Amines reduction, preferential

Imines were preferentially formed and the carbon-carbon bond was selectively formed at the C(2) position of the cyclic amine. With ethylene and propene, only imines were formed but with more bulky olefins and 7-membered cyclic amines, reduction to 2-alkyl cyclic amine took place, and N-alkylation was also observed from bicyclic amine. 

Preparative electrochemical reduction of aryltrimethylsilanes in methyl-amine in the presence of LiCl gives the Birch-type products, 1,4-cyclohexan-dienes (Scheme 34) [6], A mechanism involving the electrochemical formation of lithium metal which chemically reduces the substrate has been suggested. The hydrogen atom is introduced on the carbon adjacent to the silicon preferentially. This regioselectivity is consistent with the spin density of the anion radical determined by ESR spectroscopy (Sect. 2.2.1). 

Extension (70) of this investigation to the reduction of A-phenylazomethines with 36d-LAH gave optically active secondary amines (eq. [IS]). The products had the S configuration, as predicted by reference to Scheme 9, with hydride transfer of the less shielded H2 occurring preferentially when the phenyl points away from the shielding 3-O-benzyl group of the sugar derivative. 

Using an approach similar to that discussed previously, Pd nanoparticles were prepared within amine-terminated PAMAM dendrimers. To prevent coordination of Pd + to the primary amine groups of the dendrimers, the solution pH was adjusted to around 2, which preferentially protonates the exterior amines to a greater extent than the interior tertiary amines. Accordingly, Pd + binds preferentially to the interior tertiary amines and upon reduction Pd particles form only within the dendrimer interior. G4-NH2 dendrimer-encapsulated nanoparticles can then be quantitatively transported from an aqueous phase into toluene by addition of 10-20% of dodecanoic acid to the organic phase (Fig. 21) [19]. This transition is readily visualized by the color change the brown aqueous solution of Pd nanoparticles becomes clear after addition of the acid, while the toluene layer turns brown. Our studies have shown that this is a consequence of... 

In 2004, Rayner and coworkers reported a dynamic system for stabilizing nucleic acid duplexes by covalently appending small molecules [34]. These experiments started with a system in which 2-amino-2 -deoxyuridine (U-NH ) was site-specifically incorporated into nucleic acid strands via chemical synthesis. In the first example, U-NH was incorporated at the 3 end of the self-complementary U(-NH2)GCGCA DNA. This reactive amine-functionalized uridine was then allowed to undergo imine formation with a series of aldehydes (Ra-Rc), and aldehyde appendages that stabilize the DNA preferentially formed in the dynamic system. Upon equilibration and analysis, it was found that the double-stranded DNA modified with nalidixic aldehyde Rc at both U-NH positions was amplified 34% at the expense of Ra and Rb (Fig. 3.16). The Rc-appended DNA stabilizing modification corresponded to a 33% increase in (melting temperature). Furthermore, imine reduction of the stabilized DNA complex with NaCNBH, resulted in a 57% increase in T. ... 

List later reported the asymmetric reductive amination of a wide spectrum of aromatic and aliphatic a-branched aldehydes via dynamic kinetic resolution (Scheme 5.27) [49]. The initial imine condensation product is believed to undergo fast racemization in the presence of the acid catalyst Ih through an imine/enamine tautomerization pathway. Preferential reductive amination of one of the imine enantiomers furnishes the optically pure P-branched amine. 

The optical isomers of DOM have been prepared in two ways. The racemic base has been resolved as the ortho-nitrotartranilic acid salt by recrystallization from EtOH. The (+) acid provides the (+) or S isomer of DOM preferentially. Also, the above-mentioned l-(2,5-dimethoxy-4-methylphenyl)-2-propanone can be reductively aminated with optically active alpha-methyl benzylamine with Raney Nickel. This amine is isolated and purified by recrystallization of the hydrochloride salt. When optically pure, the benzyl group was removed by hydrogenolysis with palladium on carbon. The mp of either of the optical isomers, as the hydrochloride salts, was 204-205 °C. 

