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The use of immobilized metal-free catalysts offers the unique possibility to develop sustainable processes in flow mode. The challenging intermolecular organocatalyzed enantioselective alkylation of aldehydes was performed for the first time under continuous flow conditions. By using a packed-bed reactor filled with readily available supported enantiopure imidazolidinone, different aldehydes were treated with three distinct cationic electrophiles. In the organocatalyzed α-alkylation of aldehydes with 1,3-benzodithiolylium tetrafluoroborate, excellent enantioselectivities, in some cases even better than those obtained in the flask process (up to 95% ee at 25 °C), and high productivity (more than 3800 h(-1) ) were obtained, which thus shows that a catalytic reactor may continuously produce enantiomerically enriched compounds. Treatment of the alkylated products with Raney-nickel furnished enantiomerically enriched α-methyl derivatives, key intermediates for active pharmaceutical ingredients and natural products., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Dual photoredox catalysis is modifying the approach to sustainable metal catalysis based on metals in low oxidation state, as the use of stoichiometric metal as reductants are avoided. In this study, we showcase the potential use of vanadium in a dual photoredox process, allowing us to effectively control the formation of V(II) and its corresponding chemical reactions. A diastereoselective pinacol coupling with aromatic aldehydes is described. The process shows broad scope, and interestingly, unprotected salicylic aldehydes are compatible with the reaction protocol. Additionally, among all the ligands investigated we found that inexpensive bipyridines control the diastereoselection of the reaction favoring the d,l chiral compound (dr>20:1 for most of the aldehydes investigated). To promote the reaction and avoid an unproductive and not stereoselective radical coupling of the generated ketyl radical, the use of [DMQA]+, a stable organic dye, was found crucial. Furthermore, this dye possesses the remarkable capability of efficiently capturing light in the red segment of the visible spectrum, effectively raising efficiency of the protocol. The utilization of red light carries notable advantages in terms of penetration and safety, making it particularly significant. Moreover, careful photophysical investigations were able to give indications about the mechanism of the reaction. [ABSTRACT FROM AUTHOR]

For the first time, a dual photoredox‐ and titanocene‐catalyzed methodology for the regioselective access to α‐vinyl‐β‐hydroxy esters towards aldehyde allylation with 4‐bromobut‐2‐enoate is reported. The protocol is based on the Barbier‐type properties of the inexpensive and available Cp2TiCl2 in catalytic amount (5 mol%). The developed mild reaction conditions gave access to a library of differently functionalized α‐vinyl‐β‐hydroxy esters in moderate diastereoselectivity, employing the commercially available ethyl 4‐bromobut‐2‐enoate and both aromatic and aliphatic aldehydes. The reaction was realized under visible light irradiation, in the presence of an organophotocatalyst (3DPAFIPN, 2 mol%) combined with Hantzsch's ester as the sacrificial reductant. In contrast to other Barbier‐type reactions employing ethyl 4‐bromobut‐2‐enoate, the photoredox system ensures a better regioselectivity. Moreover, the use of preformed organometallic nucleophilic species (e. g. dienolborinates), and the need of metal reductants or stoichiometric amount of transition metals in low oxidation state for Barbier‐type reactions, is avoided. To support the experimental evidence, a detailed photophysical study shed light on the mechanism of the reaction. [ABSTRACT FROM AUTHOR]

A regioselective vinylation of aromatic and aliphatic aldehydes promoted by the merging of photoredox and nickel catalysis is here reported. A comprehensive investigation on the reaction conditions allowed the disclosure of a valid and reproducible protocol based on a nickel‐mediated reductive coupling approach under visible light irradiation. The employment of 3CzClIPN (2,4,6‐tris(carbazol‐9‐yl)‐5‐chloro‐isophthalonitrile) as the photocatalyst and Hantzsch's ester as the sacrificial organic reductant replace the use of boron‐, silicon‐ or zinc‐based reducing agents, making this method a worthy alternative to the already known protocols. The developed mild reaction conditions allow the access to a wide range of substituents decorating both the aldehyde and the alkyne. Moreover, careful photophysical investigations shed light on the mechanism of the reaction. [ABSTRACT FROM AUTHOR]

Organochromium(III) species are multipurpose nucleophiles used in the synthesis of complex organic molecules due to their high functional group tolerance and extraordinary chemoselectivity for aldehydes. The preparation of organochromium(III) species starting from organic halides requires the use of a stoichiometric amount of chromium(II) salts or a catalytic amount of chromium(III) salts in the presence of stoichiometric reductants (such as Mn(0)). Recently, radicals formation from readily available alkenes, followed by their trapping with stoichiometric or catalytic amount of chromium(II) salts were reported in photoredox conditions for the generation of Cr(III) organometallic species. In this paper we disclose a real Nozaki‐Hiyama reaction (NH) in which photoredox conditions enable the preparation of Cr(III) allyl reagents starting from available allyl halides and stable Cr(III) salts. [ABSTRACT FROM AUTHOR]

