Recent advances in organocatalytic asymmetric aza-Michael reactions of amines and amides

• Pratibha Sharma,
• Raakhi Gupta and
• Raj K. Bansal

Beilstein J. Org. Chem. 2021, 17, 2585–2610, doi:10.3762/bjoc.17.173

• accomplishing highly useful organic syntheses without causing environmental pollution in compliance with ‘Green Chemistry” has been a landmark development in the recent past. Application of many of these organocatalysts has been extended to asymmetric aza-MR during the last two decades. The present article

• number of publications in this field. These organocatalysts have been found compatible with many aspects of ‘Green Chemistry’ on the one hand, and highly selective in many organic syntheses on the other hand [17]. It has an added advantage that a large number of enantiomerically pure organocatalysts can

• the nitrogen nucleophiles, such as aromatic amines and amides which are otherwise averse to reacting. The organocatalysts have emerged as catalysts of choice due to various reasons, such as their compatibility with the ‘Green Chemistry’ and possibility of tailoring them according to the requirements

Visible-light-mediated copper photocatalysis for organic syntheses

• Yajing Zhang,
• Qian Wang,
• Zongsheng Yan,
• Donglai Ma and
• Yuguang Zheng

Beilstein J. Org. Chem. 2021, 17, 2520–2542, doi:10.3762/bjoc.17.169

• renewable energy and green chemistry for many years. Ruthenium and iridium, which can be used as photoredox catalysts, are expensive and scarce in nature. Thus, the further development of catalysts based on these transition metals is discouraged. Alternative photocatalysts based on copper complexes are

• complexes to photocatalysis are reported. Copper-photocatalyzed reactions, including alkene and alkyne functionalization, organic halide functionalization, and alkyl C–H functionalization that have been reported over the past 5 years, are included. Keywords: copper-photocatalyzed reactions; green chemistry

Recent advances in the tandem annulation of 1,3-enynes to functionalized pyridine and pyrrole derivatives

• Yi Liu,
• Puying Luo,
• Yang Fu,
• Tianxin Hao,
• Xuan Liu,
• Qiuping Ding and
• Yiyuan Peng

Beilstein J. Org. Chem. 2021, 17, 2462–2476, doi:10.3762/bjoc.17.163

• Yi Liu Puying Luo Yang Fu Tianxin Hao Xuan Liu Qiuping Ding Yiyuan Peng Key Laboratory for Green Chemistry of Jiangxi Province, Key Laboratory of Functional Small Organic Molecules, Ministry of Education, Jiangxi Normal University, 99 Ziyang Road, Nanchang 330022, China Department of Gynaecology

A visible-light-induced, metal-free bis-arylation of 2,5-dichlorobenzoquinone

• Pieterjan Winant and
• Wim Dehaen

Beilstein J. Org. Chem. 2021, 17, 2315–2320, doi:10.3762/bjoc.17.149

• salts; Green Chemistry; Meerwein arylation; photoredox; Introduction Quinones or quinoid-based structures are ubiquitous in nature [1][2][3]. These versatile structures have shown promising antimalarial [4][5], antibacterial [6], and chemotherapeutic [6][7][8] properties. Their inherent oxidative

Asymmetric organocatalyzed synthesis of coumarin derivatives

• Natália M. Moreira,
• Lorena S. R. Martelli and
• Arlene G. Corrêa

Beilstein J. Org. Chem. 2021, 17, 1952–1980, doi:10.3762/bjoc.17.128

• , the advances in asymmetric organocatalyzed synthesis of coumarin derivatives are discussed in this review, according to the mode of activation of the catalyst. Keywords: asymmetric synthesis; green chemistry; 2H-chromen-2-one; organocatalysis; Introduction Coumarins are important naturally occurring

• as harsh reaction conditions, has become paramount in the field of organic synthesis in recent years [19]. In this sense, Molnar et al. published a review on green chemistry approaches to the synthesis of coumarin derivatives [20] and Chandrakar et al. reviewed the developments of multicomponent

• synthesis of biologically relevant coumarins in aqueous medium [21]. Catalysis is one of the fundamental pillars of green chemistry [22], and the transition-metal-catalyzed synthesis of coumarins has been reviewed by Sharma et al. [23]. More recently, Kanchana et al. published an account on the palladium

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

• deliver ‘greener’ chemical processes at the lowest possible cost. The 12 principles of green chemistry were introduced in 1998 by Paul Anastas and John Warner [40] and outline what is meant by and to be expected of a green chemical, process or product. Principles for which flow chemistry may be pertinent

