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