Cerium-photocatalyzed aerobic oxidation of benzylic alcohols to aldehydes and ketones

• Girish Suresh Yedase,
• Sumit Kumar,
• Jessica Stahl,
• Burkhard König and
• Veera Reddy Yatham

Beilstein J. Org. Chem. 2021, 17, 1727–1732, doi:10.3762/bjoc.17.121

• the corresponding halo-substituted benzaldehydes 2a–d in good yields. The oxidation of simple benzyl alcohol (1e) under our reaction conditions gave benzaldehyde (2e) in 55% yield. A variety of electron-donating para-substituted benzyl alcohols (1f–h) gave lower isolated yields of the corresponding

• benzaldehydes 2f–h. Our methodology tolerates a variety of functional groups containing benzylic alcohols such as -OH (1h), -CN (1i), -NO2 (1j), methyl ester (1k), and benzyloxy (1v) to produce the corresponding aldehydes (2h–k and 2v) in moderate yields. Next, electronically different ortho-substituted

• ) benzylic alcohols yielded the corresponding benzaldehydes 2o and 2p in moderate yields and to our surprise we did not observe any oxidation of the methyl or methoxy groups via hydrogen atom transfer processes [57]. Interestingly, we found that a variety of ortho-phenoxy-substituted benzylic alcohols (1q

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

• ., benzaldehydes) and low-molecular-weight enolate nucleophiles, therefore, temperature regulation is vital for selectivity. This requirement for strict temperature control makes aldol reactions highly suited to flow processing conditions. In 2008, Tanaka et al. [96] disclosed several examples of aldol reaction in

• . In 2008, the group of Sartori developed a flow setup for nitroaldol condensations of different benzaldehydes exploiting a silica-supported amine (KG-60-NH2) as a heterogeneous catalyst (Scheme 21) [133]. Secondary and tertiary amine-supported catalysts were also investigated, although they were found

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

• perspective, we herein disclose environmentally benign, atom-economical, catalyst-free nucleophilic additions of benzylic-like azaarene C–H groups to various benzaldehydes under neat conditions (Scheme 3). Results and Discussion With the purpose to develop an environmentally benign process, we first examined

One-pot multicomponent green Hantzsch synthesis of 1,2-dihydropyridine derivatives with antiproliferative activity

• Giovanna Bosica,
• Kaylie Demanuele,
• José M. Padrón and
• Adrián Puerta

Beilstein J. Org. Chem. 2020, 16, 2862–2869, doi:10.3762/bjoc.16.235

• , irrespective of the electronic effect of the substituted benzaldehydes studied [19]. This was a further improvement of the reaction since the usual regioisomer has always been reported to be the 1,4-DHP. Cao et al. have suggested an alternative mechanism for this route. When the same reaction was conducted

• versatility of the developed method. The selectivity was promising even for the other substrates used (Table 2). Various substituted benzaldehydes were used, and all gave similar results. Deviations from the model reaction occurred in terms of the expected reaction time and yield, but generally, the

Metal-free synthesis of phosphinoylchroman-4-ones via a radical phosphinoylation–cyclization cascade mediated by K₂S₂O₈

• Qiang Liu,
• Weibang Lu,
• Guanqun Xie and
• Xiaoxia Wang

Beilstein J. Org. Chem. 2020, 16, 1974–1982, doi:10.3762/bjoc.16.164

• IV affords the final products 3 [45][46]. Conclusion In summary, an environmentally benign and practical radical cascade cyclization was developed to synthesize a series of phosphonate-functionalized chroman-4-ones from 2-(allyloxy)benzaldehydes and diphenylphosphine oxides. This protocol proceeds

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

• (hetero)aromatic aldehydes was investigated. The obtained results are presented in Table 5. o-Phenylenediamine (1) reacted well with benzaldehyde (2a) to obtain the corresponding product 3a with 98% yield (Table 5, entry 1). The reactions of o-phenylenediamine (1) with substituted benzaldehydes having

Clickable azide-functionalized bromoarylaldehydes – synthesis and photophysical characterization

