Einhorn reaction

An attempt to react 2b with ethyl chloroformate in the presence of pyridine, the Einhorn reaction, gave 73 in low yield and other unknown products. The expected 3-ethoxycarbonyltetramic acid was not isolated (91UP1). An analogous reaction is described for Meldrum s acid (92LA813) (See Fig. 34.)... 

Tscherniac-Einhorn reaction. Introduction of the amidomethyl group into aromatic rings or activated methylene groups in the presence of sulfuric acid. 

This reaction was initially reported by Einhorn and Hollandt in 1898. It is the acylation of alcohols using anhydride or acyl haUde in a tertiary amine such as pyridine. Therefore, this reaction is known as the Einhorn acylation, Einhorn reaction, and Deninger-Einhorn method." The function of tertiary amines in this reaction have been identified as both nucleophilic acylation catalyst and acid scavenger. The solid evidence of nucleophilic catalyst is to record the UV spectrum of the intermediate acetylpyridinium salt in water. Subsequently, a number of highly nucleophilic tertiary amines have been employed for the acylation of alcohols. These tertiary amines include triethylamine, 4-(dimethylamino)pyridine (DMAP), l,4-diazabicyclo[2.2.2]octane and... 

The r/ireo-3-amino-2-hydroxy-acids (225a,b) have been prepared by regio-specific ring-opening of the appropriate cw-2,3-epoxy-acids by ammonia. Both compounds have recently been found in nature. A review has been published on the preparation of a-amino-acid derivatives by the Tscherniac-Einhorn reaction. ... 

Experiments in deoxygenated ethanol solution in the dark showed that, by stirring, 4-nitrobenz-aldehyde is obtained in 60% yield, accompanied by 13% 2-(4-nitrobenzyl)-2-nitropropane. Under the same conditions, but with sonication, the yields are 23% of 4-nitrobenzaldehyde and 48% of 2-(4-nitrobenzyl)-2-nitropropane (Einhorn et al. 1990). The importance of this result consists in the following conclusion The ultrasonic irradiation has a marked influence on the relative rates of the competing reactions and stimnlates just the ion-radical one. 

For a review of this and related reactions, see Screttas Steele Org. Prep. Proced. Int. 1990, 22, 271-314. LeBel Cherluck Curtis Synthesis 1973, 678. For another method, see Einhorn Luche Tetrahedron Lett. 1986, 27. 501. 

Replacement of =0 by CI2 or OH by Cl in the diacylamine function —CONHCO or —CON=C(OH)— also affords triazoles by analogy with the Einhorn-Brunner reaction (Scheme 72) (66AG(E)960, 76ZOR673). 

The use of ultrasonic techniques in virtually every field of chemistry has expanded greatly in recent years. Sonochemical methods have probably been most successful for heterogeneous reactions in general and, in particular, for organometallic synthesis. Ultrasonic synthesis allows the use of safer solvents that need not be anhydrous, cheaper chloride starting materials and, frequently, lower reaction temperatures. An excellent review-on the use of sonochemistry in organic and organometallic chemistry is that of Einhorn and co-workers [141]. A second Einhorn publication on the ultrasonically assisted Barbier reaction is also very informative [142],... 

Another example on the use of the ultrasonic technique with the magnesium Barbier reaction is reported by Einhorn and Luche in their study of organometallic intermediates from isocyanates [Eq. (78) 147]. 

Danhui, Y., Einhorn, J., Einhorn, C., Aurell, M. J., Luche, J.-L. The sonochemical Barbier reaction applied to carboxylates. Study of a model case. J. Chem. Soc., Chem. Common. 1994,1815-1816. 

Einhorn-Brunner reaction. Formation of substituted 1,2,4-triazoles by condensation of hydrazines or semicarbazides with diacylamines in the presence of acid catalysts. 

