Biosynthesis of oxygen and nitrogen-containing heterocycles in polyketides

• Franziska Hemmerling and
• Frank Hahn

Beilstein J. Org. Chem. 2016, 12, 1512–1550, doi:10.3762/bjoc.12.148

• thiotetronates 166–168, it was postulated that this mechanism is general for the formation of this type of heterocycle. 1.7.2 Oxidative cyclisation: Aurones. Aurones are yellow coloured pigments of ornamental flowers that belong to the flavonoids. They are structurally closely related to chalcones, from which

• they differ by a central, annelated furan-3-one moiety instead of an acrylate unit (Scheme 25) [149]. Their biosynthesis proceeds from chalcones by an oxidation–conjugate addition cascade catalysed by plant phenol oxidases (PPOs) [150][151]. The PPO aureusidin synthase plays a central role in aurone

• consumption of hydrogen peroxide. It has been shown that the AS is substrate tolerant and accepts different hydroxylation patterns as well as glycosylations on the chalcone A and B rings [154]. However, the oxidative half-reaction only occurs with chalcones and not with other aryl substrates like L-tyrosine

Recent advances in N-heterocyclic carbene (NHC)-catalysed benzoin reactions

• Rajeev S. Menon,
• Akkattu T. Biju and
• Vijay Nair

Beilstein J. Org. Chem. 2016, 12, 444–461, doi:10.3762/bjoc.12.47

• salt 57 catalysed the intramolecular cross-benzoin reaction of chalcones derived from o-phthalaldehydes. The reaction proceeded rapidly (20 min) at room temperature to afford good yields (75–94%) of naphthalenone-based tertiary alcohols 58 (Scheme 35) [52]. The synthesis of bicyclic tertiary alcohols

• . Intramolecular cross-benzoin reaction of chalcones. Synthesis of bicyclic tertiary alcohols by intramolecular benzoin reaction. A multicatalytic Michael–benzoin cascade process for cyclopentanone synthesis. Enamine-NHC dual-catalytic, Michael–benzoin cascade reaction. Iminium-cross-benzoin cascade reaction of

Facile synthesis of 4H-chromene derivatives via base-mediated annulation of ortho-hydroxychalcones and 2-bromoallyl sulfones

• Srinivas Thadkapally,
• Athira C. Kunjachan and
• Rajeev S. Menon

Beilstein J. Org. Chem. 2016, 12, 16–21, doi:10.3762/bjoc.12.3

• . Polycyclic aromatic hydrocarbon frameworks (naphthalene and anthracene rings) as well as a representative heterocyclic ring (furan) may be incorporated into the 4H-chromene skeleton product by using chalcones (7c, 7d, and 7e, respectively) functionalized with these moieties. Disappointingly, attempts to

Synthesis, antimicrobial and cytotoxicity evaluation of new cholesterol congeners

• Mohamed Ramadan El Sayed Aly,
• Hosam Ali Saad and
• Shams Hashim Abdel-Hafez

Beilstein J. Org. Chem. 2015, 11, 1922–1932, doi:10.3762/bjoc.11.208

• –c and 7a,b were prepared by reacting 3β-azidocholest-5-ene (3) with propargylated chalcones 4a–c and 5a,b [24] under CuAAC conditions [35]. The reactions proceeded fairly in gently refluxing THF/H2O mixture containing L-ascorbic acid as reducing agent and a catalytic amount of CuSO4·5H2O. The 13C

• chalcones possessing unsubstituted phenyl, and p-dimethylaminophenyl as well as 2-thienyl alternatives were more active than other congeners against E. coli. Despite, derivatives 6b, 7a, 11b, 12, 13, 17, 20 and 24 varied significantly with the control, they insignificantly varied with each other and they

Natural phenolic metabolites with anti-angiogenic properties – a review from the chemical point of view

