N-tert-Butanesulfinyl imines in the asymmetric synthesis of nitrogen-containing heterocycles

• Joseane A. Mendes,
• Paulo R. R. Costa,
• Miguel Yus,
• Francisco Foubelo and
• Camilla D. Buarque

Beilstein J. Org. Chem. 2021, 17, 1096–1140, doi:10.3762/bjoc.17.86

• ) [105]. Li and Xu reported a method for the enantioselective synthesis of β,γ-unsaturated α-amino acids 100, by a Lewis acid-promoted diastereoselective Petasis reaction of vinylboronic acids 98, (R)-N-tert-butanesulfinamide and glyoxylic acid (99). They found that the best results were obtained working

• with InBr3 as Lewis acid, in dichloromethane at room temperature [106]. Under these reaction conditions, sulfinyl imine is formed first along with the boronate by interaction of the corresponding vinylboronic acid with the carboxylic group of the imino acid intermediate. The transfer of the vinyl unit

• to the electrophilic iminic carbon took place in a quite rigid system, with chelation of the Lewis acid with the nitrogen of the imine and carboxylate oxygen, forming a five-membered ring. The migration of the vinyl group occurred to the Re face of the imine, which is less shielded than the Si face

Synthetic accesses to biguanide compounds

• Oleksandr Grytsai,
• Cyril Ronco and
• Rachid Benhida

Beilstein J. Org. Chem. 2021, 17, 1001–1040, doi:10.3762/bjoc.17.82

• benzoxazoles might be explained by the subsequent hydrolysis of this relatively fragile ring under the strongly acidic aqueous conditions. Recently, a protocol using a Lewis acid (AlCl3) as an activating agent of the cyanoguanidine in dry THF allowed improving the yields up to 70% (Scheme 11B) [32]. Related

• 90% yield. A Lewis acid-promoted cyclization (boron trifluoride etherate at 60 °C) avoided the use of high temperatures, while providing the products in comfortable yields. Dicyanamide has also been shown to react with hydroxylamine hydrochloride to form [1,2,4]oxadiazole-3,5-diamine (Scheme 29A) [49

• substituted cyanoguanidine as the intermediate. Practically, very little improvement was made over synthetic procedures reported 50 years ago. To the best of our knowledge modern activations such as Lewis acid-promoted additions, catalysis or microwave irradiation have never been tried for this reaction

Synthesis of 10-O-aryl-substituted berberine derivatives by Chan–Evans–Lam coupling and investigation of their DNA-binding properties

• Peter Jonas Wickhorst,
• Mathilda Blachnik,
• Denisa Lagumdzija and
• Heiko Ihmels

Beilstein J. Org. Chem. 2021, 17, 991–1000, doi:10.3762/bjoc.17.81

• products 4b–f was available in low yields (16–26%) by the Chan–Evans–Lam coupling of berberrubine (1b, Scheme 1). The formation of the 10-O-arylated products may be explained by an initial Lewis acid-catalyzed demethylation of berberrubine (1b) [38] to derivative 6 (Scheme 2) that reacts subsequently in

Metal-free glycosylation with glycosyl fluorides in liquid SO₂

• Krista Gulbe,
• Jevgeņija Lugiņina,
• Edijs Jansons,
• Artis Kinens and
• Māris Turks

Beilstein J. Org. Chem. 2021, 17, 964–976, doi:10.3762/bjoc.17.78

• , Riga, LV-1006, Latvia Department of Chemistry, University of Latvia, Jelgavas str. 1, Riga, LV-1004, Latvia 10.3762/bjoc.17.78 Abstract Liquid SO2 is a polar solvent that dissolves both covalent and ionic compounds. Sulfur dioxide possesses also Lewis acid properties, including the ability to

• equilibrium. Keywords: fluorosulfite; glycosyl fluoride; Lewis acid; liquid sulfur dioxide; metal-free glycosylation; Introduction The glycosylation reaction is still one of the most important and basic synthetic strategies in carbohydrate chemistry that provides access to the various types of

• conventional solvents are: (1) it is aprotic solvent with Lewis acid properties; (2) it dissolves both covalent and ionic compounds [39]; (3) it has good price–quality ratio: ≤5 EUR/kg for the high-purity product (99.98%, H2O content ≤50 ppm); (4) it can be easily recycled by changing temperature and/or

Prins cyclization-mediated stereoselective synthesis of tetrahydropyrans and dihydropyrans: an inspection of twenty years

