A versatile way for the synthesis of monomethylamines by reduction of N-substituted carbonylimidazoles with the NaBH₄/I₂ system

• Lin Chen,
• Xuan Zhou,
• Zhiyong Chen,
• Changxu Wang,
• Shunjie Wang and
• Hanbing Teng

Beilstein J. Org. Chem. 2022, 18, 1032–1039, doi:10.3762/bjoc.18.104

• monomethylamines by reduction of N-substituted carbonylimidazoles with NaBH4/I2 in THF at reflux temperature is described. This method used no special catalyst and various monomethylamines can be easily obtained in moderate to good yields from a wide range of raw materials including amines (primary amines and

• cyanoformamides [75]. However, all of these works are primarily focused on the substitution reaction of N-substituted carbonylimidazoles. In our previous work, we conveniently prepared formamides by reducing N-substituted carbonylimidazoles with NaBH4 [62] (Scheme 1). The reaction mechanism shows that the H− ion

• reducibility of NaBH4. In this work, our goal is to reduce the carbonyl group in N-substituted carbonylimidazoles. The inexpensive NaBH4/I2 system has great attraction because it is more reductive due to the generation of highly reactive BH3–THF by adding iodine to NaBH4 in THF [76][77][78] and the reaction

An isoxazole strategy for the synthesis of 4-oxo-1,4-dihydropyridine-3-carboxylates

• Timur O. Zanakhov,
• Ekaterina E. Galenko,
• Mikhail S. Novikov and
• Alexander F. Khlebnikov

Beilstein J. Org. Chem. 2022, 18, 738–745, doi:10.3762/bjoc.18.74

• ][28], we checked the possibility of using NaBH4/NiSO4·7H2O [25], H2/PtO2/NiRaney [26][27] and H2/NiRaney [28] to obtain pyridone 2g from isoxazole 1g. However, analysis of reaction mixtures, obtained by using the above reductants, showed the formation of a large amount of products, but pyridone 2g was

Menadione: a platform and a target to valuable compounds synthesis

• Acácio S. de Souza,
• Ruan Carlos B. Ribeiro,
• Dora C. S. Costa,
• Fernanda P. Pauli,
• David R. Pinho,
• Matheus G. de Moraes,
• Fernando de C. da Silva,
• Luana da S. M. Forezi and
• Vitor F. Ferreira

Beilstein J. Org. Chem. 2022, 18, 381–419, doi:10.3762/bjoc.18.43

• the reaction of menadione (10) with formaldehyde in the presence of gaseous HCl bubbled into the reaction medium [129][130]. Then, the chloromethyl derivative 84 was treated with diselenides, generated in situ from the reaction between Se0, NaBH4 and different acid chlorides, to form conjugates 86 in

Synthesis of a novel aminobenzene-containing hemicucurbituril and its fluorescence spectral properties with ions

• Qingkai Zeng,
• Qiumeng Long,
• Jihong Lu,
• Li Wang,
• Yuting You,
• Xiaoting Yuan,
• Qianjun Zhang,
• Qingmei Ge,
• Hang Cong and
• Mao Liu

Beilstein J. Org. Chem. 2021, 17, 2840–2847, doi:10.3762/bjoc.17.195

• reduction of 5-nitroisophthalic acid with NaBH4 and BF3·Et2O followed by subsequent bromination with PBr3 [46] and 2-imidazolidinone (6) were used as building blocks. By controlling the molar ratio of 5 and 6 at 1:10 or 6:1 and the reaction conditions, products 7 and 8 were readily accessible with 25.3

Synthesis of highly substituted fluorenones via metal-free TBHP-promoted oxidative cyclization of 2-(aminomethyl)biphenyls. Application to the total synthesis of nobilone

