Quinoline, preparation reactions

The wide variety of ketomethylene and amino ketone monomers that could be synthesized, and the abiUty of the quinoline-forming reaction to generate high molar mass polymers under relatively mild conditions, allow the synthesis of a series of polyquinolines with a wide stmctural variety. Thus polyquinolines with a range of chain stiffness from a semirigid chain to rod-like macromolecules have been synthesized. Polyquinolines are most often prepared by solution polymerization of bis(i9-amino aryl ketone) and bis (ketomethylene) monomers, where R = H or C H, in y -cresol with di-y -cresyl phosphate at 135—140°C for a period of 24—48 h (92). 

PUtzing erReaction. Quinoline-4-carboxyhc acids are easily prepared by the condensation of isatin [91-56-5] (16) with carbonyl compounds (50). The products may be decarboxylated to the corresponding quinolines. The reaction of isatin with cycHc ketones has been reported, eg, the addition of cyclohexanone gives the tricycHc intermediate (17) [38186-54-8] which upon oxidation produces quinoline-2,3,4-tricarboxyhc acid [16880-83-4] (51). 

Unsaturated 5(4//)-oxazolones derived from aromatic and heterocyclic aldehydes including phthalic anhydride/ antipyrine/ " chromone/ indoles/ pyridines/" ° quinolines/" diazines/" benzoxazoles/" and benzimidazoles " " have been prepared. Reaction with nitrogen nucleophiles and subsequent cycliza-tion leads to the expected 5(477)-imidazolones. 

The rearrangement of pyrroles to 3-halo-pyridines upon treatment with haloforms (CHX3 where X = Cl, Br, I) in the presence of a strong base was first described by G.L. Ciamician. Its synthetic utility was later extended by M. Dennstedt to the sodium methoxide catalyzed reaction of pyrrole with methylene iodide to give pyridine. Soon after the initial discovery, the methodology was also extended for the indole series to prepare substituted quinolines. The reaction is known as the Ciamician-Dennstedt rearrangement, but it is also referred to as the abnormal Relmer-Tiemann reaction. 

Diethyl 1-fonnyhnethylphosphonate has recently been used as an effective acetaldehyde synthon for the preparation of a tricyclic quinoline. The reaction proceeds efficiently through the formation of an aromatic enamine, which undergoes ring closure under basic conditions (Scheme 5.80). ... 

Ring expansion during Reimer-Tiemann reaction conditions on pyrroles and indoles to furnish pyrid-ines and quinolines was observed by Ciamician in 1881 (equations 13 and 14). Although a preparative reaction of little use due to the low yield, this transformation stimulated others to carry out ring expansion attempts on nonphenolic substrates with considerable success. ... 

In 1880, Skraup synthesized quinolines by reaction of aniline and glycerol in a solution of sulfuric acid and an oxidizing reagent. What Skraup discovered was generalized one year later by Doebner and von Miller by using a,P-unsaturated aldehydes instead of glycerol in order to prepare substituted quinolines. 

On acetylation it gives acetanilide. Nitrated with some decomposition to a mixture of 2-and 4-nitroanilines. It is basic and gives water-soluble salts with mineral acids. Heating aniline sulphate at 190 C gives sulphanilic add. When heated with alkyl chlorides or aliphatic alcohols mono- and di-alkyl derivatives are obtained, e.g. dimethylaniline. Treatment with trichloroethylene gives phenylglycine. With glycerol and sulphuric acid (Skraup s reaction) quinoline is obtained, while quinaldine can be prepared by the reaction between aniline, paraldehyde and hydrochloric acid. 

The reaction is best carried out in the apparatus used in the preparation of quinoline, a 1500 ml. flask being fitted with a wide-bore air-condenser carrying in turn a water-condenser a still-head to fit the flask for subsequent steam-distillation should be assembled in advance. 

The stock solution of quinoline-sulphur poison is prepared by refluxing I g. of sulphur with 6 g. of quinoline for 5 hours and diluting the resulting brown liquid to 70 nJ. with xylene which has been purified by distilling over anhydrous aluminium chloride. The addition of the quinoline - sulphur poison ensures that the reduction does not proceed beyond the aldehyde stage it merely slows up the reaction and has no harmful effects. 

Quinoline may be prepared by heating a mixture of aniline, anhydrous glycerol and concentrated sulphuric acid with an oxidising agent, such as nitrobenzene. The reaction with nitrobenzene alone may proceed with extreme violence, but by the addition of ferrous sulphate, which appears to function as an oxygen carrier, the reaction is extended over a longer period of time and Is under complete control. 