• the compatibility of the flow approach with a green chemical manufacturing future. It is also not difficult to see how continuous manufacturing has implications for important green chemistry metrics such as atom economy, reaction mass efficiency, effective mass yield, carbon efficiency and

• yield of 91% under optimal conditions. Beneficially as all components were liquids the need for a solvent was completely avoided; from a green chemistry standpoint this is highly attractive and the intrinsic low melting points of many fragrance ingredients and precursors lend themselves to continuous

Nitroalkene reduction in deep eutectic solvents promoted by BH₃NH₃

• Chiara Faverio,
• Monica Fiorenza Boselli,
• Patricia Camarero Gonzalez,
• Alessandra Puglisi and
• Maurizio Benaglia

Beilstein J. Org. Chem. 2021, 17, 1041–1047, doi:10.3762/bjoc.17.83

• materials that can be used to form eutectic mixtures offers an incredibly high variety of combinations to generate new, safe and biodegradable DESs [5]. Another fundamental principle of green chemistry is the atom economy concept. In this context, ammonia borane (AB) is receiving increasing attention as

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

• majority of the atoms of the starting materials. The ability of forming multiple bonds in one-pot via a multicomponent reaction provides a novel and sustainable method in drug discovery [4]. In the recent years, these reactions have emerged as a promising strategy following green chemistry principles such

Synthetic reactions driven by electron-donor–acceptor (EDA) complexes

• Zhonglie Yang,
• Yutong Liu,
• Kun Cao,
• Xiaobin Zhang,
• Hezhong Jiang and
• Jiahong Li

Beilstein J. Org. Chem. 2021, 17, 771–799, doi:10.3762/bjoc.17.67

• in line with the theme of green chemistry. This review discusses the synthetic reactions concerned with EDA complexes as well as the mechanisms that have been shown over the past five years. Keywords: EDA complex; electron acceptor; electron donor; radical; visible light; Review Introduction

• majority cases. Moreover, in line with the theme of green chemistry, light is the sole external energy source in EDA complex pathways. Except for the pioneering research on EDA complexes in the 20th century, there was not much progress in the follow-up. Until the past few years, EDA-complex photochemistry

• external energy source, which is consistent with the theme of green chemistry. However, the comprehension of EDA complexes was established relatively late, mainly owing to the fact that the formation of EDA complexes was regarded as a unique chemical reaction rather than a branch of photochemistry; in

A sustainable strategy for the straightforward preparation of 2H-azirines and highly functionalized NH-aziridines from vinyl azides using a single solvent flow-batch approach

• Michael Andresini,
• Leonardo Degannaro and
• Renzo Luisi

Beilstein J. Org. Chem. 2021, 17, 203–209, doi:10.3762/bjoc.17.20

• and potentially automatable method for the synthesis of interesting strained compounds. Keywords: aziridines; 2H-azirines; flow chemistry; green chemistry; organolithium compounds; Introduction Since their conception in the early 1990s, Green Chemistry Principles (GCP) have been applied with

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

• azaarene derivatives under neat conditions through a highly atom-economical pathway. To evaluate the preparative potential of this process, gram-scale reactions were performed up to a 10 g scale. Keywords: aldehydes; azaarenes; benzylic addition; green chemistry; solvent-free conditions; Introduction

• reevaluated. Therefore, alternatives with environmentally benign reagents are much in focus. Correspondingly, considering the exemplar shift from conventional synthetic methodologies towards green chemistry, there have been some alternatives or replacements of toxic catalysts and hazardous solvents in

Regioselective synthesis of heterocyclic N-sulfonyl amidines from heteroaromatic thioamides and sulfonyl azides

• Vladimir Ilkin,
• Vera Berseneva,
• Tetyana Beryozkina,
• Tatiana Glukhareva,
• Lidia Dianova,
• Wim Dehaen,
• Eugenia Seliverstova and
• Vasiliy Bakulev

Beilstein J. Org. Chem. 2020, 16, 2937–2947, doi:10.3762/bjoc.16.243

• amidines of azolyl and pyridine carboxylic acids. The most promising aspect for organic synthesis and green chemistry is a solvent-free process which was successfully applied to prepare sulfonyl amidines containing pyridine and isoxazolyl rings and 1-alkyl-1,2,3-triazole-4-N-sulfonylamidino-1,2,3-triazoles

Ultrasound-assisted Strecker synthesis of novel 2-(hetero)aryl-2-(arylamino)acetonitrile derivatives

