Ni-based catalytic systems for the arylation of heteroarenes with aryl halides and triflates have been established. Ni(OAc)(2)/bipy is a general catalyst for aryl bromides/iodides, and Ni(OAc)(2)/dppf is effective for aryl chlorides/triflates. Thiazole, benzothiazole, oxazole, benzoxazole, and benzimidazole are applicable as heteroarene coupling partners. A rapid synthesis of febuxostat, a drug for gout and hyperuricemia, is also demonstrated.
A new synthetic methodology for the rapid methylation and fluoromethylation on aryl and alkenyl frameworks by using methyl and fluoromethyl iodide with an organoboronic acid ester has been developed under the simple and mild conditions of [Pd(2)(dba)(3)]/P(o-CH(3)C(6)H(4))(3)/K(2)CO(3) (dba= dibenzylideneacetone) in DMF at 60 degrees C for 5 min (see scheme). This boron protocol provides a firm chemical basis for the synthesis of (11)C- and (18)F-incorporated PET tracers.The rapid methylation and fluoromethylation on aryl and alkenyl carbon frameworks by reacting methyl and fluoromethyl iodide with aryl and alkenyl boronates have been studied with the focus on the realization of the synthesis of [(11)C]CH(3)- and [(18)F]FCH(2)-labeled positron emission tomography (PET) tracers. The coupling of methyl iodide and pinacol phenylboronate (40 equiv) is accomplished in >91 % yield within 5 min at 60 degrees C under the conditions of [Pd(2)(dba)(3)]/P(o-CH(3)C(6)H(4))(3)/K(2)CO(3) (0.5:2:2; dba=dibenzylideneacetone) in DMF. The reaction shows a high generality and is applicable to various types of aryl and alkenyl boronates, giving the corresponding methylated derivatives in high yields (80-99 %). This reaction is also useful for the rapid incorporation of the fluoromethyl group. Thus, this boron protocol provides a firm chemical basis for the synthesis of (11)C- and (18)F-incorporated PET tracers and can be used as a complementary method for [(11)C]methylation together with our previous and ongoing processes using organotributylstannanes.
A new copper-mediated cross-coupling of arenes and arylboronic acids is described. Under the influence of Cu(OCOCF 3) 2, the C-H bond arylation of electron-rich arenes with arylboronic acids takes place to afford a range of biaryls in good yields. The reaction is selective for cross-coupling; no homocoupling product arising from arenes or arylboronic acids is detected. Multiple C-H bond arylation is possible with indoles and pyrroles furnishing interesting extended pi-systems.
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