Selectivity control towards CO versus H₂ for photo-driven CO₂ reduction with a novel Co(II) catalyst

• Lisa-Lou Gracia,
• Philip Henkel,
• Olaf Fuhr and
• Claudia Bizzarri

Beilstein J. Org. Chem. 2023, 19, 1766–1775, doi:10.3762/bjoc.19.129

• , the system produced preferentially molecular hydrogen (Table 2, entry 2). The role of TEOA was studied thoroughly. In many cases, it is a suitable electron donor [47], however, for PS such as Cu(dmp)DPEPhos a higher reducing power is needed. Besides that, TEOA works not only as a Brønsted base

N-Sulfenylsuccinimide/phthalimide: an alternative sulfenylating reagent in organic transformations

• Fatemeh Doraghi,
• Seyedeh Pegah Aledavoud,
• Mehdi Ghanbarlou,
• Bagher Larijani and
• Mohammad Mahdavi

Beilstein J. Org. Chem. 2023, 19, 1471–1502, doi:10.3762/bjoc.19.106

• complex as a catalyst and a Brønsted base were applied in the procedure. It is interesting to note that in such a method, sulfenylation of NH-oxindoles resulted in the thiolated products with excellent enantioselectivities (up to 99% ee). In 2013, sulfenylation and chlorination of β-ketoesters 93, and 95

New advances in asymmetric organocatalysis

• Radovan Šebesta

Beilstein J. Org. Chem. 2022, 18, 240–242, doi:10.3762/bjoc.18.28

• transformations using chiral Brønsted acids, Brønsted base, and hydrogen bond donors. Recently noncovalent activation continues to expand into other types of weak attractive interactions such as halogen and chalcogen bonds. Not surprisingly, all activation modes allow further expansion and diversification via a

• cyclopropenimines exemplify Brønsted base organocatalysts that are useful for diverse reactions not easily accessible by other means. Here, Lambert and co-workers employed this type of catalyst in the formation of pyroglutamates via enantioselective Michael addition of amino ester imines [22]. Phase-transfer

α-Ketol and α-iminol rearrangements in synthetic organic and biosynthetic reactions

• Scott Benz and
• Andrew S. Murkin

Beilstein J. Org. Chem. 2021, 17, 2570–2584, doi:10.3762/bjoc.17.172

• . Subsequent methanolysis yields α-hydroxy-β-ketoamide 23 (Figure 6). The overall reaction occurs diastereospecifically, with greater than 80% yield across each of 5 distinct amide derivatives [8]. Tandem α-ketol rearrangements Because α-ketol rearrangements can be initiated by simple reagents like a Brønsted

• base or Lewis acid, the possibility exists to couple the rearrangement to other compatible reactions without any intervention. Such tandem reactions are attractive synthetic “tricks” that can allow for complex modifications with efficiency and often high selectivity. This short section introduces this

A novel methodology for the efficient synthesis of 3-monohalooxindoles by acidolysis of 3-phosphate-substituted oxindoles with haloid acids

• Li Liu,
• Yue Li,
• Tiao Huang,
• Dulin Kong and
• Mingshu Wu

Beilstein J. Org. Chem. 2021, 17, 2321–2328, doi:10.3762/bjoc.17.150

• rearrangement under Brønsted base catalysis and the subsequent acidolysis with haloid acids. The mild reaction conditions, simple operation, good yield, and readily available and inexpensive starting materials make this protocol a valuable method for the preparation of various 3-halooxindoles on a large-scale

Enantioenriched α-substituted glutamates/pyroglutamates via enantioselective cyclopropenimine-catalyzed Michael addition of amino ester imines

• Zara M. Seibel,
• Jeffrey S. Bandar and
• Tristan H. Lambert

Beilstein J. Org. Chem. 2021, 17, 2077–2084, doi:10.3762/bjoc.17.134

• substitution is discussed. Compared to other methods, this protocol allows for a broader and more enantioselective access to pyroglutamate derivatives. Keywords: Brønsted base; cyclopropenimine; enantioselective catalysis; Michael addition; pyroglutamate; Introduction α-Substituted glutamates have value as

