89 / 2023-09-26 16:34:08

Access to π-Conjugated 1,3-Azaphospholes from Alkynes via [3+2]-Cycloaddition and Reductive Aromatization

Phospholes,Polyaromatic Compounds,Dipolar Cycloaddition

New Technologies in Phosphorus Chemistry > 1) New reagents and methods in organophosphorus Chemistry

The incorporation of heteroatoms into large aromatic frameworks has proven to be a valuable strategy for modifying the chemical and physical properties of compounds.^[1] Within this context, phosphorus-containing heterocycles featuring σ³λ³ or σ³λ⁵-P atoms are state of the art, while σ²λ³-phospholes remain largely underrepresented.^[2] Notably, their properties differ drastically, depending on the constitution of the phosphorus atom.

This contribution outlines a convenient method for the synthesis of σ²λ³-1,3-azaphospholes from readily available alkynes. 1,3-Dipolar imidazoliumyl-substituted triflato-phosphanes 1[OTf] readily react with alkynes in a [3+2]-cycloaddition reaction to azaphospholium salts 2[OTf]₂. These compounds can be reduced to yield azaphospholes 3 in a convenient, scalable reduction reaction. The reaction’s versatility is showcased with 19 examples, achieving yields of up to 99%. Additionally, mechanistic details will be discussed.