Imines name reactions

Allyltitanium complexes derived from a chiral acetal have been reacted with carbonyl compounds and imines [63], While the chiral induction proved to be low with carbonyl compounds, high induction was observed with imines. This complex represents the first chiral homoenolate equivalent that reacts efficiently with imines. Finally, the reactions with electrophiles other than carbonyl compounds and imines, namely a proton source, NCS, and I2, furnished the corresponding alkene, chloro, and iodo derivatives in good yields [64]. 

Nitrilium ions are highly reactive intermediates that serve as imine synthons and are used in a multitude of synthetic named reactions however, their lack of stability hampers their use. DMAP has been shown to stabilize nitrilium ions in the presence of trimethylsilyl triflate to create the base-stabilized triflate salts, which are stable in air with only 3% decomposition over a period of 1 month (eq 20). ... 

The area of reactions of phosphate derivatives has been dominated by highly stereoselective reactions in which the latter were used as chiral catalysts or achiral reagents. Among this group of reactions, it is worthy to note several asymmetric reactions ring opening of w 50-aziridinium and episulfonium ions, addition of alcohols to imines, 1,3-dipolar addition of aldehydes, amino esters and dipolarophiles, protonation of silyl enol ethers, epoxidation of a,p-unsaturated aldehydes, aza-ene-type reactions as well as asymmetric versions of named reactions Mannich, Friedel-Crafts, Kabachnik-Fields, aza-Darzens and aza-Henry. 

In 2009, List and coworkers reported a highly diastereo and enantioselective proline-catalyzed double Mannich reaction of acetaldehyde with A-Boc imines [3], The treatment of 1 equiv of acetaldehyde with 3 equiv of A-Boc imine derived from benzaldehyde in the presence of 20 mol% of L-Pro produced the double Mannich adduct 2 in quantitative yield and with exceptionally high diastereo and enantiose-lectivities (dr > 99 1, ee > 99%) (Scheme 12.2). The reaction was performed with a variety of A-Boc imines, namely aromatic and heteroaromatic substituted imines, and furnished the products in excellent yields (76-99%) and with similar stereoselectivities (dr > 99 1, ee > 99%). Even the unstable isovaleraldehyde-derived A-Boc imine gave the double Mannich adduct stereoselectively, albeit with a moderate yield (30%). 

Schiemann reaction (Section 22 17) Preparation of an aryl fluonde by heating the diazonium fluoroborate formed by addition of tetrafluorobonc acid (HBF4) to a diazonium ion Schiffs base (Section 17 10) Another name for an imine a compound of the type R2C=NR ... 

Preliminary experiments prove that the substitution pattern of the /V-aryl moiety of imine 1 is crucial for the stereoselectivity of this reaction. The 2-substituent on the aryl group is of special importance. Namely, introduction of a methoxy group leads to a considerable decrease of enantioselectivity compared to the corresponding 2-H derivative, probably due to disfavor-able coordination with the organolithium complex. In contrast, alkyl groups show the reverse effect along with increased bulkiness (e.g., Tabic 1, entries l-3a) but 2,6-dimethyl substitution provides lower ee values. Furthermore, the 4-substituent of the TV-aryl moiety is of minor importance for the stereoselectivity of the reaction [the Ar-phcnyl and the /V-(4-methoxyphenyl) derivatives give similar results], whereas a substituent in the 3-position results in lower stereoselectivities (e.g., Et, Cl, OCHj)41. 

The nitrogen analogs of ketones and aldehydes are called imines, azomethines, or Schiff bases, but imine is the preferred name and we use it here. These compounds can be prepared by condensation of primary amines with ketones or aldehydes.102 The equilibrium constants are unfavorable, so the reaction is usually driven forward by removal of water. 