An atom-economical addition of methyl azaarenes with aromatic aldehydes via benzylic C(sp³)–H bond functionalization under solvent- and catalyst-free conditions

• Divya Rohini Yennamaneni,
• Vasu Amrutham,
• Krishna Sai Gajula,
• Rammurthy Banothu,
• Murali Boosa and
• Narender Nama

Beilstein J. Org. Chem. 2020, 16, 3093–3103, doi:10.3762/bjoc.16.259

• mmol of 1a will inter react to another 1 mmol of 1a) and this inter reaction influences the nitrogen atom present in the compound to act as a Brønsted base. This resulting Brønsted base accepts benzylic C–H protons to furnish the respective enamine A, which facilitates the further nucleophilic addition

Visible-light-induced addition of carboxymethanide to styrene from monochloroacetic acid

• Kaj M. van Vliet,
• Nicole S. van Leeuwen,
• Albert M. Brouwer and
• Bas de Bruin

Beilstein J. Org. Chem. 2020, 16, 398–408, doi:10.3762/bjoc.16.38

• . However, the use of 2,6-lutidine gave a 32% yield. This could be caused by the reduced Brønsted base strength in apolar solvents. Thus, to avoid using a base that deprotonates monochloroacetic acid, we added sodium chloroacetate to capture HCl from the reaction. However, under these conditions the desired

β-Hydroxy sulfides and their syntheses

• Mokgethwa B. Marakalala,
• Edwin M. Mmutlane and
• Henok H. Kinfe

Beilstein J. Org. Chem. 2018, 14, 1668–1692, doi:10.3762/bjoc.14.143

• the thiolysis of alkyl and aryl epoxides under solvent-free conditions with 5 mol % of catalyst loading, the activity was highly dependent of the nature of the acid or base catalyst employed. The Lewis acid InCl3 and the Brønsted base K2CO3 provided superior yields and reaction rates in comparison to

Reagent-controlled regiodivergent intermolecular cyclization of 2-aminobenzothiazoles with β-ketoesters and β-ketoamides

• Irwan Iskandar Roslan,
• Kian-Hong Ng,
• Gaik-Khuan Chuah and
• Stephan Jaenicke

Beilstein J. Org. Chem. 2017, 13, 2739–2750, doi:10.3762/bjoc.13.270

• and amides have been developed, controlled by the reagents employed. With the Brønsted base KOt-Bu and CBrCl3 as radical initiator, benzo[d]imidazo[2,1-b]thiazoles are synthesized via attack at the α-carbon and keto carbon of the β-ketoester moiety. In contrast, switching to the Lewis acid catalyst

• ][21][22]. Interestingly, by replacing the radical initiator and Brønsted base system with a Lewis acid catalyst, benzo[4,5]thiazolo[3,2-a]pyrimidin-4-ones were formed instead (Scheme 1b). This highlights the versatility of β-ketoesters where the regioselectivity of the reaction is directed by the

• reagents. With the Brønsted base and radical initiator system of KOt-BU/CBrCl3, in situ α-bromination occurs and nucleophilic attacks at the α-carbon and keto carbon lead to the formation of benzo[d]imidazo[2,1-b]thiazoles. On the other hand, the Lewis acidic catalyst In(OTf)3 allows for nucleophilic

A Brønsted base-promoted diastereoselective dimerization of azlactones

• Danielle L. J. Pinheiro,
• Gabriel M. F. Batista,
• Pedro P. de Castro,
• Leonã S. Flores,
• Gustavo F. S. Andrade and
• Giovanni W. Amarante

