A hybrid electron donor comprising cyclopentadithiophene and dithiafulvenyl for dye-sensitized solar cells

• Gleb Sorohhov,
• Chenyi Yi,
• Michael Grätzel,
• Silvio Decurtins and
• Shi-Xia Liu

Beilstein J. Org. Chem. 2015, 11, 1052–1059, doi:10.3762/bjoc.11.118

• Discussion Synthesis Under Knoevenagel condensation reaction conditions, the corresponding aldehydes 4 and 7 can readily react with cyanoacetic acid leading to the target sensitizers 1 and 2, as depicted in Scheme 1. For the synthesis of the aldehyde precursor 4, the Horner–Wadsworth–Emmons (HWE) reaction

Multicomponent reactions in nucleoside chemistry

• Mariola Koszytkowska-Stawińska and
• Włodzimierz Buchowicz

Beilstein J. Org. Chem. 2014, 10, 1706–1732, doi:10.3762/bjoc.10.179

• considerable number of pacidamycin analogues. 4. The multicomponent domino reactions initiated by the Knoevenagel condensation The Knoevenagel condensation can be considered as one of the most useful tools for the formation of C=C double bonds. The condensation products, i.e., electron-deficient alkenes

• , readily act in subsequent reactions as Michael acceptors, Diels–Alder (hetero)dienes or dienophiles, or dipolarophiles. Multicomponent domino reactions initiated by the Knoevenagel condensation are a valuable tool for the construction of many compounds with complex molecular structures [90]. The syntheses

• shown in Scheme 23 and Scheme 24 represent examples of the Knoevenagel condensation-initiated domino reactions where the nucleoside aldehyde (i.e., 5-formyl-3',5'-di-O-acetyl-2'-deoxyuridine (14) or 5-formyl-2'-deoxyuridine (27)) acted as the Knoevenagel acceptor. Compounds 61 to 65 were prepared by the

Chemistry of polyhalogenated nitrobutadienes, 14: Efficient synthesis of functionalized (Z)-2-allylidenethiazolidin-4-ones

• Viktor A. Zapol’skii,
• Jan C. Namyslo,
• Mimoza Gjikaj and
• Dieter E. Kaufmann

Beilstein J. Org. Chem. 2014, 10, 1638–1644, doi:10.3762/bjoc.10.170

• thiazolidinone atropisomers, due to hindered rotation between the trichlorovinyl and the arylamino groups. X-ray analysis proved the Z-configuration of the nitrovinylidene group of 11. Subsequent reactions of the thiazolidinones, such as the SNVin thiolation in 2-position of the allylidene backbone, Knoevenagel

• condensation of the heterocyclic rings with aromatic aldehydes, and an unusual formation of persubstituted pyrazoles demonstrate the chemical versatility of these heterocyclic systems. The newly formed thiazolidinones deserve additional synthetic interest as starting materials, also due to their trichlorovinyl

Primary-tertiary diamine-catalyzed Michael addition of ketones to isatylidenemalononitrile derivatives

• Akshay Kumar and
• Swapandeep Singh Chimni

Beilstein J. Org. Chem. 2014, 10, 929–935, doi:10.3762/bjoc.10.91

• involves the initial formation of isatylidenemalononitrile by Knoevenagel condensation of isatin with malononitrile followed by the addition of acetone to provide Michael adduct 4a. Thus, catalyst 1a also finds its successful application in the multicomponet version of this reaction without compromising

• isatylidenemalononitrile. Substrate scope of the addition of 2 with 3 catalyzed by 1a D-CSA. One-pot, three-component Knoevenagel condensation–Michael addition. Cascade reduction–cyclization for the synthesis of spirooxindole. Solvent screening the Michael addition of acetone (2a) to isatylidenemalononitrile (3a

Substrate dependent reaction channels of the Wolff–Kishner reduction reaction: A theoretical study

• Shinichi Yamabe,
• Guixiang Zeng,
• Wei Guan and
• Shigeyoshi Sakaki

Beilstein J. Org. Chem. 2014, 10, 259–270, doi:10.3762/bjoc.10.21

• (C=O → C=C, alkene) conversion reaction, the Knoevenagel condensation [12] was utilized. While the condensation is traditionally base-catalyzed, it was found to proceed readily in water even without any catalyst [13][14]. Not only can this synthesis be considered as clean (green chemistry), but also

