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How low can Pd go? The direct arylation of heteroaryl compounds under very low loadings of Pd(OAc)2 as catalyst and in the absence of any added ligand proceeds in high yield. Turnover numbers up to 10 000 are observed for the coupling of activated aryl bromides with thiazole, thiophene or furan derivatives (see scheme; DMAc=N,N-dimethylacetamide).
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Požgan et al. (2008) studied this question.
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