Chalcone synthesis

The readily prepared support was then used for dihydropyrimidine and chalcone synthesis (Scheme 7.29). Thus, the modified support was activated prior to reaction by treatment with tosyl chloride. Solutions of the appropriate acetophenones were then spotted onto the membrane and the support was submitted to microwave irradiation for 10 min [45]. In the next step, several aryl aldehydes were attached under microwave irradiation to form a set of corresponding chalcones through a Claisen-Schmidt condensation. 

A four-step synthesis may be considered by linking together the Friedel-Crafts reaction with the synthesis of a chalcone (Experiment 61) and then preparing an epoxide (Experiment 62) from the chalcone and/or a cyclopropanated chalcone (Experiment 63). It is likely that the Friedel-Crafts reaction should produce enough acylated product for the reactions that follow. If you choose to link together the chalcone synthesis followed by epoxidation and cyclopropanation, it is suggested that you choose to prepare the acetyl derivatives of toluene, p-xylene, mesitylene, or anisole and use one of the recommended aldehydes shown in the following table to make the chalcone in Experiment 61. 

Flavonoids may be synthesized by using reactions similar to those used in the chalcone synthesis. For example, the basic flavone structure (II) can be simply derived firom a Claisen condensation between ethyl benzoate and 2-methoxyacetophenone, followed by treatment with HI ... 

Vogel S, Ohmayer S, Brunner G, Heilmann J (2008) Natural and non-natural prenylated chalcones synthesis, cytotoxicity and anti-oxidative activity. Bioorg Med Chem 16 4286... 

Scheme 1.29 Chalcone synthesis from aryl halides...

Scheme 1.30 Chalcone synthesis from aryl tiiflates...

A 1 1 adduct from diphenylsulfilimine and a benzoylacetylene underwent an intramolecular cyclization reaction to give an isoxazole in good yield (equation 40). Similarly, the 1 1 adduct from iodoazide and chalcone gave 3,5-diphenylisoxazole (equation 41). These two approaches to regiospecific isoxazole synthesis are of little practical significance. Additional examples of the (OCCCN) reaction are given in equations (42) and (43). 

Ceroplastol synthesis, 1, 428 Cetyl alcohol synthesis, 1, 478 Chaetoglobasins structures, 4, 376 Chalcone, o -azido-2 -oxy-synthesis, 3, 823 Chalcone, 2-hydroxy-reduction, 3, 751 Chalcone, 2 -hydroxy-mass spectra, 3, 618 Chalcone dibromides flavone synthesis from, 3, 823 Chalcones polymers, 1, 304 Chanoclavine synthesis, 6, 423 Charge density waves in stacks of ions, 1, 351-352 Chartreusin... 

An obvious outcome of the Hantzsch synthesis is the symmetrical nature of the dihydropyridines produced. A double protection strategy has been developed to address this issue. The protected chalcone 103 was reacted with an orthogonally protected ketoester to generate dihydropyridine 104. Selective deprotection of the ester at C3 could be accomplished and the resultant acid coupled with the appropriate amine. Iteration of this sequence with the C5 ester substituent ultimately gave rise to the unsymmetrical 1,4-dihydropyridine 105. 

As described earlier one of the possible products from the AFO reaction is dihydroxyflavonols. Simpson and coworkers took advantage of this outcome in their synthesis of the flavonol rhamnocitrin (23). Chalcone 24 was subjected to the typical AFO conditions to deliver dihydroxyflavonol 25. The isolated product was further subjected to hydrogen peroxide to afford flavonol 25a in 30% yield. However, treatment of 25 with bismuth acetate, generated in situ from bismuth carbonate and acetic acid, gave 25a in 77% yield for a respectable 52% overall yield over two steps. 25a was then selectively demethylated with anilinium chloride to deliver rhamnocitrin (23). 

