10.1002/cctc.201500053
The study presented in the PDF document titled "Dual [Fe+Phosphine] Catalysis: Application in Catalytic Wittig Olefination" focuses on the development and application of a dual catalysis system involving iron hydride complexes and phosphines for the selective reduction of carbonyl and phosphine oxide groups. The researchers explored the use of Fe-based complexes for the hydrosilylation of aldehydes, ketones, and phosphine oxides, demonstrating that these complexes could effectively reduce phosphine oxides to phosphines. This reduction process was then integrated into a catalytic Wittig olefination reaction, which is a synthetically useful transformation for the formation of olefins from aldehydes or ketones and a-halocarboxylic acid esters. The study successfully utilized a readily accessible Fe-H complex in conjunction with triphenylphosphine as an organocatalyst and phenylsilane as a stoichiometric reductant, achieving moderate to good yields of the desired olefination products. This work not only expands the application scope of Fe-based catalysis but also provides a potential avenue for the in situ recycling of phosphines, which is beneficial for large-scale applications and more sustainable chemical processes.
10.1055/s-0031-1289746
The research focuses on a divergent synthetic strategy based on the regioselective reductive ring-opening of a cyclic 1,2-p-methoxybenzylidene acetal. The study employs a common intermediate, (1S)-N,N-dibenzyl-1-[(4R)-2-(4-methoxyphenyl)-1,3-dioxolan-4-yl]ethanamine, synthesized in five steps from an α-bromo-α'-(R)-sulfinyl ketone, to produce p-methoxybenzyl-protected primary and secondary alcohols. These alcohols serve as precursors for the synthesis of a fully protected syn-3-amino-2-hydroxybutanoic acid and an N-benzyl 2-hydroxymethylaziridine. Key reactants include α-bromo-α'-(R)-sulfinyl ketones, diisobutylaluminum hydride, p-anisaldehyde, and various other reagents used in the synthesis and purification processes. The research involves a series of chemical reactions, such as Pummerer rearrangement, reduction with lithium aluminum hydride, and reductive cleavage using diisobutylaluminum hydride. Analytical techniques used to characterize the compounds include NMR spectroscopy, high-resolution mass spectrometry (HRMS), and optical rotation measurements. The experiments demonstrate a regioselective approach to synthesize the desired alcohols and further transform them into the target molecules, showcasing the synthetic potential of the methodology for creating biologically important molecules.
10.1080/00397919208021343
The research aimed to develop a strategy for synthesizing optically active ring-A methoxylated indole alkaloids, specifically targeting the preparation of 1-benzenesulfonyl-6-methoxy-D(+)-tryptophan ethyl ester (16). This amino ester is crucial for the synthesis of Alstonia bisindole alkaloids, such as macralstonine, which exhibit potent hypotensive properties. The researchers employed the Moody azide/Schollkopf chiral auxiliary protocol to achieve the stereospecific synthesis of the target compound. Key chemicals used in the research included methyl azidoacetate, 4-methoxybenzaldehyde, benzenesulfonyl chloride, sodium borohydride, and various reagents for specific reactions like formylation and decarboxylation. The study successfully synthesized the desired compound in high yield, demonstrating the feasibility of the chosen synthetic route. The findings open avenues for the synthesis of other biologically active indole alkaloids, highlighting the potential for further exploration in the field of natural product synthesis.
10.1039/jr9300002674
The study investigates the synthesis, resolution, and properties of optically active diphenylhydroxyethylamines and their derivatives. The researchers synthesized di-p-methoxyphenylhydroxyethylamine and di-3:4-methylenedioxyphenylhydroxyethylamine by condensing glycine with anisaldehyde and piperonal respectively. These compounds were then resolved into their optically active components using fractional crystallization of their hydrogen d-tartrates. The study also explored the reaction of these bases with nitrous acid, resulting in the formation of a substituted ethylene oxide in the case of di-p-methoxyphenylhydroxyethylamine, which was found to be optically inactive and highly stable. Various derivatives of the synthesized compounds, such as hydrochlorides, monoacetyl and diacetyl derivatives, benzylidene derivatives, and quaternary ammonium iodides, were prepared and characterized. The study provides a detailed comparison of the physical properties of these bases and their derivatives, highlighting the enhancement of rotatory power due to substitution in the aromatic nuclei.
