The Stable (Phosphino)(Silyl)Carbene As A Useful Building Block: Synthesis And Reactivity of 2‐Phosphorus‐Substituted 2 H ‐Azirines

[Bis(dicyclohexylamino)phosphino]trimethylsilylcarbene ( 1 ) reacts with benzonitrile leading to the corresponding 2‐phosphino‐2 H ‐azirine 3 in 85% yield. Treatment of 3 with trifluoro‐methanesulfonic acid, methyl trifluoro‐methanesulfonate, or elemental sulfur leads to the P ‐hydrogeno‐2‐phosphonio‐, P ‐methyl‐2‐phosphonio‐, or 2‐thioxo‐phosphoranyl‐2 H ‐azirine ( 4, 5 , and 7 ) in 77, 87, and 91% yields, respectively. Irradiation of 3 gives rise to the 1,2λ 5 ‐azaphosphete 8 (98% yield). Treatment of 3 with BF 3 ·OEt 2 , BH 3 ·SMe 2 , Lawesson's reagent, or methyl isothiocyanate gives heterocycles 9 (90% yield), 10 (76% yield), 12 (83% yield), or 13 (80% yield), while under the same experimental conditions, heterocycle 8 reacts with the same reagents to give 9 (82% yield), 11 (83% yield), 12 (86% yield), and 15 (56% yield), respectively. Thermolysis of the P ‐hydrogeno‐2‐phosphonio‐2 H ‐azirine 4 at 55°C leads to the cationic, four‐membered heterocycle 17 (96% yield), while photolysis of the P ‐methylazirine analogue 5 in the presence of dimethyl acetylenedicarboxylate affords pyrrole 19 (64% yield). Irradiation of the thiox‐ophosphoranyl azirine 7 gives the 1,3,5λ 5 ‐thiazaphosphole 20 in 79% yield. The influence of the coordination state of phosphorus on the reactivity of 2‐phosphorus‐substituted 2 H ‐azirines is studied.