The stereoselective synthesis of vicinal amino alcohols derivatives from 1-substituted cyclopropanols and chiral N-tert-butanesulfinyl imines is described. Cyclopropanols are easily prepared from carboxylic esters upon reaction with ethylmagnesium bromide in the presence of titanium tetraisopropoxide and undergo carbon-carbon bond cleavage by means of diethylzinc to produce, upon base deprotonation, enolized zinc homoenolates, which react with chiral sulfinyl imines in a highly regio- and stereoselective manner.

Multilayer graphene (MLG), obtained by mild sonication of graphite in NMP, was functionalised via 1,3-dipolar cycloaddition with azomethine ylides generated by thermal 1,2-prototropy from various imino esters. The microwave-assisted functionalisation took place in five hours at 100 degrees C. The resulting MLG, containing substituted proline-based amine functional groups, was characterized using XPS and showed a nitrogen loading three times that obtained for the same transformation performed for five days using convection-assisted heating. The preparation of the imino ester containing a bipyridine unit at the arylidene position allowed for the preparation of the corresponding functionalised MLG, which incorporated the ruthenium atom to achieve a heterogeneous MLG-Ru complex. This supported complex was tested, as a proof of concept, as a photocatalyst of the aerobic oxidative hydroxylation of 4-methoxyphenylboronic acid. Multilayer graphene (MLG), obtained by mild sonication of graphite in NMP, was functionalised via 1,3-dipolar cycloaddition with azomethine ylides generated by thermal 1,2-prototropy from various imino esters. The final use as heterogeneous metallophotocatalyst is demonstrated.

Single-walled carbon nanotubes (SWCNTs) were functional-ized by treatment with imino esters through 1,3-dipolar cycloaddition activated by thermal 1,2-prototropy. The reaction was optimized and analyzed by using various heating methods. The functionalization af-forded pyrrolidino-functionalized nanotubes that were characterized by using several techniques. The ester group was then transformed into the corresponding SWCNT-iridium carboxylate and, as a proof of con-cept, the product was tested as a catalyst in the hydrogen-transfer reac-tion of acetophenone to yield 1-phenylethanol.

The pseudo-multicomponent reaction between propargyl amine, an aldehyde and an electron-deficient alkene is described. The C-H activation takes place thermally and allows the obtaining of cycloadducts in very good yields with high diastereoselectivities. The relative configuration is determined by X-ray diffraction analysis of the chiral molecule, obtained as a single diastereoisomer, using a chiral maleimide. A brief study of the stability of the possible ylides involved in the process is also mentioned, confirming the high diastereoselectivity observed. The high functional group density of these cycloadducts permits the synthesis of complex heterocycles. After allylation or propargylation of the pyrrolidine nitrogen atom, RCM-DA cycloaddition or cyclotrimerization with an alkyne is studied, respectively. In this last example, the resulting tetracyclic structures are of potential interest as drugs for the treatment of cystic fibrosis.

The deacetylative aldol reaction of N-methyl-3-acetyl-3-fluoro-2-oxindole is optimized with benzaldehyde and the most appropriate conditions are used for the survey of the scope of this transformation with different aldehydes. The relative configuration of the resulting compounds is also confirmed. The reaction is diastereoselective and affords the syn-stereoisomer in good yields. DFT calculations are used for the explanation of this diastereoselectivity through a traditional chair-like transition state. [GRAPHICS] .

Enantioconvergent catalysis has expanded asymmetric synthesis to new methodologies able to convert racemic compounds into a single enantiomer. This review covers recent advances in transition-metal-catalyzed transformations, such as radical-based cross-coupling of racemic alkyl electrophiles with nucleophiles or racemic alkylmetals with electrophiles and reductive cross-coupling of two electrophiles mainly under Ni/bis(oxazoline) catalysis. C-H functionalization of racemic electrophiles or nucleophiles can be performed in an enantioconvergent manner. Hydroalkylation of alkenes, allenes, and acetylenes is an alternative to cross-coupling reactions. Hydrogen autotransfer has been applied to amination of racemic alcohols and C-C bond forming reactions (Guerbet reaction). Other metal-catalyzed reactions involve addition of racemic allylic systems to carbonyl compounds, propargylation of alcohols and phenols, amination of racemic 3-bromooxindoles, allenylation of carbonyl compounds with racemic allenolates or propargyl bromides, and hydroxylation of racemic 1,3-dicarbonyl compounds.