• Asha Budakoti,
• Pradip Kumar Mondal,
• Prachi Verma and
• Jagadish Khamrai

Beilstein J. Org. Chem. 2021, 17, 932–963, doi:10.3762/bjoc.17.77

• Lewis acid, which furnished the expected tetrahydropyran 23 as a single diastereomer via an oxocarbenium intermediate 21 (Scheme 5) [29][30]. The reaction was dependent from the nature of the aromatic ring, which plays a crucial role in the product formation. Homoallylic alcohols with an electron-rich

• ][33]. The racemization occurs during allyl transfer as a result of 2-oxonia-Cope rearrangement through a 3,3-sigmatropic shift, which plays a crucial role during the reaction, as shown in Scheme 7. The Prins cyclization between alcohol (R)-35 and aldehyde 36 was investigated under different Lewis acid

• a 2-oxonia-Cope-mediated side-chain exchange reaction and is entirely consistent with Willis and co-workers’ result [29], which leads to the partial racemization observed in the desired product formation. Another Lewis acid, SnBr4, was found to be more efficient than BF3·OEt2/HOAc in terms of

Microwave-assisted multicomponent reactions in heterocyclic chemistry and mechanistic aspects

• Shivani Gulati,
• Stephy Elza John and
• Nagula Shankaraiah

Beilstein J. Org. Chem. 2021, 17, 819–865, doi:10.3762/bjoc.17.71

• between benzimidazole-linked aminopyridine and Lewis acid activated aldehyde which further on nucleophilic addition with substituted isocyanide leads to intermediate B. A 5-exo-dig intramolecular cyclization with isocyanide aids in the formation of the imidazo[1,2-a]pyridine intermediate C. The final

α,γ-Dioxygenated amides via tandem Brook rearrangement/radical oxygenation reactions and their application to syntheses of γ-lactams

• Mikhail K. Klychnikov,
• Radek Pohl,
• Ivana Císařová and
• Ullrich Jahn

Beilstein J. Org. Chem. 2021, 17, 688–704, doi:10.3762/bjoc.17.58

• γ-lactam scaffold [40][41][42][43][44]. The pyrrolidinone fragment is often synthesized by transition metal- [45][46][47][48][49][50] or Lewis acid-catalyzed cyclization reactions [51][52][53][54]. The Diels–Alder reaction can also be used for the preparation of functionalized γ-lactams in a single

Synthesis, structural characterization, and optical properties of benzo[f]naphtho[2,3-b]phosphoindoles

• Mio Matsumura,
• Takahiro Teramoto,
• Masato Kawakubo,
• Masatoshi Kawahata,
• Yuki Murata,
• Kentaro Yamaguchi,
• Masanobu Uchiyama and
• Shuji Yasuike

Beilstein J. Org. Chem. 2021, 17, 671–677, doi:10.3762/bjoc.17.56

• phosphorus center can be easily chemically modified and converted to phosphole derivatives with different electronic properties by reactions such as oxidation, alkylation, and coordination to a Lewis acid [1][2][3][4][5][6][7][8]. Theoretically, pentacyclic benzonaphthophosphindole contains six structural

Valorisation of plastic waste via metal-catalysed depolymerisation

• Francesca Liguori,
• Carmen Moreno-Marrodán and
• Pierluigi Barbaro

Beilstein J. Org. Chem. 2021, 17, 589–621, doi:10.3762/bjoc.17.53

• supported metal species (Ru, Ir), due to the ability to activate molecular hydrogen, functioning as redox centres. The mechanisms of the metal-catalysed solvolytic reactions of plastics are all very similar and typical of conventional organic processes: a metal ion acts as Lewis acid centre for the

• weight ratio of 35 was required. The catalyst could be reused, showing significant activity decrease starting from the fourth cycle due to biochar formation. A mechanism was hypothesised in which Zn2+ ions act as a Lewis acid activator for the carbonyl ester bond. In a previous work, complete

• which Zn ions act as Lewis acid activators for the C=O ester bonds toward nucleophilic attack by EG. In addition to soluble catalysts, metal-containing insoluble materials, namely solid acid catalysts, were developed for the glycolytic depolymerisation of PET by EG. Representative data are summarised in

CF₃-substituted carbocations: underexploited intermediates with great potential in modern synthetic chemistry

• Anthony J. Fernandes,
• Armen Panossian,
• Bastien Michelet,
• Agnès Martin-Mingot,
• Frédéric R. Leroux and
• Sébastien Thibaudeau

