Ullmann-type cross coupling

The 1,4-conjugate addition of triorganoindium to enones is promoted by a catalytic amount of Ni(COD)2 (Scheme 8.71) [100], Allylindium reagents can be used in Pd-catalyzed cross-coupling reaction with aryl halides (Scheme 8.72). The Pd-catalyzed allylic substitution of allyl carbonate produces 1,5-dienes (Scheme 8.73) [101]. The indium-mediated palladium-catalyzed Ullmann-type reductive coupling of aryl halides proceeds in aqueous media under air (Scheme 8.74) [102]. 

Over the past century, several methods have been developed for the synthesis of biaryl compounds [7]. Among these are the Ullmann-type coupling [8,9], the Scholl reaction [10], the Gomberg-Bachmann reaction [11], and recently transition-metal-catalyzed cross-coupling reactions [12], In particular, palladium-catalyzed crosscoupling reactions have been successfully applied to the synthesis of biaryls due to their generally high yields and excellent selectivities. 

At last, it should be noted that PAFs, especially synthesized by Yamamoto-type Ullmann cross-coupling, are costly to deploy on a large scale as a carbon capture adsorbent. There is stiU a great challenge to find a more convenient and low-cost synthesis method to prepare PAFs. Besides, the incorporation of useful and novel functions within robust PAFs with ultrahigh surface area remains a formidable challenge and an exciting opportunity for material chemists. 

Yamamoto-type Ullmann Cross-coupling Reaction... 

PAF-1 Yamamoto-type Ullmann cross-coupling 5640 1.4 2.43 Disorder... 

Copper was selected as the metal of choice for the decarboxylation step, IX to X, as it is widely used in protodecarboxylation procedures [39]. However, taking into account the known, limited catalyst productivity and selectivity of copper in Ullmann-type coupling [25], the authors decided to use a second metal for the crosscoupling step. Here, palladium turned out to be the best choice, as it is known for efficient mediation of a large number of two-electron cross-coupling reactions [40]. 

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