• Emese Gal,
• Luiza Gaina,
• Hermina Petkes,
• Alexandra Pop,
• Castelia Cristea,
• Gabriel Barta,
• Dan Cristian Vodnar and
• Luminiţa Silaghi-Dumitrescu

Beilstein J. Org. Chem. 2020, 16, 2929–2936, doi:10.3762/bjoc.16.242

• contributor to green chemistry mainly due to the ability of minimizing the energy consumption required by chemical transformations and allowing the development of environmentally friendly chemical procedures which may be eventually scaled up for industrial applications [1]. For the synthesis of organic

• ] was customized for phenothiazinyl aldimine substrates (Scheme 1), but an extremely long reaction time was required (72 hours) for the reaction to complete. In order to enhance the reaction rate, alternative energy sources were taken into consideration and ultrasonic irradiation was selected as a green

• chemistry protocol capable of inducing a more efficient energy input. Indeed, the reaction rate was significantly increased by applying the new protocol modified by means of an indirect ultrasound irradiation technique and high yields of the α-(arylamino)acetonitrile products were obtained after 30 minutes

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

• chemistry and has attracted much interest. For 1,3-dipolar cycloaddition reactions microwave irradiation not only allows to reduce the reaction time and to increase yields, but in some cases also can affect the selectivity of the reaction [34][35][36]. The efficiency of microwave irradiation has been shown

Dawn of a new era in industrial photochemistry: the scale-up of micro- and mesostructured photoreactors

• Emine Kayahan,
• Mathias Jacobs,
• Leen Braeken,
• Leen C.J. Thomassen,
• Simon Kuhn,
• Tom van Gerven and
• M. Enis Leblebici

Beilstein J. Org. Chem. 2020, 16, 2484–2504, doi:10.3762/bjoc.16.202

• selective, which would potentially reduce the downstream costs significantly if the process is optimized properly. With the transition towards green chemistry, the traditional batch photoreactor operation is becoming abundant in this field. Process intensification efforts led to micro- and mesostructured

• designing multiphase photoreactors, and this complicates the design even further [10]. Photoreactions are typically performed in batch reactors. With the process intensification efforts towards green chemistry approaches, continuous flow technologies, micro- and mesostructured flow photoreactors having

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

• inefficient initiation step (i.e., Φinitiation << 1) (Equation 1). A less common use of quantum yields by organic synthetic chemists is as a measure of how efficiently the reaction uses the light source. Considering photocatalysis is often purported as a green chemistry because it uses light, a more efficient

A proposed sustainability index for synthesis plans based on input provenance and output fate: application to academic and industrial synthesis plans for vanillin as a case study

• John Andraos

Beilstein J. Org. Chem. 2020, 16, 2346–2362, doi:10.3762/bjoc.16.196

• ) consumption, input enthalpic energy (IEE) consumption, Rowan solvent greenness index (RSGI), and sustainability index (SI). Keywords: Borda count; green chemistry; input enthalpic energy; process mass intensity; poset dominance analysis; Rowan solvent greenness index; sacrificial reagent; sustainability

• recent article published in Chemical and Engineering News in 2019 [1] nicely highlighted the problem in the context of distinguishing the terms green chemistry from sustainable chemistry. It was noted that “the term sustainable chemistry has been introduced more recently and possesses countless

• -derived materials. In any event, the task of tracing starting materials, catalysts, and reaction solvent syntheses is very tedious, especially for time-pressed chemists who wish to practice green chemistry. However, such a task can be significantly alleviated if synthesis databases of first, second, and

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

• employing 2-(allyloxy)benzaldehyde (1a) and diphenylphosphine oxide (DPPO, 2a) as the model substrates with K2S2O8 as the oxidant, which is a cheap, readily available, and versatile oxidant. On the basis of literature reports [29][30] and our continuing interest in green chemistry [31][32], we set the

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

• reported. Evaluation of the green chemistry metrics for the synthesis of benzimidazoles 3, dihydropyrimidinones 7, and highly functionalized pyridines 11 In order to evaluate the “greenness” of the proposed methodologies, the green chemistry metrics, such as the atom economy (AE), E-factor, process mass

• excellent AE (88–95%) and Curzon’s RME (78–93%) as well as a low to moderate E-factor (26.202–50.760) and PMI (27.202–51.760). The detailed calculations of the green chemistry metrics (AE, E-factor, PMI, Curzon’s RME, and gRME) for the synthesis of the compounds 3a, 7a, and 11a (Table 8, entry 1, Table 9

