Chemical approaches to discover the full potential of peptide nucleic acids in biomedical applications

• Nikita Brodyagin,
• Martins Katkevics,
• Venubabu Kotikam,
• Christopher A. Ryan and
• Eriks Rozners

Beilstein J. Org. Chem. 2021, 17, 1641–1688, doi:10.3762/bjoc.17.116

• –C triplets than J when binding to dsRNA, which was suggested to be a combined effect of improved van der Waals contacts, base stacking, hydrogen bonding, and reduced dehydration energy [98]. Replacement of three Js with Ls increased the binding affinity of a PNA 8-mer ≈4-fold [98]. In addition, the

Chemical synthesis of C6-tetrazole ᴅ-mannose building blocks and access to a bioisostere of mannuronic acid 1-phosphate

• Eleni Dimitriou and
• Gavin J. Miller

Beilstein J. Org. Chem. 2021, 17, 1527–1532, doi:10.3762/bjoc.17.110

• in 80% yield as a 6.7:1 mixture of C=N isomers. Dehydration of 8 using POCl3 gave 9 in a low 40% yield, alongside 10 (26% yield). Formation of 10 was attributed to the acidic reaction conditions concomitantly effecting TBS removal. However, further amounts of 9 could be accessed through reprotection

Cascade intramolecular Prins/Friedel–Crafts cyclization for the synthesis of 4-aryltetralin-2-ols and 5-aryltetrahydro-5H-benzo[7]annulen-7-ols

• Jie Zheng,
• Shuyu Meng and
• Quanrui Wang

Beilstein J. Org. Chem. 2021, 17, 1481–1489, doi:10.3762/bjoc.17.104

• alkynyl-Prins cyclization, Friedel–Crafts alkenylation, and dehydration/aromatization reaction between 1-aryl-3-hexyne-2,6-diol derivatives and aldehydes, that led to the formation of 1,4-dihydro-2H-benzo[f]isochromenes [16]. The Prins reaction-induced cyclization, inter alia, became a versatile tool for

Synthesis of 1-indolyl-3,5,8-substituted γ-carbolines: one-pot solvent-free protocol and biological evaluation

• Premansh Dudhe,
• Mena Asha Krishnan,
• Kratika Yadav,
• Diptendu Roy,
• Krishnan Venkatasubbaiah,
• Biswarup Pathak and
• Venkatesh Chelvam

Beilstein J. Org. Chem. 2021, 17, 1453–1463, doi:10.3762/bjoc.17.101

• 5, which undergoes nucleophilic addition with another molecule of aldehyde 1 to furnish the iminoalcohol intermediate 6. The iminoalcohol 6 undergoes dehydration under the reaction conditions to give E-imine/Z-enamine 7a or Z-imine/E-enamine 7c intermediates irreversibly, which plays a decisive role

A comprehensive review of flow chemistry techniques tailored to the flavours and fragrances industries

• Guido Gambacorta,
• James S. Sharley and
• Ian R. Baxendale

Beilstein J. Org. Chem. 2021, 17, 1181–1312, doi:10.3762/bjoc.17.90

• method was applied on different aldehydes and ketones obtaining moderate-good yields (38–84%). The results obtained for aldehydes 39 and 56 are low as partial dehydration occurs. It was noticed that by reducing the quantity of catalyst less dehydrated product was observed. A similar approach in aqueous

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

• [35] Another example is the cyclocondensation of anthranilic acid with cyanoguanidine which occurs under sulfuric acid conditions via dehydration leading to the corresponding 2-guanidinoquinazolinones (Scheme 13A) [36]. However, performing this reaction in acetonitrile in a closed microwave tube

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

• enaminone B. Later, the successive Michael addition of A and enaminone B followed by an intramolecular cycloaddition with concomitant dehydration delivered the final product 7 (Scheme 2). In 2018, our research group [39] contemplated and developed an expeditious process for the synthesis of phenanthrene

• dehydration forms D and finally 12. The synthesized naphthoacridines 12 with 2,3-diaminonaphthalene produces 14 via dehydration and dehydrogenation. 2 Azepines Azepines are represented by unsaturated seven atom heterocyles with nitrogen replacing a carbon atom. The benzene-fused azepines known as

• intermediate B generated by the addition of aldehyde to enaminone A on intramolecular cyclization furnishes the final product 24 via C. Cyclic isoindole-fused furo[1,4]diazepines 26 were obtained by dehydration of the carbonyl group on the aromatic ring on treatment with an amino group. The authors attributed

Total synthesis of pyrrolo[2,3-c]quinoline alkaloid: trigonoine B

• Takashi Nishiyama,
• Erina Hamada,
• Daishi Ishii,
• Yuuto Kihara,
• Nanase Choshi,
• Natsumi Nakanishi,
• Mari Murakami,
• Kimiko Taninaka,
• Noriyuki Hatae and
• Tominari Choshi

