Abstract
Coupling of haloarenes to arenes has been facilitated by a diverse range of organic additives in the presence of KO(t)Bu or NaO(t)Bu since the first report in 2008. Very recently, we showed that the reactivity of some of these additives (e.g., compounds 6 and 7) could be explained by the formation of organic electron donors in situ, but the role of other additives was not addressed. The simplest of these, alcohols, including 1,2-diols, 1,2-diamines, and amino acids are the most intriguing, and we now report experiments that support their roles as precursors of organic electron donors, underlining the importance of this mode of initiation in these coupling reactions.
Highlights
Formation of biphenyls[1] is of great importance both in industry and in academic chemistry
Loss of hydride to form the imine is likely to have a very high activation barrier and likely to be the rate-determining step in formation of the initiating electron donor(s). (We emphasize that we are speaking about the slow step in the process of forming the initiator, not the slow step in the main chain reaction shown in Scheme 1.) We proposed to test for this using deuterium-labeled analogs of diamine 90
In our earlier paper,[51] we showed that fully characterized organic electron donors like 28 can initiate the coupling reactions between haloarenes and arenes in the presence of KOtBu in benzene as solvent
Summary
Formation of biphenyls[1] is of great importance both in industry and in academic chemistry. We reported that organic electron donors, e.g., 28, can act as initiators in coupling reactions between haloarenes and arenes,[51] forming aryl radicals by electron transfer to the haloarene.
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