2- pyridylzinc bromide preparation

Pyridylzinc bromide, a commercially available reagent, was used in the synthesis of a series of bipyridyl derivatives (7.20.). Activated coupling partners, such as 2-chloro-4-cyanopyridine, reacted readily at room temperature in the presence of a palladium based catalyst, while less electron deficient halopyridines were coupled at elevated temperatures.27 The same approach was also extended to the preparation of other heterobiaryls.28... 

Preparation and Cross-Coupling of2-Pyridyl and 3-Pyridylzinc Bromides 77... 

Preparation and Cross-Coupling of 2-Pyridyland 3-Pyridylzinc Bromides 79... 

In general, the preparation of 2-pyridyl organometallics is mostly performed by lithiation of 2-halopyridine at cryogenic conditions followed by transmetal-lation with an appropriate metal halide. As mentioned previously, this procedure causes some limitations on the use of the 2-pyridyl organometallics. In our study, readily available 2-bromopyridine was treated at it with active zinc prepared by the Rieke method [138]. The oxidative addition of the active zinc to carbon-bromine bond was completed in an hour at refluxing temperature to give rise to the corresponding 2-pyridylzinc bromide (PI). 

As described in many previous reports, bipyridine units are very important for many natural products as well as many molecules used in material chemistry [141]. Significantly, this structural moiety can be readily prepared utilizing 2-pyridylzinc bromides. As described in Table 3.36, not only symmetrical 2,2 -bipyridine (7a) but also several different types of unsymmetrical 2,2 -bipyri-dines (7b-7h) were prepared in moderate yields. Again, the coupling reaction was completed in the presence of lmol% Pd(PPh3)4 in THF at rt, and, in general, 3-methyl-2-pyridylzinc bromide (P2) and 6-methyl-2-pyridylzinc bromide (P6) produced 2,2 -bipyridines, 7e and 7h, in low yields (Table 3.36, entries 5 and 8). It should be emphasized that the preparation of bipyridines using readily available 2-pyridylzinc bromides (P1-P6) could be a very practical approach because considerable effort has been directed toward the preparation of unsymmetrical 2,2 -bipyridines. 

Preparation and Cross-Coupling of 2-Pyridyl and 3-Pyridylzinc Bromides 87 Table 3.36 Preparation of 2,2 -bipyridines. ... 

We have demonstrated a practical synthetic route for the preparation of 2-pyridyl and 3-pyridyl derivatives. It has been accomplished by utilizing a simple coupling reaction of readily available 2-pyridylzinc bromides and 3-pyridylzinc bromides, which were prepared via the direct insertion of active zinc to the corresponding bromopyridines, or they can be purchased (Rieke... 

In 2010, Andreas Leitner and coworkers [174] at BASF reported the preparation of a very stable 2-pyridylzinc bromide (an sp organometallic nucleophile) on a multi-kilogram scale using Rieke technology and its application in the Negishi-Baba cross-coupling reaction. 

Functionalized heterocyclic zinc reagents are quite usefiil for the preparation of polyfunctional heterocycles. The pyridylzinc derivative 400 has been prepared by reductive lithiation followed by a transmetalation with zinc bromide (Scheme 2-130, eq. (a)). Its cross-coupling with a quinolyl chloride provides the new polyheterocyclic compound 401 in 81% yield. The selective functionalization of positions 3 and 4 of... 

---