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

Abstract

Treatment of 2‐ethynylanilines with P(OPh)3 gives either 2,2‐diphenoxy‐2‐λ5‐phosphaquinolines or 2‐phenoxy‐2‐λ5‐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PV 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.

Impact of Internal Charge Transfer on the Photophysical Properties of Pyridine‐Fused Phosphorus‐Nitrogen Heterocycles

“…Since 2015, we have been studying the properties of the rarely‐accessed phosphaquinolinone scaffold [10–14] . The heterocyclic core is structurally similar to both coumarin and carbostyril‐coumarin's aza‐counterpart‐the difference being that the carbonyl has been replaced with an isolobal phosphonyl group (Figure 1).…”

“…X‐ray data of both forms suggested that the imidates possess more uniform bond lengths across the heterocyclic core, implying superior conjugation (Figure 2). [10] In prior studies, we have generally omitted data concerning the imidate form because of its facile hydrolysis into the amidate, and its inability to engender the hydrogen bond dimerization observed in the amidates. However, the inclusion of the 3‐pyridine motif in the core of the PN‐heterocycle dramatically increases imidate stability, affording a good opportunity to explore this species.…”

Tunable Regio- and Stereoselective Synthesis of Z-Acrylonitrile Indoles and 3-Cyanoquinolines from 2-Alkynylanilines and Alkynylnitriles

“…In this realm, the 2-(phenylethynyl)­aniline moiety has received much attention due to its aniline and o -alkyne functionalities in a single molecule. These molecules can be easily tuned in a way to synthesize a plethora of N -heterocyclic derivatives . Li and co-workers observed a remarkable transformation of 2-(phenylethynyl)­anilines with terminal alkynes leading to the formation of N -vinylindoles by using gold­(III) catalyst (Scheme a) .…”