Acyls isomerization

In manchen Fallen ist das 2-Acyl-Produkt so stabil, daB es auch durch Erhitzen nicht in das 1 -Acyl-Isomere umgelagert werden kann z. B. ... 

At high partial pressure of carbon monoxide the but3trylcobalt tetracarbonyl precursor is mainly the product from the kinetically favored n-isomer of the addition of HCo(CO)4 to the olefin double bond of propene. This conclusion was further supported by the comparison of rates of propene hydroformylation with the rates of n-butyrylcobalt tetracarbonyl isomerization at 0.25 MPa and at 9.0 MPa of carbon monoxide partial pressure. The data in Table 18 show that at 0.25 MPa partial pressure of carbon monoxide, the rate of acyl isomerization is indeed higher than the rate of the overall aldehyde formation, and this makes an equilibration of the acyl isomers prior to the irreversible aldehyde formation conceivable vm-der these conditions. At 9.0-MPa partial pressure of carbon monoxide, however, the rate of acyl isomerization is 29 times slower than the rate of the aldehyde formation, and this severally hampers the isobutyrylcobalt formation from the primarily formed straight-chain acyl isomer. 

Acyl halides, both aliphatic and aromatic, react with the sodium derivative, but the product depends largely on the solvent used. Thus acetyl chloride reacts with the sodium derivative (E) suspended in ether to give mainly the C-derivative (t) and in pyridine solution to give chiefly the O-derivative (2). These isomeric compounds can be readily distinguished, because the C-derivative (1) can still by enolisation act as a weak acid and is therefore... 

Apart from Bronsted acid activation, the acetyl cation (and other acyl ions) can also be activated by Lewis acids. Although the 1 1 CH3COX-AIX3 Friedel-Crafts complex is inactive for the isomerization of alkanes, a system with two (or more) equivalents of AIX3 was fonnd by Volpin to be extremely reactive, also bringing abont other electrophilic reactions. 

Acyl halides are intermediates of the carbonylations of alkenes and organic-halides. Decarbonylation of acyl halides as a reversible process of the carbo-nylation is possible with Pd catalyst. The decarbonylation of aliphatic acid chlorides proceeds with Pd(0) catalyst, such as Pd on carbon or PdC, at around 200 °C[109,753]. The product is a mixture of isomeric internal alkenes. For example, when decanoyl chloride is heated with PdCF at 200 C in a distillation flask, rapid evolution of CO and HCl stops after I h, during which time a mixture of nonene isomers was distilled off in a high yield. The decarbonylation of phenylpropionyl chloride (883) affords styrene (53%). In addition, l,5-diphenyl-l-penten-3-one (884) is obtained as a byproduct (10%). formed by the insertion of styrene into the acyl chloride. Formation of the latter supports the formation of acylpalladium species as an intermediate of the decarbonylation. Decarbonylation of the benzoyl chloride 885 can be carried out in good yields at 360 with Pd on carbon as a catalyst, yielding the aryl chloride 886[754]. 

Imino-4-thiazolines are far more basic than their isomeric 2-aminothiazoles (see Table VI-1). They react with most electrophDic centers through the exocyclic nitrogen and are easily acylated (37, 477, 706) and sulfonated (652). The reaction of 2-imino-3-methyi-4-thiazoline (378) with a-chloracetic anhydride yields 379 (Scheme 217) (707). This exclusive reactivity of the exocyclic nitrogen precludes the direct synthesis of endocyclic quaternary salts of 2-imino-4-thiazolines. although this class of compounds was prepared recently according to Scheme 218 (493). 

The preference for O acylation of phenols arises because these reactions are kmetically controlled O acylation is faster than C acylation The C acyl isomers are more stable how ever and it is known that aluminum chloride is a very effective catalyst for the conversion of aryl esters to aryl ketones This isomerization is called the Fries rearrangement... 

Fluorosulfuric acid [7789-21-17, HSO F, is a colodess-to-light yellow liquid that fumes strongly in moist air and has a sharp odor. It may be regarded as a mixed anhydride of sulfuric and hydrofluoric acids. Fluorosulfuric acid was first identified and characterized in 1892 (1). It is a strong acid and is employed as a catalyst and chemical reagent in a number of chemical processes, such as alkylation (qv), acylation, polymerization, sulfonation, isomerization, and production of organic fluorosulfates (see Friedel-CRAFTSreactions). 