Beilstein J. Org. Chem. 2021, 17, 730–736, doi:10.3762/bjoc.17.62

• . Consequently, we decided to develop a new synthetic strategy for the preparation of trigonoine B (1). Carbodiimides are valuable synthetic intermediates that can be obtained by an aza-Wittig reaction of isocyanates with iminophosphoranes or by dehydration of urea [26]. Molina et al. previously reported the

β-Lactamase inhibition profile of new amidine-substituted diazabicyclooctanes

• Zafar Iqbal,
• Lijuan Zhai,
• Yuanyu Gao,
• Dong Tang,
• Xueqin Ma,
• Jinbo Ji,
• Jian Sun,
• Jingwen Ji,
• Yuanbai Liu,
• Rui Jiang,
• Yangxiu Mu,
• Lili He,
• Haikang Yang and
• Zhixiang Yang

Beilstein J. Org. Chem. 2021, 17, 711–718, doi:10.3762/bjoc.17.60

• The preparation of intermediate 1 is the key step for the synthesis of the final compounds (Scheme 1). Compound 1 was synthesized by dehydration of amide [28] 6 which is commercially available. Dehydration was achieved by reacting 6 with trifluoroacetic anhydride in CH2Cl2 at room temperature (rt) and

Helicene synthesis by Brønsted acid-catalyzed cycloaromatization in HFIP [(CF₃)₂CHOH]

• Takeshi Fujita,
• Noriaki Shoji,
• Nao Yoshikawa and
• Junji Ichikawa

Beilstein J. Org. Chem. 2021, 17, 396–403, doi:10.3762/bjoc.17.35

• derivatives readily underwent intramolecular Friedel–Crafts-type C–C bond formation followed by dehydration or alcohol elimination, leading to the construction of benzene rings in the biaryl systems (Scheme 2) [20][21]. The reaction proceeded via oxocarbenium ion intermediates stabilized by HFIP. This method

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

• analogue (dC–O = 1.438 Å) and strongly inhibits the formation of the α-(trifluoromethyl)bisarylcarbenium ion, as illustrated by the higher activation energy needed for the dehydration (ΔECF3 = 21.0 kcal⋅mol−1 vs ΔECH3 = 14.8 kcal⋅mol−1 at the B3LYP/6-31+G(d,p) level). On the other hand, the first arylation

• reaction seems to be facilitated by the CF3 group (ΔECF3 = 16.9 kcal⋅mol−1 vs ΔECH3 = 21.2 kcal⋅mol−1 at the B3LYP/6-31+G(d,p) level). Raising the temperature finally favors the dehydration and the second Friedel–Crafts reaction to afford bisarylated products 151. In complementary studies, Sasaki et al

Synthesis of legonmycins A and B, C(7a)-hydroxylated bacterial pyrrolizidines

• Wilfred J. M. Lewis,
• David M. Shaw and
• Jeremy Robertson

Beilstein J. Org. Chem. 2021, 17, 334–342, doi:10.3762/bjoc.17.31

• Baeyer–Villiger-type ring expansion, hydrolysis and decarboxylation, cyclization and dehydration, and finally hydroxylation at C(7a). Just one month later, Bode reported the identification of an unknown gene cluster in the symbiotic bacterium Xenorhabdus stockiae [23]. Cloning and expression of this

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

• –dehydration reactions, via intermediate anti-aldol (−)-67 (Scheme 8). The addition of Grignard reagent to the enone (E)-(−)-68 occurred anti to the group TpMo(CO)2 to give adduct (E)-69, which was used in the next step without purification. The treatment of this adduct with HCl in dioxane promoted

Regioselective cobalt(II)-catalyzed [2 + 3] cycloaddition reaction of fluoroalkylated alkynes with 2-formylphenylboronic acids: easy access to 2-fluoroalkylated indenols

• Tatsuya Kumon,
• Miroku Shimada,
• Jianyan Wu,
• Shigeyuki Yamada and
• Tsutomu Konno

Beilstein J. Org. Chem. 2020, 16, 2193–2200, doi:10.3762/bjoc.16.184

• C. Then, dehydration of C using p-TsOH⋅H2O, followed by a 1,2-reduction led to 3-fluoroalkylated indenol D. All of these reactions produced the desired products in good yield, however, this protocol is limited to the introduction of a trifluoromethyl group at the 3-position of the indenol. To the

Convenient access to pyrrolidin-3-ylphosphonic acids and tetrahydro-2H-pyran-3-ylphosphonates with multiple contiguous stereocenters from nonracemic adducts of a Ni(II)-catalyzed Michael reaction

