Beilstein J. Org. Chem.2011,7, 1584–1601, doi:10.3762/bjoc.7.187
the ring-close oxazole, a trend that is evidenced by 1H NMR spectroscopy and attributed to the strong covalent carbon–zinc bond along with the zinc’s low oxophilicity, and this thus allows subsequent palladium-catalyzed Negishicross-coupling [31][32][33]. This first, highly efficient, stoichiometric
dehydrogenative couplings of (benz)oxazoles with (hetero)arenes have been developed.
Stoichiometric and catalytic direct (hetero)arylation of arenes.
Stille and Negishicross-coupling methodologies in oxazole series [28][30][31][33][34].
Stoichiometric direct (hetero)arylation of (benz)oxazole with magnesate
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Graphical Abstract
Scheme 1:
Stoichiometric and catalytic direct (hetero)arylation of arenes.
Beilstein J. Org. Chem.2011,7, 1261–1277, doi:10.3762/bjoc.7.147
obtained in 63% yield. Also, the dibromothiazole 19 allows insertion of zinc only into the most labile C–Br bond (in position 2) leading to the zincated thiazole 20. After Negishicross-coupling [10][11][12], the 2-arylated thiazole 21 is obtained in 85% yield. Polar functional groups, such as a tosyloxy
is obtained in 75% yield. Coumarine (46) can be directed zincated leading to the zinc reagent 47. After a Negishicross-coupling with an aromatic iodide, the substituted coumarine 48 is obtained in 83% yield (Scheme 8 and Supporting Information File 1, Procedure 3) [28]. This procedure tolerates most
iPrMgCl·LiCl (64) at −40 °C for 1 h leading to an intermediate magnesium reagent, which after transmetalation to the corresponding zinc reagent using ZnBr2 provides, after Negishicross-coupling reaction with the bromoquinoline 80, the polyfunctinal triazene 81 in 75% yield. The conversion of the triazene
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Graphical Abstract
Scheme 1:
Preparation of polyfunctional heteroarylzinc reagents.