• Qiu Sun,
• Jörg Heilmann and
• Burkhard König

Beilstein J. Org. Chem. 2015, 11, 249–264, doi:10.3762/bjoc.11.28

• 71% and the overall yields to 52% over two steps. According to this, a synthesis of fisetin and quercetin with methyl-protected chalcones as starting materials was proposed (Scheme 11). (2S)-2’,4’,7-Trihydroxy-5-methoxy-8-(dimethylallyl)flavanone (2S)-7,2’,4’-Trihydroxy-5-methoxy-8-(dimethylallyl

Regioselective 1,4-trifluoromethylation of α,β-unsaturated ketones via a S-(trifluoromethyl)diphenylsulfonium salts/copper system

• Satoshi Okusu,
• Yutaka Sugita,
• Etsuko Tokunaga and
• Norio Shibata

Beilstein J. Org. Chem. 2013, 9, 2189–2193, doi:10.3762/bjoc.9.257

• chalcones. During the preparation of this article, the Nicewicz group showed a single example of conjugate trifluoromethylation of chalcone with sodium trifluoromethanesulfinate salt in the presence of N-methyl-9-mesitylacridinium as a photoredox catalyst resulting in a low product yield of 31% as a mixture

• of regioisomers (C2/C3 1.1:1) [22]. We disclose herein the regioselective 1,4-addition of the CF3 group into simple conjugated acyclic enones including chalcones using S-(trifluoromethyl)diphenylsulfonium salt 3 and a copper system in 11–37% yields (12 examples). Results and Discussion We initiated

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

• effect on the outcome of the reaction (Table 2, entries 3 and 4). The Claisen–Schmidt condensation We moved next to study the Claisen–Schmidt condensation of benzaldehyde with acetophenone to yield chalcone (Scheme 3). Chalcones display interesting biological properties such as antioxidant, cytotoxic

Total synthesis of ochnaflavone

• Monica M. Ndoile and
• Fanie R. van Heerden

Beilstein J. Org. Chem. 2013, 9, 1346–1351, doi:10.3762/bjoc.9.152

• cyclization of chalcones to flavones [25]. However, at this temperature, the reaction resulted in decomposition of the starting material. The reaction was repeated under microwave conditions as described by Menezes et al. [26] to decrease the time in which 6 was exposed to a high temperature, but

Amyloid-β probes: Review of structure–activity and brain-kinetics relationships

• Todd J. Eckroat,
• Abdelrahman S. Mayhoub and
• Sylvie Garneau-Tsodikova

Beilstein J. Org. Chem. 2013, 9, 1012–1044, doi:10.3762/bjoc.9.116

• introduce radiolabels into PET probes are outlined in Scheme 1. These general strategies will be abbreviated as Gs A–D in all subsequent schemes in this review. Chalcone and its conformationally restricted analogues Chalcone derivatives Chalcones and indolochalcones, such as 18a–l, 19a,b, 20a,b, and 21

• , have been widely reported as Aβ-imaging tracers (Scheme 2A). Structure–activity-relationship (SAR) studies on fluorinated chalcones 18a–l have shown that, in general, chalcones with tertiary amines in their structures demonstrate good affinity for Aβ plaques in in vitro models (Ki = 20–50 nM) (Table 1

• and [11C]-labeled chalcones 19a and 19b were synthesized using similar methods, and a representative synthesis of 19a is shown (Scheme 2B). Aldol condensation between the appropriate acetophenone 22 and benzaldehyde 23 afforded the chalcone backbone, which was subsequently pegylated to give 24 and

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

• acetophenone derivatives 7 to give the corresponding chalcones of type 9 in 66–85% yields. Contrary to Xue’s reduction method where H2/Pd was used, we used NaBH4 in the reduction of both the carbon–carbon and carbon–oxygen double bonds of chalcone derivatives 9 to give the corresponding alcohols 17. It is

Features of the behavior of 4-amino-5-carboxamido-1,2,3-triazole in multicomponent heterocyclizations with carbonyl compounds

• Eugene S. Gladkov,
• Katerina A. Gura,
• Svetlana M. Sirko,
• Sergey M. Desenko,
• Ulrich Groth and
• Valentin A. Chebanov