• Dominik Göbel,
• Marius Friedrich,
• Enno Lork and
• Boris J. Nachtsheim

Beilstein J. Org. Chem. 2020, 16, 1683–1692, doi:10.3762/bjoc.16.139

• cycloadditions with model alkynes. Besides two ortho- and para-bromo-substituted benzaldehydes, the azide functionalization of a fluorene-based structure will be presented. The copper(I)-catalyzed azide–alkyne cycloaddition (CuAAC) of the so-synthesized azide-functionalized bromocarbaldehydes with terminal

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

• )benzaldehydes under acidic conditions resulted in the formation of the regioisomeric aldehydes and/or dimer-like products. Detailed NMR studies and single-crystal X-ray measurements supported the structure elucidation of the compounds. DFT calculations were also carried out to clarify the reaction mechanism

• reaction described in Scheme 1 to further o-(pivaloylaminomethyl)benzaldehydes and to support the results by density functional theory (DFT) calculations, single-crystal X-ray measurements and comprehensive NMR studies. Results and Discussion Acid-catalyzed transformations of compounds 1a–d First we kept

• DCM reaction medium. This is further supported by the recent results of Allen et al., who have shown that CHCl3 and DCM molecules exhibited the same interactions also in crystal packing [33]. Conclusion When alkoxy-substituted o-(pivaloylaminomethyl)benzaldehydes 1a,b were kept in solution (DCM or THF

Azidophosphonium salt-directed chemoselective synthesis of (E)/(Z)-cinnamyl-1H-triazoles and regiospecific access to bromomethylcoumarins from Morita–Baylis–Hillman adducts

• Soundararajan Karthikeyan,
• Radha Krishnan Shobana,
• Kamarajapurathu Raju Subimol,
• J. Helen Ratna Monica and
• Ayyanoth Karthik Krishna Kumar

Beilstein J. Org. Chem. 2020, 16, 1579–1587, doi:10.3762/bjoc.16.130

• , salicylaldehydes, and methyl- or methoxy-substituted benzaldehydes were also inert under the optimized reaction conditions. Therefore, it is evident that the electronic variation of the substituents on the aromatic moiety of the MBH adducts played a crucial role in determining the outcome of the optimized

One-pot synthesis of 1,3,5-triazine-2,4-dithione derivatives via three-component reactions

• Gui-Feng Kang and
• Gang Zhang

Beilstein J. Org. Chem. 2020, 16, 1447–1455, doi:10.3762/bjoc.16.120

• reaction also worked well with other 4-alkylbenzaldehydes 1e and 1f, giving the expected products 6ea and 6fa in very good yields. We found benzaldehydes featuring other electron-donating groups such as methoxy (1g) and methylthio (1h) in the para-position of the aldehyde group were also applicable in the

• reaction, and provided products 6ga and 6ha in still moderate yields. When an electron-deficient aromatic aldehyde such as 4-phenylbenzaldehyde (1i) was used, the reaction effectively afforded product 6ia in 45% yield. Similarly, benzaldehydes having other electron-withdrawing groups such as cyano, nitro

• , and trifluoromethyl they smoothly took part in the three-component reaction and provided the desired products 6ja–na in moderate yields. It is noteworthy that benzaldehydes containing a halogen atom such as fluorine, chlorine, bromine, and iodine in the para and meta-positions were also compatible

Synthesis of pyrrolidinedione-fused hexahydropyrrolo[2,1-a]isoquinolines via three-component [3 + 2] cycloaddition followed by one-pot N-allylation and intramolecular Heck reactions

• Xiaoming Ma,
• Suzhi Meng,
• Xiaofeng Zhang,
• Qiang Zhang,
• Shenghu Yan,
• Yue Zhang and
• Wei Zhang

Beilstein J. Org. Chem. 2020, 16, 1225–1233, doi:10.3762/bjoc.16.106

• related to natural products [18][19][20]. Among the well-established MCRs, three-component 1,3-dipolar cycloadditions of benzaldehydes, maleimides, and amino esters have been developed for making N-containing 5-membered heterocycles (Scheme 1) [21][22]. The [3 + 2] cycloadditions of maleimides with