Beilstein J. Org. Chem. 2017, 13, 2663–2670, doi:10.3762/bjoc.13.264

• Brønsted base system for the diastereoselective dimerization of azlactones using trichloroacetate salts and acetonitrile has been developed. Desired products were obtained in good yields (60–93%) and with up to >19:1 dr after one hour of reaction. Additionally, the relative stereochemistry of the major

Phosphazene-catalyzed desymmetrization of cyclohexadienones by dithiane addition

• Matthew A. Horwitz,
• Elisabetta Massolo and
• Jeffrey S. Johnson

Beilstein J. Org. Chem. 2017, 13, 762–767, doi:10.3762/bjoc.13.75

• in principle provide access to highly functionalized products with orthogonally protected carbonyl groups in a novel glycolic acid scaffold. We envisioned utilizing para-quinol derivatives featuring a tethered nucleophile as desymmetrization substrates, with the intention of implementing a Brønsted

• base organocatalyzed addition (Scheme 1). This reaction would lead to bicyclic systems with the salient attribute of having a convex-concave facial differentiation, allowing subsequent diastereoselective transformations. With the aim of using a dithiane nucleophile, we selected 1,3-dithiane-2

Highly chemo-, enantio-, and diastereoselective [4 + 2] cycloaddition of 5H-thiazol-4-ones with N-itaconimides

• Shuai Qiu,
• Choon-Hong Tan and
• Zhiyong Jiang

Beilstein J. Org. Chem. 2016, 12, 2293–2297, doi:10.3762/bjoc.12.222

• /bjoc.12.222 Abstract A dipeptide-based urea-amide tertiary amine (DP-UAA) was shown to be an effective Brønsted base catalyst for the first asymmetric annulation reaction between 5H-thiazol-4-ones and N-itaconimides. High levels of enantioselectivity (up to 99% ee) and diastereoselectivity (>19:1 dr

A chiral analog of the bicyclic guanidine TBD: synthesis, structure and Brønsted base catalysis

• Mariano Goldberg,
• Denis Sartakov,
• Jan W. Bats,
• Michael Bolte and
• Michael W. Göbel

Beilstein J. Org. Chem. 2016, 12, 1870–1876, doi:10.3762/bjoc.12.176

• countless applications [2][3]. The bicylic guanidine 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD, 1, Figure 1) [4], another important Brønsted base in preparative chemistry, may also act as a powerful nucleophilic catalyst [3]. Substituted analogs of TBD [5], such as the chiral compound 2, have become popular

• control exerted by 10 when used as a catalyst. In this article we describe the synthesis of guanidine 10 together with some initial applications as a chiral Brønsted base. Results and Discussion Previous syntheses of bicylic guanidines 2 and 6–9 started from enantiomerically pure α-amino acids [6][8][10

• molecule are also connected by a number of very weak intermolecular C–H···π (phenyl) and C–H···O contacts (see Supporting Information File 2). The chiral guanidine 10 was tested as a Brønsted base catalyst to promote the reaction of anthrones 20 or 21 with maleimides 22–24 (Scheme 2) [19][25][26][27][28

Development of chiral metal amides as highly reactive catalysts for asymmetric [3 + 2] cycloadditions

• Yasuhiro Yamashita,
• Susumu Yoshimoto,
• Mark J. Dutton and
• Shū Kobayashi

Beilstein J. Org. Chem. 2016, 12, 1447–1452, doi:10.3762/bjoc.12.140

• biologically active compounds are particularly important. Chiral Lewis acid/Brønsted base-catalyzed carbon–carbon bond-forming reactions are one of the most efficient methods from the viewpoint of atom economy because only proton transfer occurs between starting materials and target products [2]. Several kinds

• of chiral Lewis acid/Brønsted base-catalyst systems have been developed; however, decreasing the catalyst loading is sometimes problematic either because of the low reactivity of catalysts or because the catalyst activity can be reduced through Lewis acid–Lewis base interaction between catalysts and

