Imines derivatives

Rj = H, R2 = COOH) and isobetanidine (96, R2 = H, Rj = COOH). Furthermore, it would appear that all betacyanins or betaxanthins may simply be imine derivatives (with the appropriate amino acid) of betalamic acid (97). 

Under conditions similar to those already outlined, stable aziridin imine derivatives, e.g. (422) and (423), can be prepared in excellent yields (70-80%) by treating the appropriate a-bromoamidines (easily accessible from the amide precursor) with potassium t-butoxide in ether <70AG(E)38l). At low temperatures the elimination proceeds with high regio- and stereo-selectivity at -40 °C (421) yields predominantly (422). 

A number of imine derivatives have been prepared as amine protective groups, but few of these have seen extensive use. The most widely used are the benzylidene... 

The formation of oximes, hydrazones, and related imine derivatives is usually catalyzed by both general acids and general bases. General base catalysis of dehydration of the tetrahedral intermediate involves nitrogen deprotonation concerted with elimination of hydroxide ion. ... 

The kinetics of the hydrolysis of some imines derived from benzophenone anc primary amines revealed the normal dependence of mechanism on pH with ratedetermining nucleophilic attack at high pH and rate-determining decomposition of the tetrahedral intermediate at low pH. The simple primary amines show a linear correlation between the rate of nucleophilic addition and the basicity of the amine Several diamines which were included in the study, in particular A, B, and C, al showed a positive (more reactive) deviation from the correlation line for the simple amines. Why might these amines be more reactive than predicted on the basis of thei ... 

A number of imine derivatives have been prepared as amine protective groups, but most of these have not seen extensive use. The most widely used are the ben-zylidene and diphenylmethylene derivatives. The less used derivatives are listed, for completeness, with their references at the end of this section. For the most part, they are prepared from the aldehyde and the amine by water removal cleavage is effected by acid hydrolysis. 

Asymmetric dipolar cycloaddition of azomethine imines derived from diazoal-kane-pyridazine cycloadducts 98JHC1187. 

Another route to the amido complexes originates from [(>j-Tp )W(CO) (PhC=CMe)(OTf)l and benzylamine and yields [(i -Tp )W(CO)(PhC=CMe) (NHCH2Ph)] (96JA6916). The latter can be protonated with tetrafluoroboric acid to give the amine derivative [(> -Tp )W(CO)(PhC=CMe)(NH2CH2Ph)](Bp4), and this process can be reversed by -butyllithium. Hydride abstraction by silver tetrafiuoroborate, molecular iodine, or PhsCPEe leads to the cationic imine derivatives [(> -Tp )W(CO)(PhC=CMe)(HN=CHPh)]". -Butyllithium deproto-nates the product and gives the neutral azavinylidene species [(> -Tp )W(CO) (PhC=CMe)(N=CHPh)]. The latter with silver tetrafiuoroborate forms the cationic nitrile species [(j -Tp )W(CO)(PhC=CMe)(N=CPh)](Bp4). 

A range of electron-withdrawing groups on the nitrogen - N-P(0)Ph2, N-tosyl, and N-SES, for example - were tolerated. Imines derived from aromatic, heteroaromatic, unsaturated, and even aliphatic aldehydes and ketones were employed... 

Chiral imines derived from 1-phenylethanone and (I. Sj-exo-l, 7,7-trimethyIbicyclo-[2.2.1]heptan-2-amine [(S)-isobornylamine], (.S>1-phenylethanamine or (R)-l-(1-naphthyl) ethanamine are transformed into the corresponding (vinylamino)dichloroboranes (e.g., 3) by treatment with trichloroborane and triethylamine in dichloromethane. Reaction of the chiral boron azaenolates with aromatic aldehydes at 25 "C, and subsequent acidic hydrolysis, furnishes aldol adducts with enantiomeric excesses in the range of 2.5 to 47.7%. Significantly lower asymmetric inductions are obtained from additions of the corresponding lithium and magnesium azaenolates. Best results arc achieved using (.S )-isobornylamine as the chiral auxiliary 3. 

Addition of organometallics to hydrazones provides hydrazines1, which can be converted to the corresponding amines by hydrogenolysis. Hydrazones can therefore be regarded as masked imine derivatives of ammonia. This methodology has been utilized successfully for numerous stereoselective syntheses of amines and amine derivatives2-23. 

The addition of electron-rich enamines2-5 to preformed imines and imine derivatives so far has scarcely been investigated6 -15 compared to the addition of enolatcs (see Section 1.4.3., refs 16 and 17 and literature cited therein). Most of the known examples refer to iminium salts because they are more reactive than the corresponding iinines due to their highly polarized C-N double bond (see Section 1.4.1.6., ref 16 and literature cited therein). 

Diastereoselective preparation of a-alkyl-a-amino acids is also possible using chiral Schiff base nickel(II) complexes of a-amino acids as Michael donors. The synthetic route to glutamic acid derivatives consists of the addition of the nickel(II) complex of the imine derived from (.S )-,V-[2-(phenylcarbonyl)phenyl]-l-benzyl-2-pyrrolidinecarboxamide and glycine to various activated olefins, i.e., 2-propenal, 3-phenyl-2-propenal and a,(f-unsaturated esters93- A... 

