Pyridines alkenylation

NQR, 2, 125 Pyridines, acetylalkyl-alkyl deacetylation, 2, 301 Pyridines, acetyltrimethyl-synthesis, 2, 470 Pyridines, acyl-conformation, 2, 162 reactions, 2, 337 Pyridines, alkenyl-ozonolysis, 2, 334 reactions, 2, 334 Pyridines, alkenyldihydro-disproportiation, 2, 62 Pyridines, alkyl-... 

Alkoxythiazoles are prepared by heterocyclization (274, 462). The Williamson method using catalytic amounts of KI and cupric oxide is also possible (278. 288, 306). 5-Acetoxy-4-alkenylthiazoles are obtained by treatment of 242 with acetyl chloride and triethylamine or with acetic anhydride and pyridine (450). Similarly, the reaction of diphenylketene with 242 affords 5-acyloxy-4-alkenylthiazoles (243) (Scheme 120) (450). The readiness of these o-acetylations suggests that 4-alkylidene thiazoline-5-one might be in equilibrium with 4-alkenyl-5-hydroxythiazoles (450). 

The pyridine ligand in some alkenyl cobalt(III) DMG complexes may be replaced by methyl or ethyl phosphite by addition of the phosphite to a solution of the (DMG)2 complex in ethanol. In a similar manner aniline may be displaced by (CH30)3P from [CH2=CHCo(DMG)2C6HjNH2] (129). 

High density brine completion fluids also often require the use of corrosion inhibitors (8,9). Blends of thioglycolates and thiourea alkyl, alkenyl, or alkynyl phosphonium salts thiocyanate salts mercaptoacetic acid and its salts and the reaction products of pyridine or pyrazine derivatives with dicarboxylic acid monoanhydrides have been used as high density brine corrosion inhibitors. 

Most studies on nickel-catalyzed domino reactions have been performed by Ikeda and colleagues [287], who observed that alkenyl nickel species, obtained from alkynes 6/4-41 and a (jr-allyl) nickel complex, can react with organometallics as 6/4-42. If this reaction is carried out in the presence of enones 6/4-43 and TM SCI, then coupling products such as 6/4-44 are obtained. After hydrolysis, substituted ketones 6/4-45 are obtained (Scheme 6/4.12). With cyclic and (5-substituted enones the use of pyridine is essential. Usually, the regioselectivity and stereoselectivity of the reactions is very high. On occasion, alkenes can be used instead of alkynes, though this is rather restricted as only norbornene gave reasonable results [288]. 

Nickel-bpy and nickel-pyridine catalytic systems have been applied to numerous electroreductive reactions,202 such as synthesis of ketones by heterocoupling of acyl and benzyl halides,210,213 addition of aryl bromides to activated alkenes,212,214 synthesis of conjugated dienes, unsaturated esters, ketones, and nitriles by homo- and cross-coupling involving alkenyl halides,215 reductive polymerization of aromatic and heteroaromatic dibromides,216-221 or cleavage of the C-0 bond in allyl ethers.222... 

ArN=CMe)2 -R-C5H2N] (1 R = f-butyl [55]), allyl [69], O(co-alkenyl) [57, 58], benzyl [69], Cl [56], 2-methyl-2-phenylpropyl [69]) in which the 4-position of the central pyridine unit in 1 can be varied this latter site also being used to facilitate the linking of two bis(imino)pyridine units [54],... 

Similar 1,2,3-diheterocyclizations have been performed by addition of other Af, N- or Al,5-dinucleophiles, such as pyridine-2-thiol, 2-aminopyridine, 2-aminothia-zole, thioisonicotinamide, and l//-benzotriazole, to complexes 6 and 46 giving rise to the formation of the five- and six-membered cyclic alkenyl derivatives 96-100 (Fig. 19) [289, 291,292],... 

Double bonds in alkenyl pyridines may be hydrogenated under mild conditions (Raney nickel at room temperature) to give alkyl pyridines [450]. If the double bond is conjugated with the pyridine ring sodium in alcohol will reduce both the double bond and the pyridine ring in good yields [450]. 

The oxidation of substituted pyridines to iV-oxides was reported by Sharpless and coworkers to proceed with yields between 78 and 99% (Scheme 154). A variety of substituents like electron donor as well as acceptor groups and alkenyl substituents are tolerated. In 1998, Sharpless and coworkers reported an alternative method for the preparation of pyridine-A-oxides in which the MTO/H2O2 catalyst could be replaced by cheaper inorganic rhenium derivatives (ReOs, Re207, HOReOs) in the presence of bis(trimethylsilyl) peroxide (equation 73). Yields of the prepared A-oxides after simple workup (filtration and bulb to bulb distillation) ranged from 70-98%. Molecular sieves slowed down the reaction while small amounts of water (0-15%) were essential for the reaction. Both electron-poor or electron-rich pyridines give high yields of their A-oxides and while para-... 

Under these standard reaction conditions, the acetonitrile/pyridine mixture can replace the DMF/pyridine one. This solvent mixture is also quite convenient for running the preparation of arylzinc halides. Yields are good to excellent (60-90%) and even higher than those obtained in DMF. However, with bromophenol, no organozinc species was formed in acetonitrile as observed in DMF. The formation of arylzinc species is also effective in a mixture of solvents of acetonitrile-DMF-pyridine (8/1/1) in the presence of C0CI2 (13%) as the catalyst precursor and zinc bromide (30%). This method has also been applied to the formation of organozinc halides from alkyl and alkenyl halides. So far, only low yields have been obtained using the standard reaction conditions in DMF-pyridine. Results are reported in Table 8. 

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