Beilstein J. Org. Chem. 2012, 8, 2100–2105, doi:10.3762/bjoc.8.236

• polyfunctional aminoazoles that have been studied in heterocyclization reactions [5][6][7][8][20], derivatives of 4-amino-1,2,3-triazole have been less well investigated. There are only a few examples of their heterocyclizations with β-diketones [21], N-cyanomethaneimidates [22], isocyanates [23], chalcones [24

Syntheses and applications of furanyl-functionalised 2,2’:6’,2’’-terpyridines

• Jérôme Husson and
• Michael Knorr

Beilstein J. Org. Chem. 2012, 8, 379–389, doi:10.3762/bjoc.8.41

• [19][21] was tested, since it is known to be an efficient promoter of aldol condensations and Michael additions under solvent-free conditions [22][23]. Nevertheless, the treatment of furanyl-substituted aldehydes 1, 3 and 15 did not yield the targeted diketo-intermediates, but instead the chalcones 5

Continuous-flow hydration–condensation reaction: Synthesis of α,β-unsaturated ketones from alkynes and aldehydes by using a heterogeneous solid acid catalyst

• Magnus Rueping,
• Teerawut Bootwicha,
• Hannah Baars and
• Erli Sugiono

Beilstein J. Org. Chem. 2011, 7, 1680–1687, doi:10.3762/bjoc.7.198

• of α,β-unsaturated ketones starting from alkynes and aldehydes by employing a heterogeneous catalyst in a flow microwave. The procedure presents a straightforward and convenient access to valuable differently substituted chalcones and can be applied on multigram scale. Keywords: chalcones; flow

• of valuable differently substituted chalcones. Starting from commercially available alkynes and aldehydes, a continuous-flow hydration–condensation protocol leads to the desired products in good to excellent yields. The reactions were sequentially introduced into the flow cell and performed several

• times without the heterogeneous catalyst needing to be changed, demonstrating the high robustness of this catalytic system. Additionally, this new method was readily applied for the preparation of chalcones in multigram quantities. The technology presented is advantageous over classical non-microwave

Prediction of reduction potentials from calculated electron affinities for metal-salen compounds

• Sarah B. Bateni,
• Kellie R. England,
• Anthony T. Galatti,
• Handeep Kaur,
• Victor A. Mendiola,
• Alexander R. Mitchell,
• Michael H. Vu,
• Benjamin F. Gherman and
• James A. Miranda

Beilstein J. Org. Chem. 2009, 5, No. 82, doi:10.3762/bjoc.5.82

• as electrocatalysts that have unknown electrochemistry. Fry demonstrated that the density functional B3LYP/6-31G(d) level of theory can be used to accurately predict the reduction potentials for a series of chalcones [7]. The electron affinities (EAs) of a training set of 29 monosubstituted chalcones

• were computed, while the reduction potentials of the training set were measured experimentally. The EAs and reduction potentials of the training set showed a linear correlation (R2 = 0.969). The reduction potentials of an additional 72 di-, tri-, and tetrasubstituted chalcones were then accurately

An improved synthesis of 1,3,5-triaryl- 2-pyrazolines in acetic acid aqueous solution under ultrasound irradiation

• Ji-Tai Li,
• Xiao-Hui Zhang and
• Zhi-Ping Lin

Beilstein J. Org. Chem. 2007, 3, No. 13, doi:10.1186/1860-5397-3-13

• used in organic synthesis in the last three decades. A large number of organic reactions can be carried out in higher yields, shorter reaction time or milder conditions under ultrasound irradiation. Results Preparation of a series of 1,3,5-triaryl-2-pyrazolines through the reaction of chalcones and

• -unsaturated aldehydes and ketones with phenylhydrazine in acetic acid by refluxing became one of the most popular methods for the preparation of 2-pyrazolines. [7] In 1998, Powers et al. [8] reported that the reaction of chalcones and phenylhydrazine hydrochloride in the presence of sodium hydroxide was

• synthesis, we wish to report an efficient and practical procedure for the synthesis of 1,3,5-triaryl-2-pyrazolines with chalcones and phenylhydrazine hydrochloride in sodium acetate-acetic acid aqueous solution under ultrasound irradiation (Scheme 1). Results and discussion The effect of the reaction