No abstract

Using TMPZnCl·LiCl as a kinetically highly active base, nitriles and esters undergo a Pd-catalyzed α-arylation under mild conditions. Remarkably, in the case of α,β- or β,γ-unsaturated nitriles, a regioselective γ-arylation or a γ-alkenylation is observed.

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A new general Pd-catalyzed arylation of various 2-methyl-5-membered heterocycles is reported. This novel method requires Li-, Mg-, or Zn-TMP bases and allows selective metalation of the benzylic position. Subsequent Negishi cross-coupling provides the corresponding arylated heterocycles.

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Deprotonating substituted cyclohexanecarbonitriles with TMPZnCl·LiCl affords zincated nitriles that diastereoselectively couple with aryl bromides in the presence of catalytic Pd(OAc)(2) and S-Phos. Steric and electronic effects influence the diastereoselectivity; 4-t-butyl-, 4-TBSO-, and 2-Me-cyclohexanecarbonitriles exert virtually complete diastereocontrol whereas modest diastereoselectivity is observed with 4-i-Pr-, 4-Me-, and 3-Me-cyclohexanecarbonitriles. The unusual diastereoselectivity trends should prove useful for synthesizing substituted cyclohexanecarbonitrile-containing pharmaceuticals.

ZnCl2, Sc(OTf)3 oder BF3⋅OEt2 vermitteln die Pd‐katalysierte Arylierung von Methylpyridinen und ähnlichen Heterocyclen (siehe Beispiel). Die Komplexierung des Stickstoffatoms im Heterocyclus durch die Lewis‐Säure erleichtert die reduktive Eliminierung, was in hohen Ausbeuten zu zahlreichen arylierten Produkten führt. Mit BF3⋅OEt2 gelingt darüber hinaus im Fall des 2,4‐Lutidins eine hoch regioselektive Metallierung.

Pd-Catalyzed α-Arylation of Nitriles and Esters and γ-Arylation of UnsaturatedNitriles with TMPZnCl·LiCl. -The reactions of α,βand β,γ-unsaturated nitriles proceeds regioselectively. In the reaction of (XII) with 4-bromobenzonitrile (IIc) the γ-arylation occurs with migration of the double bond into conjugation with the aromatic ring. Alkenylation reactions proceed regioselectively and with retention of the double bond stereochemistry. -(DUEZ, S.; BERNHARDT, S.; HEPPEKAUSEN, J.; FLEMING, F. F.; KNOCHEL*, P.; Org. Lett. 13 (2011) 7, 1690-1693, http://dx.