• conversion? An investigation about the role of the proton transfers along the hydrogen bonds may be of interest. Is a base-free W-K reduction comparable to the Knoevenagel condensation possible? Which path (a) or (b) in Scheme 2 is more favorable? Is the carbanion R1(R2)HC− a probable intermediate? Is the

• uncatalyzed (without base) Knoevenagel condensation in water. Experimental conditions and yields are taken from a) ref. [13] and b) ref. [14], respectively. Reaction models of neutral (a) and anionic (b) systems. Water molecules are linked to oxygen lone-pair orbitals and to H–N bonds of hydrazine. In the

Recent applications of the divinylcyclopropane–cycloheptadiene rearrangement in organic synthesis

• Sebastian Krüger and
• Tanja Gaich

Beilstein J. Org. Chem. 2014, 10, 163–193, doi:10.3762/bjoc.10.14

• ozonolysis to give aldehyde 136 [123]. Knoevenagel condensation with 4-iodooxindole was achieved in the next step. Pfitzner–Moffatt oxidation [124] followed by elimination furnished trans-divinylcycloproane 137. Submission of this compound to elevated temperature initiated a very smooth DVCPR yielding

Investigating the continuous synthesis of a nicotinonitrile precursor to nevirapine

• Ashley R. Longstreet,
• Suzanne M. Opalka,
• Brian S. Campbell,
• B. Frank Gupton and
• D. Tyler McQuade

Beilstein J. Org. Chem. 2013, 9, 2570–2578, doi:10.3762/bjoc.9.292

• complicate downstream operations. We immediately recognized the water formed in the Knoevenagel condensation would quench the DMF-DMA in the second step. In addition, our batch Knoevenagel condensation was base catalyzed and we discovered that base increased dimer byproducts in the enamine step. Therefore

• of normal process windows [45]. Attempts to increase the reaction concentration beyond 1.0 M led to reactor clogging due to the limited of solubility of 5. We proceeded to develop a continuous process by coupling the enamine step with the Knoevenagel condensation (Scheme 4). To achieve this, we

• that the Knoevenagel condensation occurred primarily in the Al2O3 column, we only varied the temperature of the Al2O3 column. The Al2O3 column temperature was initially set to 25 °C which yielded 91% of 5 from acetone and malononitrile (Table 2, entry 2). We observed that the Al2O3 column reactor

An overview of the synthetic routes to the best selling drugs containing 6-membered heterocycles

• Marcus Baumann and
• Ian R. Baxendale

Beilstein J. Org. Chem. 2013, 9, 2265–2319, doi:10.3762/bjoc.9.265

• readily prepared by chlorination of 2-pyridone (1.42) with phosphorous oxychloride (Scheme 8) [31][32]. The resulting primary alcohol 1.45 is then subjected to a second SNAr reaction with 4-fluorobenzaldehyde [33]. A Knoevenagel condensation of the aldehyde functionality in compound 1.47 with

• chromium(VI) oxide yielded the aldehyde 1.67 required for the previously described Knoevenagel condensation. The five membered heterocycle 2,4-thiazolidinedione (1.68) is readily available commercially, but can be easily prepared at scale via a simple cyclocondensation between thiourea and chloroacetic

• crude material in the subsequent Knoevenagel condensation with thiazolidinedione 1.68. In order to reduce the intermediate benzylidene double bond in this example sodium borohydride is used in the presence of cobalt chloride efficiently delivering pioglitazone in high purity. Other syntheses of

Raman spectroscopy as a tool for monitoring mesoscale continuous-flow organic synthesis: Equipment interface and assessment in four medicinally-relevant reactions

• Trevor A. Hamlin and
• Nicholas E. Leadbeater

Beilstein J. Org. Chem. 2013, 9, 1843–1852, doi:10.3762/bjoc.9.215

• conversion using NMR spectroscopy. Comparison of the values shows a good correlation (Table 1). Expanding the technique to other reactions The Knovenagel condensation We turned our attention next to the Knoevenagel condensation of ethyl acetoacetate with a range of aromatic aldehydes (Scheme 2). Our

