Pyridines aroyl

The reaction of aryl and alkenyl halides and triflates with the Reformatsky reagent 613 in polar solvents affords the Q-aryl carboxylic esters 614[475,476], Facile elimination of /7-hydrogen takes place with a-alkylated Reformatsky reagents. Iodides of. V-heterocyclic compounds such as pyridine, quinoline, and pyrimidine react smoothly with Reformatsky reagents The position of iodine with respect to the ring nitrogen determines the ratio of the cross-and homocoupling products. The cross-coupling of 613 takes place smoothly with 4-iodo-2,6-dimethyl- and 2-iodo-4,6-dimethylpyrimidine (615), but no reaction takes place with 5-iodo-2,4-dimethylpyrimidine[477].  [c.215]

Sulfation by sulfamic acid has been used ia the preparation of detergents from dodecyl, oleyl, and other higher alcohols. It is also used ia sulfating phenols and phenol—ethylene oxide condensation products. Secondary alcohols react ia the presence of an amide catalyst, eg, acetamide or urea (24). Pyridine has also been used. Tertiary alcohols do not react. Reactions with phenols yield phenyl ammonium sulfates. These reactions iaclude those of naphthols, cresol, anisole, anethole, pyrocatechol, and hydroquinone. Ammonium aryl sulfates are formed as iatermediates and sulfonates are formed by subsequent rearrangement (25,26).  [c.62]

Other acids that have been used for this cleavage are phosphoric acid, pyridine hydrochloride, boron tribromide, trifluoroacetic acid, and nitric acid. Acid cleavage of aryl alkyl ethers always gives phenol because the aromatic carbon—oxygen bond is much stronger than the aUphatic carbon—oxygen bond. Unsymmetrical aUphatic ethers usually yield a mixture of alkyl haUdes and alcohols when cleaved by halogen containing acids.  [c.425]

The other major type of [5 -I-1] cyclization from pyridines involves that of o- aminopyridine amides or their congeners with a one-carbon fragment, usually a phosgene equivalent, giving 0X0 derivatives (177), a carboxylic acid equivalent, leading to unsubstituted, alkyl or aryl derivatives (178), or an aldehyde, initially giving partially reduced analogues (179). Ketones give gem-disubstituted derivatives. Apart from phosgene itself, equivalents used  [c.222]

Although the concerted displacement of the C-3 substituent concomitant with /3-lactam opening is an important feature of cephalosporin reactivity under physiological conditions, direct displacement at C-3 has proved to be particularly useful for the synthesis of cephalosporin analogs. Of the thousands of cephalosporins produced by partial synthesis, all but a small fraction differ only in the nature of the 7-acyl and C-3 substituents. The starting material for semisynthetic cephalosporins is cephalosporin C (8a) which bears an acetoxy substituent at C-3 therefore, it is the displacement of acetate that has received the most attention. The facility with which the acetoxy group is displaced by nucleophiles was first observed when a solution of cephalosporin C in aqueous pyridine acetate buffer was found to produce a new component with increased antimicrobial activity. This proved to be the corresponding 3 -pyridinium derivative (8b). This eventually led to the development of cephaloridine (8c) as a broad spectrum antibiotic. Displacements with other nitrogen nucleophiles such as azide and anilines have been reported but have not led to useful antibacterial agents. Another early observation was the displacement of acetate by sodium thiosulfate to give (8d). Since then a large number of derivatives have been prepared by displacement with alkyl, aryl and heterocyclic thiols as well as thioureas, xanthates, dithiocarbamates and sulfinates. In particular, those analogs derived from heterocyclic thiols have proved to be most important in terms of providing useful antibacterial agents.  [c.288]

Imidazo[l,2-n]pyridine, 8-amino-synthesis, 5, 631 Imidazo[l,2-n]pyridine, 3-aryl-synthesis, 5, 631-632 Imidazo[l,2-n]pyridine, 3-bromo-synthesis, 5, 631  [c.661]

Triazolo[4,3-a]pyridine, 3-aryl-synthesis, 5, 882, 883  [c.913]