• Ilya A. P. Jourjine,
• Lukas Zeisel,
• Jürgen Krauß and
• Franz Bracher

Beilstein J. Org. Chem. 2021, 17, 2668–2679, doi:10.3762/bjoc.17.181

• , NaBH4, DCM, rt, 62–78%; c) TBHPaq, 1,2-DCE, 100 °C, 18 h (yields in parentheses). Substrate scope for the oxidative cyclization of 2-(aminomethyl)biphenyls. Conditions: a) Boc2O, NEt3, DCM, rt, 18 h, 89%; b) Pd(PPh3)4 (5 mol %), Na2CO3, DMF/H2O, 18 h, 100 °C, 83–99%; c) LAH, AlCl3, THF, 18 h, 43–78%; d

Synthesis of new substituted 7,12-dihydro-6,12-methanodibenzo[c,f]azocine-5-carboxylic acids containing a tetracyclic tetrahydroisoquinoline core structure

• Agnieszka Grajewska,
• Maria Chrzanowska and
• Wiktoria Adamska

Beilstein J. Org. Chem. 2021, 17, 2511–2519, doi:10.3762/bjoc.17.168

• ) carried out in refluxing toluene using a Dean–Stark apparatus followed by the reduction with NaBH4 (not shown). When the condensation of acetal 1 and aldehyde 2f and the subsequent reduction were carried out in EtOH at rt, according to our procedure applied for the synthesis of aminoacetals 3a–e, the

Strategies for the synthesis of brevipolides

• Yudhi D. Kurniawan and
• A'liyatur Rosyidah

Beilstein J. Org. Chem. 2021, 17, 2399–2416, doi:10.3762/bjoc.17.157

• into the PMB-protected α,β-unsaturated ester 97 in four steps adopting the literature procedure (Scheme 12). The chemoselective reduction of the olefin in 97 was furnished in 88% yield applying NiCl4·6H2O/NaBH4 as reagents in methanol followed by reduction of the ester part with DIBAL-H providing the

Advances in mercury(II)-salt-mediated cyclization reactions of unsaturated bonds

• Sumana Mandal,
• Raju D. Chaudhari and
• Goutam Biswas

Beilstein J. Org. Chem. 2021, 17, 2348–2376, doi:10.3762/bjoc.17.153

• carbohydrate alkene precursor 7 and Hg(OAc)2 proceeds with high stereoselectivity to give the α-ᴅ-C-glycopyranosyl derivative (1,5-trans-isomer) 8 as a single isomer [41]. Treatment of compound 8 with sodium borohydride (NaBH4) under phase transfer conditions (PTC) yields compound 9 as the only product. The

• selectivity of α-stereochemistry was primarily due to the strong directing effect of the neighboring benzyl ether group with the Hg(OAc)2. When cyclic mercuric halide 8 was treated with NaBH4 and oxygen (O2) in DMF oxidative demercuration takes place to give alcohol 10 in quantitative yield (Scheme 4). The

• [46]. A similar type of reaction methodology was employed for the formation of a bicyclic nucleoside analog. 4'-C-vinylribofuranoside derivative 21 on treatment with Hg(TFA)2 followed by reduction with NaBH4 leads to the formation of bicyclic nucleoside derivative 22 (Scheme 10) [49]. Pyrrolidine and

Catalyzed and uncatalyzed procedures for the syntheses of isomeric covalent multi-indolyl hetero non-metallides: an account

• Ranadeep Talukdar

Beilstein J. Org. Chem. 2021, 17, 2102–2122, doi:10.3762/bjoc.17.137

• )-tryptophan amide 129 (Scheme 17a) [92]. Bis(indol-2-yl)selane 130 was found as a byproduct having very low such bioactivity. The polyselanes formed were separated by treating them with NaBH4, which did not affect the monoselane 130. On the other hand, selenopyrans structurally resemble indolocarbazoles

Recent advances in the syntheses of anthracene derivatives

• Giovanni S. Baviera and
• Paulo M. Donate

Beilstein J. Org. Chem. 2021, 17, 2028–2050, doi:10.3762/bjoc.17.131

• (70c) from the corresponding 9,10-anthraquinones 69 in good yields (53–79%) (Scheme 16) [49]. In 2017, Skalamera and co-workers reported a new synthetic pathway to produce 2,3-disubstituted anthracenes by functionalizing the corresponding anthraquinone and subsequent reduction with NaBH4 [50]. Via a