• Alexander N. Reznikov,
• Dmitry S. Nikerov,
• Anastasiya E. Sibiryakova,
• Victor B. Rybakov,
• Evgeniy V. Golovin and
• Yuri N. Klimochkin

Beilstein J. Org. Chem. 2020, 16, 2073–2079, doi:10.3762/bjoc.16.174

• assumed by analogy. Dehydration of compound 13b in the presence of p-toluenesulfonic acid gives dihydropyran 14 as a single stereoisomer (Scheme 4). Conclusion In summary, a convenient protocol for the synthesis of phosphoryl-substituted pyrrolidines with three contiguous stereocenters via asymmetric

Regiodivergent synthesis of functionalized pyrimidines and imidazoles through phenacyl azides in deep eutectic solvents

• Paola Vitale,
• Luciana Cicco,
• Ilaria Cellamare,
• Filippo M. Perna,
• Antonio Salomone and
• Vito Capriati

Beilstein J. Org. Chem. 2020, 16, 1915–1923, doi:10.3762/bjoc.16.158

• by dehydration. The two tautomers 3/3' would most probably originate by two competitive pathways (a and b; Scheme 4) via a [1,5]-hydrogen shift [28][29]. Hydrogen-bond catalysis promoted by DES components may be playing an important role in favoring the loss of nitrogen under mild conditions from a

• -azide 4a, would undergo either dimerization to give 6a, and then imidazoles 3a/3a' after cyclization and dehydration (see Scheme 5), or trimerization to afford adduct 8a further to an additional attack of 5a to the internal imino group of 6a and dehydration. Consecutive tautomerization, followed by an

Natural dolomitic limestone-catalyzed synthesis of benzimidazoles, dihydropyrimidinones, and highly substituted pyridines under ultrasound irradiation

• Kumar Godugu,
• Venkata Divya Sri Yadala,
• Mohammad Khaja Mohinuddin Pinjari,
• Trivikram Reddy Gundala,
• Lakshmi Reddy Sanapareddy and
• Chinna Gangi Reddy Nallagondu

Beilstein J. Org. Chem. 2020, 16, 1881–1900, doi:10.3762/bjoc.16.156

• 1.0 mmol was used), which are activated by the carbonate part of the NDL, followed by dehydration to obtain 3h (Scheme 2). Due to the mild basic nature of the NDL catalyst, it acts as a dual activator of the electrophilic carbonyl and the nucleophilic NH2 groups. The formation of the bisimine I was

Synthesis and highly efficient light-induced rearrangements of diphenylmethylene(2-benzo[b]thienyl)fulgides and fulgimides

• Vladimir P. Rybalkin,
• Sofiya Yu. Zmeeva,
• Lidiya L. Popova,
• Valerii V. Tkachev,
• Andrey N. Utenyshev,
• Olga Yu. Karlutova,
• Alexander D. Dubonosov,
• Vladimir A. Bren,
• Sergey M. Aldoshin and
• Vladimir I. Minkin

Beilstein J. Org. Chem. 2020, 16, 1820–1829, doi:10.3762/bjoc.16.149

• heterocyclic aldehydes or ketones with methylene succinates followed by subsequent hydrolysis and dehydration processes. Under exposure of solutions or crystals of thus prepared hetaryl(aryl)-substituted dihydrofuran-2,5-diones to UV light, those bearing an isopropylidene fragment attached to the furandione

Tuneable access to indole, indolone, and cinnoline derivatives from a common 1,4-diketone Michael acceptor

• Dalel El-Marrouki,
• Sabrina Touchet,
• Abderrahmen Abdelli,
• Hédi M’Rabet,
• Mohamed Lotfi Efrit and
• Philippe C. Gros

Beilstein J. Org. Chem. 2020, 16, 1722–1731, doi:10.3762/bjoc.16.144

• process, leading respectively to an indole 6 (after dehydration and aromatization) or an indolone 7. The reaction was first investigated by mixing the diketone 5b as the Michael acceptor and benzylamine under various conditions (Table 1). We first investigated the reactivity in the presence of a set of

One-pot synthesis of isosorbide from cellulose or lignocellulosic biomass: a challenge?

