Imines nucleophilic addition reactions

Imine formation and enamine formation appear different because one leads to a product with a C=N bond and the other leads to a product with a C=C bond. Actually, though, the reactions are quite similar. Both are typical examples of nucleophilic addition reactions in which water is eliminated from the initially formed tetrahedral intermediate and a new C=Nu bond is formed. 

Each of the following substances can be prepared by a nucleophilic addition reaction between an aldehyde or ketone and a nucleophile. Identify the reactants from which each was prepared. If the substance is an acetal, identify the carbonyl compound and the alcohol if it is an imine, identify the carbonyl compound and the amine and so forth. 

Reductive amination takes place by the pathway shown in Figure 24.4. An imine intermediate is first formed by a nucleophilic addition reaction (Section 19.8), and the C=N bond of the imine is then reduced. 

Step 1 of Figure 29.14 Transimination The first step in transamination is trans-imination—the reaction of the PLP—enzyme imine with an a-amino acid to give a PLP—amino acid imine plus expelled enzyme as the leaving group. The reaction occurs by nucleophilic addition of the amino acid -NH2 group to the C=N bond of the PLP imine, much as an amine adds to the C=0 bond of a ketone or aldehyde in a nucleophilic addition reaction (Section 19.8). The pro-tonated diamine intermediate undergoes a proton transfer and expels the lysine amino group in the enzyme to complete the step. 

The addition of terminal acetylenes to imines is an important reaction because of the importance of these products as building blocks. Conventionally, the addition reaction shown in Scheme 5.2 is performed with stoichiometric amounts of butyllithium in a step that is, separate from the subsequent nucleophilic addition reaction (see (b)). Carreira has recently developed a procedure that utilizes an iridium catalyst to effect the addition reaction to a wide range of aldimines and ketimines (see (a)). ... 

Nitrones have a more reactive C=N bond toward nucleophilic addition compared to imines. In spite of this fact, there have been only a limited number of studies on the nucleophilic addition reactions of nitrones, particularly organometallic reagents.352-355 During the last decade, research related to reactions of nitrones with zinc-containing reagents was essentially focused on (i) dialkylzinc-assisted alkynylations356-358 and vinylations359 of nitrones, (ii) catalytic asymmetric nucleophilic additions to the C=N bond,360-364 and (iii) nitrone allylations by allylzinc halides.365,366... 

In addition to alkenes and alkynes, allenes have attracted considerable interest due to their unique reactivity and multireaction sites. Therefore, transition-metal-catalyzed nucleophilic addition reaction of amines and imines to allenes has been extensively studied to prepare biologically important amines and nitrogen-heterocycles.31,31d... 

We saw in Section 7.7.1 that imines and iminium ions could act as carbonyl analogues and participate in nucleophilic addition reactions. 

The reactions of ketone dilithio ,/i-dianions with imines and hydrazones have been investigated.77 The nucleophilic addition reaction to C—N double bonds took place selectively at the -position of dianions to form lithium (Z)-enolates containing a lithium amide portion, which is then transformed into y-amino ketones and related compounds by the subsequent reaction with electrophiles. 

Aldehydes and ketones undergo a variety of reactions that lead to many different products. The most common reactions are nucleophilic addition reactions, which lead to the formation of alcohols, alkenes, diols, cyanohydrins (RCH(OH)C=N) > and imines (R2C =NR) 5 to mention a few representative examples. 

Coordination of the Lewis acid zinc(II) chloride to glycosyl imines has strong influence on the stereodifferentiation in nucleophilic addition reactions to these imines (see Scheme 3). 

Carbohydrate-derived auxiliaries exhibit an efficient stereoselective potential in a number of nucleophilic addition reactions on prochiral imines. a-Amino acids, P amino acids and their derivatives can be synthesized in few synthetic steps, and with high enantiomeric purity. A variety of chiral heterocycles can readily be obtained from glycosyl imines by stereoselective transformations, providing evidence that carbohydrates have now been established as useful auxiliaries in stereoselective syntheses of various interesting classes of chiral compounds. 

Enamine catalysis using proline or related catalysts has now been applied to both intermolecular and intramolecular nucleophilic addition reactions with a variety of electrophiles. In addition to carbonyl compounds (C = O), these include imines (C = N) in Mannich reactions (List 2000 List et al. 2002 Hayashi et al. 2003a Cordova et al. 2002c ... 