A large number of Brpnsted and Lewis acid catalysts have been employed in the Fischer indole synthesis. Only a few have been found to be sufficiently useful for general use. It is worth noting that some Fischer indolizations are unsuccessful simply due to the sensitivity of the reaction intermediates or products under acidic conditions. In many such cases the thermal indolization process may be of use if the reaction intermediates or products are thermally stable (vide infra). If the products (intermediates) are labile to either thermal or acidic conditions, the use of pyridine chloride in pyridine or biphasic conditions are employed. The general mechanism for the acid catalyzed reaction is believed to be facilitated by the equilibrium between the aryl-hydrazone 13 (R = FF or Lewis acid) and the ene-hydrazine tautomer 14, presumably stabilizing the latter intermediate 14 by either protonation or complex formation (i.e. Lewis acid) at the more basic nitrogen atom (i.e. the 2-nitrogen atom in the arylhydrazone) is important.  [c.117]

The Zincke reaction is an overall amine exchange process that converts N- 2,A-dinitrophenyl)pyridinium salts (e.g, 1), known as Zincke salts, to iV-aryl or iV-alkyl pyridiniums 2 upon treatment with the appropriate aniline or alkyl amine. The Zincke salts are produced by reaction of pyridine or its derivatives with 2,4-dinitrochlorobenzene. This venerable reaction, first reported in 1904 and independently explored by Konig, proceeds via nucleophilic addition, ring opening, amine exchange, and electrocyclic reclosure, a sequence that also requires a series of proton transfers. By  [c.355]

Heterocyclic bases which readily form quaternary salts with the more usual reagents will also react with suitably activated aryl and heterocyclyl halogen compounds, the classic case being the salt formed from pyridine and l-chloro-2,4-dinitrobenzene. Reactions of this type have been studied by Chapman et Salt formation between  [c.7]

In peptide syntheses, where partial racemization of the chiral a-carbon centers is a serious problem, the application of 1-hydroxy-1 H-benzotriazole ( HBT") and DCC has been very successful in increasing yields and decreasing racemization (W. Kdnig, 1970 G.C. Windridge, 1971 H.R. Bosshard, 1973), l-(Acyloxy)-lif-benzotriazoles or l-acyl-17f-benzo-triazole 3-oxides are formed as reactive intermediates. If carboxylic or phosphoric esters are to be formed from the acids and alcohols using DCC, 4-(pyrrolidin-l -yl)pyridine ( PPY A. Hassner, 1978 K.M. Patel, 1979) and HBT are efficient catalysts even with tert-alkyl, choles-teryl, aryl, and other unreactive alcohols as well as with highly bulky or labile acids.  [c.145]

The cross-coupling of aromatic and heteroaromatic rings has been carried out extensively[555]. Tin compounds of heterocycles such as oxazo-lines[556,557], thiophene[558,559], furans[558], pyridines[558], and seleno-phenes [560] can be coupled with aryl halides. The syntheses of the phenylo.xazoline 691[552], dithiophenopyridine 692[56l] and 3-(2-pyridyl)qui-noline 693[562] are typical examples.  [c.229]

Alkylselenazoles are oily alkaline liquids possessing a smell similar to that of the corresponding thiazole or pyridine derivatives. The crystalline picrates or 3-methylselenazolium iodides have been used for the purpose of characterization. Alkyl derivatives are partially soluble in water aryl derivatives are insoluble.  [c.221]

Displacement reactions with oxygen nucleophiles are of potential commercial interest. Alkaline hydrolysis provides 2-fluoro-6-hydroxypyridine [55758-32-2], a precursor to 6-fluoropyridyl phosphoms ester insecticides (410—412). Other oxygen nucleophiles such as bisphenol A and hydroquinone have been used to form aryl—pyridine copolymers (413).  [c.336]

The elimination of two ring hydrogens accompanied by the formation of an aryl—aryl bond under Friedel-Crafts conditions is known as the SchoU reaction (1). The dehydrogenating condensations can take place by either iater- or iatra-molecular pathways. Intermolecular SchoU reactions are numerous and iaclude such reactions as formation of biphenyl from ben2ene, of perylene from naphthalene (through biaaphthyl), of 2,2 -dipyridyl from pyridine, and the formation of high molecular weight polycondensed aromatics.  [c.556]