The stereocontrolled synthesis of 1-substituted homotropanones, using chiral N-tert-butanesulfinyl imines as reaction intermediates, is described. The reaction of organolithium and Grignard reagents with hydroxy Weinreb amides, chemoselective N-tert-butanesulfinyl aldimine formation from keto aldehydes, decarboxylative Mannich reaction with β-keto acids of these aldimines, and organocatalyzed L-proline intramolecular Mannich cyclization are key steps of this methodology. The utility of the method was demonstrated with a synthesis of the natural product (−)-adaline, and its enantiomer, (+)-adaline.

Two supported noble metal species, gold and palladium anchored on an ionic liquid-modified Fe-based metal-organic framework (MOF), were successfully synthesized and characterized by FT-IR, XRD, TEM, XPS, SEM, EDX, and elemental mapping. The ionic liquid post-modified MOF was used for anchoring Au or Pd at ppm levels, and the resulting materials were employed as catalysts in the reduction of nitrophenol isomers, dyes, and Sonogashira-Hagihara reactions. Using the Au@Fe-MOF-IL catalyst, reduction of nitrophenol isomers, as well as the reductive degradation of dyes, e.g., methylene blue (MB), methyl orange (MO), and methyl red (MR) were performed efficiently in water. On the other hand, Pd@Fe-MOF-IL was used as an effective catalyst in the Sonogashira-Hagihara coupling reaction of aryl iodides and bromides using very low amounts of Pd. These catalysts were recycled and reused for several runs without deteriorating remarkably in catalytic performance.

This review covers the recent developments (since 2015) of enantioselective desymmetrization reactions using metal-catalyzed, organocatalyzed and enzymatic processes of prochiral and meso-compounds. This asymmetric strategy has been applied to a great number of organic compounds such as diarylalkanes, silanes, alcohols, amines and dibenzylmethylamines, as well as unsaturated compounds comprising dienes, diynes and cyclohexenes. The classical desymmetrization of 1,2-, 1,3-diols and other polyols by inter- and intramolecular acylation and alkylation reactions, but also by oxidation methods are important processes. Carbonyl compounds such as cycloalkanones, cyclohexadienones, cyclic and acyclic 1,3-diketones, cyclic 1,4-diketones are desymmetrized and applied to the synthesis of a wide range of natural products. In the case of dicarboxylic acid derivatives, diesters and lactones, anhydrides, diamides and dinitriles are mainly desymmetrized by intra- and intermolecular esterifications and hydrolysis. Small ring carbocycles such as cyclopropanes and cyclopropenes, cyclobutanes and cyclobutenes, and also cyclopentanes and cyclopentenes, cyclohexanes and cyclohexenes are considered. Heterocyclic systems such as small ring oxygen containing epoxides, oxetanes and oxabenzonorbornadienes as well as nitrogen containing aziridines, azetidines, azabenzonorbornadienes and diazanorbornenes are desymmetrized mainly by asymmetric ring opening reactions. The synthetic applications of these desymmetrization methodologies in the total synthesis of natural products and biologically active compounds are highlighted. (C) 2022 Published by Elsevier Ltd.

The enantioselective 1,3-dipolar cycloaddition between imino esters and (Z)-nitroalkenes bearing a masked amino group in the β-position was studied using several chiral ligands and silver salts. The optimized reaction conditions were directly applied to the study of the scope of the reaction. The determination of the absolute configuration was evaluated using NMR experiments and electronic circular dichroism (ECD). The reduction and hydrolysis of both groups was performed to generate in an excellent enantiomeric ratio the corresponding cis-2,3-diaminoprolinate.