Towards the total synthesis of keramaphidin B

• Pavol Jakubec,
• Alistair J. M. Farley and
• Darren J. Dixon

Beilstein J. Org. Chem. 2016, 12, 1096–1100, doi:10.3762/bjoc.12.104

• nitroolefin 9 under the control of a cinchona-derived bifunctional Brønsted base/H-bond donor organocatalyst developed in our group and others [16][17][18][19]. Bifunctional organocatalysed Michael addition studies In our previous total syntheses of nakadomarin A [5][7][20] and manzamine A [10] the

• hydroxypropyl chain attached to the quaternary stereocentre, poised for further functionalisation. Having established that the cinchonine-derived bifunctional Brønsted base/thiourea organocatalyst 12 was effective for installing two stereocentres including the quaternary carbon in a model system, we next

1H-Imidazol-4(5H)-ones and thiazol-4(5H)-ones as emerging pronucleophiles in asymmetric catalysis

• Antonia Mielgo and
• Claudio Palomo

Beilstein J. Org. Chem. 2016, 12, 918–936, doi:10.3762/bjoc.12.90

• inherent lower reactivity and the limitations associated to the activation/coordination of these compounds to a suitable chiral catalyst. Although recently it has been shown that the problem of this low reactivity may be addressed through the development of Brønsted base catalysts with increased basicity

• published [73]. This study shows that α’-oxyenones are very efficient key enoate equivalents in Brønsted base-catalyzed asymmetric conjugate addition of a range of soft nucleophiles such as α-substituted oxindoles, cyanoesters, oxazolones, azlactones and thiazolones to afford the corresponding

• reactions. 2.2.1 Michael addition reactions, nitroalkenes as acceptors. The first example of the utility of the thiazol-4(5H)-ones 2 as pronucleophiles in asymmetric catalysis was reported in 2013 in the Michael addition to nitroalkenes catalyzed by the bifunctional ureidopeptide-like Brønsted base C5

Stereoselective amine-thiourea-catalysed sulfa-Michael/nitroaldol cascade approach to 3,4,5-substituted tetrahydrothiophenes bearing a quaternary stereocenter

• Sara Meninno,
• Chiara Volpe,
• Giorgio Della Sala,
• Amedeo Capobianco and
• Alessandra Lattanzi

Beilstein J. Org. Chem. 2016, 12, 643–647, doi:10.3762/bjoc.12.63

• increased to 50% ee for diastereoisomer 7a when using chlorobenzene as the solvent at room temperature (Table 2, entry 5). It is worth noting that bifunctional organocatalyst VII appears to be more effective in terms of diastereocontrol than previously employed Brønsted base/Lewis acid system TMG/ZnI2

• tetrahydrothiophenes, bearing a quaternary stereocenter, in good yield and moderate enantiocontrol. It has been demonstrated that a simple bifunctional amine thiourea secures a more effective control of the diastereoselectivity than Brønsted base/Lewis acid systems. Data herein illustrated suggest that fine tuning of

Recent advances in N-heterocyclic carbene (NHC)-catalysed benzoin reactions

• Rajeev S. Menon,
• Akkattu T. Biju and
• Vijay Nair

Beilstein J. Org. Chem. 2016, 12, 444–461, doi:10.3762/bjoc.12.47

• the combination of NHC 24 and a Brønsted base (4-methoxyphenolate) promoted a formal dimerisation of 2-(aroylvinyl)arylaldehydes 70 to afford benzo[a]tetrahydrofluorenones 71 [60]. This stereoselective reaction proceeds via a benzoin–Michael–Michael cascade process (Scheme 43). Further investigations

• enals and β-oxo sulfones. Intramolecular benzoin condensation of carbohydrate-derived dialdehydes. Enantioselective intramolecular benzoin reactions of N-tethered keto-aldehydes. Asymmetric cross-benzoin reactions promoted by camphor-derived catalysts. NHC-Brønsted base co-catalysis in a benzoin–Michael