Beilstein J. Org. Chem. 2021, 17, 343–378, doi:10.3762/bjoc.17.32

• also confirmed by DFT calculations at the B3LYP/6-31G* level, with a C2–C3 bond considerably shorter than the C1–C2 bond, with dC2–C3 = 1.359 Å and dC1–C2 = 1.427 Å. More recently, Vasilyev et al. reported that Lewis acid activation of α-(trifluoromethyl)allyl alcohol 101 allowed the transient

• a longer reaction time, allenes 127 undergo a subsequent intramolecular hydroarylation reaction leading to indenes 128. The authors suggested the formation of FeCl3–HFIP complexes being involved in a Lewis acid-assisted Brønsted acid catalysis. The CF3-substituted propargyl alcohol 129 was found to

• ↔142’ (Scheme 35). Oxygen-stabilized α-(trifluoromethyl)carbenium ions (oxocarbenium ions) have been exploited for chemical synthesis [92][93][94]. Ketone 143a and ketoxime 143b undergo Friedel–Crafts reactions in the presence of Brønsted or Lewis acid to furnish the corresponding CF3-containing

The preparation and properties of 1,1-difluorocyclopropane derivatives

• Kymbat S. Adekenova,
• Peter B. Wyatt and
• Sergazy M. Adekenov

Beilstein J. Org. Chem. 2021, 17, 245–272, doi:10.3762/bjoc.17.25

• imines 115, which led to alkylideneazetidines 116 (Scheme 52) [102]. The MgI2 acted as a Lewis acid and reducing agent, effecting the distal C–C bond cleavage in 113a to form an allenyl ketone, or an equivalent fluoro,iodo-enone species, either of which could then have added to the imine 115 and led to

• O–H and N–H bonds of water, alcohols, carboxylic acids, and amines to form the observed products 121. 1,1-Difluoro-2-siloxy-2-vinylcyclopropane (122) was subjected to a fluoride-catalyzed ring opening to afford 1-fluorovinyl vinyl ketones such as 123. These compounds underwent a Lewis acid-catalyzed

• , Br, Scheme 63) [114]. In this transformation, BX3 played a dual role as both a Lewis acid catalyst and a source of the halide ion nucleophile. This reaction resulted in the generation of the trifluoromethyl ketones 145 and halodifluoromethyl ketones 146 and 147 in high yields. As in the previous

Total synthesis of decarboxyaltenusin

• Lucas Warmuth,
• Aaron Weiß,
• Marco Reinhardt,
• Anna Meschkov,
• Ute Schepers and
• Joachim Podlech

Beilstein J. Org. Chem. 2021, 17, 224–228, doi:10.3762/bjoc.17.22

• Lewis acid, while the utilization of 1.5 equivalents led to a significant overreaction with the predominant formation of 5-bromobenzene-1,3-diol (59%) together with a smaller amount of the required product 8 (30%). The subsequent protection with the TBS group yielded the known aryl bromide 9a [24] with

Direct synthesis of anomeric tetrazolyl iminosugars from sugar-derived lactams

• Michał M. Więcław and
• Bartłomiej Furman

Beilstein J. Org. Chem. 2021, 17, 115–123, doi:10.3762/bjoc.17.12

• , even at an elevated temperature. Path A with a barrier of 22.6 kcal·mol−1 is certainly more feasible. We assume that the Cp2Zr(OH)Cl species just leaves the initial complex, as this seems to be the simplest possibility in absence of any Lewis acid which could catalyze this decomposition. Scheme 9 shows

Pentannulation of N-heterocycles by a tandem gold-catalyzed [3,3]-rearrangement/Nazarov reaction of propargyl ester derivatives: a computational study on the crucial role of the nitrogen atom

• Giovanna Zanella,
• Martina Petrović,
• Dina Scarpi,
• Ernesto G. Occhiato and
• Enrique Gómez-Bengoa

Beilstein J. Org. Chem. 2020, 16, 3059–3068, doi:10.3762/bjoc.16.255

• piperidine derivatives 1 because of the accelerating effect of the nitrogen atom that stabilizes the oxyallyl cation intermediate 4 formed upon the ring closure. This was in analogy to that found for the classical Brønsted or Lewis acid-catalyzed Nazarov reaction involving N-heterocycles [27][28][29][30][31