• Green chemistry metrics for the synthesis of 2-aryl-1-arylmethyl-1H-benzo[d]imidazoles 3. Green chemistry metrics for the synthesis of dihydropyrimidinones/-thiones 7. Green chemistry metrics for the synthesis of 2-amino-4-(hetero)aryl-3,5-dicarbonitrile-6-sulfanylpyridines 11. Supporting Information

Stereoselective Biginelli-like reaction catalyzed by a chiral phosphoric acid bearing two hydroxy groups

• Xiaoyun Hu,
• Jianxin Guo,
• Cui Wang,
• Rui Zhang and
• Victor Borovkov

Beilstein J. Org. Chem. 2020, 16, 1875–1880, doi:10.3762/bjoc.16.155

• compound making its application highly attractive from the viewpoint of sustainability and green chemistry. Recently, our group reported an asymmetric Biginelli reaction catalyzed by a new chiral phosphoric acid derived from natural tartaric acid, that yielded a high enantioselectivity (up to 99% ee) [17

Et₃N/DMSO-supported one-pot synthesis of highly fluorescent β-carboline-linked benzothiophenones via sulfur insertion and estimation of the photophysical properties

• Dharmender Singh,
• Vipin Kumar and
• Virender Singh

Beilstein J. Org. Chem. 2020, 16, 1740–1753, doi:10.3762/bjoc.16.146

• found to be slow reacting and produced 2aA in a lower yield (42%). From the perspective of green chemistry, one-pot reactions are preferred as less waste is generated due to the avoidance of work-up, isolation, and purification of intermediates [66]. Accordingly, the feasibility of a one-pot synthesis

Mechanochemical green synthesis of hyper-crosslinked cyclodextrin polymers

• Alberto Rubin Pedrazzo,
• Fabrizio Caldera,
• Marco Zanetti,
• Silvia Lucia Appleton,
• Nilesh Kumar Dhakar and
• Francesco Trotta

Beilstein J. Org. Chem. 2020, 16, 1554–1563, doi:10.3762/bjoc.16.127

• , and rhodamine B) and the still reactive imidazoyl carbonyl group of the NS. Keywords: β-cyclodextrin; ball-milling; crosslinking; green chemistry; mechanochemistry; nanosponges; Introduction The research in the fields of nanomedicine and nanotechnology has nowadays become predominant

• recycle because of their high boiling points. According to the Green Chemistry Principles, published in 1998 [10], processes have to be designed in order to “minimize the quantity of final waste and to avoid hazardous or toxic solvents”. Nanosponges themselves, nevertheless, are synthesized from starch

In silico rationalisation of selectivity and reactivity in Pd-catalysed C–H activation reactions

• Liwei Cao,
• Mikhail Kabeshov,
• Steven V. Ley and
• Alexei A. Lapkin

Beilstein J. Org. Chem. 2020, 16, 1465–1475, doi:10.3762/bjoc.16.122

• for in silico prediction of reaction outcomes. This approach was tested on the for green chemistry important class of C–H activation reactions. Whilst this study does not completely solve the problem of developing a robust chemical reaction, it offers an approach that is complementary to efforts of

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

• Xiaoming Ma Suzhi Meng Xiaofeng Zhang Qiang Zhang Shenghu Yan Yue Zhang Wei Zhang School of Pharmaceutical Engineering and Life Science, Changzhou University, Changzhou 213164, China Center for Green Chemistry and Department of Chemistry, University of Massachusetts Boston, 100 Morrissey Boulevard

The charge-assisted hydrogen-bonded organic framework (CAHOF) self-assembled from the conjugated acid of tetrakis(4-aminophenyl)methane and 2,6-naphthalenedisulfonate as a new class of recyclable Brønsted acid catalysts

• Svetlana A. Kuznetsova,
• Alexander S. Gak,
• Yulia V. Nelyubina,
• Vladimir A. Larionov,
• Han Li,
• Michael North,
• Vladimir P. Zhereb,
• Alexander F. Smol'yakov,
• Artem O. Dmitrienko,
• Michael G. Medvedev,
• Igor S. Gerasimov,
• Ashot S. Saghyan and
• Yuri N. Belokon

Beilstein J. Org. Chem. 2020, 16, 1124–1134, doi:10.3762/bjoc.16.99

• , 117198 Moscow, Russian Federation Green Chemistry Centre of Excellence, Department of Chemistry, University of York, Heslington, YO10 5DD, United Kingdom Siberian Federal University, School of Non-Ferrous Metals and Material Science, 95 Krasnoyarskiy Rabochiy pr., 660025 Krasnoyarsk, Russian Federation N