Phenols. Phenols are unreactive toward chloroformates at room temperature and at elevated temperatures the yields of carbonates are relatively poor (< 10%) in the absence of catalysis. Many catalysts have been claimed in the patent Hterature that lead to high yields of carbonates from phenol and chloroformates. The use of catalyst is even more essential in the reaction of phenols and aryl chloroformates. Among the catalysts claimed are amphoteric metals or thek haUdes (16), magnesium haUdes (17), magnesium or manganese (18), secondary or tertiary amines such as imidazole (19), pyridine, quinoline, picoline (20—22), heterocycHc basic compounds (23) and carbonamides, thiocarbonamides, phosphoroamides, and sulfonamides (24).  [c.39]

Composition. The functional groups within coal contain the elements C, H, O, N, or S (3,4,5,19). The significant oxygen-containing groups found in coals are carbonyl, hydroxyl, carboxyUc acid, and methoxy. The nitrogen-containing groups include aromatic nitriles, pyridines, carba2oles, quinolines, and pyrroles (20). Sulfur is primarily found in thiols, dialkyl and aryl—alkyl thioethers, thiophene groups, and disulfides. Elemental sulfur is observed in oxidi2ed coal (20).  [c.217]

Thieno[3,2-c]pyridine-6-carboxylic acid, 4-aryl-synthesis, 4, 1008 Thienopyridines, 4, 1002-1015 acidity, 4, 1012 biological activity, 4, 1015 electrophilic substitution, 4, 1013 HMO data, 4, 1003, 1004 NMR, 4, 1012, 1013 oxidation, 4, 1014 UV spectra, 4, 1013 Thieno[2,3-6]pyridines halogenation, 4, 1014 lithiation, 4, 1014 nitration, 4, 1014 synthesis, 4, 1004 Thieno[2,3-c]pyridines nitration, 4, 1014 synthesis, 4, 1006 Thienop, 2-6]py ridines synthesis, 4, 1009-1011 Thieno[3,2-c]pyridines nitration, 4, 1014 synthesis, 4, 788, 1007-1009 Thieno[3,4-b]pyridines synthesis, 4, 1011 UV spectra, 4, 1012 Thieno[3,4-c]pyridines synthesis, 4, 1012 UV spectra, 4, 1012  [c.880]

A drawback of the use of a pyridine-hydrogen fluoride complex is that substrates having an acid-sensitive functionality such as oxirane cannot tolerate the reaction conditions. A mixture of tetrabutylammonium dihydrogen trifluoride and A-halo imide or amides is a reagent ot choice tor the oxidative tluoro-desulfurization of dithioacetals and dithioketals, particularly those containing an acid-sensitive functionality [J], Difluoromethylene compounds are obtained in good yields from 2-aryl-1,3-dithiolanes and 2-ary 1-1,2-dithianes derived from the corresponding aromatic aldehydes and ketones. Substrates having an epoxide and a hydroxyl group are converted to the corresponding gem-difluoro compounds without any damage to these functionalities (equation 5).  [c.264]

A recently discovered variant of the Wallach technique is the silver ion cata lyzed fluorination of aryl diazo sulfides in hydrogen fluonde-pyridine-toluene solvent [57] (equation 12) Electron withdrawing substituents such as acetyl give higher yields of aryl fluoride (71%) than electron donating groups (butyl 39%, methoxy, 2-14%), reductive dediazoniation competes with fluorination  [c.277]

Thermal stability of arenediazonium fluorides can influence yields of aryl fluorides during decomposition in hydrogen fluoride [52, 61] Use of 70% hydrogen fluoride 30% pyridine (w/w) mixture having a lower pressure of hydrogen fluoride permits higher fluorodediazoniation temperatures and improves yields [6, 61 62, 63 64] This technique has also been extended to complexes of hydrogen fluoride with terbary amines [65]  [c.278]