• procedure involving the cyclization of 2-arylmethylbenzoic acid 85b with triflic acid, followed by a NaBH4-mediated reductive dehydration. Some representative examples included anthracenes 86a–g. For those interested, the cyclodehydration was also extended to 2-(arylmethyl)naphthaldehydes and 2-(arylmethyl

• agent. One-pot procedure to synthesize substituted 9,10-dicyanoanthracenes. Reduction of bromoanthraquinones with NaBH4 in alkaline medium. In(III)-catalyzed reductive-dehydration intramolecular cycloaromatization of 2-benzylic aromatic aldehydes/ketones. Acid-catalyzed cyclization of new O-protected

A recent overview on the synthesis of 1,4,5-trisubstituted 1,2,3-triazoles

• Pezhman Shiri,
• Ali Mohammad Amani and
• Thomas Mayer-Gall

Beilstein J. Org. Chem. 2021, 17, 1600–1628, doi:10.3762/bjoc.17.114

• ) tetrafluoroborate (138) in the presence of HBF4 and NaNO2 at 0 °C. Next, the nanoparticles were obtained from the reduction of Pd(OAc)2 and Cu(OAc)2 employing NaBH4 in the presence of diazonium salt [63]. A possible mechanism for the synthesis of polycyclic triazoles 142 was proposed by Sekar et al. as well [63

Double-headed nucleosides: Synthesis and applications

• Vineet Verma,
• Jyotirmoy Maity,
• Vipin K. Maikhuri,
• Ritika Sharma,
• Himal K. Ganguly and
• Ashok K. Prasad

Beilstein J. Org. Chem. 2021, 17, 1392–1439, doi:10.3762/bjoc.17.98

• 116 following previously reported procedures [65]. Then, the nucleoside 116 was converted into the primary alcohol 117 by treatment with OsO4 and oxidative cleavage by NaIO4 followed by reduction using NaBH4. The primary alcohol 117 was further converted into nucleoside monomer 118 by introduction of

• was reduced in the presence of NaBH4 followed by the treatment with MsCl in pyridine to get the nucleoside salt 129. Next, the pyridinium group was replaced by an N3-protected thymine in basic medium followed by removal of the protecting groups and the selective DMTr protection of the C-5′-hydroxy

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

• state, the metal cation of the enolate is being coordinated with both nitrogen and oxygen atoms of the sulfinimine [25][26] (Scheme 3). In 1999, Ellman and co-workers described the reduction of sulfinyl imines using sodium borohydride (NaBH4) [34] or o ʟ-selectride [35]. Davis–Ellman transition state

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

• LiAlH4 pyrrolidone trans-12b was reduced to pyrrolidine trans-15 in 95% yield, whereas no reaction was observed with DIBAL-H, NaBH4 or LiHBEt3 as the reducing agents; the starting material was typically recovered in 95% yield. However, the reduction of trans-12b by Red-Al in the presence of KOt-Bu was

Designed whole-cell-catalysis-assisted synthesis of 9,11-secosterols

• Marek Kõllo,
• Marje Kasari,
• Villu Kasari,
• Tõnis Pehk,
• Ivar Järving,
• Margus Lopp,
• Arvi Jõers and
• Tõnis Kanger

Beilstein J. Org. Chem. 2021, 17, 581–588, doi:10.3762/bjoc.17.52

• Discussion Synthesis of starting compounds for enzymatic hydroxylation In order to estimate the possible diversity of the substrates as starting materials for the biocatalytic transformation, cortisol (1) was converted to a hydroxylated steroid derivative 2 by reduction of the C20 carbonyl group with NaBH4

• until further analysis. Synthesis of substrates 11β-Hydroxyandrost-4-ene-3,17-dione (2) To a stirred solution of cortisol (1, 1.2 g, 3.36 mmol) in a 1:1 mixture of EtOH and CH2Cl2 (23 mL), NaBH4 (51.2 mg, 1.35 mmol) was added in one portion at room temperature. After 2 h, acetone (5.8 mL) was added