Fluorinated phenylalanines: synthesis and pharmaceutical applications

• Laila F. Awad and
• Mohammed Salah Ayoup

Beilstein J. Org. Chem. 2020, 16, 1022–1050, doi:10.3762/bjoc.16.91

• . Thus, a three-component condensation of a series of fluorinated benzaldehydes 50a–h, N-acetyl- or N-benzoylglycine 51a or 51b, respectively, and an excess of acetic anhydride in the presence of sodium acetate afforded the oxazolones 52a–h. The subsequent reductive ring cleavage of 52a–h without

Recent applications of porphyrins as photocatalysts in organic synthesis: batch and continuous flow approaches

• Rodrigo Costa e Silva,
• Luely Oliveira da Silva,
• Aloisio de Andrade Bartolomeu,
• Timothy John Brocksom and
• Kleber Thiago de Oliveira

Beilstein J. Org. Chem. 2020, 16, 917–955, doi:10.3762/bjoc.16.83

• obtained by photooxidation of benzaldehydes using Pt porphyrin (Pt-TMP) [49] and Pd porphyrin (2Pd) [50] (Scheme 23). Overall, the fine-tuning of the electrochemical potential of metals and porphyrins enables the oxidation of alcohols to aldehydes or aldehydes to carboxylic acids in a very controlled and

• using CNH as photocatalyst. Sulfonic acid scope of the sulfonation reactions. Regioselective sulfonation reaction of arimistane. Synthesis of quinazolin-4-(3H)-ones. Selective photooxidation of aromatic benzyl alcohols to benzaldehydes using Pt/PCN-224(Zn). Photooxidation of benzaldehydes to benzoic

Aldehydes as powerful initiators for photochemical transformations

• Maria A. Theodoropoulou,
• Nikolaos F. Nikitas and
• Christoforos G. Kokotos

Beilstein J. Org. Chem. 2020, 16, 833–857, doi:10.3762/bjoc.16.76

• of the benzoyl radical (10) to 80 and 81. In 1976, Davidson and co-workers reported the formation of N-tert-butylbenzamides, such as 83, from tert-butylamine (84) and substituted aromatic aldehydes, such as 8 [53]. The reaction between the substituted benzaldehydes and tert-butylamine (84) took place

• (116) decomposition, initiating the radical chain reaction. Other substituted benzaldehydes were also investigated. Finally, experiments employing benzaldehyde-α-d1, showing no hydrogen/deuterium exchange, indicated no formation of a benzoyl radical (10) in this reaction. In 2019, Hashmi and co-workers

• (64), benzophenone, as well as substituted benzaldehydes were not as efficient as benzaldehyde (8). Using 4-anisaldehyde (52) and irradiation with CFL bulbs, no product was obtained. The reaction could also take place in acetone as the solvent using 10 equivalents of THF and applying irradiation for

Design, synthesis and investigation of water-soluble hemi-indigo photoswitches for bioapplications

• Daria V. Berdnikova

Beilstein J. Org. Chem. 2019, 15, 2822–2829, doi:10.3762/bjoc.15.275

• the phenyl ring was performed through the aldol condensation of indoxyl-3-acetate with the corresponding benzaldehydes under alkaline conditions (Scheme 1) [13]. All compounds 1a–c were obtained in good yields as pure Z-isomers as supported by the NMR data (Figures S5–S13 in Supporting Information

1,5-Phosphonium betaines from N-triflylpropiolamides, triphenylphosphane, and active methylene compounds

• Vito A. Fiore,
• Chiara Freisler and
• Gerhard Maas

Beilstein J. Org. Chem. 2019, 15, 2603–2611, doi:10.3762/bjoc.15.253

• (PR3 = alkyl-substituted phosphane, but not PPh3) have been obtained from isonicotinaldehyde [15], and betaines IV from aryl tosylimines [16]. For the stability of betaines III, the nature of the aryl substituent is critical; with the combination Ph3P/DMAD/EWG-substituted benzaldehydes, cyclization