The optically active Schiff bases containing intramolecular hydrogen bonds are of major interest because of their use as ligands for complexes employed as catalysts in enantioselective reactions or model compounds in studies of enzymatic reactions. In the studies of intramolecularly hydrogen bonded Schiff bases, the NMR spectroscopy is widely used and allows detection of the presence of proton transfer equilibrium and determination of the mole fraction of tautomers [21]. Literature gives a few names of tautomers in equilibrium. The OH-tautomer has been also known as OH-, enol- or imine-form, while NH tautomer as NH-, keto-, enamine-, or proton-transferred form. More detail information concerning the application of NMR spectroscopy for investigation of proton transfer equilibrium in Schiff bases is presented in reviews.42-44... 

The reverse reaction, namely hydrogenation, has also frequently been used to decrease the degree of unsaturation present in macrocyclic systems - typically converting imine linkages to amine groups. Such hydrogenations have usually been performed catalytically (for example, using H2 in the presence of Raney nickel or a precious metal catalyst) or by means of chemical reductants such as sodium borohydride. 

A Schiff base is the common name for the (usually acyclic) imine product of the reaction of a primary aryl amine with an aldehyde or ketone. These imines are stable if there is at least one aryl group on the imino nitrogen or on the imino carbon (54). A cyclidene is generically a cyclic, multidentate imine. 

Despite its formal simplicity, the stepwise mechanism of the reaction between ketenes and imines raises a complex stereochemical situation since ketenes can be unsymmetrically substituted and imines can exist in either (E)- or -configurations [49]. As far as the first step of the reaction is concerned, the nucleophilic attack of the nitrogen atom of the imine can occur through the less hindered exo face, namely that which has the shortest substituent, or through the endo face, which incorporates the largest substituent (Scheme 8). In principle, the exo attack leads to second transition structures that exhibit the largest substituents at the 3-out position. 

Sertraline (16) is an antidepressant that inhibits the uptake of serotonin in the central nervous system.148 It is marketed by Pfizer under the name Zoloft.149 One methodology that can be used relies on an asymmetric reduction (see also Chapter 16) (Scheme 31.11).150-156 The lactone can be used as a chiral starting material for the Friedel-Crafts reaction. The established stereogenic center in the tetralone controls the reduction of the imine.157 The alternative is a resolution approach (Scheme 31.12).148-153-158-161... 

Aziridines. The synthesis of aziridines has been covered in several major reviews <2003CRV2905, 2004T2701, B-2006MI1 >. The intermolecular cycloaddition of an electron-deficient species such as a nitrene, a nitrenium cation, or a carbene (or their formal equivalents) to the -bond of an alkene, alkyne, imine, or nitrile is a significant approach to aziridines and azirines (Scheme 5). These reactions are often named aziridinations. 

As carried out industrially, the processes pose problems in almost all their aspects. The catalysts generally operate between 800 and 1100 °C and at very high space velocities (>100 000 h ) with contact times of the order of 10" — 10 s the question arises therefore whether the reactions are wholly surface catalysed, or whether surface initiated gas-phase reactions are important. Since there is a considerable reorganization of atoms in reactants during their conversion to products, the nature of the reaction intermediates has been the subject of considerable speculation over many years. Reaction theories for ammonia oxidation were named, prior to 1960, after the principle intermediate proposed, viz. the imide (NH), nitroxyl (HNO), and hydroxylamine (NH2OH) theories. Similarly, alternative theories for the Andrussow cyanide process have proposed methylene-imine (CH2=NH) and nitrosomethane (CH3.NO) as reaction intermediates. Modern techniques might now reasonably be expected to discriminate amongst these hypotheses. 

Bromotellurenylbenzaldehyde (or its oxime) serves as the precursors to another tellurium-containing heterocyclic system, namely benzoisotellurazole 34 (78JHC865). The reaction of the aldehyde with ammonia proceeds through the formation of imine 35 followed by its dehydrobromination. The cyclization reaction of oxime 36 is catalyzed by polyphosphorous acid (Scheme 19). 

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