All-carbon [3 + 2] cycloaddition in natural product synthesis

• Zhuo Wang and
• Junyang Liu

Beilstein J. Org. Chem. 2020, 16, 3015–3031, doi:10.3762/bjoc.16.251

• product 145 in 76% yield. The hexacyclic compound 145 was converted to kopsanone (19) in three steps. Miscellaneous In 2012, Wang and co-workers reported a Lewis acid-catalyzed intramolecular [3 + 2] cross-cycloaddition (IMCC) of cyclopropane 1,1-diesters with non-activated alkene to generate bridged [n

• mechanism. (C) The completion of total synthesis of kopsanone (19). (A) Synthesis of phyllocladanol (21) features a Lewis acid-catalyzed formal intramolecular [3 + 2] cross-cycloaddition of cyclopropane 1,1-diesters with alkenes [68]. (B) (5,6-Dihydro-1,4-dithiin-2-yl)methanol 151 used as a versatile allyl

Three-component reactions of aromatic amines, 1,3-dicarbonyl compounds, and α-bromoacetaldehyde acetal to access N-(hetero)aryl-4,5-unsubstituted pyrroles

• Wenbo Huang,
• Kaimei Wang,
• Ping Liu,
• Minghao Li,
• Shaoyong Ke and
• Yanlong Gu

Beilstein J. Org. Chem. 2020, 16, 2920–2928, doi:10.3762/bjoc.16.241

• -bromoacetaldehyde acetal by using aluminum(III) chloride as a Lewis acid catalyst through [1 + 2 + 2] annulation. This new versatile methodology provides a wide scope for the synthesis of different functional N-(hetero)aryl-4,5-unsubstituted pyrrole scaffolds, which can be further derived to access multisubstituted

• under the conditions; the obtained results are listed in Table 1. The mixture was heated in 1,4-dioxane at 80 °C. No reaction occurred in the absence of the catalyst (Table 1, entry 1); however, in the presence of the strong Lewis acid Bi(OTf)3, the expected product 4a was obtained in 36% yield after 6

Selective and reversible 1,3-dipolar cycloaddition of 6-aryl-1,5-diazabicyclo[3.1.0]hexanes with 1,3-diphenylprop-2-en-1-ones under microwave irradiation

• Alexander P. Molchanov,
• Mariia M. Efremova,
• Mariya A. Kryukova and
• Mikhail A. Kuznetsov

Beilstein J. Org. Chem. 2020, 16, 2679–2686, doi:10.3762/bjoc.16.218

• that the Lewis acid-catalyzed reaction of diaziridines with donor–acceptor cyclopropanes and aziridines affords the perhydropyridazine or triazine derivatives, respectively, in good yields [31][32][33]. The use of microwave irradiation in organic synthesis complies with the principles of green

Recent developments in enantioselective photocatalysis

• Callum Prentice,
• James Morrisson,
• Andrew D. Smith and
• Eli Zysman-Colman

Beilstein J. Org. Chem. 2020, 16, 2363–2441, doi:10.3762/bjoc.16.197

• desired products 267 or 268 in moderate yields and enantioselectivities (3 examples, up to 75:25 er for 267 and 2 examples, up to 68:32 er for 268). Lewis acid catalysis Lewis acids have been known for decades to activate carbonyl compounds through the formation of coordination complexes that increases

• likely operates via a radical chain mechanism. Initiation begins with the reductive quenching of the photocatalyst using iPr2NEt as a sacrificial reductant to give [Ru]•−, which then reduces the Lewis acid-coordinated enone 271 to give alkyl radical 271•. In the presence of a second enone 270 and chiral

• chiral ligand L3 (Scheme 44a) [109]. The putative mechanism proceeds via a reductive quenching cycle to give nucleophilic α-amino radicals 277•, which can add to the β-position of Lewis acid complex 280 to give the α-carbonyl radical 280•. Instead of a cyclisation, this radical is then reduced by the

Hierarchically assembled helicates as reaction platform – from stoichiometric Diels–Alder reactions to enamine catalysis

• David Van Craen,
• Jenny Begall,
• Johannes Großkurth,
• Leonard Himmel,
• Oliver Linnenberg,
• Elisabeth Isaak and
• Markus Albrecht

Beilstein J. Org. Chem. 2020, 16, 2338–2345, doi:10.3762/bjoc.16.195

• auxiliary, Lewis acid or catalyst. In the previously reported system two different induction pathways were conceivable: (1) A chiral ligand is located close to the diene and controls the stereochemistry of the cycloaddition. (2) The chiral ligand controls the helicity of the helicate (ΔΔ or ΛΛ) and the