Synthesis and Properties. Polyquinolines are formed by the step-growth polymerization of o-aminophenyl (aryl) ketone monomers and ketone monomers with alpha hydrogens (mosdy acetophenone derivatives). Both AA—BB and AB-type polyquinolines are known as well as a number of copolymers. Polyquinolines have often been prepared by the Friedlander reaction (88), which involves either an acid- or a base-catalyzed condensation of an (9-amino aromatic aldehyde or ketone with a ketomethylene compound, producing quinoline. Surveys of monomers and their syntheses and properties have beenpubhshed (89—91). 

Hydroxyquinolines (Quinolinols). A number of methods have been employed for their preparation. A modified Chichibabia reaction of quinoline ia fused KOH—NaOH at 240°C produces 70% of 2-hydroxyquiQoline [59-31-4] (121). Alternative names based on the facile keto—enol tautomerism of two of these compounds are 2(1H) and 4(lJd)-quiQolinone none of the other quinolinols show this property. The treatment of... 

Triphenylethylene has been prepared by the reaction of phenylmagnesium bromide with benzyl benzoate, with desoxy-benzoin, or with ethyl pheaniylacetate, and by the reaction of diphenylketene-quinoline with benzaldehyde. The above procedure is an adaptation of that described by Hell and Wiegandt. ... 

The Reissert-Henze reaction offers a method to prepare cyanopyridines and extends the Reissert and Kaufmann reactions in the quinoline and isoquinoline series. 

In 1883, Bottinger described the reaction of aniline and pyruvic acid to yield a methylquinolinecarboxylic acid. He found that the compound decarboxylated and resulted in a methylquinoline, but made no effort to determine the position of either the carboxylic acid or methyl group. Four years later, Doebner established the first product as 2-methylquinoline-4-carboxylic acid (8) and the second product as 2- methylquinoline (9). Under the reaction conditions (refluxing ethanol), pyruvic acid partially decarboxylates to provide the required acetaldehyde in situ. By adding other aldehydes at the beginning of the reaction, Doebner found he was able to synthesize a variety of 2-substituted quinolines. While the Doebner reaction is most commonly associated with the preparation of 2-aryl quinolines, in this primary communication Doebner reported the successful use of several alkyl aldehydes in the quinoline synthesis. 

Due to the commercial availability of EMME in good purity, there has not been a need to develop new methods to prepare 3-anilino-acrylates therefore, only a few alternatives have been reported. One approach described thermal carbene generation from 37, and rearrangement to form 38. Cyclization in refluxing 1,2-dichlorobenzene (1,2-DCB) provided the 2, 3, 4-trisubstituted quinolines. An electron-withdrawing group (EWG) on the carbene carbon was required for this reaction, and therefore led to the EWG substitution in the 2-position of the quinoline. 

The preparation and use of derivatized Meldrum s acid has led to an alternative preparation of 2-substituted quinolines (49 and 50) and the preparation of pyridopyrimidines (52). When Meldrum s acid derivatives are used (as shown in this example) decarboxylation occurred under the cyclization conditions. Three component coupling has been used to readily assemble the desired 3-anilino-acrylate from reaction of Meldrum s acid, (EtO)3CH and an aniline (e.g. 54 or 55).< ... 

Although regio-isomers have been reported in some cases as being problematic, due to the wide range of substituents that withstand the cyclization, the Gould-Jacobs reaction is one of the more general methods used to prepare quinolines. 

Similarly, W-methyl-D-aspartate (NMDA) antagonists 32 with analgesic activity were prepared, again using the Meth-Cohn quinoline synthesis as the key entry reaction, subsequent functional group manipulation giving the desired target compound. 

The preparation of 3-alkyl quinolines by traditional Skraup/Doebner-von Miller reaction typically results in very low yields. When ethylacrolein (9) is condensed with m-toluidine (8) under typical Skraup/Doebner-von Miller conditions, the yield of 10 is only 25%, compared to 65% with di-acetyl acetal 11. 

A number of dihydroquinolines have been prepared by treating aniline derivatives with acetone or mesityl oxide in the presence of iodine. In these cases aromatization to the fully unsaturated quinoline would require the loss of methane, a process known as the Riehm quinoline synthesis. Such Skraup/Doebner-von Miller-type reactions are often low yielding due to large amounts of competing polymerization. For example, aniline 37 reacts with mesityl oxide to give dihydroquinolines 39, albeit in low yield. ... 

Methoxythiophene and 3-cyanothiophene have been prepared from 3-bromothiophene by means of a cupric oxide-catalyzed Williamson synthesis and by reaction with cuprous cyanide in quinoline, respectively. 

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