• )-one (4a) across a range of reaction conditions (scan time = 15 s, integration = 10 s). The reaction between salicylaldehyde and ethyl acetoacetate to form 3-acetyl coumarin (1). The Knoevenagel condensation of benzaldehyde and ethyl acetoacetate to yield (Z)-ethyl 2-benzylidene-3-oxobutanoate (2a

Enhancement of efficiency in organic photovoltaic devices containing self-complementary hydrogen-bonding domains

• Rohan J. Kumar,
• Jegadesan Subbiah and
• Andrew B. Holmes

Beilstein J. Org. Chem. 2013, 9, 1102–1110, doi:10.3762/bjoc.9.122

• ] followed by a Knoevenagel condensation provided the target compound 2 in excellent yield. The solubilizing strategy of incorporating alkyl groups on the thiophene unit provided the compound with excellent solubility in a wide range of common solvents. Optoelectronic properties In chloroform solution the UV

Synthesis of functionalized spiro[indoline-3,4’-pyridines] and spiro[indoline-3,4’-pyridinones] via one-pot four-component reactions

• Li-Juan Zhang,
• Qun Wu,
• Jing Sun and
• Chao-Guo Yan

Beilstein J. Org. Chem. 2013, 9, 846–851, doi:10.3762/bjoc.9.97

• ester A from the addition of arylamine to methyl propiolate. The second reaction is a Knoevenagel condensation of isatin with malononitrile or ethyl cyanoacetate under the catalysis of triethylamine to give the isatylidene deriatives B. The third reaction is a Michael addition of β-enamino ester

Reactions of salicylaldehyde and enolates or their equivalents: versatile synthetic routes to chromane derivatives

• Ishmael B. Masesane and
• Zelalem Yibralign Desta

Beilstein J. Org. Chem. 2012, 8, 2166–2175, doi:10.3762/bjoc.8.244

• a C-2 phenyl substituent. The synthesis of flavans and flavones generally involves treatment of acetophenone (7) with a base to give enolate 8, which undergoes a Knoevenagel condensation with salicylaldehyde (5) to yield a chalcone 9. These chalcone derivatives are then cyclized by using various

• of salicylaldehyde (5) with dimedone (18) in the presence of a catalytic amount of KF/Al2O3 (Scheme 6) [21]. The reaction is thought to proceed through a Knoevenagel condensation, a Michael addition and an intramolecular cyclization. The reaction was repeated with chloro-, bromo-, dichloro-, dibromo

• synthetic procedures involve a Knoevenagel condensation followed by intramolecular cyclization. In a detailed study directed towards understanding the pathway of the reaction of salicylaldehyde (5) and malononitrile (20), Costa and co-workers reported the efficient synthesis of 2-iminochromene 21 in 90

Total synthesis and biological evaluation of fluorinated cryptophycins

• Christine Weiß,
• Tobias Bogner,
• Benedikt Sammet and
• Norbert Sewald

Beilstein J. Org. Chem. 2012, 8, 2060–2066, doi:10.3762/bjoc.8.231

• synthesis of the para-trifluoromethyl substituted unit A started with a modified Knoevenagel condensation [23][31]. The required aldehyde 9 was obtained by DIBAL-H reduction of the corresponding methyl ester 8 and was found to decompose upon chromatographic purification (Scheme 1). However, it can usually

• be employed in the Knoevenagel condensation without purification. Reaction of 9 with malonic acid in the presence of piperidine/acetic acid gave the β,γ-unsaturated carboxylic acid 10. The latter compound was transformed into the methyl ester by treatment with SOCl2 in methanol. The resulting ester

Catalyst-free and solvent-free Michael addition of 1,3-dicarbonyl compounds to nitroalkenes by a grinding method

• Zong-Bo Xie,
• Na Wang,
• Ming-Yu Wu,
• Ting He,
• Zhang-Gao Le and
• Xiao-Qi Yu

Beilstein J. Org. Chem. 2012, 8, 534–538, doi:10.3762/bjoc.8.61

• reactions occur more efficiently in the solid state than in solution due to a more tight and regular arrangement of the substrate molecules [14]. Thus, the grinding mode for solid-state reactions had been applied in the Reformatsky reaction [15], Dieckmann condensation [16], Knoevenagel condensation [17

An overview of the key routes to the best selling 5-membered ring heterocyclic pharmaceuticals