Efficient [(NHC)Au(NTf₂)]-catalyzed hydrohydrazidation of terminal and internal alkynes

• Maximillian Heidrich and
• Herbert Plenio

Beilstein J. Org. Chem. 2020, 16, 2080–2086, doi:10.3762/bjoc.16.175

• (Table 2). The obvious consequence being a decrease in the substrate conversion. This, however, could be compensated to some extent by longer reaction times. Based on this observation catalyst decomposition appeared to be negligible and it seemed, that the role of gold is primarily that of a Lewis acid

Reactions of 3-aryl-1-(trifluoromethyl)prop-2-yn-1-iminium salts with 1,3-dienes and styrenes

• Thomas Schneider,
• Michael Keim,
• Bianca Seitz and
• Gerhard Maas

Beilstein J. Org. Chem. 2020, 16, 2064–2072, doi:10.3762/bjoc.16.173

• with cyclic enol ethers [49] and of other very electrophilic alkynes (i.e., Lewis acid-activated acetylenic esters [50], 1-(trifluoroacetyl)-3-haloacetylenes [44] and 4-chloro-2-oxobut-3-ynoic esters [51][52][53] with unactivated alkenes (including cyclohexene [51], which did not react with 1a). For

Controlling the stereochemistry in 2-oxo-aldehyde-derived Ugi adducts through the cinchona alkaloid-promoted electrophilic fluorination

• Yuqing Wang,
• Gaigai Wang,
• Anatoly A. Peshkov,
• Ruwei Yao,
• Muhammad Hasan,
• Manzoor Zaman,
• Chao Liu,
• Stepan Kashtanov,
• Olga P. Pereshivko and
• Vsevolod A. Peshkov

Beilstein J. Org. Chem. 2020, 16, 1963–1973, doi:10.3762/bjoc.16.163

• stereocontrol was achieved with the aid of different Lewis acid promoters bearing chiral ligands, while the most recent and at the same time the most general procedure developed by Liu, Tan and co-workers relied on the stereoinduction by a chiral phosphoric acid (Table 1) [40]. In the standard Ugi four

Selective preparation of tetrasubstituted fluoroalkenes by fluorine-directed oxetane ring-opening reactions

• Clément Q. Fontenelle,
• Thibault Thierry,
• Romain Laporte,
• Emmanuel Pfund and
• Thierry Lequeux

Beilstein J. Org. Chem. 2020, 16, 1936–1946, doi:10.3762/bjoc.16.160

• already reported in the literature from oxetane-containing α,β-unsaturated carbonyl derivatives through a Lewis acid-catalyzed rearrangement [31]. When the previous conditions (HBr/AcOH) were tried (3.5 h, 0 °C to 20 °C), hydroxymethyllactone 14 (87%, Table 4, entry 1) was the main product with traces of

When metal-catalyzed C–H functionalization meets visible-light photocatalysis

• Lucas Guillemard and
• Joanna Wencel-Delord

Beilstein J. Org. Chem. 2020, 16, 1754–1804, doi:10.3762/bjoc.16.147

• catalysis with a second catalytic system has sparked significant interest from the scientific community. Accordingly, numerous unprecedented reactions involving photoredox catalysis in synergy with other activation modes including Brønsted/Lewis acid catalysis, organocatalysis, enzymatic biocatalysis, or

Pauson–Khand reaction of fluorinated compounds

• Jorge Escorihuela,
• Daniel M. Sedgwick,
• Alberto Llobat,
• Mercedes Medio-Simón,
• Pablo Barrio and
• Santos Fustero

Beilstein J. Org. Chem. 2020, 16, 1662–1682, doi:10.3762/bjoc.16.138

• concomitant detrifluoromethylation. Furthermore, the Lewis acid-mediated retro Diels–Alder reaction was carried out uneventfully on product 61, affording the corresponding cyclopentenone 62 in moderate yield (Scheme 33). In order to rationalize the unexpected loss of the trifluoromethyl group upon

• conjugated addition of trimethylaluminum to form 66, followed by Lewis acid-mediated retro Diels–Alder reaction (Scheme 38). In another study by Riera and co-workers, they studied the influence of the olefin counterpart on the regioselectivity of the reaction [79]. Two olefins other than norbornadiene were