Here we report a practical, highly enantioselective photoredox allylation of aldehydes mediated by chiral nickel complexes with commercially available allyl acetate as the allylating agent. The methodology allows the clean stereoselective allylation of aldehydes in good to excellent yields and up to 93 % e.e. using a catalytic amount of NiCl2(glyme) in the presence of the chiral aminoindanol‐derived bis(oxazoline) as the chiral ligand. The photoredox system is constituted by the organic dye 3DPAFIPN and a Hantzsch's ester as the sacrificial reductant. The reaction proceeds under visible‐light irradiation (blue LEDs, 456 nm) at 8–12 °C. Compared to other published procedures, no metal reductants (such as Zn or Mn), additives (e.g. CuI) or air‐sensitive Ni(COD)2 are necessary for this reaction. Accurate DFT calculations and photophysical experiments have clarified the mechanistic picture of this stereoselective allylation reaction. [ABSTRACT FROM AUTHOR]

Organometallic allylic reagents are widely used in the construction of C−C bonds by Barbier‐type reactions. In this communication, we have described a photoredox Barbier allylation of aldehydes mediated by bismuth, in absence of other metals as co‐reductants. Mild reaction conditions, tolerance of oxygen, and use of aqueous solvent make this photoredox methodology attractive for green and sustainable synthesis of homoallylic alcohols. [ABSTRACT FROM AUTHOR]

The preparation of homoallylic alcohols by addition of organometallic allyl compounds to carbonyls is an important strategy in organic chemistry. Allylating organometallic cobalt species can be generated employing stoichiometric quantities of Zn acting as reductant. To avoid the employment of stoichiometric amount of Zn, we have developed an allylation reaction of aromatic and aliphatic aldehydes promoted by photoredox catalysis in the presence of a cobalt complex, and we present herein a full account of our research. In the presence of the abundant CoBr2 (10 mol %), 4,4′‐di‐tert‐butyl‐2,2′‐dipyridyl (dtbbpy, 10 mol %), allyl acetate (3 equiv.), [Ir(dtbbpy)(ppy)2]PF6 (ppy=2‐phenylpyridine, 2 mol %), and N,N‐diisopropylethylamine (4 equiv.), an allylation of aldehydes is taking place, in moderate to good yields. Substrates scope, limitations, and photophysical investigations of this new process are reported. [ABSTRACT FROM AUTHOR]

Here we report the application of dual nickel/photoredox catalysis to the allylation of aliphatic, aromatic and heteroaromatic aldehydes by using commercially available reagents. The process utilizes the combination of a Ni(ii) complex, [Ru(bpy)3]2+ as a photoredox catalyst, and allylacetate under blue LED irradiation, and allows the synthesis of a large variety of homoallylic alcohols. [ABSTRACT FROM AUTHOR]

A direct and simple activation of quinolines, without isolating unstable intermediates, or using isolated N,O-acetals in the presence of Lewis or Brønsted acids, is described. The procedure is quite straightforward and allows the addition in a stereoselective manner of different aldehydes to various differently substituted quinolines. The desired products were obtained in 28-76 % yields, with dr values up to 83:17 in favor of the syn isomer, and up to 99 % ee. Studies towards the use of acetaldehyde were also performed with different catalysts and the addition was promoted affording the desired product in 62 % yield with 46 % ee. Finally, deprotection and chemical transformations of the enantioenriched adducts were performed. [ABSTRACT FROM AUTHOR]

The combination of a practical and highly enantioselective organocatalytic reaction, which allows the stereoselective introduction of a benzodithiol group, with a fluorination step, gives a new and effective strategy for the stereoselective synthesis of difluorinated building blocks. The benzodithiol group is a versatile and chameleonic group that can be further functionalized before fluorination, giving customized and tailored useful synthetic strategies. As an example of the application of this facile strategy, the effective enantioselective synthesis of difluoroarundic acid is described. [ABSTRACT FROM AUTHOR]

Stable diarylcarbenium salts, obtained by the direct coupling of indole or indole derivatives with aryl (or heteroaryl) aldehydes in the presence of a strong organic Brønsted acid, have been employed in the direct alkylation of aldehydes. Excellent enantiomeric excesses and good diastereomeric ratios were obtained with a number of aryl or heteroaryl(3-indolyl)carbenium ions as the highly stable o-benzenedisulfonimide (OBS) salts and with the reaction promoted by the Hayashi-Jørgensen catalyst. A one-pot, three-component, stereoselective alkylation of aldehydes affording the same compounds was also investigated with various aldehydes, indole derivatives, and organocatalysts. The results obtained with the isolated carbenium ions were superior in terms of yields and stereoselectivity. [ABSTRACT FROM AUTHOR]