Mainly sulfoxide groups are introduced as chiral auxiliaries for the modification of a,/J-unsat-urated enones (see Section D.1.5.3.5.). Chiral imine derivatives have also been used (see Section D.1.5.3.1.). Various chiral alcohols, and in particular 8-phenylmenthol, have been successfully used as auxiliaries, mainly in two-fold Michael additions to a,/ -unsaturatcd esters. 

Keywords imines derived from formylphosphonate undergo Diels-Alder reactions only in those cases which carry a strongly electron-withdrawing N-substituent. Lewis acidity, solvent effect, lithium perchlorate in diethyl ether... 

Dipolar [3 + 2] cycloadditions are one of the most important reactions for the formation of five-membered rings [68]. The 1,3-dipolar cycloaddition reaction is frequently utihzed to obtain highly substituted pyrroHdines starting from imines and alkenes. Imines 98, obtained from a-amino esters and nitroalkenes 99, are mixed together in an open vessel microwave reactor to undergo 1,3-dipolar cycloaddition to produce highly substituted nitroprolines esters 101 (Scheme 35) [69]. Imines derived from a-aminoesters are thermally isomerized by microwave irradiation to azomethine yhdes 100,... 

The reaction can be applied to aldehydes, indirectly, by alkylating an imine derivative of the aldehyde.The derivative is easily prepared (16-12) and the product easily hydrolyzed to the aldehyde (16-2). Either or both R groups may... 

The use of chiral auxilliaries in the Staudinger reaction has been explored extensively. Chiral imines derived from (15)-(-t-)-camphor 10-sulfonic acid <96TA2733>,... 

In the future, further studies should be addressed to improve the chemose-lectivity and diastereoselectivity of the reductive coupling process, especially searching for novel reagents and milder experimental conditions. As a matter of fact, a few novel reductive couphng procedures which showed improved efficiency and/or stereoselectivity have not been further apphed to optically active imines. For example, a new electrochemical procedure which makes use of the spatially addressable electrolysis platform with a stainless steel cathode and a sacrificial aluminum anode has been developed for imines derived from aromatic aldehydes, and the use of the N-benzhydryl substituent allowed 1,2-diamines to be obtained with good yields and dl-to-meso ratios... 

Double asymmetric induction operates when the azomethine compound is derived from a chiral a-amino aldehyde and a chiral amine, e.g., the sulfin-imine 144 [70]. In this case, the R configuration at the sulfur of the chiral auxihary, N-tert-butanesulfinamide, matched with the S configuration of the starting a-amino aldehyde, allowing complete stereocontrol to be achieved in the preparation of the diamine derivatives 145 by the addition of trifluo-romethyl anion, which was formed from trifluoromethyltrimethylsilane in the presence of tetramethylammonium fluoride (Scheme 23). The substituents at both nitrogen atoms were easily removed by routine procedures see, for example, the preparation of the free diamine 146. On the other hand, a lower diastereoselectivity (dr 80 20) was observed in one reaction carried out on the imine derived from (it)-aldehyde and (it)-sulfinamide. 

Starting from the benzylidene diimine 24 (Scheme 15) and only one equivalent of TosMlC, the same reaction afforded the imidazole-imine derivative and then, after alkylation, the corresponding salt 25. After hydrolysis, an... 

The catalysts bearing a cyclohexylamine moiety combined with a bulky sal-icylidene compound linked via one thiourea function to a terf-leucine ben-zylamide (Scheme 38, Ri = Bn, R2 = H) was the most efficient. The test was performed in solution at - 78 °C, with HCN as the cyanide source. Excellent results were obtained 78% isolated yield with 91% ee for the optimised substrate and 70-86% ee for other imine derivatives (65-92% isolated yield) [148,152-157]. 

One of the potentially most useful aspects of the imine anions is that they can be prepared from enantiomerically pure amines. When imines derived from chiral amines are alkylated, the new carbon-carbon bond is formed with a bias for one of the two possible stereochemical configurations. Hydrolysis of the imine then leads to enantiomerically enriched ketone. Table 1.4 lists some examples that have been reported.118... 

Another example of the addition of terminal alkynes to C=N in water is the coupling of alkynes with in-situ-generated A-acylimines (Eq. 4.32) and A-acyliminium ions (Eq. 4.33). In 2002, Li et al. developed a coupling reaction of alkynes with A-acylimines and A-acyliminium ions mediated by Cu(I) in water to generate propargyl amide derivatives.57 Either an activated imine derivative or imininum derivative was proposed as the intermediate, respectively. 

Amines can react with various carbonyl compounds and their derivatives in aqueous media to give the corresponding imine derivatives. These reactions have been discussed in related chapters. The synthetically most useful reaction of this type is the formation of imines and imine derivatives from the condensation of amines with aldehydes and ketones. Water is an excellent solvent for such condensation reactions. For example, water was found to be an ideal solvent for a high-yield, fast preparation of easily hydrolyzable 2-pyrrolecarbaldimines.23 In the presence of Cu2+, the reaction afforded the corresponding Cu(II) chelates (Eq. 11.19). 

The stereoselective allylation of carbon-nitrogen multiple bonds have also been studied. The addition of allylzinc bromide to aromatic imines derived from (. S j-valine esters was affected by reversibility, which caused the lowering of the diastereoisomeric ratio with increasing reaction time. The retroallylation reaction could be avoided by performing the reaction in the presence of trace amounts of water or by using CeC - 7H2O as the catalyst with a decreased reaction rate.71... 

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