Potent antimicrobial l,2,4-triazolo[3,4-fc]-l,3,4-thiadiazepines derivatives were prepared from readily accessible substituted 2-mercapto-l-aminotria-zoles and substituted chalcones on basic alumina in a solvent-free microwave-assisted synthesis (Scheme 28). Exposure of the reaction mixtures to microwaves led to an important decrease of the reaction time, which has been brought down from hours to seconds, accompanied by improved yields as compared with conventional heating [36]. This facile, rapid, and economic... 

Chalcone dibromides are advantageous intermediates for the preparation of various nitrogen-containing heterocycles (refs. 1-4). In the case of exocyclic a,P-unsaturated ketones, however, only few examples are known concerning the utilization of their dibromides for such purposes (ref. 5). Our aim was, therefore, the synthesis of the dibromides of various exocyclic a,P-unsaturated ketones (ref. 6) and to study their chemical transformations. In our present paper the reaction of such dibromides with azide nucleophile is reported. 

The first enantioselective synthesis of cis- and trans- 3-hydroxyflavanones is based on the Lewis-acid-catalysed reaction of phenylmethanethiol with chalcone epoxides <96CC2747>. Further support for the intermediacy of epoxides in the Algar-Flynn-Oyamada flavone synthesis has been provided by the isolation of epoxides in the corresponding preparation of 3-hydroxy-2-phenylquinol-4-ones <96JCS(P2)269>. 

Lawton, M.A., Dixon, R.A., Rowell, P.M., Bailey, J.A. Lamb, C.J. (1983). Rapid induction of the synthesis of phenylalanine ammonia-lyase and of chalcone synthase in elicitor-treated plant cells. European Journal of Biochemistry, 129, 593-601. 

Fig. 5 Scheme of the flavonoid pathway leading to synthesis of proanthocyanidins. The enzymes involved in the pathway are shown as follows CHS = chalcone synthase CHI = chalcone isomerase F3H = flavanone-3B-hydroxylase DFR = dihydroflavonol-4-reductase LDOX = leucoanthocynidin dioxygenase LAR = leucoanthocyanidin reductase ANR = anthocyanidin reductase adapted from [27] and [28]... 

Brown T, Holt H Jr, Lee M (2006) Synthesis of Biologically Active Heterocyclic StUbene and Chalcone Analogs of Combretastatin. 2 1-51... 

ZnEt2 to chalcone with mercaptocam-phan-2-ol-derived hgand 96-7 A, 0-heterocycle ligands 120 (+)-5-e/7i-nojirimycin-5-lactam, synthesis of 338, 340 Noyori, Ryoji 2... 

The successfully generated chalcones could be cleaved by treatment with trifluoro-acetic acid or used for the subsequent synthesis of pyrimidines [45], Condensation of the polymer-bound chalcones with benzamidine hydrochloride under microwave irradiation for 30 min furnished the corresponding pyrimidines in good yields after TFA-induced cleavage. This new robust support/linker system for SPOT synthesis has been demonstrated to be compatible with a range of organic reactions and highly applicable for microwave conditions. 

For example, large rate enhancements have been reported in the synthesis of chal-cones by crossed-aldol condensations in open vessels, suggesting the participation of specific MW effects [41]. The chalcone 24 was synthesized from cyclohexanone and benzaldehyde in ethanol, in the presence of a catalytic amount of sodium hydroxide (Scheme 4.13), in a MW oven in 90% yield in only 1 min. 

Tab. 5.31 Synthesis of diaryl-a-tetralones from isophorone and chalcone under MW + PTC conditions.

Flavonoids are the largest class of phenylpropanoids in plants. The basic flavonoid structure is two aromatic rings (one from phenylalanine and the other from the condensation of three malonic acids) linked by three carbons (Fig. 3.6). Chalcone is converted to naringenin by the enzyme chalcone isomerase, which is a key enzyme in flavonoid synthesis. This enzyme, like PAL and chalcone synthase (CHS), is under precise control and is inducible by both internal and external signals. Naringenin is the... 

Figure 3.6. Synthesis of chalcone, flavanone, and stilbene from p-coumaric and malonic acids.

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