Facile Synthesis and Properties of 2‐λ⁵‐Phosphaquinolines and 2‐λ⁵‐Phosphaquinolin‐2‐ones

Abstract

Abstract Treatment of 2‐ethynylanilines with P(OPh) 3 gives either 2,2‐diphenoxy‐2‐λ 5 ‐phosphaquinolines or 2‐phenoxy‐2‐λ 5 ‐phosphaquinolin‐2‐ones under transition‐metal‐free conditions. This reaction offers access to an underexplored heterocycle, which opens up the study of the fundamental nature of the NP V double bond and its potential for delocalization within a cyclic π‐electron system. This heterocycle can serve as a carbostyril mimic, with application as a bioisostere for pharmaceuticals based on the 2‐quinolinone scaffold. It also holds promise as a new fluorophore, since initial screening reveals quantum yields upwards of 40 %, Stokes shifts of 50–150 nm, and emission wavelengths of 380–540 nm. The phosphaquinolin‐2‐ones possess one of the strongest solution‐state dimerization constants for a D–A system (130 M −1 ) owing to the close proximity of a strong acceptor (PO) and a strong donor (phosphonamidate NH), which suggests that they might hold promise as new hydrogen‐bonding hosts for optoelectronic sensing.