the Ring: Phospholenes from Phosphabenzenes via Selective Ring Contraction
Lin, Jinxiong and Coles, Nathan T. and Dettling, Lea and Steiner, Luca and Witte, Jan Felix and Paulus, Beate and Müller, Christian – 2022
A 3-aminofunctionalized phosphabenzene (phosphinine) was synthesized and structurally characterized. The pyramidalized nitrogen atom of the dimethylamino substituent indicates only a weak interaction between the lone pair of the nitrogen atom and the aromatic phosphorus heterocycle, resulting in somewhat basic character. It turned out that the amino group can indeed be protonated by HCl. In contrast to pyridines, however, the phosphabenzene-ammonium salt undergoes a selective ring contraction to form a hydroxylphospholene oxide in the presence of additional water. Based on deuterium labelling experiments and quantum chemical calculations, a rational mechanism for this hitherto unknown conversion is proposed.