Hagihara-Sonogashira coupling

Cross-coupling Polymerization at sp-Hybridized Carbons 11.19.3.1 Polymerization by Sonogashira-Hagihara Coupling... 

Polyarylbismuth(V) compounds, in (7-arylations, 9, 444 445 Poly(arylene-ethynylene)s, via Sonogashira-Hagihara coupling, 11, 670-671... 

Terminal alkynes can be alkenylated by alkenyl triflates (bromides, iodides) in the presence of catalytic amounts of a palladium(O) complex (or a precursor thereof) and usually an additional substoichiometric amount of copper(I) iodide (Cul), and they can be arylated by aryl triflates (bromides, iodides). These reactions are called Cacchi coupling reactions if triflate reagents are employed, and Sonogashira-Hagihara coupling reactions if halides are used. 

Cacchi- and Sonogashira-Hagihara couplings occur only if a primary, secondary, or tertiary amine is present, and it is best to have the amine present in large excess. Under these conditions the acetylene will at least form a small equilibrium concentration of the corresponding ammonium acetylide or copper complex thereof. The copper iodide serves to trap this species as a copper acetylide. The copper acetylide represents a substantially improved nucleophile in comparison to the free acetylene. Without the Cul addition, the acetylide content of the reaction mixture is so small that a reaction occurs only at higher temperatures. 

Our convergent approach to this class of natural products utilizes the iron-mediated arylamine cyclization for construction of the carbazole framework. The retrosynthetic analysis of the antiostatins B (69a-d) leads to cyclohexa-1,3-diene (33) and the arylamines 70 as building blocks (Scheme 18) [134]. The different side chains at C-1 are introduced by a palladium(0)-catalyzed Sonogashira-Hagihara coupling. The amino group at C-4 is attached to the preformed carbazole skeleton. For introduction of the biuret side chain, we have developed 5-isobutyl-1-nitro-biuret (71) as reagent to access the antiostatins of the B-series. 

Figure 5.20 Sonogashira-Hagihara coupling polymerization of monomers 31.

Several other chiral polymers were synthesized by Sonogashira-Hagihara coupling polymerization. These structures were composed of optically active poly(m-phenyleneethynylene-aryleneethynylene) with varying arylene groups (Figure 5.20). 

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