Pubhcations have described the use of HFPO to prepare acyl fluorides (53), fluoroketones (54), fluorinated heterocycles (55), as well as serving as a source of difluorocarbene for the synthesis of numerous cycHc and acycHc compounds (56). The isomerization of HFPO to hexafluoroacetone by hydrogen fluoride has been used as part of a one-pot synthesis of bisphenol AF (57). HFPO has been used as the starting material for the preparation of optically active perfluorinated acids (58). The nmr spectmm of HFPO is given in Reference 59. The molecular stmcture of HFPO has been deterrnined by gas-phase electron diffraction (13). 

The synthesis of 2,4-dihydroxyacetophenone [89-84-9] (21) by acylation reactions of resorcinol has been extensively studied. The reaction is performed using acetic anhydride (104), acetyl chloride (105), or acetic acid (106). The esterification of resorcinol by acetic anhydride followed by the isomerization of the diacetate intermediate has also been described in the presence of zinc chloride (107). Alkylation of resorcinol can be carried out using ethers (108), olefins (109), or alcohols (110). The catalysts which are generally used include sulfuric acid, phosphoric and polyphosphoric acids, acidic resins, or aluminum and iron derivatives. 2-Chlororesorcinol [6201-65-1] (22) is obtained by a sulfonation—chloration—desulfonation technique (111). 1,2,4-Trihydroxybenzene [533-73-3] (23) is obtained by hydroxylation of resorcinol using hydrogen peroxide (112) or peracids (113). 

Potassium Amides. The strong, extremely soluble, stable, and nonnucleophilic potassium amide base (42), potassium hexamethyldisilazane [40949-94-8] (KHMDS), KN [Si(CH2]2, pX = 28, has been developed and commercialized. KHMDS, ideal for regio/stereospecific deprotonation and enolization reactions for less acidic compounds, is available in both THF and toluene solutions. It has demonstrated benefits for reactions involving kinetic enolates (43), alkylation and acylation (44), Wittig reaction (45), epoxidation (46), Ireland-Claison rearrangement (47,48), isomerization (49,50), Darzen reaction (51), Dieckmann condensation (52), cyclization (53), chain and ring expansion (54,55), and elimination (56). 

Hop "bitter" acids are isomeric mixtures of cyclohexadienone stmctures in both keto and enol forms, substituted at various positions on the ring by hydroxyl, acyl, and alkenyl groups. See Figure 2. 

Several triazinyl ketones isomerize to 4-acetamidopyrimidines. TTiis is seen in the C-acylation of 2,4,6-trimethyl-l,3,5-triazine (708) with benzoyl chloride in the presence of sodium amide to give the ketone (709) which undergoes a Dimroth-like rearrangement in boiling water to afford A-(2-methyl-6-phenylpyrimidin-4-yl)acetamide (710) it can be seen that the acylating agent determines the identity of the 6-substituent 64JHC145). 

Similarly, no systematic study of the IR spectra of the pyridopyridazines has been recorded, but the spectra of the [2,3-d] derivatives have been discussed <68AJCl29l). The diones of this series have also been studied <69MI21501), and IR used to distinguish between the structure (303) and the possible isomeric formulation (304) <74JHC35l). The IR spectra of some of the azodicarboxylic ester adducts <79X2027) have been recorded, whilst in the benzo fused systems some problems with the structure of acyl derivatives in the pyridazino[4,5-6]quinoline series have been resolved with the help of IR spectroscopy <71BSF906, 72BSF1588). 

Acyl-pyrroles, -furans and -thiophenes in general have a similar pattern of reactivity to benzenoid ketones. Acyl groups in 2,5-disubstituted derivatives are sometimes displaced during the course of electrophilic substitution reactions. iV-Alkyl-2-acylpyrroles are converted by strong anhydrous acid to A-alkyl-3-acylpyrroles. Similar treatment of N-unsubstituted 2- or 3-acyIpyrroles yields an equilibrium mixture of 2- and 3-acylpyrroles pyrrolecarbaldehydes also afford isomeric mixtures 81JOC839). The probable mechanism of these rearrangements is shown in Scheme 65. A similar mechanism has been proposed for the isomerization of acetylindoles. 

Azoles containing a free NH group react comparatively readily with acyl halides. N-Acyl-pyrazoles, -imidazoles, etc. can be prepared by reaction sequences of either type (66) -> (67) or type (70)->(71) or (72). Such reactions have been carried out with benzoyl halides, sulfonyl halides, isocyanates, isothiocyanates and chloroformates. Reactions occur under Schotten-Baumann conditions or in inert solvents. When two isomeric products could result, only the thermodynamically stable one is usually obtained because the acylation reactions are reversible and the products interconvert readily. Thus benzotriazole forms 1-acyl derivatives (99) which preserve the Kekule resonance of the benzene ring and are therefore more stable than the isomeric 2-acyl derivatives. Acylation of pyrazoles also usually gives the more stable isomer as the sole product (66AHCi6)347). The imidazole-catalyzed hydrolysis of esters can be classified as an electrophilic attack on the multiply bonded imidazole nitrogen. 

