Acyl nitrates coupling reactions

From a synthetic point of view, the above studies have stimulated the synthesis of new types of /3-diketonato complexes. Thus, reactions at position 4 of the l-metalla-2,6-diox-acyclohexane rings, usually denominated the y-position (equation 2), such as halogen-ation , thiocyanogenation, chlorosulfenylation , arylsulfenylation, acylation, nitration, formylation , chloromethylation and dimethylaminomethylation (equation 2) ° have been performed as well as Suzuki coupling reactions (equation 3) , or an aldol reaction with p-nitrobenzaldehyde under Lewis acidic conditions (equation 4f. ... 

The fact that the one-pot synthesis of caUxarenes works best with p-f-butylphenoP was beneficial for the whole area, since the f-butyl groups are easUy removed by trans-butylation with AICI3 in toluene (as solvent and acceptor), converting calixarenes 2a-e into the p-unsubstituted calixarenes 2na-e. Thus, the p-positions at the wide rim are available for virtually all kinds of electrophilic substitution reactions which are possible with phenols . Sulphonation, nitration, bromination (or iodination), bromomethyla-tion, aminomethylation, formylation, acylation and coupling with diazonium salts are examples. 

Other typical electrophilic aromatic substitution reactions—nitration (second entry) sul fonation (fourth entry) and Friedel-Crafts alkylation and acylation (fifth and sixth entnes)—take place readily and are synthetically useful Phenols also undergo elec trophilic substitution reactions that are limited to only the most active aromatic com pounds these include mtrosation (third entry) and coupling with diazomum salts (sev enth entry)... 

The electrophilic substitution reactions of 1,3-dimethylpyrrolo[3,2-coupling yield 7-substituted products. However, nitration in acetic acid gives primarily attack at position 6. In some reactions 6,7-disubstitution is observed [95CHE(30)1077]. 

This reaction was exploited by Pass, Amit and Patchornik to directly couple two peptide fragments (Scheme 13.30) [117]. However, one of the main issues to date has been the preparation of such activable amino acids. Two approaches (which, unfortunately, are limited in their scope) are nitration of the parent indoline derivative after acylation with the amino acid, or use of the amino acid chloride prepared in situ. 

While there are several reports concerning electrophilic substitution on to (5,5)-fused heterocycles, very few of these involve a study with the parent system. The ir-excessive systems (50), (51), (52) and (53) were found to be susceptible to attack by electrophilic reagents at the positions indicated, leading to alkylation, formylation (Vilsmeier-Haack reaction), acylation, tritylation, metalation, tricyanoethylation, halogenation, thiocyanation, nitrosation, nitration and diazo coupling (77HC(30)l). 

Instead, these heterocycles and their derivatives most commonly undergo electrophilic substitution nitration, sulfonation, halogenation. Friedel-Crafts acylation, even the Reimer-Tiemann reaction and coupling with diazonium salts. Heats of combustion indicate resonance stabilization to the extent of 22-28 kcal/ mole somewhat less than the resonance energy of benzene (36 kcal/mde), but much greater than that of most conjugateci dienes (about Tlccal/mole). On the basis of these properties, pyrrole, furan, and thiophene must be considered aromatic. Clearly, formulas I, II, and III do not adequately represent the structures of these compounds. 

Like other aromatic compounds, these five-membered heterocycles undergJ nitration, halogenation, sulfonation, and Friedel-Crafts acylation. They are mucji more reactive than benzene, and resemble the most reactive benzene derivatives (amines and phenols) in undergoing such reactions as the Reimer-Tiemann reaction, nitrosation, and coupling with diazonium salts. 

Examples of the selective substitution of phenol units in partially O-alkylated (or 0-acylated) calixarenes (reaction c)) are the bromination , iodination, nitration , formylation , chloromethylation , alkylation and coupling with diazonium salts. ... 

Reactions of Pyrroles. 1,3-Di-t-butylpyrrole forms the first stable protonated pyrrole, the salt (104). Electrophilic substitution of pyrrole with MeaC or Me FC in the gas phase occurs mainly at the j3-position, as does nitration and Friedel-Crafts acylation of l-phenylsulphonylpyrrole2 Pyrrole-2,5-dialdehyde has been prepared by Vilsmeier-Haack formylation of the ester (105), followed by hydrolysis. A similar method has been used to convert the di-acetal (106) into pyrrole-2,3,5-tricarbaldehyde. AT-Benzoyl-pyrrole reacts with benzene in the presence of palladium(II) acetate to yield a mixture of l-benzoyl-2,5-diphenylpyrrole, the bipyrrolyl (107), and compound (108). Treating lithiated A-methylpyrrole with nickel(II) chloride results in the polypyrrolyls (109 = 0-4). 2-Aryl-1-methylpyrroles are obtained by cross-coupling of l-methylpyrrol-2-ylmagnesium bromide with aryl halides in the presence of palladium(0)-phosphine complexes. ... 

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. 

Alkylthio-5-alkylthiophens are chloromethylated at position 3 by chloromethyl methyl ether. 3-Methylthiothiophen has been nitrated at position 2. The influence of the reaction conditions on the isomer distribution in the acylation of 2-methoxy-, 2-methylthio-, and 2-dimethyl-amino-thiophen has been studied. Azo-coupling and aminomethylation occur at position 3 of some 4,5-disubstituted 2-acylaminothiophens. 3-Acetylamino-2-benzoylthiophen yields the 4,5-dichloro-derivative with sulphuryl chloride, while 3-acetylamino- or 3-benzoylamino-4-carbonyl-thiophen derivatives are chlorinated at position 2. ... 

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