Elimination with amines

Chlorovinyl complexes undergo HCl elimination with amine bases to form the acetylide complexes. The rate of this reaction (equation 221) is solvent dependent, decreasing in the order PhN02 > CDCls == CD2CI2 CeDe = CCI4, and dependent on the group bonded irons to the vinyl. The order is C TH = CCl = CH2 > Cl C(OMe)Me. 

There also exists an acidregioselective condensation of the aldol type, namely the Mannich reaction (B. Reichert, 1959 H. Hellmann, 1960 see also p. 291f.). The condensation of secondary amines with aldehydes yields Immonium salts, which react with ketones to give 3-amino ketones (=Mannich bases). Ketones with two enolizable CHj-groupings may form 1,5-diamino-3-pentanones, but monosubstitution products can always be obtained in high yield. Unsymmetrical ketones react preferentially at the most highly substituted carbon atom. Sterical hindrance can reverse this regioselectivity. Thermal elimination of amines leads to the a,)3-unsaturated ketone. Another efficient pathway to vinyl ketones starts with the addition of terminal alkynes to immonium salts. On mercury(ll) catalyzed hydration the product is converted to the Mannich base (H. Smith, 1964). 

Clearly, the tertiaiy nature of the chloride would make an Sn2 mechanism highly unlikely. Furthermore, the nitro substituent is essential to the success of these reactions. Cumyl chloride itself undergoes elimination of HCl on reaction with amines. 

Heating the sugar with strong acid yields furfural derivatives. Aldohexoses can eliminate water and formaldehyde under these conditions yielding furfural. This adehyde reacts with amines according to I to yield colored Schiff s bases. Ketohex-oses condense with diphenylamine in acid medium with simultaneous oxidation according to II to yield the condensation product shown. 

Heating the sugars with strong add yields furfural derivatives. Under these conditions aldohexoses can eliminate formaldehyde and water to yield furfural. This aldehyde reacts with amines to yield colored Schiff s bases. 

It is believed (54IZV47 72JPR353) that in the first stage the intermediate 282 is formed due to the addition of the CH acid to the enamine moiety with subsequent elimination of amine. The enol form of the intermediate 282 undergoes cyclization in two fashions, depending on the nature of substituent X. In the case of the ester (X = OMe) the attack is directed to the cyano group to form substituted 3-methoxycarbonyl-I//-pyridin-2-one (283) or its tautomer (2-hydroxy-3-methoxycarbonylpyridine). With the amide (X = NH2) intramolecular condensation leads to 3-cyano-l//-pyridin-2-one and its hydroxy tautomer (284). 

Formation of C—Nu The second mode of nucleophilic addition, which often occurs with amine nucleophiles, involves elimination of oxygen and formation of a C=Nu bond. For example, aldehydes and ketones react with primary amines, RNH2, to form imines, R2C=NR. These reactions proceed through exactly the same kind of tetrahedral intermediate as that formed during hydride reduction and Grignard reaction, but the initially formed alkoxide ion is not isolated. Instead, it is protonated and then loses water to form an imine, as shown in Figure 3. 

Hydroxyalkyl sulphoxides 515 can be dehydrated either by treatment with phosphoric acid (equation 315) or by the alkylation with Mel in the presence of an excess of sodium hydride611 (equation 316). For other dehydration reactions see References 475 and 505 (Section IV.A.2.d). For elimination of amines see References 164 and 529 (Section IV.A.2.e). 

Bromo-4-chloro-lH-pyrazolo[3,4-d]pyrimidine could be easily fimc-tionalized at C-3 and C-4 in a one-pot two-step microwave-assisted process (Scheme 34) [55]. Ding and Schultz reported that nucleophilic substitution of the addition-elimination type at the C-4 position with amines and anilines smoothly occurred under acidic conditions in dioxane upon irradiation... 

First, condensation of the epoxide 230 with the amine 358 was conducted, and dehydration of the condensate (361) was attempted by chlorination with sulfonyl or sulfuryl chloride in pyridine, followed by elimination with... 

Several studies were performed in order to establish the mechaiusm (5-7). The currently accepted mechartism, presented in Scheme 26.1 for the Pd(BINAP) catalyzed amination, involves the formation of a complex, Pd(BINAP)2 from a catalyst precursor (usually Pd(OAc)2 or Pd2(dba)3) and ligand this complex lies outside the catalytic cycle and undertakes dissociation of one BINAP to form Pd(BINAP) the following steps are the oxidative addition of the aryl halide to the Pd(BINAP), reaction with amine and base, and the reductive elimination of the product to reform Pd(BlNAP). 

