Chalcones crystallization

Since nonsubstituted chalcone crystallizes into a noncentrosymmetric structure, numerous derivatives have been examined for SHG activity. Daivatives with a 4-methylthio group in the benzylidene moiety were found to frequently give SHG-active crystals. An intracavity SHG experiment by an Nd YLV laso- excited by a laser diode was performed on a chalcone derivative with a cutoff wavelength around 450 nm. 

Table 1. Crystal forms, melting points, and vOH values of inclusion complexes with chalcones and analogues as guest molecules...

Chalcone la (1 g, 4.8 mmol) was placed in between two Pyrex plates and the sample was melted by being heated at 60 °C on a hot-plate, and thereafter was irradiated with a 400-W high-pressure Hg lamp for 24 h. The oily crude product was crystallized by addition of a small amount of MeOH to give, after recrystallization from MeOH, compound 2a as prisms (0.31 g, 31%), mp 123-125 °C. 

Keywords chalcone, dibenzylidene acetone, inclusion crystal, [2+2]photo-cycloaddition, cyclobutane... 

Zhang,G.J. Kinoshita,T. Sasaki,K./ Goto,Y. Nakayama, A. "Second Harmonic Generation in a New Organic Nonlinear Chalcone Derivative Crystal," CLEO, 1989, THH1, Baltimore, MD. 

Basic alumina (18 g) was added to the solution of phenylhydrazine (1.4 g, 0.013 mol) and chalcone 1 (2.38 g, 0.01 mol) dissolved in dichloromethane (5 ml) at room temperature. The reaction mixture was thoroughly mixed and the adsorbed material was dried in air (beaker) and placed in an alumina bath inside a microwave oven. Upon completion of the microwave reaction (1-2 min), based on thin-layer chromatography (TLC) examination, the mixture was cooled to room temperature and then the product was extracted into dichloromethane (4x15 ml). Removal of the solvent under reduced pressure gave the product, which was purified by crystallization from a mixture of methanol and dichloromethane. The yield of 2 was 82%. 

A mixture of 5,6-diamino-1,3-dimethyl-uracil 1 (0.2 g, 1.2 mmol), chalcone 2 (0.25 g, 1,2 mmol) and 0.4 ml of glacial acetic acid in 20 ml of methanol was refluxed for 3 h (Scheme A.33). After cooling, the colorless crystals of 3 precipitated and were filtered. Yield 82%. Melting point 229-231°C. 

Since photochemical reactions in inclusion compounds have been described in one chapter of the previous book [1], enantioselective (3-lactam formation reactions are summarized in this present chapter as a typical application of the inclusion technique for enantioselective photosynthesis. In addition, as a representative enantioselective single-crystal-to-single-crystal photoreaction, the photodimerization reactions of coumarin and thiocoumarin in their inclusion compound with a chiral host are also described. Furthermore, a host-catalyzed photodimerization reaction of chalcone and 2-pyridone in the solid state is also added to this chapter as a unique example of the application of inclusion techniques to selective photoreaction. 

Chiral crystals generated from non-chiral molecules have served as reactants for the performance of so-called absolute asymmetric synthesis. The chiral environments of such crystals exert asymmetric induction in photochemical, thermal and heterogeneous reactions [41]. Early reports on successful absolute asymmetric synthesis include the y-ray-induced isotactic polymerization of frans-frans-l,3-pentadiene in an all-frans perhydropheny-lene crystal by Farina et al. [42] and the gas-solid asymmetric bromination ofpjp -chmethyl chalcone, yielding the chiral dibromo compound, by Penzien and Schmidt [43]. These studies were followed by the 2n + 2n photodimerization reactions of non-chiral dienes, resulting in the formation of chiral cyclobutanes [44-48]. In recent years more than a dozen such syntheses have been reported. They include unimolecular di- r-methane rearrangements and the Nourish Type II photoreactions [49] of an achiral oxo- [50] and athio-amide [51] into optically active /Mactams, photo-isomerization of alkyl-cobalt complexes [52], asymmetric synthesis of two-component molecular crystals composed from achiral molecules [53] and, more recently, the conversion of non-chiral aldehydes into homochiral alcohols [54,55]. 

