Reducing agents three-component reactions

Two essentially different mechanisms, (i) oxidative cyclization of two 7T-components (formation of metallacycle) and (ii) oxidative addition of reducing or alkylating agents followed by insertion of 7t-components, can operate in these three-component reactions.426 However, the aforementioned phenomena such as the reversal of regiochemistry and the crossover from reductive to alkylative manifolds remain unsolved. 

In addition, Zhou et al have developed diastereo- and enantioselective reductive coupling of 1,3-dienes, such as l,4-diphenylbuta-l,3-diene, with aromatic and heteroaromatic aldehydes by using ZnEt2 as the reducing agent and nickel complexes of chiral spiro phosphoramidites such as 21 (Scheme 4.21). In this case, the three-component reaction provided the... 

Hasenkopf et al. (306) reported the synthesis of a dynamic 12-member, template-directed imine library L27 obtained from the reversible condensation of three aldehydes (monomer set Mi, Fig. 8.54) with four primary amines (monomer set M2, Fig. 8.54) in buffered aqueous conditions followed by irreversible reduction to amines L28 with sodium cyanoborohydride. The library was prepared in the presence of a large excess of M2, to prevent further condensation of an aldehyde onto the secondary amine product. A template-driven imine library L27 was prepared in the presence of the metalloenzyme carbonic anhydrase 11 (CAll). After the template-assisted, reversible dynamic reaction was complete, the reducing agent was added and the amine library L28 was produced (Fig. 8.54). Without any template the unbiased, equilibrated imine mixture L29 was then reduced to the mixture of amines L30 (Fig. 8.54). The different abundance of library components L28 and L30, reflecting the affinity of library components for CAll, was determined by comparing the HPLC traces of the stable amine mixtures. 

Nickel-Catalyzed Couplings via Internal Redox Reactions In contrast with the reductive couplings discussed earlier, where two tt-systems are joined via C—C bond formation and a net two-electron reduction takes place by the action of a reducing agent, Montgomery et al. observed that an alkyne and an enal can be coupled via an internal redox process where the aldehyde is oxidized and the alkyne is reduced [60]. A three-component... 

Each reaction process has three components and three phases, i.e., the number of degree of freedom of the system is two. Therefore, there are only two values that can be changed among four of them (total pressure, temperature, partial pressure of reducing agent and products), the other two values are their functions, and the equilibrium of the system has nothing to do with total pressure, that is ... 

Other important molecules that are useful intermediates in the synthesis of natural products are chiral diols. anli-l,2-Diols of type 30 were obtained in good yields (75-85%) and moderate to good diastereoselectivity (76-96% de) by a nickel-catalyzed three-component addition of a-silyloxy aldehydes 27, alkynyl silanes 28a, and reduction with triisopropyl silane (29a) (Scheme 11.11) [31]. The diastereoselectivity of this process could be explained by the Felkin model. Alternatively, a chiral alkynyl derivative can control the outcome of the reaction. Thus, the coupling of optically active, oxazolidinone-derived ynamides, aldehydes, and silane as reducing agent led to the formation of y-siloxyenamide derivatives with diastereoselectivities up to 99% [32]. 

Saita and Maenosono have reported the synthesis of FePt NPs using iron(ni) ethoxide [Fe(OEt)3] and platinum(II) acetylacetonate [Pt(acac)2] as precursors without any reducing agent. Fe(OEt)3 is a brown powder at room temperature (nonvolatile) and is a highly reactive late transition metal alkoxide [248]. In addition, decomposition products of Fe(OEt)3 are less toxic. For these reasons, the use of Fe(OEt)3 as a precursor is suitable for industrialization. An amount of 1 mmol of Fe(OEt)3, 0.5 mmol of Pt(acac)2, 17 mL of octyl ether, 1.6 mL of oleic acid, and 1.7 mL of oleylamine were placed in a three-necked flask at ambient air. The color of the resulting mixture was brown. The molar ratio of Fe to Pt in the mother reaction solution was adjusted to 2. The flask was then evacuated to remove oxygen and volatile components from the reaction solution. After evacuation, the flask was... 

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