A new approach to silicon rhodamines by Suzuki–Miyaura coupling – scope and limitations

• Thines Kanagasundaram,
• Antje Timmermann,
• Carsten S. Kramer and
• Klaus Kopka

Beilstein J. Org. Chem. 2019, 15, 2569–2576, doi:10.3762/bjoc.15.250

• observation than cyanine-based fluorophores [24]. Different synthetic approaches were established to form the silicon rhodamine framework 1 (Scheme 1). While the group of Wu used a copper(II) bromide-catalyzed solvent-free condensation of a diarylsilane 2 with various benzaldehydes 3 [25], Sparr and Fischer

Recent advances in transition-metal-catalyzed incorporation of fluorine-containing groups

• Xiaowei Li,
• Xiaolin Shi,
• Xiangqian Li and
• Dayong Shi

Beilstein J. Org. Chem. 2019, 15, 2213–2270, doi:10.3762/bjoc.15.218

• –H fluorination of benzaldehydes. Notably, these transformations were achieved with orthanilic acids as new transient directing groups (TDGs) in DCE in the presence of air (Scheme 23). This approach employed 1-fluoro-2,4,6-trimethylpyridinium salts as a bystanding F+ oxidant or an electrophilic

Recent advances on the transition-metal-catalyzed synthesis of imidazopyridines: an updated coverage

• Gagandeep Kour Reen,
• Ashok Kumar and
• Pratibha Sharma

Beilstein J. Org. Chem. 2019, 15, 1612–1704, doi:10.3762/bjoc.15.165

• iron MOFs have resulted in lesser yield than Cu-MOF. The reaction has well tolerated different substituent on the reactants except for 4-NO2; 3,4-dichlorobenzaldehyde, 2-aminopyrimidine, and 2,4,6-triamino-1,3,5-triazine which failed to give the desired product. Also, benzaldehydes substituted with

• been tried with various Cu(I)- and Cu(II)-based catalysts but the use of a mixed nano-CuO/CuAl2O4 and ᴅ-glucose system has resulted in appreciable yields. This three-component one-pot reaction involved 2-AP, phenylacetylene and substituted benzaldehydes as the starting substrates (Scheme 34). The

Extending mechanochemical porphyrin synthesis to bulkier aromatics: tetramesitylporphyrin

• Qiwen Su and
• Tamara D. Hamilton

Beilstein J. Org. Chem. 2019, 15, 1149–1153, doi:10.3762/bjoc.15.111

• reaction medium [18]. This widened the variety of substituted aldehydes successfully converted to porphyrins, but employment of a caustic solvent at high temperature is a drawback. These conditions also proved inappropriate for several substituted benzaldehydes, and the best yields have been in the order

• yield similar to that obtained from the Lindsey synthesis. Additionally, several monosubstituted benzaldehydes, as well as two isomers of naphthaldehyde, were shown to undergo successful mechanochemical reaction in reasonable yields. Mesitaldehyde has been considered a representative “sterically

• groups become oriented above and below the plane of the porphyrin ring, forming a protective shroud around the reactive center, much like some protein systems (Figure 1B) [12][20][21][22]. The corresponding substituted benzaldehydes, however, have not easily yielded results upon reaction with pyrrole

Unexpected polymorphism during a catalyzed mechanochemical Knoevenagel condensation

• Sebastian Haferkamp,
• Andrea Paul,
• Adam A. L. Michalchuk and
• Franziska Emmerling

Beilstein J. Org. Chem. 2019, 15, 1141–1148, doi:10.3762/bjoc.15.110

• condensation in detail. Results and Discussion The catalyzed Knoevenagel condensations of mono-fluorinated benzaldehydes 1a–c with malonodinitrile (2) are depicted in Scheme 1. In contrast to previous work, which reported the uncatalyzed reaction [19], piperidine was used as a basic catalyst. This was done as

• the fluorinated benzaldehydes 1a–c no XRPD pattern could be recorded. For the reaction of 1a with 2, the amount of catalyst was varied and the reaction monitored in each case. XRPD analysis confirmed that, independent of the amount of catalyst, the same bulk product was formed. The intensity of the

