3- fluoropyridinium

Using a more reactive polymer-supported reagent (polymer-supported-2-fluoropyridinium triflate, PS-FPT) gave the desired product, but the reaction at room temperature was very slow and complete conversions could rarely be observed, which of course represents a serious limitation as the unreacted hy-droxyamide would need to be removed in order to obtain the products in high... 

T. Mukaiyama, Y. Hashimoto, Y. Hayashi, and S.-l. Shoda, Stereoselective synthesis of a-ribonucleosides from 1-hydroxy sugars by using 2-fluoropyridinium tosylate, Chem. Lett 557 (1984). 

In the presence of a solvent capable of reacting with a carbene center, products other than 2-fluoropyridines were formed. Indeed, these can become the major reaction products (87TL2705 89JOC1726), but not all products can be explained in terms of the carbene mechanism since in the 6-chloro-2-fluoropyridinium triflate (25 R = 6-C1, X = S03CF3) it is obvious that chloro is being replaced by fluoride (89JOC1726). 

Acyl-2-fluoro-l,4-dihydropyridines 149, easily synthesized by alkylation of 2-fluoropyridinium salts, undergo hydrolysis to form dihydro-2-pyridones 150 in which only the more stable 3,4-/ra t-isomer is formed. 1,4-Dihydropyridines 149 can also be oxidized with DDQ to form 2-pyridones 151 (Scheme 40) <2002JOC7465, 2000CC2459>. 

Reagents i, H2-Pd ii, HN03-AcCH iii, KOH iv, H+ v, LiAlH4 vi,BuaLi vii, TiCl4-LiAlH4 viii, l-methyl-2-fluoropyridinium salts... 

The previously reported biogenetic-type cyclization of nerol and geraniol to limonene using 2-fluoropyridinium salts has been extended to the sesquiter-penoid area. Thus treatment of cw,rran5-farnesol (77) with 2-fluoropyridinium (74), 2-fluorobenzothiazolium (75), or 2-chlorobenzothiazolium (76) salts resulted in the formation of a-bisabolene (78) and y-bisabolene (79) in 55—75% yield. 

Pyridyl sulfides can be prepared by reaction of alcohols with l-methyl-2-fluoropyridinium tosylate and base followed by reaction with pyrid-2-thione (equation TV). ... 

The condensation of ketoximes with 2-fluoropyridinium salts leads to salts (157), which on aqueous hydrolysis undergo a Beckmann rearrangement, giving amides (158) in high yields. ... 

Three new synthetic methods for the conversion of alcohols into azides (and hence potentially into amines) have been published. One route involves a further application of the chemistry of 2-alkoxypyridinium salts (formed in situ from an alcohol and the 2-fluoropyridinium salt) in their reaction with azide ion " (Scheme 17). Another extends the utility of the triphenylphosphine-ethyl diazodicarboxylate system, using diphenylphosphoryl azide as azide donor (Scheme 18), but is sensitive to steric hindrance at the alcohol carbon. The third route (Scheme 19) achieves oxygen activation through the alkoxyphosphonium salts (39), which are prepared from the alcohol, a phosphine, and a positive halogen donor such as carbon tetrachloride (with primary alcohols) or Af-chlorodi-isopropylamine (in... 

A new route to thiols employs the l-methyl-2-fluoropyridinium salt (69) which reacts with alcohols to give the 2-alkoxy-derivatives ° (Scheme 49). Treatment with sulphur nucleophiles as shown proceeds with inversion and thiols are available from the products by reduction. 

Several substituted-2-pyridones have been dimerized to XII-720. A photoinduced diradical intermediate was suggested as the species leading to dimerization. When irradiated in water 7/-benzyl-2-fluoropyridinium bromide gives the same dimer as is formed from A -benzyl-2-pyridone in ethanol. Photoisomerization of W-methyl-2-pyridone in ether, followed by careful workup of products, gives XII-722. ... 

Fluoropyridinium 1,3 Dimethyl-2-nitFoimidaxolium 4-Dimethylainino-l-mcthyl-12. 4-triazolium... 

A-Acyl-4-pyridones can serve as useful acyl group transfer reagents for the esterification of alcohols in >80% yields.Two notable points about these reagents are their effectiveness in the preparation of formate esters (c/. ref. 157), and their much greater rate of reaction with primary alcohols, (c/. ref. 147). Thioesters and amides can also be prepared from such pyridones by reaction with thiols or amines, respectively. Other useful reagents for the direct formation of esters from carboxylic acids and alcohols are 2-fluoropyridinium salts in the presence of caesium fluorideand certain benzoisothiazole derivatives. Primary alcohols can be esterified with 2,2 -bipyridyl-6-yl carboxylates and CsF. Selective esterification of a primary alcohol in the presence of a secondary alcohol can be achieved in acceptable yields with this reagent (c/. ref. 144). 

Fluoropyridinium salt sodium dithionite Replacement of hydroxyl by hydrogen Ketones from a-hydroxyketones... 

Sodium iodide s. under PhgP and 2-Fluoropyridinium salt Nal... 

Fluoropyridinium salt Carboxylic acid fluorides from carboxylic acids... 

Fluoropyridinium salt sodium iodide Iodides from alcohols... 

Alkyl iodides can be prepared by treatment of 2-fluoropyridinium salts with alcohols, followed by inorganic iodide reaction with the 2-alkoxypyridinium intermediates so formed (Scheme 25). A similar sequence involving 2-alkoxy-3-ethylbenzothiazolium salts (63), produced in situ, allows conversion of alcohols into inverted chlorides, bromides, or iodides (Scheme 26) of high optical purity. 

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