• ) NaBH4, EtOH/CH2Cl2 1:1, 2 h, rt, then acetone, H2O, NaIO4, overnight, rt, 99%; ii) Ac2O, p-TsOH (1 mol %), MW (800 W), 6 min, 52% for 3 and 33% for 4; iii) Ac2O, DMAP, Et3N, CH2Cl2, overnight, rt, 93%. Oxidation of diols 5 and 6 with NaOCl·5H2O. Enzymatic hydroxylation. Supporting Information

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

• was modified by Wang and co-workers [76]. It is also possible to remove the fluorine substituents from difluorocyclopropanes while preserving the three-membered ring. The reductive defluorination of the difluorocylopropane derivative 75 by the treatment with excess NaBH4 in hot DMSO (Scheme 31) gave

• the corresponding cyclopropane 76 [77]. Caution is advised in view of a recent report that NaBH4 lowers the onset temperature for the thermal decomposition of DMSO [78]. The asymmetric difluorocyclopropanation has not yet been developed to the extent achieved for the epoxidation. Consequently, the

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

• methodology followed by NaBH4 reduction. This structure with three condensed rings can be seen as a new class of unnatural, chiral alkaloid scaffolds, potentially exhibiting pharmacological activity (Scheme 3) [40]. Various unsuccessful attempts were made to deprotect compound 3e. Unexpectedly, however, one of

Progress in the total synthesis of inthomycins

• Bidyut Kumar Senapati

Beilstein J. Org. Chem. 2021, 17, 58–82, doi:10.3762/bjoc.17.7

• PdCl2(MeCN)2 produced (E,E,E)-triene 32 in 84% yield. Finally, NaBH4 reduction of 32 gave alcohol (rac)-13, in which the triene moiety is analogous to inthomycin C ((rac)-3) and oxazolomycin B (5b) (Scheme 2). After the successful application of the Stille reaction to construct the (E,E,E)-triene system

Recent progress in the synthesis of homotropane alkaloids adaline, euphococcinine and N-methyleuphococcinine

• Dimas J. P. Lima,
• Antonio E. G. Santana,
• Michael A. Birkett and
• Ricardo S. Porto

Beilstein J. Org. Chem. 2021, 17, 28–41, doi:10.3762/bjoc.17.4

• -carboxaldehyde, 9:1 77a/77b, 67% (after chromatographic separation); ii) butyl vinyl ether, Hg(OAc)2, (10 mol %), sealed tube, 130–135 °C, 79%; iii) vinylmagnesium bromide, −78 °C; iv) Dess–Martin periodinane, 83% over two steps; v) Grubbs catalyst 2nd gen., CH2Cl2, reflux, 74%; vi) 1. (PhSe)2, NaBH4, EtOH; 2

• , 83% over two steps; vi) Grubbs catalyst 2nd gen., CH2Cl2, reflux, 74%; vii) 1. (PhSe)2, NaBH4, EtOH; 2. EtOH/THF, 99%; viii) 1. O3, CH2Cl2, −78 °C; 2. DMS, −78 °C to rt; 3. NaClO2, Na2HPO4, t-BuOH/H2O, 2-methy-2-butene, 90%; ix) DPPA, Et3N, toluene, reflux, 65%; x) 1. CuCl, H2O/THF, rt to 40 °C; 2

Amine–borane complex-initiated SF₅Cl radical addition on alkenes and alkynes

• Audrey Gilbert,
• Pauline Langowski,
• Marine Delgado,
• Laurent Chabaud,
• Mathieu Pucheault and
• Jean-François Paquin

Beilstein J. Org. Chem. 2020, 16, 3069–3077, doi:10.3762/bjoc.16.256

• freshly prepared [37]. It is therefore of interest to address this challenge in order to widen the scope of this transformation. Compared to trialkylboranes, amine–borane complexes have shown to be more stable [38]. Indeed, they are usually air-stable, and their preparation from NaBH4, H2SO4 and amines

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

• NaBH4 afforded alcohol 79. Alcohol 79 was converted into the corresponding xanthate ester 80. This ester 80 was exposed to an excessive amount of AIBN and N,O-bis(trimethylsilyl)acetamide in the presence of a catalytic amount of tributylstannane producing bicyclo[2.2.2]diazaoctane 81 in 54% yield. The

