Elimination amines

Sulphoxides also undergo Mannich-type condensation when reacted with aldehydes and secondary amines or their salts. In some cases, stable Mannich bases 462 can be isolated. They undergo amine elimination upon heating to give the corresponding a,/ -unsaturated sulphoxides 463164,529 (equation 276). 

Unfortunately, the chemistry of the deamlnation/condensation process is poorly understood thus, little can be said about the mechanisms and kinetics of the amine elimination step, the nature of the "silaimine" (7,8) intermediate or the condensation step. It seems reasonable to predict that if one could learn to control the relative rates for these two steps, more control could be exerted over the condensation process and the properties of the precursor polymer. 

Another elimination triggered tetrafold anionic domino process has been reported by Risch and coworkers [301]. These authors synthesized polycyclic bipyridine scaffolds as 2-585 (Scheme 2.132) which are potentially useful as ligands for host-guest systems or interesting building blocks for supramolecular applications [302]. The process combines an amine elimination from 2-584 and a Michael addi-... 

The A-oxoammonium ion is theoretically expected to react with an amine, eliminating a proton and forming the hydroxylamine while the amine is converted to imines and/or nitriles (Scheme 4). These were indeed observed by Semmelhack and Schmid (equation 28)". ... 

Using l-(2-nitrovinyl)pyrrolidines 108 or 111 as Michael acceptors, the addition of the Reformatsky reagent is followed by amine elimination. A formal vinylic substitution ensues, which can take advantage of the presence of stereocenters in the pyrrolidine moiety, affording new chiral nitroolefins 110151 and 113152, as reported in equations 64 and 65, respectively. In both cases, zinc enolates 109 and 112 are prepared by lithia-tion/transmetallation of the parent ester. 

This mechanism is of importance in radical induced amino acid damage catalyzed by copper ions. The study of the decomposition of transients with a metal-carbon -bond containing two potential leaving groups (both an amine and a carboxylate group) at the p position of the carbon centered radical is of special interest. It was reported that the intermediate formed with the amino acid 2-methylalanine with cupric ions decomposes via p-carboxyl elimination whereas the intermediate formed with cuprous ions decomposes via p-amine elimination (102). 

More recent investigations have shown that the reaction of a Na(tmp)/Bu Mg(tmp)/ tmeda mixture with 0.5 equivalent of benzene leads to dideprotonation of the arene to afford [ (tmeda)Na(p-tmp)Mg(tmp)2 2C6H4]. 5 The reaction of the magnesium amide Mg(tmp)2 with LiN(SiMe5)2 resulted in a deprotonation/amine elimination process as shown in Scheme 3.7. The product, a dimeric lithium/magnesium mixed amide has a conformationaUy locked structure with two stereogenic nitrogen centres. ... 

Scheme 3.7 Deprotonation/amine elimination in a mixed lithium/magnesium amide ...

This is an area developed by Ephritikhine and coworkers the majority (66-71) of the salts are monoanionic U amides.The synthetic strategy was based on the amine elimination reactions of Equation (5.9), as summarised in Table 5.1. Erom Table 5.1 it is evident that NEt2 is more readily displaced from U than N(SiMe3)2 (67), Cp (68), cot (69,70,73), or Cl (71) upon protolysis. 

When R1 = CN, a molecule of hydrogen cyanide is lost and the 5-amino-triazole is obtained.249 Spontaneous amine elimination also occurs when R2 is hydrogen and an aliphatic secondary amino group is present,214 which is similar to what is observed in the addition of tosyl azide to /3-enamino esters233 and nitriles.402 Thermal elimination of amine proceeds more... 

The bicyclic triazoline in Scheme 122 substituted with a secondary aryl-amino group gives a triazole,208 but only degradation products are obtained from the triazoline in Scheme 123, bearing an aliphatic amino group, when treated with dilute acid.208 However, in an anhydrous medium under the action of heat or p-toluenesulfonic acid, two possible modes of amine elimination can occur and two different triazoles are formed (Scheme 123).214 223 224... 

The nature of the transition state for the E2 reaction of some 3-thiophenoxypro-panones in aprotic solvents has been investigated.5 The linear free energy correlation and the calculated activation parameters Aand Aof the reactions suggested an unequal and synchronous E2cB mechanism via base-catalysed amine-elimination reaction. 

Amidocarbonylation aldehydes, 11, 512 enamides, 11, 514 overview, 11, 511-555 Amido complexes with bis-Cp titanium, 4, 579 Group 4, surface chemistry on oxides, 12, 515 Group 5, surface chemistry on oxides, 12, 524 with molybdenum mono-Cp, 5, 556 with mono-Cp titanium(IV) alkane elimination, 4, 446 amine elimination, 4, 442 characteristics, 4, 413 via dehalosilylation reactions, 4, 448 HCL elimination, 4, 446 metathesis reactions, 4, 438 miscellaneous reactions, 4, 448 properties, 4, 437... 

The acetoxy group may also be substituted using N-nucleophiles such as pyrrolidine or morpholine. Since the products of nucleophilic substitution are aminals, elimination results in /3-substituted ethane sulfonamides 108. Moreover, while no reaction occurs with phthalimide or sodium azide, trimethylsilyl azide reacts in the presence of Lewis acids such as zinc chloride or tin chloride to give a diazido compound 109 as product (Scheme 32) <1997PHA482>. 

Attack of nucleophiles at the a-position of the enaminone predominates, leading to Michael addition which mostly results in substituted, mainly cyclic end-products. Also observed are subsequent amine elimination and reactions at the carbonyl. Some initial reactions of nucleophilic reagents at the enaminone carbonyl carbon are known. Enaminones are often better starting materials for several reactions than the corresponding dicarbonyls. As a result, a-aminomethylene ketones act as 1,3-biselectrophiles. Due to their combined electrophilic and nucleophilic properties, enaminones act as 1,3-bisnucleophiles as well. The assumed first step in the following reactions is the one used for classification of the reactions. In addition, enaminones are used as heterodienes in 4 + 2-cycloaddition mostly with electron-deficient dienophiles. 

Cycloaddition of arynes to enamines gives aminobenzocyclobutenes, which undergo amine elimination or ring expansion on thermolysis of the amine oxide269 (Scheme 116). 

Nucleophilic attack by enamines, e.g. 248, on dichlorophenylphosphine gives an intermediate 249, which can react with a second mole of enamine to give 250. Further amine elimination from 250 and cyclization yield 2-amino-1-phenylphospholes 251 (equation 52)132. 

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