10.1246/bcsj.54.1844
The study investigates the synthesis of oxazolidines, thiazolidines, and 5,6,7,8-tetrahydro-1H,3H-pyrrolo[1,2-c]oxazole (or thiazole)-1,3-diones from β-hydroxy- or β-mercapto-α-amino acid esters. Aromatic aldehydes such as benzaldehyde, p-anisaldehyde, p-chlorobenzaldehyde, and p-nitrobenzaldehyde are used to react with amino acid ethyl esters like L-serine, 3-phenyl-DL-serine, L-threonine, or L-cysteine to form oxazolidines or thiazolidines. These compounds can then be converted into oxazoles and thiazoles through dehydrogenation using N-bromosuccinimide. Acetylation of oxazolidines and thiazolidines leads to N-acetylderivatives, which can undergo cyclization in the presence of anhydrous ZnCl? to form the tetrahydro-pyrrolo[1,2-c]oxazole (or thiazole)-1,3-diones. The study also explores the interaction of oxazolidines and thiazolidines with p-nitrobenzaldehyde and piperidine to form Mannich bases. The IR spectra of the synthesized compounds are analyzed, showing characteristic shifts and absorptions related to functional groups such as the ester group and the oxazole or thiazole ring.
10.1016/S0957-4166(97)00178-X
The research investigates the catalytic enantioselective addition of hydrogen cyanide to benzaldehyde and p-methoxybenzaldehyde using cyclo-dipeptides based on His and the unnatural (αMe)Phe as catalysts. The LL dipeptide, specifically cyclo-[L-His-L-(αMe)Phe] (15), is a key catalyst in the study. It is a cyclic dipeptide composed of L-histidine (His) and L-(α-methyl)phenylalanine ((αMe)Phe). This compound is synthesized through a series of chemical reactions starting from L-(αMe)Phe and L-histidine, involving protection, coupling, and cyclization steps. The LL dipeptide 15 is notable for its conformational rigidity, which is attributed to the incorporation of the unnatural (αMe)Phe residue. This rigidity is crucial for its catalytic activity in the enantioselective addition of hydrogen cyanide to benzaldehyde and p-methoxybenzaldehyde. The study demonstrates that 15 achieves high enantiomeric excesses (up to 99% e.e. for benzaldehyde and 89% e.e. for p-methoxybenzaldehyde derivatives) at low temperatures (-40°C) with excellent yields (98% and 93%, respectively). NMR studies suggest that the orientation of the aldehyde in the reaction complex with 15 is different from the Tanaka model, with the aldehyde hydrogen-bonded to the NH of the (αMe)Phe residue rather than the histidine residue.
10.1021/ja00212a030
The study presented in the document investigates the biomimetic oxidation of 1,2-diols using molecular oxygen in the presence of iron-porphyrin catalysts, mimicking the function of metal-containing oxidases and oxygenases found in biological systems. The researchers utilized a catalytic system comprising an iron-porphyrin complex, 1-benzyl-3-carbamoyl-1,4-dihydropyridine (BNAH), and molecular oxygen to selectively cleave the carbon-carbon bonds of aryl-substituted ethane-1,2-diols at room temperature, producing aldehydes or ketones as the main oxidation products. The reaction rates were influenced by the steric hindrance of substituents in both the catalysts and diols, and no significant differences in reactivities were observed between the two stereoisomers (meso and dl) of the diols. The study provides insights into the mechanism of the diol cleavage reaction, which involves the initial binding of the diol to the active catalyst forming an intermediate complex, followed by a rate-determining breakdown step in the catalytic cycle. The findings have implications for understanding the activation of molecular oxygen and oxygen atom transfer to organic substrates, processes that are crucial for cytochrome P-450 in biological systems.
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