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

Abhishek Koner, Susanne Sauerbrey, Gregor Schnakenburg, Antonio Bauzá, Antonio Frontera, Rainer Streubel

Index: 10.1002/ejic.201701338

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Abstract

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(Me2N)IMSR,R]2–; IMSR,R = 1,3-dialkylimidazole-2-thione-4-yl}, first detected as side products, has been optimized to access 4d–f {–[P(Et2N)IMSR,R]2–; IMSR,R = 1,3-dialkylimidazole-2-thione-4-yl}. The 1,4-dihydro-1,4-dichloro-1,4-diphosphinines 8a,b {–[P(Cl)IMSR,R]2–; IMSR,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 = nBu, TMSC2–). 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(Me2N)-IMSMeR,R}2–](CF3SO3)2; IMSMeR,R = 1,3-dialkyl-2-thiomethyl-imidazolium-4-yl}. Imidazole-2-thione-based tricyclic 1,4-dihydro-1,4-diphosphinines II were synthesized by LDA-induced cyclization starting from moncyclic 1,4-dihydro-1,4-diphosphinines ; the molecular electrostatic potential indicates competing nucleophilic centers.