Fluorine effect in nucleophilic fluorination at C4 of 1,6-anhydro-2,3-dideoxy-2,3-difluoro-β-D-hexopyranose

• Danny Lainé,
• Vincent Denavit,
• Olivier Lessard,
• Laurie Carrier,
• Charles-Émile Fecteau,
• Paul A. Johnson and
• Denis Giguère

Beilstein J. Org. Chem. 2020, 16, 2880–2887, doi:10.3762/bjoc.16.237

• hardly reproducible because a thick gel was formed after neutralisation with an acidic resin, thus resulting in yield loss after a difficult filtration. Next, we evaluated sodium borohydride (NaBH4) as reducing reagent. Difluoroglucose 21 was subjected to 5 equivalents of NaBH4 in EtOH at rt and compound

3-Acetoxy-fatty acid isoprenyl esters from androconia of the ithomiine butterfly Ithomia salapia

• Florian Mann,
• Daiane Szczerbowski,
• Lisa de Silva,
• Melanie McClure,
• Marianne Elias and
• Stefan Schulz

Beilstein J. Org. Chem. 2020, 16, 2776–2787, doi:10.3762/bjoc.16.228

• o-iodoxybenzoic acid (IBX) [31]. The resulting aldehyde was transformed into β-ketoacid 16 with ethyl diaazoacetate and SnCl2 [32], which upon reduction with NaBH4 in methanol delivered methyl 3-hydroxyoctadecanoate (17). Transesterification was performed with 3-methyl-3-buten-1-ol using distannoxan

• ) and ithomiolide A (3). Biosynthetic formation of hedycaryol (7) and α-elemol (8). Synthesis of isoprenyl 3-acetoxyoctadecanoate (11). a) IBX, EtOAc, 60 °C, 3.15 h, 99%; b) SnCl2, CH2Cl2, rt, 70%; c) NaBH4, 12 h, 98%; d) SnOBu2, 140°C, 36 h, 78%; e) Ac2O, pyridine, DMAP, CH2Cl2, 12 h rt, 67%. a) 48

A new method for the synthesis of diamantane by hydroisomerization of binor-S on treatment with sulfuric acid

• Rishat I. Aminov and
• Ravil I. Khusnutdinov

Beilstein J. Org. Chem. 2020, 16, 2534–2539, doi:10.3762/bjoc.16.205

• , PtO2) in glacial acetic acid under high pressure conditions at 70 °С and 200 psi of H2 [8][9]. In the presence of superacid catalysts, such as B(OSO2CF3)3, CF3SO3H/SbF5 1:1, CF3SO3H/B(OSO2CF3)3 1:1 [10], NaBH4/CF3SO3H [11], or zeolite Y in the NaH form (NaY) [12], hydrocarbons 3a–c isomerize to

Palladium nanoparticles supported on chitin-based nanomaterials as heterogeneous catalysts for the Heck coupling reaction

• Tony Jin,
• Malickah Hicks,
• Davis Kurdyla,
• Sabahudin Hrapovic,
• Edmond Lam and
• Audrey Moores

Beilstein J. Org. Chem. 2020, 16, 2477–2483, doi:10.3762/bjoc.16.201

• the use of ammonium persulfate as a mild oxidizing agent to liberate the nanocrystallites existing within bulk chitin to yield ChNC with carboxylate functionalities [16]. Moreover, deacetylation of ChNCs in alkaline conditions, in the presence of NaBH4, led to chitosan nanocrystals (ChsNCs) with

• Information File 1) [16]. ChNCs were treated with ammonium persulfate (APS) for 16 h to form disperse ChNCs after washing. ChsNCs were made by deacetylating ChNCs in the presence of concentrated NaOH as well as a small amount of NaBH4 (Scheme 1). As seen through transmission electron microscopy (TEM) in

• selected here because it is one of cleanest reductants in this context as it will limit the production of byproducts to chloride salts, by opposition to more classic reducing agents such as NaBH4. Prior to characterization, the non-dried samples were purified by dialysis. The zeta potential measurements