• led directly to formation of m3b [23] and m3c [28], respectively, at both 30 Hz and 50 Hz milling frequency (Figures S4 and S5 in Supporting Information File 1). Conclusion The mechano-assisted catalyzed Knoevenagel condensation of mono-fluorinated benzaldehydes and malonodinitrile was explored in

Novel (2-amino-4-arylimidazolyl)propanoic acids and pyrrolo[1,2-c]imidazoles via the domino reactions of 2-amino-4-arylimidazoles with carbonyl and methylene active compounds

• Victoria V. Lipson,
• Tetiana L. Pavlovska,
• Nataliya V. Svetlichnaya,
• Anna A. Poryvai,
• Nikolay Yu. Gorobets,
• Erik V. Van der Eycken,
• Irina S. Konovalova,
• Svetlana V. Shiskina,
• Alexander V. Borisov,
• Vladimir I. Musatov and
• Alexander V. Mazepa

Beilstein J. Org. Chem. 2019, 15, 1032–1045, doi:10.3762/bjoc.15.101

• Knoevenagel–Michael adducts (Figure 2) [24]. By analogy with our results obtained with the use of other aminoazoles in the reactions with benzaldehydes and Meldrum’s acid [25] we expected the formation of one or several isomers of tetrahydroimidazopyrimidinone derivatives (Figure 2). However, a short time (3

• –5 min) and reflux of the equimolar amounts of amines 1, para-substituted benzaldehydes 2, and Meldrum’s acid 3 in 2-propanol led to Knoevenagel–Michael adducts 4a–h (Table 1). Beside the short reaction times and mild conditions, this catalyst-free three-component condensation is characterized by a

• active compounds, that can lead to cyclic products, has a high potential for diversity-oriented synthesis. In the three-component condensations of equimolar amounts of 2-amino-4-arylimidazoles 1, para-substituted benzaldehydes 2 and malononitrile (12) in 2-propanol the Knoevenagel–Michael adduct was not

Mechanochemistry of supramolecules

• Anima Bose and
• Prasenjit Mal

Beilstein J. Org. Chem. 2019, 15, 881–900, doi:10.3762/bjoc.15.86

• achieved from benzyl alcohol using a Br+ source as the catalyst (Figure 16). In the reaction pot subcomponents such as benzaldehydes and H+ were formed which further participated in a cascade transformation to give dihydropyrimidones 29. Dynamic combinatorial chemistry and mechano-milling Dynamic

Volatiles from the hypoxylaceous fungi Hypoxylon griseobrunneum and Hypoxylon macrocarpum

• Jan Rinkel,
• Alexander Babczyk,
• Tao Wang,
• Marc Stadler and
• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2018, 14, 2974–2990, doi:10.3762/bjoc.14.277

• Geniculosporium sp. [18] and on a series of structurally related phenols, benzaldehydes and anisole derivatives from Hypoxylon invadens [19] that could only be identified with certainty following this approach of extensive compound comparisons. Members of the family Hypoxylaceae are regarded to be extremely rich

The mechanochemical synthesis of quinazolin-4(3H)-ones by controlling the reactivity of IBX

• Md Toufique Alam,
• Saikat Maiti and
• Prasenjit Mal

Beilstein J. Org. Chem. 2018, 14, 2396–2403, doi:10.3762/bjoc.14.216

• benzaldehydes, aniline and IBX under ball-milling conditions an explosion was observed (Figure 1a; Caution! see experimental section) [30][31] and similar observations were made with Dess–Martin periodinane (DMP). On the other hand, benzamide was found to be unreactive with IBX and no reaction was observed

• when monoalkyl-substituted benzaldehydes (3a,b and 3d–f) were used compared to the reaction with unsubstituted benzaldehyde (3c). However, sterically congested aromatic aldehydes afforded the desired quinazolin-4(3H)-ones 3g and 3u in relatively poor yields. The reactions were found to proceed smoothly