• Isaline Bonnin,
• Raphaël Mereau,
• Thierry Tassaing and
• Karine De Oliveira Vigier

Beilstein J. Org. Chem. 2020, 16, 1713–1721, doi:10.3762/bjoc.16.143

• to sorbitol and 3) dehydration of sorbitol to isosorbide (Scheme 1). Isosorbide, a molecule obtained from biomass can find many applications such as additives, pharmaceuticals [2][3] and monomers for polymer industries [4][5][6]. For instance, one polymer obtained from isosorbide, poly(ethylene-co

• dehydration of ᴅ-sorbitol using a strong acid catalyst [10][11]. ᴅ-Sorbitol is produced from the hydrogenation of glucose obtained mostly from the hydrolysis of starch, but also from sucrose or cellulose. Consequently, the cellulose valorization can be realized from the one-pot conversion of cellulose to

• pressures and high temperatures to allow efficient hydrogenation of glucose and dehydration of sorbitol and sorbitans [12][18]. In 2010, Almeida et al. studied each step for the synthesis of isosorbide from cellulose using molten ZnCl2 associated with different catalysts [19]. Based on the study of each

Rearrangement of o-(pivaloylaminomethyl)benzaldehydes: an experimental and computational study

• Csilla Hargitai,
• Györgyi Koványi-Lax,
• Tamás Nagy,
• Péter Ábrányi-Balogh,
• András Dancsó,
• Gábor Tóth,
• Judit Halász,
• Angéla Pandur,
• Gyula Simig and
• Balázs Volk

Beilstein J. Org. Chem. 2020, 16, 1636–1648, doi:10.3762/bjoc.16.136

• the transformation of trimethoxy derivative 1d reveals that dehydration is almost isoergonic (ΔG9d→11d = −1.6 kJ·mol−1), but the formation of the isoindole intermediate (11d→4d) is endergonic (unlike in the case of the three other derivatives), with a larger activation free energy (ΔG#11TS = 40.2

• turned out that the acid catalyst (TFA in this case), as expected, had a crucial role in the protonation and deprotonation as well as in the dehydration and hydration elementary steps of the reaction sequence. Without catalyst, the 9a→11a→4a transformations required an energy investment of 150.7 and

Activated carbon as catalyst support: precursors, preparation, modification and characterization

• Melanie Iwanow,
• Tobias Gärtner,
• Volker Sieber and
• Burkhard König

Beilstein J. Org. Chem. 2020, 16, 1188–1202, doi:10.3762/bjoc.16.104

• agents promote a cross-link formation due to their dehydration properties, which causes a rigid matrix. This structure is less susceptible to volatile loss and volume contraction during the carbonization resulting in higher activated carbon yields since no carbon burn-off is necessary [6][85]. Additional

• to the precursor solution consisting of sucrose as carbon source and NaCl or NaNO3 as inorganic salt. The pyrolysis of the precursor solution leads to dehydration of carbon as well as iron salt conversion to crystalline or non-crystalline iron species depending on the production conditions. The

• components lignin, cellulose and xylan by KOH activation with TPD. The different prepared materials showed no significant difference of the surface functionalities. All TPD spectra show a water peak at about 500 K according to dehydration of carboxylic acid during formation of anhydrides, a CO peak at 900 K

A systematic review on silica-, carbon-, and magnetic materials-supported copper species as efficient heterogeneous nanocatalysts in “click” reactions

• Pezhman Shiri and
• Jasem Aboonajmi

Beilstein J. Org. Chem. 2020, 16, 551–586, doi:10.3762/bjoc.16.52

• reactions, Ugi–Smiles reactions, Mizoroki–Heck reactions, aldol reactions, oxidation and dehydration reactions, Mannich reactions, and multicomponent reactions. Because of the mentioned reasons as well as due to the low toxicity of silica nanoparticles, they are often a good option [24]. For this review

Efficient synthesis of 3,6,13,16-tetrasubstituted-tetrabenzo[a,d,j,m]coronenes by selective C–H/C–O arylations of anthraquinone derivatives

• Seiya Terai,
• Yuki Sato,
• Takuya Kochi and
• Fumitoshi Kakiuchi

Beilstein J. Org. Chem. 2020, 16, 544–550, doi:10.3762/bjoc.16.51

• examining various carbonyl methylenation methods, we found that the dimethylenation products 6 can be obtained in high yields through methylation of the carbonyl groups, followed by dehydration. Thus, the reaction of 4aa with methyllithium and subsequent treatment of the crude diol with NaH2PO2·H2O and NaI

Synthesis of 4-amino-5-fluoropyrimidines and 5-amino-4-fluoropyrazoles from a β-fluoroenolate salt

• Tobias Lucas,
• Jule-Philipp Dietz and
• Till Opatz

Beilstein J. Org. Chem. 2020, 16, 445–450, doi:10.3762/bjoc.16.41

• (5). First, a Finkelstein halogen exchange reaction and a dehydration reaction were combined to obtain fluoroacetonitrile (7) in 82% yield [36]. The latter then underwent a Claisen condensation with ethyl formate to obtain 8 in 77% yield with a purity of 90%. The product contained about 10% (1H NMR