Pyrazoles, isoxazoles and isothiazoles with a hydroxyl group in the 3-position (491 Z = NR, O, S) could isomerize to 3-azolinones (492). However, these compounds behave as true hydroxy derivatives and show phenolic properties. They give an intense violet color with iron(III) chloride and form a salt (493) with sodium hydroxide which can be O-alkylated by alkyl halides (to give 494 R = alkyl) and acylated by acid chlorides (to give 494 R = acyl). 

Acyl derivatives of azoles containing two different environments of nitrogen atoms can rearrange. For example, 1-acyl-1,2,3-triazoles are readily isomerized to the 2H-isomers in the presence of triethylamine or other bases the reaction is intermolecular and probably involves nucleophilic attack by N-2 of one triazole on the carbonyl group attached to another (74AHC(16)33). 

Isomerism about a formal Csp —Csp double bond Isomensm about a formal (C—C C-aryl and C-acyl derivatives... 

From a general point of view, the tautomeric studies can be divided into 12 areas (Figure 20) depending on the migrating entity (proton or other groups, alkyl, acyl, metals. ..), the physical state of the study (solid, solution or gas phase) and the thermodynamic (equilibrium constants) or the kinetic (isomerization rates) approach. 

A well-known example of non-prototropic tautomerism is that of azolides (acylotropy). The acyl group migrates between the different heteroatoms and the most stable isomer (annular or functional) is obtained after equilibration. In indazoles both isomers are formed, but 2-acyl derivatives readily isomerize to the 1-substituted isomer. The first order kinetics of this isomerization have been studied by NMR spectroscopy (74TL4421). The same publication described an experiment (Scheme 8) that demonstrated the intermolecular character of the process, which has been called a dissociation-recombination process. 

As would be anticipated, amino groups in the homocyclic ring of 1,2-benzisoxazoles behave as normal aromatic amines, forming mono- and bis-acyl derivatives, etc. (67AHC(8)277,p. 296). In th e isomeric 2,1-benzisoxazoles the 3-amino compound exists as such and not in the tautomeric 3-imino form (65CB1562). Amino groups in 3-phenyl substituents behave as normal aromatic amines (67AHC(8)277,p. 331). 

Isomerization of 3-cephems (27) to 2-cephems (28) takes place in the presence of organic bases (e.g. pyridine) and is most facile when the carboxyl is esterified. Normally an equilibrium mixture of 3 7 (3-cephem/2-cephem) is reached. Since the 2-cephem isomers are not active as antibacterial agents, the rearrangement proved to be an undesirable side reaction that complicated acylation of the C-7 amine under certain conditions. A method for converting such mixtures to the desired 3-cephem isomer involves oxidation with concomitant rearrangement to the 3-cephem sulfoxide followed by reduction. Additions... 

Oxazol-5(2H)-one, 2-benzylidene-4-methyl-tautomerism, 6, 186 Oxazol-5(2ff)-one, 2-methylene-isomerization, 6, 226 Oxazol-5(2H)-one, 2-trifluoromethyl-acylation, 6, 201 Oxazol-5(4ff)-one, 4-allyl-thermal rearrangements, 6, 199 Oxazol-5(4H)-one, 4(arylmethylene)-Friedel-Crafts reactions, 6, 205 geometrical isomerism, 6, 185 Oxazol-5(4ff)-one, 4-benzylidene-2-phenyl-configuration, 6, 185 photorearrangement, 6, 201 Oxazol-5(4ff)-one, 4-benzyl-2-methyl-Friedel-Crafts reactions, 6, 205 Oxazol-5(4ff)-one, 4-methylene-in amino acid synthesis, 6, 203 Oxazol-5(4ff) -one. 2-trifluoromethyl-hydrolysis, 6, 206 Oxazolones... 

Rearrangement of fluorine with concomitant ring opening takes place in fluorinated epoxides Hexafluoroacetone can be prepared easily from perfluo-ropropylene oxide by isomerization with a fluorinated catalyst like alumina pre treated with hydrogen fluoride [26, 27, 28] In ring-opening reactions of epoxides, the distribution of products, ketone versus acyl fluoride, depends on the catalyst [29] (equation 7) When cesium, potassium, or silver fluoride are used as catalysts, dimenc products also are formed [29]... 

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