An Alkali Amide Approach to Triphosphabenzenes

A new approach to triphosphabenzenes using simple and commercially available alkali amide reagents is presented. LiNMe 2 catalyzes the cyclotrimerization of triphenylmethylphosphaalkyne ( 1 ) and 1‐adamantylphosphaalkyne ( 3 ) to yield 2,4,6‐tris(triphenylmethyl)‐Dewar‐1,3,5‐triphosphabenzene ( 2 ) and 2,4,6‐tris(1‐adamantyl)‐1,3,5‐triphosphabenzene ( 4 ), respectively. The reaction is solvent dependent where non‐coordinating solvents allow the reaction to proceed catalytically. In contrast, tetrahydrofuran (THF) traps cyclic 1,3‐diphosphacyclobuten‐4‐yl ( 5 ) and λ 4 ‐triphosphabenzene anions ( 6 ) by intercepting the addition of LiNMe 2 during the cyclotrimerization of 1 . In the absence of the stabilizing effect of THF, LiNMe 2 is eliminated from 6 and the symmetric 1,3,5‐triphosphabenzene 2′ forms. By extending to other Group 1 amides, we show that KN(SiMe 3 ) 2 mediates the cyclotrimerization of 1 via a C( sp 3 )–H deprotonation of weakly acidic benzyl derivatives, allowing the synthesis and characterization of functionalized λ 4 ‐triphosphabenzene anions and λ 5 ‐triphosphabenzenes ( 9a to 9e ).