Quantitative Construction of C≡C Bond: Renaissance of Reductive Coupling of Benzotribromides Promoted by Cu/Polyamine

Abstract

Quantitative construction of carbon‐carbon triple bonds via reductive coupling of benzotribromides promoted by Cu/polyamine is realized under mild conditions. It provides a simple and efficient pathway to synthesize symmetrical diarylethynes using readily available and cheap reagents without acetylene group after simple workup.

Polymer Constructed Through the Formation of Carbon–Carbon Triple Bonds: Reductive Coupling Polymerization of Bis(benzylic gem-tribromide)s

“…CuBr was generated in redox reaction between Cu/ polyamine and alkyl bromide. The in situ formed CuBr has proven to be an efficient reductant for benzyl bromide, benzal bromide, and benzotribromide in the presence of polyamine by our previous results, 29,31,34 which generates C−C, CC, and CC bonds, respectively. Polymerization was carried out in the presence of CuBr/Me 6 TREN, and polymer with high M n was also obtained (run 14 in Table 1), which proves that in situ formed CuBr promotes the reductive coupling reaction as well.…”

“…The same result was found in the reductive coupling of benzotribromide. 31 Since Me 6 TREN as a ligand shows stronger capacity in debromination of Z-1,2-dibromo stilbene than the other two ligands, 31 it is selected as the ligand for further study. As shown in Figure 1, the peak at 90.14 ppm detected in the 13 C NMR spectrum of polymer 2a is a characteristic signal attributed to CC bonds.…”

“…The two-step process is consistent with the formation of a CC bond in reductive coupling of benzotribromides. 31 The evolution of linkage formation during the polymerization was tracked by three tandem polymerizations, which were (1) 0.5 h at 30 °C, (2) 1.5 h at 40 °C, and (3) 3 h at 60 °C, respectively. The resulting products were analyzed by NMR.…”

“…We have reported reductive coupling polymerizations of both bis­(benzylic bromide)­s and bis­(benzylic gem -dibromide)­s promoted by Cu/polyamine, which afford polymers through formation of C–C and CC bonds, respectively. , Recently, we have reported quantitative construction of the CC bond via reductive coupling of various benzotribromides promoted by Cu/polyamine (Scheme D). Here we present the first example of synthesizing ethynylene-bridged polymers through CC bond formation via reductive coupling polymerization of bis­(benzylic gem -tribromide)­s (Scheme E).…”

“…The solution was precipitated with methanol, and light yellow solid polymer was obtained. The effect of ligand on the polymerization was first investigated because we found it strongly affected the reductive coupling of benzotribromides . According to runs 1–3 given in Table , polymer containing only CC bonds was produced when tris­(2-dimethylaminoethyl)­amine (Me 6 TREN) was employed as ligand, while polymers obtained by tris­(2-pyridylmethyl)­amine (TPMA) and N , N , N ′, N ″, N ″-pentamethyldiethylenetriamine (PMDETA) contained CC and (Br)­CC­(Br) bonds, which were evidenced by 1 H NMR (Figure and Figure S3 in SI).…”