The use of ultrasound is found to alter the reaction pathway and selectivity ratio in some eases. For reactions where reagents may react either by an ionie or a free radical pathway, ultrasound prefers the latter at the expense of the ionic pathway (Einhorn et al, 1990 Ando and Kimura, 1990 Luche et al., 1990). Neumann and Sasson (1985b) reported the use... 

Luche, J. L., C. Einhom, J. Einhorn J. C. De Souza Barboza, C. Pettier, C. Depuy, P. Delair, C. Allavena, and T. Tuschl, Ultrasonic Waves as Promoters of Radical Processes in Chemistry The Case of Organometallic Reactions, Ultrasonics, 28, 316 (1990). 

For acylation in pyridine by Einhorn s method it is not always necessary to start with preformed acyl chloride. Its preparation and reaction can be effected in one operation by dissolving the amine and carboxylic acid together in pyridine, adding the calculated amount of thionyl chloride with cooling, and after some time pouring the mixture into water the amide is precipitated and is washed successively with dilute acid, dilute alkali hydroxide, and water. 

With pyridine, acid chlorides and acid anhydrides yield A-acyl pyridinium salts 6 which are very reactive and sensitive to hydrolysis, unlike the quaternary salts 2-5 they are involved in the acylation of alcohols and amines in pyridine as solvent (Einhorn variant of the Schotten-Baumann reaction). However, 4-dimethylaminopyridine 12 (Steglich reagent) and 4-(pyrrolidin-l-yl)pyridine 13 are better acylation catalysts by a factor of 10 [46a]. Reactions with sulfonyl chlorides in pyridine proceed via A-sulfonylpyridinium salts 14. 

This reaction was initially reported by Einhorn in 1905 and was extended by Brunner in 1914, therefore, it is known as the Einhorn-Brunner reaction. It is the synthesis of 1,2,4-triazoles by acid-catalyzed condensation between hydrazines (or semicarbazides) and diacylamines. It should be pointed out when two side chains in diacylamine are different, two isomeric triazoles will form. It was found that the substituent in the diacylamine derived from the stronger acid would appear in position 3 of the resulting triazole, indicating that the reaction is initiated by the attack of the free amino group of hydrazine on the more electrophilic carbonyl group of the stronger acid moiety. ... 

Other references related to the Einhorn-Brunner reaction are cited in the literature." ... 

This reaction is related to the Einhorn-Brunner Reaction. 

Einhorn, J., et al.. Gas Phase lon/Molecule Reactions of Unsaturated Hydroxy Fatty Acid... 

A suitably designed chiral analog of NHPI can be used as an enantioselective oxidation catalyst. Einhorn reported the synthesis of axially chiral NHPI analogs (Scheme 6.21). These NHPI derivatives can be used in several catalytic asymmetric oxidation reactions, such as indane oxidation and oxidative deprotection of acetal. 

Tsdierniac-Einhorn-type reaction C-Imidomethylation via carbonium ions j -Imido-a-dilorocarboxylic acids... 

Goldschmidt in 1896 [121 studied the reaction of urea with formaldehyde in various strength acid solutions and obtained a granular white deposit of the empirical formula C5H10N4O3. In 1908, Einhorn and Hamburger [13] studied the same reaction in the presence of hydroxyl ions and, depending on the mole ratio of formaldehyde to urea, isolated mono- or dimethylolurea. 

Polycarbonates are polyesters of carbonic acid formed by reaction of diols (aromatic, aliphatic or a mixture of both) with a derivative of carbonic acid. The first preparations of polycarbonates were reported by Einhorn in 1898 [155], by reaction of phosgene with resorcinol or hydroquinone in a pyridine solution. Bischoff and van Hedenstrom in 1902 [156] obtained the same aromatic polycarbonates via transesterification with diphenyl carbonate (DPC). Thus the main routes to polycarbonates were established early, but the properties of the products seemed uninteresting. Around 1930 aliphatic polycarbonates were studied by Carothers and van Natta [157]. These carbonates have low melting points and thermal resistance and are not commercially interesting as stand-alone thermoplastics. Low molecular... 

---