2-pyridinyl halide

Recently, the required heteroaromatic organozinc halides for the Negishi reaction have also been prepared using microwave irradiation [23]. Suna reported that a Zn - Cu couple (activated Zn), prepared using a slightly modified LeGoff procedure from Zn dust and cupric acetate monohydrate, allowed the smooth preparation of (3-pyridinyl)zinc iodide and (2-thienyl)zinc iodide... 

Kosower s radical (66) reacts with alkyl halides by a mechanism which transfers a halogen atom to the pyridinyl radical in the rate determining step (Py is 66) ... 

The kinetics and mechanism of the reaction of 4 with halocarbons (dichloro-, trochloro- and tetrachloromethane, various benzyl halides) have been reported Earlier work on pyridinyl radicals has been reviewed as well as the organic chemistry of stable free radicals This chapter will concentrate on developments of the past decade, since new techniques, described specifically, have increa our understanding of pyridinyl radical behavior considerably. 

Pyridinium halides are easily reduced to pyridinyl radicals (e in place of hv, eq. 1) with scKiium amalgam in oxygen-fr acetonitrile using a vacuum line and the apparatus shown in Fig. 1 After filtration, the pure pyridinyl irulicals are isolated by several distillations. Magnesium or zinc have been used on a preparative scale various other metals (e.g., calcium, strontium and barium) are suitable for preparing solutions of pyridinyl diradicals... 

Pyridinyl radicals react with haloorganic compotinds at ratra that are very sensitive to the strength of the halogen-carbon bond. Both atom-transfer and electron-transfer mechanisms for the reaction have been detected, with the latter exhibiting a large response to solvent polarity change and to variations in the electron affinity of the organic halide. 

Radicals stable enough to be transferred from one environment to another have been useful for (a) analyzing the effect of the molecular milieu on the reactions of radicals and (b) probing the viscosity and polarity of the domain in which the radical is located. The simplicity and chemical reactivity of pyridinyl radicals, generated through chemical reduction of pyridinium halides (Eq.l), has provided the opportunity for studies on the mechanisms of radical reactions and on the properties of Tr-coii5)lexes of radicals. 

TABLE I. Rate Constants for the Reaction of l-Ethyl-4-carbomethoxy-pyridinyl Radical with Halides and Polyhalides at 25 C... 

Simple pyridinyl radicals, Py, like those derived from 1-ethyl-4-carbomethoxy-pyridinium ion through l reduction, have proven useful for the investigation of properties of radicals, including complexes, and the study of the mechanisms of their reactions. Discoveries include (a) distinction between atom-transfer and electron-transfer reactions by means of solvent effect on rate constants, (b) intramolecular radical complexes (ir-mers) within pyridinyl diradicals and pyridinyl diradical metal halide complexes, (c) occurrence of either electron-transfer or dimerization between pyridinyl radicals in water according to structure and (d) con5)lexation between pyridinium ions and pyridinyl radicals. Consideration of actual and potential biological roles for pyridinyl radicals is aided by these discoveries. 

Carbonylation. Pd(PhCN)2Cl2 can be readily used as the catalyst for the carbonylation of indolyl, pyridinyl, or quinolinyl halides with amines, alcohols, or even water under an atmosphere of CO (eq 1).2... 

Recently, the same type of arylation of benzylamine derivatives equipped with a 2-pyridinyl directing group was carried out with aryl halides but with the ruthenium(II) catalyst precursor ([RuCl2(p-cymene)]2) in the presence of potassium pivalate [19, 20] or directly with Ru(carboxylate)2(p-cymene) [21]. Both catalytic systems operate at 140°C for 24 h in toluene or o-xylene in the presence of 2.5-5 mol% catalyst loading and a carbonate as a base. The advantage of using the well-defined ruthenium(II)bis(carboxylate) complex is that it does not require an excess of carboxylate as it is the case with the in situ generated catalytic system. 

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