Convenient preparation of high molecular weight poly(dimethylsiloxane) using thermally latent NHC-catalysis: a structure-activity correlation

• Stefan Naumann,
• Johannes Klein,
• Dongren Wang and
• Michael R. Buchmeiser

Beilstein J. Org. Chem. 2015, 11, 2261–2266, doi:10.3762/bjoc.11.246

• effective preparation of PDMS, including high molecular weight polymers. The results of a screening of a range of different NHCs indicate that a nucleophilic action of the organocatalyst is preferred over action as a Brønsted base. Comparison of conversion over time for D4 polymerization (80 °C, bulk) using

Diastereoselective and enantioselective conjugate addition reactions utilizing α,β-unsaturated amides and lactams

• Katherine M. Byrd

Beilstein J. Org. Chem. 2015, 11, 530–562, doi:10.3762/bjoc.11.60

• /hard Brønsted base/hard Lewis base cooperative catalysis system, a strategy that has been used in other reactions [193][194][195][196] (Scheme 22). In the case of the reaction above, the alkynylide was generated from [Cu(CH3CN)4]PF6, (R)-3,5-iPr-4-Me2N-MeOBIPHEP, and Li(OC6H4-p-OMe) [197][198]. The

• agonist AMG 837 [199]. Shibasaki and co-workers expanded their application of soft Lewis acid/hard Brønsted base cooperative catalysis to the asymmetric vinylogous conjugate addition of α,β-unsaturated butyrolactones to α,β-unsaturated thioamides [200]. This reaction provides a method for producing

First chemoenzymatic stereodivergent synthesis of both enantiomers of promethazine and ethopropazine

• Paweł Borowiecki,
• Daniel Paprocki and
• Maciej Dranka

Beilstein J. Org. Chem. 2014, 10, 3038–3055, doi:10.3762/bjoc.10.322

• same token, another catalytic approach using solid Ag2O was adopted in accordance to a method proposed by D'Angeli et al. [82]. Since the authors of this report suggested that solid Ag2O behaves as both a Lewis acid and Brønsted base acting synergically on the investigated 2-bromo amides, we have

Superoxide chemistry revisited: synthesis of tetrachloro-substituted methylenenortricyclenes

• Basavaraj M. Budanur and
• Faiz Ahmed Khan

Beilstein J. Org. Chem. 2014, 10, 2531–2538, doi:10.3762/bjoc.10.264

• reactivity with different functionalities. Jiang and co-workers [25] used KO2 as an alternative oxidation reagent in a Winterfeldt reaction instead of O2/KOt-Bu and many others reported reactions of superoxide which acts as oxidant, reductant, oxygen nucleophile, or Brønsted base. However, the full potential

Electrocarboxylation: towards sustainable and efficient synthesis of valuable carboxylic acids

• Roman Matthessen,
• Jan Fransaer,
• Koen Binnemans and
• Dirk E. De Vos

Beilstein J. Org. Chem. 2014, 10, 2484–2500, doi:10.3762/bjoc.10.260

• near the site(s) where reduction will occur. The electrogenerated base must be a strong enough Brønsted base to deprotonate the weakly acidic hydrocarbon group. Ethenetetracarboxylate tetraesters are typical base precursors, suited for the electrocarboxylation of N-alkyldiglycolimides (Scheme 22). This

New hydrogen-bonding organocatalysts: Chiral cyclophosphazanes and phosphorus amides as catalysts for asymmetric Michael additions

• Helge Klare,
• Jörg M. Neudörfl and
• Bernd Goldfuss

Beilstein J. Org. Chem. 2014, 10, 224–236, doi:10.3762/bjoc.10.18

• , squaramide and phosphor-diamide-based catalysts [43][44][45]. The BINOL-based catalysts 1 and 2 (Scheme 1) without Brønsted base functional group are both ineffective and only traces of the product could be isolated even after prolonged reaction times (Table 2). In contrast, catalyst 4, derived directly from