Regioselective functionalization at the 7-position of 1,2,3-triphenylbenzo[b]phosphole oxide via PO-directed lithiation

Various 7-substituted benzo[b]phosphole derivatives were prepared by PO-directed lithiation of 1,2,3-triphenylbenzo[b]phosphole P-oxide and subsequent iodination and cross-coupling reactions. The electron-donating groups introduced at the 7-position produced dramatic solvatofluorochromism owing to the strong charge-transfer character of the excited state of the entire π-system.