Indium-mediated allylation of N-tert-butanesulfinyl imines derived from indole-2 and 3-carbaldehydes 3 and 5 with allylic bromides 6, proceed with high diastereoselectivity. Homoallylic amide derivatives 13 and 14 are transformed into dihydropyridinones 15 and 16, upon successive desulfinylation, N-acylation with acryloyl chloride and ring-closing-metathesis. Desulfinylation of amine ester derivatives 17 and 18, obtained when ethyl 2-(bromomethyl)acrylate (6 b) is used as the allylating reagent, lead to the corresponding alpha-methylene-gamma-butyrolactams 19 and 20, in modest yields.

The present review summarizes the application of magnetic ionic liquids (MILs) as efficient magnetically recoverable catalysts in different organic transformations. They are supported mainly on magnetite coated silica gel preventing agglomeration of the magnetic nanoparticles (MNPs) and are protected from acidic solutions. Depending on the functionalization they are used as catalysts in multicomponent reac-tions allowing the easy synthesis of pyrans, pyridines, pyrimidines, quinazolines and their derivatives. Other heterocyclic compounds such as thiazolidinones, furanones, pyrazoles, imidazoles and triazoles are synthesized also by three-component reactions. These multicomponent processes are applied to the preparation of 1-amidoalkyl-2-naphthols and propargylamines by an A3-coupling. Condensation reactions of carbon dioxide gives cyclic carbonates, benzimidazolones and quinazolinedione and other reactions involving amines gives amides, oxazolidinones and pyrroles. Condensation of aldehydes with different compounds provides benzoxazoles and thiazoles as well as Knoevenagel reactions. Esterification and transesterification reactions of fatty acids have been applied for biodiesel production. Oxidation of alcohols and sulfur compounds, as well as epoxidation of alkenes, are easily achieved under mild reaction conditions. Cross-coupling reactions are performed with Pd NPs immobilized on MILs and hydrogenation of alkynes and enals with Pt NPs with low metal leaching. Other reactions involve diazotation-iodination of anilines, sodium azide ring opening of epoxides, etherification of 5-hydroxymethylfurfural, aza-Michael additions and Friedel-Crafts alkylation and sulfonylation of aromatic compounds. (C) 2022 Elsevier B.V. All rights reserved.

The synthesis of nitrogen-containing heterocycles, including natural alkaloids and other compounds presenting different types of biological activities have proved to be successful employing chiral sulfinyl imines derived from tert-butanesulfinamide. These imines are versatile chiral auxiliaries and have been extensively used as eletrophiles in a wide range of reactions. The electron-withdrawing sulfinyl group facilitates the nucleophilic addition of organometallic compounds to the iminic carbon with high diastereoisomeric excess and the free amines obtained after an easy removal of the tert-butanesulfinyl group can be transformed into enantioenriched nitrogen-containing heterocycles. The goal of this review is to the highlight enantioselective syntheses of heterocycles involving the use of chiral N-tert-butanesulfinyl imines as reaction intermediates, including the synthesis of several natural products. The synthesis of nitrogen-containing heterocycles in which the nitrogen atom is not provided by the chiral imine will not be considered in this review. The sections are organized according to the size of the heterocycles. The present work will comprehensively cover the most pertinent contributions to this research area from 2012 to 2020. We regret in advance that some contributions are excluded in order to maintain a concise format.

In this account, Diels-Alder reactions of different 1-amino-1,3-dienes with dienophiles are considered. As 1-amino-1,3-dienes, dienamines, dienamides, 1,2-dihydropyridines, 2-pyridones and vinylic heterocycles, such as vinyl-pyrroles, pyrazoles, imidazoles, indoles, tetrahydropyridines and dihydropyridones are studied. As dienophiles, enals, acrylic, maleic and fumaric derivatives, quinones, tetracyanoethylene, dialkyl acetylenedicarboxylates, nitroolefins, nitrosobenzene and azocompounds play an important role. Synthetic applications of these inter or intramolecular, racemic or enantioselective reactions in order to prepare polycyclic nitrogen-containing heterocycles, are pointed out, specially in the preparation of naturally occurring and biologically active compounds mainly alkaloids. The most significant feature of the chemistry described in this account is the fact that this methodology represents a simple and selective way to get N-containing heterocyclic compounds in only one reaction step, creating at least two carbon-carbon bonds in a regio-, diastereo- and enantioselective fashion.

