3- Iodopyridines, reaction with sodium

By taking advantage of the C(2) activation, 2-allyloxy-3-iodopyridine (173) was prepared by an SNAr displacement of 2-chloro-3-iodopyridine with sodium allyloxide [137]. 2-Chloro-3-iodopyridine was prepared by orrto-lithiation of 2-chloropyridine followed by iodine quench. The intramolecular Heck reaction of allyl ether 173 under Jeffery s ligand-free conditions resulted in 3-methylfuro[2,3-6]pyridine (174). 

Cyclization of iodopyiidinyl aUyl ethers derived fom dihalopyridines and sodium aUyUc oxides leads to formation of furo[2,3-fc]pyridines 292, furo[3,2-c]pyiidines 293, and furo[2,3-c]pyridines 294 by a Heck mode of reaction (Scheme 101). In the reaction sequences, the initial step in the preparation of iodopyridine aUyl ethers involves regioselective lithiation of 3-fluoro, 2-fluoro-, and 4-chloropyridines with LDA. Subsequently, the lithiated species are treated with iodine as electrophile. A variety of iodopyiidinyl ethers have been prepared from dihalopyridines and sodium aUyhc oxides and subjected to the Pd-catalyzed cyclization reactions with formation of the furoannulated pyridine products. When the allyl groups carry a 2-substituent as in stracture 295, hydridopaUadium elimination is prevented. Instead, sodium formate reductive elimination of the palladium substituent gives the product 296. The isomeric structures 297 and 298 are available similarly. ... 

The amino function in 4-amino-3-halopyridines belraves unexceptionally. Thus 4-amino-3-diloropyridine gives the 3-chloro-4-pyridinediazonium salt dien treated with nitrous acid the diazonium salt decomposes in the presence of potassium iodide to yield 3-chloro-4-iodopyridine. 4-Amino-2,3,5,6-tetrafluoropyridine is a very weak base but it can be diazotized in 80% hydrofluoric acid. The diazonium salt is converted to 4-bromo-2,3,5,6-tetrabromopyridine with cuprous bromide, but its reaction with water or with A, lV-dimethylaniline are complex. 4-Amino-2-chloro-3-nitropyridine is not converted to 2-chloro-3-nitro-4-pyridone (K-97) on diazotization with mineral acids and sodium nitrite or with isoamyl nitrite in glacial acetic acid with the latter reagent 2-chloro-3-nitropyri-dine (K-98) is formed." Nitrous acid reacts with 4-amlno-2-pyridone to give 4-amino-3-nitroso-2-pyridone instead of the diazonium salt. ... 

To a mixture of sodium iodide (0.30 g, 2 mmol, 2 eq.), 2-iodopyridine (232, 205 mg, 1 mmol), di(2-thienyl)mercury (233, 202 mg, 0.55 mmol) in DMF (2.5 ml), was added 2-pyridylpalladium(II) iodide (3.1 mg, 1 mol%) and the reaction mixture was stirred at room temperature for 10 min under argon. The reaction mixture was diluted with water (10 ml) and extracted with diethyl ether (3x5 ml). The extracts were combined, and washed with an aqueous solution of sodium iodide. The ether layer was dried (MgS04), and then evaporated in vacuo to give the crude product. From the latter, 147 mg (91%) of pure 2-(2-thienyl)pyridine (231) was obtained by preparative chromatography, as well as 13 mg (8%) of 2,2 -bithienyl. 

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