• Marcus Baumann,
• Ian R. Baxendale,
• Steven V. Ley and
• Nikzad Nikbin

Beilstein J. Org. Chem. 2011, 7, 442–495, doi:10.3762/bjoc.7.57

• acceptor obtained from an initial Knoevenagel condensation (Scheme 5). In order to improve the overall yield as well as the convergency, the industrial route [7] introduced the fully elaborated side chain 34 by condensation with the previously described 1,4-diketone 31 (Scheme 5 and Scheme 6). The desired

The preparation of 3-substituted-1,5-dibromopentanes as precursors to heteracyclohexanes

• Bryan Ringstrand,
• Martin Oltmanns,
• Jeffrey A. Batt,
• Aleksandra Jankowiak,
• Richard P. Denicola and
• Piotr Kaszynski

Beilstein J. Org. Chem. 2011, 7, 386–393, doi:10.3762/bjoc.7.49

• ]. The second route (Method 1B) consists of a Knoevenagel condensation of malonate diester and an aldehyde followed by conjugate addition of a second equivalent of malonate diester. The tetraester is hydrolyzed, decarboxylated, esterified, and then reduced to give the diol. Yields for tetraesters are in

Chromo- and fluorophoric water-soluble polymers and silica particles by nucleophilic substitution reaction of poly(vinyl amine)

• Katja Hofmann,
• Ingolf Kahle,
• Frank Simon and
• Stefan Spange

Beilstein J. Org. Chem. 2010, 6, No. 79, doi:10.3762/bjoc.6.79

• material acenaphthylene-1,2-dione undergoes a Knoevenagel condensation with malononitrile to give mono-adduct 2. Compound 2 was originally synthesized by Junek et al. [38]. However, no detailed NMR data were reported. In a second step, cyclization with anhydrous K2CO3 converted 2 to 1 in a good yield. In

Synthesis of some novel annulated pyrido[2,3-d]pyrimidines via stereoselective intramolecular hetero Diels–Alder reactions of 1-oxa-1,3-butadienes

• Mohit L. Deb and
• Pulak J. Bhuyan

Beilstein J. Org. Chem. 2010, 6, No. 11, doi:10.3762/bjoc.6.11

• the mixtures of both the cis- and trans-isomers [52][53]. When N-methylallylamine (2b) or N-benzylallylamine (2c) was used for the reaction as shown in Scheme 1, the Knoevenagel condensation did not occur even after refluxing in the presence of piperidine. The reason might be the delocalization of the

• 3a as a yellow solid 568 mg (95%). Similarly, 3b–c were prepared from the reaction of 1 with 2b–c. Knoevenagel condensation of 3 with cyclic β-diamide/β-diketones 4 and synthesis of 5: Equimolar amounts of 3a (2 mmol, 598 mg) and 4a (2 mmol, 312 mg) were mixed thoroughly in a round-bottomed flask

• consideration of its spectroscopic data. In case of N-methylallylamine 2b and N-benzylallylamine 2c, N,N-diisopropylethylamine (DIPEA) was used as catalyst for the Knoevenagel condensation and reactions were performed under reflux in ethanol for 3 h. The method gave satisfactory yields of up to 90%. Compounds

Hydroxyapatite supported caesium carbonate as a new recyclable solid base catalyst for the Knoevenagel condensation in water

• Monika Gupta,
• Rajive Gupta and
• Medha Anand

Beilstein J. Org. Chem. 2009, 5, No. 68, doi:10.3762/bjoc.5.68

• Monika Gupta Rajive Gupta Medha Anand Department of Chemistry, University of Jammu, Jammu 180 006, India 10.3762/bjoc.5.68 Abstract The Knoevenagel condensation between aromatic aldehydes and malononitrile, ethyl cyanoacetate or malonic acid with hydroxyapatite supported caesium carbonate in

• water is described. HAP–Cs2CO3 was found to be a highly active, stable and recyclable catalyst under the reaction conditions. Keywords: ethyl cyanoacetate; hydroxyapatite supported caesium carbonate; Knoevenagel condensation; malonic acid; malononitrile; Introduction An area of recent intense

• across a diverse array of C–C bond forming reactions. Without doubt, an alternative strategy for the Knoevenagel condensation [7] by this approach is worthwhile since it produces an extended domain of useful products for use in the pharmaceutical and biomedical industries. Arylidenemalononitriles are