Tatsui G (1928) Synthesis of carboline derivatives. J Pharm Soc Jpn 48 453 159 Taylor MS, Jacobsen EN (2004) Highly enantioselective catalytic acyl-pictet-spengler reactions. J Am Chem Soc 126 10558-10559 Terada M, Uraguchi D, Sorimachi K, Shimizu H (2005) Process for production of optically active amines by stereoselective nucleophilic addition reaction of imines with C nucleophiles using chiral phosphoric acid derivative. PCT Int Appl WO 2005070875 2005-08-04... 

In these last steps, two nucleophilic addition reactions take place to yield imine products. The mechanism has been worked out in greater detail in Section 19.8, but the essential steps are additions of phenylhydrazine, first to the imine, then to the ketone. Proton transfers are followed by eliminations, first of ammonia, then of H2O. 

Aldehydes and ketones can undergo nucleophilic addition reactions. In particular, aldehydes and ketones can react with amines to form imines and enamines, reactions that might compete with formation of amide bonds between amino acids. Because of this reactivity, aldehydes and ketones are unlikely to be found in amino acid side chains. 

The nucleophilic addition reactions of enolates to imines and related compounds (the so-called Mannich-type reactions, equation 39) are important tools in organic synthesis and a variety of electrophiles have been used to obtain the resulting nitrogen-containing... 

Kobayashi et al. found that lanthanide triflates were excellent catalysts for activation of C-N double bonds —activation by other Lewis acids required more than stoichiometric amounts of the acids. Examples were aza Diels-Alder reactions, the Man-nich-type reaction of A-(a-aminoalkyl)benzotriazoles with silyl enol ethers, the 1,3-dipolar cycloaddition of nitrones to alkenes, the 1,2-cycloaddition of diazoesters to imines, and the nucleophilic addition reactions to imines [24], These reactions are efficiently catalyzed by Yb(OTf)3. The arylimines reacted with Danishefsky s diene to give the dihydropyridones (Eq. 14) [25,26], The arylimines acted as the azadienes when reacted with cyclopentadiene, vinyl ethers or vinyl thioethers, providing the tet-rahydroquinolines (Eq. 15). Silyl enol ethers derived from esters, ketones, and thio-esters reacted with N-(a-aminoalkyl)benzotriazoles to give the /5-amino carbonyl compounds (Eq. 16) [27]. The diastereoselectivity was independent of the geometry of the silyl enol ethers, and favored the anti products. Nitrones, prepared in situ from aldehydes and N-substituted hydroxylamines, added to alkenes to afford isoxazoli-dines (Eq. 17) [28]. Addition of diazoesters to imines afforded CK-aziridines as the major products (Eq. 18) [29]. In all the reactions the imines could be generated in situ and the three-component coupling reactions proceeded smoothly in one pot. 

Tlie Kresze reaction has also been used in the synthesis of N phosphinoyl imines derived from nonenolizable aldehydes, although usually in modest yields [25, 26]. The N phosphinoyl imine derived from trifluoromethyl ketones can be prepared via the ethanolate intermediate (Scheme 1.7) [27]. This adduct is directly used in the subsequent nucleophilic addition reaction. 

In the nucleophilic addition reactions of amines to substituted aromatic aldehydes where acid catalysis is required, the use of EAN seems to be convenient. The EAN can take part in an acid-base equilibrium with the aromatic aldehydes substituted by electron-withdrawing groups. The imine products from the selected aldehydes could be obtained, confirming the dual behaviour of EAN as Brbnsted acid and potential nucleophile in these type of processes (Fig. 13.7). 

In addition to the nucleophilic addition reactions of 201 shown above, the imine can also participate in cycloaddition reactions <05X9281>. Keto-piperidine 205 could be prepared in very good yield through a Diels Alder reaction of 201 with Danishefsky s diene. The observed stereoselectivity was rationalized through a chelation controlled transition state with re-face preference. 

As a part of ongoing efforts to synthesize a potent, orally active anti-platelet agent, xemilofiban 1 [1], development of an efficient chemoenzymatic process for 2, the chiral yS-amino acid ester synthon (Fig. 1) was proposed. The scheme emphasized the creation of the stereogenic center as the key step. In parallel with the enzymatic approach, chemical synthesis of the / -amino acid ester synthon emphasized formation of a chiral imine, nucleophilic addition of the Reformatsky reagent, and oxidative removal of the chiral auxiliary. This chapter describes a selective amida-tion/amide hydrolysis using the enzyme Penicillin G amidohydrolase from E. coli to synthesize (R)- and (S)-enantiomers of ethyl 3-amino-5-(trimethylsilyl)-4-pen-tynoate in an optically pure form. The design of the experimental approach was applied in order to optimize the critical reaction parameters to control the stereoselectivity of the enzyme Penicillin G amidohydrolase. 

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