An efficient stereocontrolled preparation of 2-substituted pyrrolidines and 5-substituted indolizidin-7-ones, by using chiral N-tert-butanesulfinyl imines derived from 4-halobutanal as starting materials, is detailed. Addition of Grignard reagents and a decarboxylative Mannich reaction with.-keto acids involving these chiral imines proceeded with high diastereoselectivity. The synthesis of the pyrrolidinic alkaloids (-)-bgugaine, (+)-villatamine B, (-)-norhygrine, trans-dendrochrysanine, and (-)-ruspolinone demonstrated the utility of this methodology.

Tetracyclic benzocarbazoles are examples of nitrogen-containing heterocycles, which display interesting pharmacological activities and physicochemical properties. This chapter aims to bring some examples about the synthesis of bezocarbazoles, mostly benzo[a]carbazoles (including the dihydro and tetrahydro derivatives), with interesting properties. This chapter also includes aza-pterocarpans and aza-coumestans, which are structurally similar to benzo [a] carbazoles, although their analogous natural products are formed through different biosynthetic pathways. Being aware of the potential interest of these compounds, many efforts have been made for the development of new methodologies to carry out their synthesis and will be discussed below.

AbstractHomocoupling reactions promoted by photocatalysts are not very abundant in the literature. However, the products generated from such processes are very interesting. In this review, we highlight the most relevant reports concerning photocatalyzed dimerizations covering the literature until the middle of 2020. Reactions will be classified according to the type of starting material employed, with an emphasis being placed on the corresponding mechanism.1 Introduction2 Arenes and Heteroarenes3 Alkenes4 Alkanes5 Alkynes6 Aldehydes, Ketones, Alcohols, Amines and Imines7 Carboxylic Acids8 Nitro Compounds9 Conclusions

Transition metal-catalyzed reactions of N-sulfinyl imines with several substrates lead to the corresponding chiral amines with high yields and diastereo- or enantioselectivities. As metals, titanium, copper, ruthenium, rhodium, palladium and silver have been successfully used as catalysts in different carbon-carbon forming reactions as well as hydrogenations with molecular hydrogen or transfer hydrogenations with isopropanol as hydrogen source. (C) 2021 Elsevier Ltd. All rights reserved.

The addition of functionalized organolithium compounds derived from 5-chloro-2-methoxy-1-pentene and 6-chloro-2-methoxy-1-hexene to N-tert-butanesulfinyl aldimines imines, and a subsequent hydrolysis of the enol ether moiety, yielded different δ- and ε-amino ketone derivatives, respectively, in moderate yields and diastereoselectivities. The application of these compounds in organic synthesis was demonstrated by the preparation of 2-substituted 6-methylpiperidines in a stereoselective manner, among them natural alkaloids (+)- and (−)-isosolenopsin A.

The N-propargylation of enantioenriched homopropargylic amine derivatives 3 proceeds in high yields under basic conditions. The resulting 4-azaocta-1,7-dynes 5 were transformed into 1,2,3,4-tetrahydrosioquinolines 7 bearing substituents at 3-, 6- and 7-positions, upon reaction with symmetrical alkynes, through a [2+2+2] cyclotrimerization promoted by Wilkinson catalyst. Ruthenium-catalyzed ring closing metathesis of azaocta-1,7-enynes 9a and 15a gave 1,3-dienes 10a and 16a, respectively, in high yields. Tetrahydroisoquinolines 12a and 18a, with a substitution pattern in the aromatic ring different to that of compounds 7, were prepared by a [4+2] cycloaddition of dimethyl acetylenedicarboxylate with dienes 10a and 16a, respectively.