Crystallization processes comprise two sequential steps crystal nucleation followed by crystal growth. Kondepudi et al. demonstrated in a series of experiments that spontaneous symmetry breaking may be induced by growing crystals of non-chiral molecules such as sodium chlorate, binaphthyl, and p, p -dimethyl-chalcone, which crystallize as enantiomorphous crystals of... 

Several important chalcone synthase-related PKSs have recently been discovered in bacteria. 21 RppA is a Type III PKS that synthesizes 1,3,6,8-tetrahydroxynaph-thalene (THN) from five malonyl-CoAs in Streptomyces griseusf RppA specifically cyclizes the pentaketide intermediate via two intramolecnlar condensations to yield the bicyclic THN. The crystal stractnre of a closely related THN synthase (THNS) from S. coelicolor was recently determined, uncovering the presence of a second active-site cysteine that stablizes the growing polyketide and prevents aberrant cyclization of the highly reactive pentaketide. ... 

However, in an inclusion crystal of chalcone 70a with 1,1,6,6-tetraphenylhexa-2,4-diyne-l,6-diol host compound 91, the 70a molecules aggregate in close posi-... 

The understanding of the degradation of natural products such as camphor has been greatly enhanced by understanding the catalytic cycle of the cytochrome P-450 enzyme P-450cam in structural detail.3,4 These enzymes catalyze the addition of 02 to nonactivated hydrocarbons at room temperatures and pressures - a reaction that requires high temperature to proceed in the absence of a catalyst. O-Methyltransferases are central to the secondary metabolic pathway of phenylpropanoid biosynthesis. The structural basis of the diverse substrate specificities of such enzymes has been studied by solving the crystal structures of chalcone O-methyltransferase and isoflavone O-methyltransferase complexed with the reaction products.5 Structures of these and other enzymes are obviously important for the development of biomimetic and thus environmentally more friendly approaches to natural product synthesis. 

The phosphoranylidenehydrazone 9 (10 mmol) was added to a suspension of chalcone 10 (3.3 mmol) in dry BUjO (50 mL). The mixture was heated to reflux temperature whereupon both components dissolved and the mixture turned bright yellow-orange. Heating was continued for 12-23 h and, on cooling, crystals of triphenylphosphane formed. The BuaO was completely removed by using a rotary evaporator and then... 

The first PKS crystal structure, that of alfolfa chalcone synthase (CHS) in 1999 (6), had previously revealed foe type III PKS internal active site cavity and conserved Cys/His/Asn catalytic triad responsible for starter substrate loading and iterative polyketide extension (6). CHS provides the first committed chemical intermediate in flavonoid biosynthesis by catalyzing foe sequential decarboxylative addition of three acetate units from maionyl-CoA to a p-... 

Chlorocinnamoyl-0,0 -dimethyldopamine undergoes photochemical (2 + 2)-dimerization. The crystal structure of the product has been determined." Dimerization of some oxygenated chalcone derivatives has been described. The crystal structure of the (2 + 2)-dimer obtained from the irradiation of the enone (5) has been determined. ... 

Under rare circumstances it may happen that the molecular shape of two monomers and the dimer, and their crystal parameters, are so nearly identical that a topotactic phototransformation occurs single crystal into single crystal. This is realized in intramolecular cases like [2,2]-(9,10)-an-thracenophane 17 and its [4 + 4]-photoisomer 18 [31]. However, it was also possible to find some rare intermolecular cases of topotactic single crystal into single crystal photodimerizations with chalcones like 2-ben-zyl-5-benzylidene-cyclopentanone 19 [32]. Since there is virtually no mol-... 

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