Zeolite catalyzed solvent- free one-pot synthesis of dihydropyrimidin- 2(1H)-ones – A practical synthesis of monastrol

• Mukund G. Kulkarni,
• Sanjay W. Chavhan,
• Mahadev P. Shinde,
• Dnyaneshwar D. Gaikwad,
• Ajit S. Borhade,
• Attrimuni P. Dhondge,
• Yunnus B. Shaikh,
• Vijay B. Ningdale,
• Mayur P. Desai and
• Deekshaputra R. Birhade

Beilstein J. Org. Chem. 2009, 5, No. 4, doi:10.3762/bjoc.5.4

• conditions, even on using excess of ethyl acetoacetate (2 mmol), no side product arising through Knoevenagel condensation [41] was observed. This methodology was effective for aliphatic as well as aromatic aldehydes in the preparation of dihydropyrimidones (4a–4l) with uniformly high yields (Table 1). This

Catalytic synthesis of (E)-α,β-unsaturated esters from aldehydes and 1,1-diethoxyethylene

• Rubén Manzano,
• Lidia Ozores,
• Andreas Job,
• Lars Rodefeld and
• Benjamin List

Beilstein J. Org. Chem. 2009, 5, No. 3, doi:10.3762/bjoc.5.3

• satisfactory with respect to the demand for atom economy is still needed [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]. We have recently developed a new approach based on the Knoevenagel condensation of readily available and inexpensive malonate half esters with aldehydes which

Sordarin, an antifungal agent with a unique mode of action

• Huan Liang

Beilstein J. Org. Chem. 2008, 4, No. 31, doi:10.3762/bjoc.4.31

• dioxenone 47. This allowed the Knoevenagel condensation to be performed directly. In both the racemic and asymmetric syntheses, tricyclic compound 48 was prepared by Cu(I)-catalyzed conjugate addition of vinylmagnesium chloride to 45 in the presence of TMSCl, followed by enol acetylation (Scheme 10

The tert- amino effect in heterocyclic chemistry: Synthesis of new fused pyrazolinoquinolizine and 1,4-oxazinopyrazoline derivatives

• Dipak Prajapati and
• Kalyan Jyoti Borah

Beilstein J. Org. Chem. 2007, 3, No. 43, doi:10.1186/1860-5397-3-43

• effect, which generalizes cyclization of certain derivatives of 3-methyl-1-phenyl-2-pyrazolin-5-ones. Using this strategy a variety of fused heterocycles is obtained by the Knoevenagel condensation of 5-tert-amino-3-methyl-1-phenylpyrazolone-4-carboxal-dehyde 3 with active methylene compounds such as

• Knoevenagel condensation reactions with malonodinitrile to give the corresponding pyrazolin-5-ylmethylenemalonodinitriles 4a, which in turn cyclized in the presence of anhydrous zinc chloride to get the corresponding pyrazolinoquinolizines 6a and 1,4-oxazinopyrazolines 6e in refluxing toluene (Scheme 1). The

An efficient synthesis of novel pyrano[2,3-d]- and furopyrano[2,3-d]pyrimidines via indium- catalyzed multi- component domino reaction

• Dipak Prajapati and
• Mukut Gohain

Beilstein J. Org. Chem. 2006, 2, No. 11, doi:10.1186/1860-5397-2-11

• respectively for diastereomer A. The configuration of diastereomer A may therefore be assigned as trans and cis for the diasteromer B. The formation of these heterocycles 5 can be rationalized by initial formation of a conjugated electron-deficient heterodiene by standard Knoevenagel condensation of the

• [2,3-d]pyrimidine 7 in excellent yields. Knoevenagel condensation of the aromatic aldehyde with 1,3-dimethylbarbuturic acid occurs first with the formation of an electron-deficient, sterically fixed 1-oxo-1,3-butadiene 3 which then reacts with 2,3-dihydrofuran in a Diels-Alder reaction with inverse

• comparable yields. The structure of all the products thus obtained were characterized by elemental and spectral analyses. Conclusion In conclusion, we have shown that the multicomponent domino Knoevenagel condensation/hetero-Diels-Alder reaction of aromatic aldehydes with 1,3-dimethylbarbituric acid and