Acylation formylation

It is thus apparent that the selectivity of a reagent toward thiophene and benzene can differ appreciably, and this difference in selectivity is also strongly noticeable in the proportions of 2- and 3-isomers formed. Although in certain reactions no 3-isomer has been detected, appreciable amounts have been found in other reactions. Thus 0.3% of the 3-isomer has been found in the chlorination of thiophene.- Earlier results indicated that 5-10% 3-nitrothiophene is formed in the nitration of thiophene and a recent gas-chromatographic analysis by Ostman shows that the mononitrothiophene fraction contains as much as 16% of the 3-isomer. It appears that gas-chromatographic analysis should be very useful for the detection of small amounts of 3-isomers in other substitution reactions. However, from routine analyses of IR spectra, it appears to the present author that the amount of 3-isomers formed in acylation, formylation, and bromina-tion of thiophene are certainly less than a few per cent. 

Reactions of Nondonor Chelate Ring Member in the Intact Ring. In some cases, chelate ring members will react without impairment of the stability of the complex. The most studied example involves substitution at the central carbon atom in / -diketone complexes (16-19, 21, 45, 64). This is illustrated with the bromination reaction in Equation 26. Acylation, formylation, and nitration reactions have also been carried out. 

Nondestructive reactions of trisacetylacetonates of chromium(lll), cobalt(lll), and rhodium(lll) are reviewed. Halogenation, nitration, thiocyanation, acylation, formylation, chloromethylation, and aminomethylation take place at the central carbon of the chelate rings. Trisubstituted chelates were obtained in all cases except acylation and formylation. Unsymmetrically and partially substituted chelates have been prepared. Substitutions on partially resolved acetylacetonates yielded optically active products. NMR spectra of unsymmetrically substituted, diamagnetic chelates were interpreted as evidence for aromatic ring currents. Several groups were displaced from the chelate rings under electrophilic conditions. The synthesis of the chromium(lll) chelate of mal-onaldehyde is outlined. 

Hilf, C. Bosold, F. Harms, K. Lohrenz, J. C. W. Marsch, M. Schimeczek, M. Boche, G. Carbene structure of stable acyl (formyl) anion equivalents. Chem. Ber. 1997, 130,1201-1212. 

There has been a number of developments in the use of salicylaldehydes as precursors of both chromenes and chromans. Alkenes activated by acyl, formyl, nitrile and phenylsulfonyl groups react with 2-hydroxybenzaldehydes and 2-hydroxy-1-naphthaldehyde under Bayliss-Hillman conditions to yield 3-substituted chromenes via the in situ dehydration of the initially formed chroman-4-ol <02JCS(P1)1318>. In like manner, P-nitrostyrenes yield 2- and 2,2-substituted derivatives of 3-nitrochromenes <02H(57)1033>. A simple route to 2-phenyl-2H-chromenes starting from salicylaldehyde and utilising a Pd(0)-catalysed cyclisation of an allylic acetate has been described <02SC3667>. 

Selenophene undergoes various electrophilic substitutions nitration, sulfonation, halogenation, mercuration, chloromethylation, aminomethylation, acylaminomethylation, acylation, formylation, and hydrogen exchange. 

The peptide is a synthetic acyl formyl phospholyrosyl-g u-(/>Aklipentenyl) amine. Only, the recognition site and the phosphotyrosyl interaction site are shown. (Ttie ribbon model is reconstructed with permission of the authors and Biochemistry from data in ref. 22 of Chapter 3, deposited in data banks.)... 

Reaction of the hydrazino group with nitrous acid affords the azido group or the valence tautomeric tetrazolo-l,2,4-triazine,324 e.g. 17 and 18.303 The hydrazino group can also be acylated, formylated, and sulfonylated and reacts with aldehydes to give hydrazones.356... 

Attempts to brominate the free position 6 of compound 122 failed so also did the attempt to nitrate 121 or 122 because the nitro group entered the most accessible position of the phenyl ring to give either 6-(4-nitrophenyl)- (124), or 7-(4-nitrophenyl) derivative 125. Attempts to acylate, formylate, hydroxymethylate, chloromethylate of aminomethylate 6- or 7-substituted thiazolo[2,3-/]purinediones 121 and 122 also resulted in failure. The bromo group of 7-bromo derivative 123 did not react with either ammonia or amines (81KGS1267) (Scheme 34). The alkylation at N(3) with halogenoacetate is illustrated in Scheme 30. 

Stabilized ylide reactions. However, in this series the stereochemical result is not very sensitive to phosphorus substituents, nor to structural details of the ylide stabilizing group (ester, acyl, formyl, etc.) when the reaction is performed in nonpolar solvents. Apparently, the oxaphosphetane-like TS is too rigid to respond much to changes in the phosphorus environment, and 1,2-inter-actions along the developing C—C bond are dominant. 

Initial attempts at acylating formyl acetate 53b with acyl chloride 54 using pyridine in methylene chloride at 0 °C afforded the desired enol ester 51b, unfortunately as an inseparable mixture with Knoevenagel adduct 59 in a ratio of 84 16 (Table 1, entry 1). This would not be the last time that the reactivity of the formyl acetate increased the difficulty of seemingly simple transformations. Fortunately, under the same reactimis conditions, but in the presence of less nucleophilic bases, namely either triethylamine or Hiinig s base, formation of the byproduct was reduced to 96 4 and 99 1, respectively, with 51b isolated in up to 89% yield (Table 1, entries 2 and 3). Utilizing the optimized conditions, ethyl enol ester 51c was prepared in 91% yield (Table 1, entry 4). 

Electrophilic attack on coordinated cyclopentadienyl rings, particularly those in ferrocene, is well established. This process occurs in a similar fashion to electrophilic attack on arenes and was used to establish the binding mode of the Cp ligand in ferrocene (see Equation 3.88). These reactions of the Cp ligand with electrophiles are described in more detail in Chapter 12, which covers electrophilic attack on coordinated ligands. Friedel-Crafts acylation, formylation, aminomethylation, and mercuration are all known. - ... 

Electrophilic aromatic substitution reactions are a very important class of chemical reactions that allow the introduction of substituents on to arenes by replacing a hydrogen atom covalently bonded to the aromatic ring structure by an electrophile. The most common reactions of this type are aromatic nitrations, halogenations, Friedel-Crafts alkylations and acylations, formylations, sulfonations, azo couplings and carboxylations - to name just a few. 

In order to synthesize benzaldehyde using the Friedel-Crafts acylation, formyl chloride would be required. Since this acid chloride is too reactive to be prepared, several synthetic equivalents have been developed to accomplish this formylation reaction. 

Mesoionic 3-arylthiazolo[3>2-a]-4-pyrimidones (258 RsH) are extremely susceptible to electrophilic substitution, sometimes to the detriment of their stability. It was found that generation of (258 R=H), from corresponding 4-oxo-A -thiazolium perchlorates (259), in the presence of electrophiles readily gives acyl, formyl, and arylazo derivatives (258 R=COalkyl,CH0,N=NAr, respectively)... 

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