In warm mineral acid, formazans (195) rearrange to a benzotriazine (196) eliminating an amine (Scheme 29).8,26 27 334 338 339 H owever, when R is methyl, phenylazo, or oxalyl, the main product is the phenazine 197 along with a trace amount of the benzotriazine.340 The mechanism of this reaction is not well understood.341 345... 

A variety of cleavage conditions have been reported for the release of amines from a solid support. Triazene linker 52 prepared from Merrifield resin in three steps was used for the solid-phase synthesis of aliphatic amines (Scheme 22) [61]. The triazenes were stable to basic conditions and the amino products were released in high yields upon treatment with mild acids. Alternatively, base labile linker 53 synthesized from a-bromo-p-toluic acid in two steps was used to anchor amino functions (Scheme 23) [62]. Cleavage was accomplished by oxidation of the thioether to the sulfone with m-chloroperbenzoic acid followed by 13-elimination with a 10% solution of NH4OH in 2,2,2-trifluoroethanol. A linker based on l-(4,4 -dimethyl-2,6-dioxocyclohexylidene)ethyl (Dde) primary amine protecting group was developed for attaching amino functions (Scheme 24) [65]. Linker 54 was stable to both acidic and basic conditions and the final products were cleaved from the resin by treatment with hydrazine or transamination with ra-propylamine. 

Attempts to initiate formation of a nitrene, and its rearrangement to the iminooxo-phosphorane 80, by subjecting l-chloroamino-2,2,3,4,4-pentamethylphosphetane 1-oxide to a-elimination with sodium methoxide proved unsuccessful48). In contrast, however, the phosphorylhydroxylamides 88 rearrange in the presence of tert-butyl-amine to the heterocumulene 89 and then add base to give the phosphonic diamides 90 (>90%)49). The reaction is reminiscent of the well-known Lossen degradation. 

In addition, complexes of P(/-Bu)3 have been shown to catalyze the formation of diaryl heteroarylamines from bromothiophenes.224 Aminations of five-membered heterocyclic halides such as furans and thiophenes are limited because their electron-rich character makes oxidative addition of the heteroaryl halide and reductive elimination of amine slower than it is for simple aryl halides. Reactions of diarylamines with 3-bromothiophenes occurred in higher yields than did reactions of 2-bromothiophene, but reactions of substituted bromothiophenes occurred in more variable yields. The yields for reactions of these substrates in the presence of catalysts bearing P(/-Bu)3 as ligand were much higher than those in the presence of catalysts ligated by arylphosphines. 

The preparation of similar precursors suitable for the deposition of metal nitrides is analogous to the preparations of phosphorus and arsenic compounds. The initial reaction of metal trialkyls MR3 (M = A1, Ga, In) with amines (NHR 2) results in the formation of oligomeric amido compounds [R2MNR 2] (n = 2 or 3) which eliminate alkanes on thermolysis. The incorporation of a proton as a substituent on the pnictide bridging ligand has been examined, and many compounds of the type [R2MNHR ]2 have been synthesized. The presence of this proton may facilitate /3-elimination, allowing lower deposition temperatures to be used. 

In some cases the C /C2 double bond in methylene cyclopropenes and calicenes was found to show dienophilic functionality towards diene components. Thus, di-ethylamino butadiene combines with 497 to give the Diels-Alder adduct 507, whose proton-catalyzed elimination of amine interestingly did not lead to the dibenzo heptafulvalene 508, but to the methylene norcaradiene derivative 509293 ... 

Scheme 33 illustrates the difference in reactivity between triazolines obtained from cyclohexanone and cyclo-pentanone enamines. Thus, the reactions of azidophosphonates 239 with cyclohexanone enamines produce unstable aminotriazolines 240 that cannot be isolated due to their spontaneous elimination of amines to provide triazoles 241. Contrary to that, triazolines 242, derived from cyclopentanone enamines, are isolated in good yield (76-88%) and cannot be converted to the corresponding triazoles even by thermolysis <1995H(40)543>. Probably, introduction of a double bond between two five-membered rings would involve too much molecular strain. 

I, Table X) requires tertiary phosphine-nickel halide or tertiary phosphine-nickel carbonyl complexes at 140-170°C. This implies oxidative addition of aromatic halides to nickel, replacement of the halide with amines, and reductive elimination. 

Apparently, amines act as Si-nucleophiles toward BENAs (434), and elimination of silylamines (Si N < ) and silanol (from hemiacetals A) affords nitroso-alkenes B as key intermediates of this process. According to the published data (503), a-nitrosoalkenes B react with amines to give the target oximes (453),... 

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