The seminal work by McLoughlin and Thrower [183] stimulated extensive work in the preparation and reactions of fluorinated copper reagents, and this class of fluorinated organometallic compounds has received more attention than any other class In the early work, DMSO was generally used as the solvent, although DMS, DMF, HMPA, and pyridine also have been used The coordinating ability of the solvent plays a significant role in the mechanistic direction of tlie reaction In solvents of low donor number (DN < 19), such as hexane, benzene, acetic anhydride, acetonitrile, and dioxane, perfluoroalkyl radicals are produced and can be trapped by olefins [184], In solvents of high donor number (DN >31), such as DMF, DMSO, pyridine, and HMPA, the perfluoroalkylcopper reagent is formed and can be successfully trapped by aryl iodides [184], Consequently, solvents with a high donor number should be used for generation and capture of R(Cu [184] (equation 130). Although aryl iodides give higher yields than aryl bromides, for cost effectiveness, aryl bromides can often be utilized 186] (equations 131 and 132).  [c.699]

An aryl methane- or toluenesulfonate ester is stable to reduction with lithium aluminum hydride, to the acidic conditions used for nitration of an aromatic ring (HN03/H0Ac), and to the high temperatures (200-250°) of an Ullmann reaction. Aryl sulfonate esters, formed by reaction of a phenol with a sulfonyl chloride in pyridine or aqueous sodium hydroxide, are cleaved by warming in aqueous sodium hydroxide.  [c.285]

Similarity with cobalt is also apparent in the affinity of Rh and iH for ammonia and amines. The kinetic inertness of the ammines of Rh has led to the use of several of them in studies of the trans effect (p. 1163) in octahedral complexes, while the ammines of Ir are so stable as to withstand boiling in aqueous alkali. Stable complexes such as [M(C204)3], [M(acac)3] and [M(CN)5] are formed by all three metals. Force constants obtained from the infrared spectra of the hexacyano complexes indicate that the M--C bond strength increases in the order Co < Rh < [r. Like cobalt, rhodium too forms bridged superoxides such as the blue, paramagnetic, fCl(py)4Rh-02-Rh(py)4Cll produced by aerial oxidation of aqueous ethanolic solutions of RhCL and pyridine.In fact it seems likely that many of the species produced by oxidation of aqueous solutions of Rh and presumed to contain the metal in higher oxidation states, are actually superoxides of Rh .  [c.1127]

Of the four possible oxazolopyridines, two have been studied with respect to quatemization reactions. Frazer and Tittensor prepared 2-alkyl- and 2-aryl-oxazolo[4,5-c]pyridines (105 Y = H) and converted them into methiodides, the structures of which have not been determined. Subsequently Takahashi et al. prepared the corresponding 5-methyl (105 Y = Me) and 2-methyl-5-nitro compounds and  [c.40]

In work on 6-methoxypyrimidines (130), the 4-methylsulfonyl group was found to be displaced by the sulfanilamide anion more readily than were 4-chloro or trimethylammonio groups. This reactivity may be partly due to the nature of the nucleophile (106, Section II, D, 1). However, high reactivity of alkyl- and aryl-sulfonyl heterocycles with other nucleophiles has been observed. A 2-methylsulfonyl group on pyridine was displaced by methoxide ion with alkaline but not acidic methanol. 3,6-Bis(p-tolylsulfonyl)-pyridazine reacts (100°, 5 hr) with sulfanilamide anion and even the  [c.211]

Chapman and co-workershave shown that, in the reactions of nitro-2-chloropyridines with piperidine, aryl amines, or pyridine bases, a 5-nitro group activates more than a 3-nitro group (cf. Table VII, p. 276).  [c.238]

See pages that mention the term Pyridines aroyl : [c.42]    [c.82]    [c.186]    [c.38]    [c.207]    [c.259]    [c.313]    [c.35]    [c.209]    [c.229]    [c.84]    [c.141]    [c.148]    [c.744]    [c.784]    [c.785]    [c.785]    [c.355]    [c.87]    [c.310]    [c.190]    [c.303]   
Advances in heterocyclic chemistry Vol.2 (1963) -- [ c.183 , c.185 ]