Synthesis, Substitution, and Oxidation of Imidazole‐2‐thione Based Tricyclic 1,4‐Dihydro‐1,4‐diphosphinines

Herein, the synthesis and chemistry of P‐functional tricyclic 1,4‐dihydro‐1,4‐diphosphinines is described, following a recent communication on their use as precursors of 1,4‐diphosphinines. In particular, ring formation of imidazole‐2‐thione‐based tricyclic 1,4‐dihydro‐1,4‐diphosphinines 4a , b {–[P(Me 2 N)IMS R,R ] 2 –; IMS R,R = 1,3‐dialkylimidazole‐2‐thione‐4‐yl}, first detected as side products, has been optimized to access 4d – f {–[P(Et 2 N)IMS R,R ] 2 –; IMS R,R = 1,3‐dialkylimidazole‐2‐thione‐4‐yl}. The 1,4‐dihydro‐1,4‐dichloro‐1,4‐diphosphinines 8a , b {–[P(Cl)IMS R,R ] 2 –; IMS R,R = 1,3‐dialkylimidazole‐2‐thione‐4‐yl}, easily obtained from 4 , are ideal starting materials for P‐substituted products 9a – c (P–R; R = n Bu, TMSC 2 –). The P ‐diorganoamino derivatives 4d – f are used to synthesize bis( P –oxides) 10a – c and bis( P ‐sulfides) 11a – c , and similarly, the bis( P –borane) adducts 13a – c . The first examples of bis(spirophosphorane) derivatives 12a – c , featuring two benzodioxaphosphole units, are synthesized by the reaction of 4d – f with o ‐chloranil. Attempts to access bis(phosphonium) derivatives using methyl trifluoromethanesulfonate have resulted in S‐methylation of 4d – f , and hence, have furnished the first examples of tricyclic 1,4‐dihydro‐1,4‐diphosphinines possessing two imidazolium units 14a , b {[–{P(Me 2 N)‐IMSMe R,R } 2 –](CF 3 SO 3 ) 2 ; IMSMe R,R = 1,3‐dialkyl‐2‐thiomethyl‐imidazolium‐4‐yl}.