Cover Feature: A Photoredox Nozaki-Hiyama Reaction Catalytic in Chromium (Eur. J. Org. Keywords: Aldehydes; Allylbromide; Blue LED; Nozaki-Hiyama Reaction Photoredox catalysis EN Aldehydes Allylbromide Blue LED Nozaki-Hiyama Reaction Photoredox catalysis 1 1 1 08/09/22 20220805 NES 220805 B The Cover Feature b celebrates Japanese chemists Prof. Hitosi Nozaki and Prof. Tamejiro Hiyama, who discovered the Cr-mediated allyl addition to aldehydes. This work reports a catalytic photoredox version of the Nozaki-Hiyama reaction, without any problem related to the use of stoichiometric Mn or Zn as reducing agents....Mondai arimasen!. [Extracted from the article]

ABSTRACT Recently, the direct substitution of allylic, benzylic, and tertiary alcohols has been achieved via SN1-type reactions with catalytic amounts of Brønsted or Lewis acids. When a new stereogenic center is formed most of these transformations produce the desired product as a racemate, as these reactions proceed through carbenium ions. The arsenal of activation modes available in organocatalysis can be used to set up suitable reaction conditions in which chiral nucleophiles (enamine ) or chiral electrophiles (iminium , chiral counterion ) can easily be generated. Recently, we have used stabilized carbenium ions, directly available or obtained from the corresponding alcohols, in new organocatalytic SN1-type reactions. The commercially available carbenium ion benzodithiolylium tetrafluoroborate 1 can be used for the straightforward organocatalytic . In this account we will illustrate the application of this methodology in the total synthesis of natural products and the preparation of valuable starting materials. Chirality 26:607-613, 2014. © 2014 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

The stereoselective alkylation of aldehydes with benzodithiolylium tetrafluoborate gave a straightforward access to key compounds for the synthesis of fragrances and flavors. [ABSTRACT FROM AUTHOR]

New chiral perazamacrocycles containing four pyrrole rings have been synthesized by the [2 + 2] condensation of (R,R)-diaminocyclohexane and 5,5'-(alkane-2,2-diyl)bis(1H-pyrrole-2-carbaldehydes). These macrocycles, differing for the alkyl/aryl meso-substituents, were used as ligands in the copper-catalyzed Henry reactions of aromatic and aliphatic aldehydes with nitroalkanes. In the optimized experimental conditions, the condensations of nitromethane and aromatic and aliphatic aldehydes in the presence of catalytic amounts of copper diacetate and methyl-substituted macrocyclic ligand (2:1 ratio) in ethanol at room temperature provided products often with high enantiomeric excesses (up to 95% ee). The positive influence of the macrocyclic structure on the efficiency/enantioselectivity of the catalytic system was demonstrated by comparison with the outcomes of Henry reactions performed using analogous macrocyclic ligands (trianglamines) and open-chain ligands derived from (R,R)-diaminocyclohexane. [ABSTRACT FROM AUTHOR]

The Two Towers, of fruitful collaboration betweEN the teams of Margherita Barbero at Turin University (Turin, left) and Pier Giorgio Cozzi at Bologna University (Bologna, right) came together in their Full Paper on page 337 in describing a simple and affordable procedure for organocatalytic alkylations using stable and easily prepared o ‐ bENzENedisulfonimide salts of (3 ‐ indolyl)methylium carbENium ions. Normally these ions are oftEN used as precursors in organocatalysis and are gENerated in situ. Good yields of up to 95% and high ENantioselectivity of up to 97% accompany the procedure, which works with the commercially available Hayashi–JørgENsEN catalyst and a variety of aldehydes. [ABSTRACT FROM AUTHOR]

Bismuth and photoredox catalysis get married in this photoredox allylation reaction of aldehydes in aqueous solvent. The green reaction conditions (organic photoredox catalyst, available and not toxic metal, aqueous solvent) employed and the broad scope open new perspectives in the field of photoredox radical to polar cross over reactions. Keywords: Allylation; Aldehydes; Barbier reaction; Photoredox catalysis; Organic dyes EN Allylation Aldehydes Barbier reaction Photoredox catalysis Organic dyes 1623 1623 1 03/22/21 20210319 NES 210319 B The Front Cover b shows a Dream Wedding!. [Extracted from the article]

A representative number of bench-stable nonsymmetric diarylcarbenium tetrafluoroborates have been isolated via the direct coupling of aryl (or heteroaryl) aldehydes and N-heteroarenes and fully characterized. They have proven to be highly stable in the presence of both EDG and EWG substituents. An (E)-iminium vinylogous substructure has been shown as the common cation scaffold by X-ray analysis and by NOE determination. [ABSTRACT FROM AUTHOR]

A series of chiral alcohols (III), (V), and (VII) is prepared by a reaction of cationic electrophiles with aldehydes in a packed-bed reactor filled with a polymer-supported enantiopure imidazolidinone catalyst. [ABSTRACT FROM AUTHOR]