Reductive aldol type reaction

In 1985, Matsuda et al. reported that Rh-H species promote a reaction sequence involving conjugate reduction, aldol type C - C bond formation, and... 

The synthesis pathway of quinolizidine alkaloids is based on lysine conversion by enzymatic activity to cadaverine in exactly the same way as in the case of piperidine alkaloids. Certainly, in the relatively rich literature which attempts to explain quinolizidine alkaloid synthesis °, there are different experimental variants of this conversion. According to new experimental data, the conversion is achieved by coenzyme PLP (pyridoxal phosphate) activity, when the lysine is CO2 reduced. From cadeverine, via the activity of the diamine oxidase, Schiff base formation and four minor reactions (Aldol-type reaction, hydrolysis of imine to aldehyde/amine, oxidative reaction and again Schiff base formation), the pathway is divided into two directions. The subway synthesizes (—)-lupinine by two reductive steps, and the main synthesis stream goes via the Schiff base formation and coupling to the compound substrate, from which again the synthetic pathway divides to form (+)-lupanine synthesis and (—)-sparteine synthesis. From (—)-sparteine, the route by conversion to (+)-cytisine synthesis is open (Figure 51). Cytisine is an alkaloid with the pyridone nucleus. 

Although the reduction of a-heteroatom-substituted carbonyl compounds is the most popular method for the generation of Sm(III) enolates, other substrates react with Sml2 to form Sm(III) enolates that undergo aldol-type reactions as part of larger, sequential processes. 

The ferrocenylphosphine-silver complex catalyzes the aldol-type reaction of tosylmethyl isocyanide 71 with aldehydes with higher stereoselectivity than the gold complex (Scheme 2-59) [84]. The reaction with several aldehydes produces trans-4-tosyloxazolines 72 in up to 86% ee, which can be converted into optically active l-alkyl-2-aminoethanols by reduction with LiAlH4. 

Chiral borane catalyst 47g, prepared from N-losyl-(a.S, /j R)-/i-melhyltryptophari and (p-chlorophenyl)dibromoborane, is fairly effective in asymmetric aldol-type reaction of 1,3-dioxolanes bearing an aryl or vinyl group at fhe 2-position (Scheme 10.45) [125]. The ring-cleavage products can be converted into free aldols without epimerization by iodination and subsequent reduction. The chiral borane-promoted reaction wifh 48 is very valuable for asymmetric desymmetrization of symmetric 1,3-dioxolanes and 1,3-dioxanes leading to mono protected 1,2- and 1,3-diols, respectively [126]. 

The Henry reaction is an aldol-type reaction between a nitroalkane and an aldehyde in the presence of a base. Since basic reagents are also catalysts for the aldol condensation, the nitroaldol reactions must be strictly controlled. An interesting alternative lies in the use of surfactants to perform the reaction in an aqueous medium [63], The Reformatsky reaction, which involves a-haloketones and aldehydes, can be mediated by zinc, tin or indium in water in the latter case the proportion of undesirable reduction products could be strongly reduced [64]. 

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