Pyridines aryl-, various

The arylation of potassium phenoxide has been studied by Litvak and Shein (1976). In the absence of crown ether the rate of reaction with p-nitrobromobenzene in various solvents increases in the order dioxan < methanol < pyridine < DMSO. In the presence of either 18-crown-6 [3] or dibenzo-18-crown-6 [11], the order of the reaction rates in dioxan and methanol is reversed (Table 22). The effect of crown ether addition on the rate... 

Anodic regioselective fluorination of a-phenylsulphenylated ethyl acetates, 1-naphthalene and 2-pyridine derivatives [80], l-aryl-3-(phenylthio)oxindoles and 2-substituted-3-oxo-4-(phenylthio)-l, 2, 3,4-tetrahydroisoquinolines [81], 2-benzo-thiazolyl and 5-chloro-2-benzothiazolyl sulfides [82], a-(phenylsulfenyl)lactams [83], as well as various heterocycles such as thiolanones, oxathiolanones, dithi-olanones, 3Fl-l,4-benzoxathian-2-ones [84] in Et3N-3HF or Etr NF- HF [n = 3,4), has been reported. 

C-aryl glycals in 75-92% yields. It consisted in the addition of aryllithium reagents to variously protected 2-deoxy-aldono-l,5-lactones, followed by treatment with a mixture of pyridine (Py), 4-(Dimethylamino)pyridine (DMAP), and trifluoroacetic anhydride (TFAA). 

Cyclocondensation of ethyl 2-aminonicotinate in presence of HC(OEt)3 and various primary amines gave 22 3-substituted pyrido[2,3-,7]pyrimidin-4(377)-ones 371 <1995PHA719>. Fourteen 3,5,7-triarylpyrido[2,3-r7]pyrimi-dine-2,4(l/7,37/)-diones 372 have been prepared from the reaction of either 2-amino-3-cyano-4,6-diarylpyridines or the 3-carboxamido products of alcoholic KOH hydrolysis, with aryl isocyanates better yields were obtained from the amides <1995IJB740>. 4-Aminopyrido[2,3- pyrimidin-5(8//)-one 158 was synthesized by treatment of 2-amino-3-cyano-4-methoxypyridine with trimethylsilyl iodide to give the corresponding pyridin-4(177)-one, which was refluxed with formamidine acetate in ethoxyethanol to effect the cyclization <2000JME3704>. 

In contrast to pyridine derivatives, aryl- and alkyl-substituted A -phosphorins cannot be protonated by strong, non-oxidizing acids such as trifluoroacetic acid. Addition of trifluoroacetic acid to cyclohexane solutions of various A -phosphorins fails to produce any change in the UV spectra Similarly, alkylation by such strong agents as oxonium salts or acylation by acylchlorides cannot be induced at the P atom or any ring C atom. This behavior has also been discussed theoretically 55a)... 

Nitriles can be obtained in one step by treatment of primary nitro compounds with PC13 and pyridine,420 R may be alkyl or aryl and may contain C=C double bonds or various functional groups. Yields are moderate to good. The reaction has also been carried out with Me3N-S02 and with HMPA.421 Primary azides RCH2N3 have been converted to nitriles RCN with Pd metal.422 Primary nitro compounds RCH2N02 were converted to nitrile oxides 0... 

A mixture of methyl aryl ether 1 (0.01 mol) and pyridine hydrochloride (0.05 mol) were placed in a stoppered round bottom flask and subjected to microwave irradiation at 215 W for various time intervals. After complete conversion the reaction mixture was decomposed using ice-water and extracted with diethyl ether. The ether extract was repeatedly washed with water, dried over anhydrous sodium sulfate and the ether removed to obtain the product 2. 

Oxidations of sulfides to sulfoxides can be effected with various aryl-A3-iodanes. For example, (dichloroiodo)benzene (1) in aqueous pyridine [12], [bis(ace-toxy)iodo]benzene (2, BAIB) in acetic anhydride (H2S04) [13], and [bis(trifluo-roacetoxy)iodo]benzene (3, BTIB) in chloroform [14] have all been utilized for this purpose (Scheme 1). 

Various intramolecular aryl radical reactions of pyridine derivatives have been developed <2004COR757, 2001J(P 1 )2885>. An early example of this type is found in a short synthesis of camptothecin 195. The tetracyclic intermediate 197 was cyclized by a free radical reaction to afford the natural product (Equation 106) <1994TL5331>. 

As before, a silver ion and its counterion could act together in the transmetallation step, such as depicted in Scheme 10.44. Such a hypothesis seemed supported by the discovery in 2006 that 2-pyridinyl, but not 3-pyridinyl, allylsilanes reacted under similar conditions and transferred the pyridine moiety to various aryl iodides (Scheme 10.45).78 In this coupling, the nitrogen atom of the pyridinyl moiety probably played a role similar to that of the hydroxyl group in the silanol-based Hiyama couplings. 

The homolytic arylation of pyridine has been studied somewhat more systematically but by no means exhaustively. Quantitative analysis of the phenylation products using various sources of phenyl radicals has been achieved by ultraviolet spectroscopic or gas chromatographic methods. The results of some recent determinations are given in Table XV. 

Nucleophiles containing elements of the second row have also been used in photosubstitution reactions of aryl halides. The selenocyanate ion739, selenourea740 and thiourea741 are capable of replacing halogen atoms in various derivatives of benzene, naphthalene, pyridine and pyrimidine. Both chlorine atoms in 6>rj/zc>-dichlorobenzene are substituted upon irradiation in (MeO)3P at 60 °C for 5 days and a 50% yield of 1,2-bis(phosphino)-benzene is obtained742. 

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