The different biological effects of NO and HNO are a function of distinct molecular targets for these redox siblings. For example, NO preferentially reacts with reduced metals to directly form a nitrosyl complex (Eq. 13). The identical product is formed by reductive nitrosylation of HNO toward oxidized metals (Eq. 12). Exceptions of course exist (e.g., the reverse of Eq. 19). Perhaps more importantly, HNO reacts with thiols (Eq. 21) and amines (Eq. 25) directly while NO must interact with these species indirectly, following oxidation to a nitrosating or oxidizing agent (36). 

This most versatile of amine syntheses can be used to make primary, secondary or tertiary amines providing only that an imine can be formed with an aldehyde or ketone. But tertiary carbon atoms cannot be joined to nitrogen by reductive amination as a tertiary carbon atom cannot have a carbonyl group. The method works by selective reduction of the imine 28 in the presence of the aldehyde 27 or ketone. Catalytic hydrogenation reduces the imine 28 preferentially as the C=N bond of the imine is weaker than the C—O bond of the aldehyde or ketone. 

The following reactions proceed with the participation of the allylic boron system (i) allylboration and protolytic cleavage of organic compounds with multiple bonds, (ii) allylboron-alkyne condensation,598 599 (iii) reductive mono-and trans-a,a -diallylation of nitrogen aromatic compounds, (iv) disproportionation processes between tribut-2-enylborane and BX3 (X = C1, Br, OR, SR). Allylboration of carbonyl compounds, thioketones, imines, or nitriles leads to the homoallylic alcohols, thiols, or amines (Equations (136) and (137). It is most important that 1,2-addition to aldehydes and imines proceeds with high diastereoselectivity so that ( )-allylic boranes and boronates give the anti-products, while -products are formed preferentially from (Z)-isomers. 

Reductive alkylations via a radical pathway have been performed on enamines of cyclic215,216 and acyclic217 ketones. In both cases the diastereoselectivity was high, leading to cis products preferentially in the case of the cyclic derivatives and to ul substituted amines in the case of linear systems (Scheme 143). 

By contrast, high stereoselectivity was observed in the cyclization of unsaturated acyclic amides and carbamates, the preferential formation of the trans- or m-isomer is dependent on the experimental conditions. Hence, by treating 7V-acetyl-5-hcxcn-2-amine with mercury(II) acetate in tetrahydrofuran (kinetic conditions), followed by reduction with sodium borohydride, trans-l-acetyl-2,5-dimethylpyrrolidine (4. R = CH3) was obtained in 98 % yield and only traces of the cu-isomer were shown to be present by H and 13C NMR81. 

The molecule is a chiral analogue of pyridoxamine and transamination occurs chemically by a mechanism similar to the biological one described in the chapter (pp. 1384-6). The zinc holds the molecule in a fixed conformation during reaction. The key step is the protonation of the enamine as that produces the new chiral centre. If the chain is across the top of the ring, protonation occurs preferentially from underneath. Hydrolysis gives the new amino acid (Phe) and the pyridoxal analogue, which can be recycled by reductive amination via the oxime. 

Reductive alkylation of amines proceeds by the hydrogenation of the imine or enamine formed, in situ, by the condensation of the amine with a carbonyl compound. This reaction can give a mixture of products if the amine produced initially competes with the reactant amine in the carbonyl condensation step. The proper selection of reagent concentrations avoids this difficulty and leads to the formation of good yields of the desired product. 50 jhe use of a large excess of ammonia gives the primary amine as the predominant product (Eqn. 19.50). 51 An excess of a primary amine as the reactant leads to the preferential formation of the secondary amine product. An excess of the carbonyl compound gives the symmetrical secondary or tertiary amines (Eqn. 19.51). 50... 

Aminomercuration leads to substituted organomercurials 5.5, which also suffer demercuration with sodium borohydride, preferentially under PTC conditions [BEl, EB4] (Figure 5.5). The mechanism proposed for this reduction in protic solvents is an ionic one, implying the intermediate formation of aziridinium salt [L3]. This method has been applied to the synthesis of cyclic amines from a,P-ethyienic precursors 5.6 [EB4] (Figure 5.5). When the reduction in run in alcohol or water, mixtures of five- and six-membered cyclic amines are obtained from each precursor 5.6 (n = 1 or 2). 

---