Synthesis of Donor-Acceptor-Type Benzo[b]phosphole and Naphtho[2,3-b]phosphole Oxides and Their Solvatochromic Properties

A series of donor-acceptor-type benzo[b]phosphole and naphtho[2,3-b]phosphole oxides have been synthesized through metal-catalyzed reactions as key steps: that is, (1) cobalt- and copper-catalyzed multicomponent coupling of an arylzinc reagent, an alkyne, and dichlorophenylphosphine to assemble the electron-deficient benzophosphole or naphthophosphole oxide core and (2) palladium-catalyzed cross-coupling to introduce an electron-donating substituent to the "benzo" or "naphtho" moiety. These donor-acceptor molecules are strongly fluorescent, showing weak to strong solvatochromism depending on the electron-donating substituent.