The most stable isomers of oxane, chroman and flavan as basic building blocks for flavonoids were determined by density functional methods. Excellent agreement between the theoretical vibrational frequencies and the experimental infrared (IR) absorbance spectra were obtained. Similarities and differences between the spectra of chroman and flavan were identified. The difference in the IR spectra of the two conformers of flavan, mainly related to the vibration of atoms near the stereogenic centre, makes it possible to distinguish between them. Copyright © 2013 John Wiley & Sons, Ltd.

The title compound, C29H26O4, is essentially planar in the acetophenone portion that includes both the hy­droxy and a benz­yloxy O atoms, with an r.m.s. deviation of 0.0311 Å. The other two substituents inter­sect the plane at 70.45 (3) and 59.55 (4)°. In the molecule there is an intramolecular O—H⋯O hydrogen bond. In the crystal, mol­ecules are linked by C—H⋯O hydrogen bonds, as well as C—H⋯π and π-stacking inter­actions, with centroid–centroid distances 3.6570 (2) Å.

C 37 H 32 O 6 , monoclinic, P21/c (No. 14), a = 5.5354(7) Å, CCDC no.: 1493406The crystal structure is shown in the gure. Tables 1 and 2 contain details of the measurement method and a list of the atoms including atomic coordinates and displacement parameters. Source of material2-Hydroxy-4,5,6-tribenzyloxyacetophenone (0.152 g, 0.334 mmol, 1 eq) and 4-methoxybenzaldehyde (0.05 mL,

Source of materialTo a solution of 4,6-dibenzyloxy-2-hydroxyacetophenone (0.780 g, 2.24 mmol) in glacial acetic acid (10 ml), was added drop-wise a solution of bromine (0.13 ml, 2.24 mmol) in glacial acetic acid (2 ml) at room temperature over a period of 30 min and the reaction mixture stirred for 4 h at the same temperature. The reaction was quenched by the addition of water (20 ml) and the resulting solid was filtered off. The crude product was separated by preparative thin layer chromatography (PTLC, 7:3 n-hexane:acetone, R f = 0.55) to afford the title compound 4,6-dibenzyloxy-3-bromo-2-hydroxyacetophenone as a grey solid 0.58 g (94 %) and 4,6-dibenzyloxy-3,5-dibromo-2-hydroxyacetophenone as yellow needles 0.057 g (6 %). Crystals suitable for single crystal Xray determination were grown by slow evaporation from acetone. IR ( DiscussionPhenolics are a class of compounds known for their wide range of physiological actions, ranging from anti-inflammatory, anti-bacterial, anti-oxidative, anti-allergic, anti-hypertensive, antiischemic, anti-arrhythmic, anti-thrombotic, anti-carcinogenic, immune-stimulating and hypocholesterolemic [1][2][3][4]. They are common plant secondary metabolites found in herbs, fruit, vegetables, grains, tea, coffee beans, propolis, red wine and flavouring agents which form an integral part of the human diet [4][5][6][7]. Bromination of 4,6-dibenzyloxy-3-bromo-2-hydroxyacetophenone with Br 2 in HOAc gave 4,6-dibenzyloxy-3-bromo-2-hydroxyacetophenone and 4,6-dibenzyloxy-3,5-dibromo-2-hydroxyacetophenone in a 90:10 ratio. As expected, bromination occurred preferentially at C1 and not at C5 of the substrate, leading to the title compound as the main product. The position of bromination was confirmed by NOESY NMR spectroscopy where a strong NOE effect was evident between the aromatic hydrogen (H5), observed at d 6.12 ppm, and the four benzyl CH 2 protons were seen at 5.18 ppm and 5.06 ppm respectively. The molecular structure of the title compound is an example of a highly substituted acetophenone, with substituents including two benzyloxy groups, a hydroxyl and a bromine. The weak hydrogen bonding interaction between C42-H42×××O4 plays a marginal role in the packing due to its resulting in the alignment of the phenyl ring creating an essentially planar molecule with an r.m.s. deviation of 0.0797 Å (C1-C6, C21, C22, C41-C47, O1, O2, O4, Br1), with a maximum deviation 0.153(4) Å found for atom C45.

Source of materialBaicalein (0.100 g, 0.370 mmol, 1 eq) and 60% NaH (0.011 g, 0.444 mmol, 1.2 eq) in DMF (8 ml) was stirred at -40°C for 20 min. The reaction mixture was then treated with benzyl bromide (0.05 ml, 0.444 mmol, 1.2 eq) at the same temperature. After 30 min stirring, the temperature was raised from -40°C to 0°C and stirred for a further 6 hrs. The crude product was extracted with EtOAc (3´20 ml), washed with water (20 ml), dried over Na 2 SO 4 and concentrated. The crude product was crystallized out with acetone and yielded 7-benzyloxy-5,6-dihydroxyflavone as brown crystals (0.030 g, 37 %).1 H NMR (600 MHz, CDCl 3 ) dH (ppm): 7.89 (d, 2 H, J 6.9 Hz, H-2' and H-6'); 7.55 (m, 3 H, OCH 2 C 6 H * 5 ); 7.49 (d, 2 H, J 7.3 Hz, H-2'' and H-6''); 7.45 (t, 2 H, J 7.3 Hz, H-3'' and H-5''); 7.40 (t, 1 H, J 7.3 Hz, H-4''); 6.70 (s, 1 H, H-3); 6.68 (s, 1 H, H-8); 5.40 (s, 1 H, OH); 5.28 (s, 2 H, OCH * 2 C 6 H 5 ).13 C NMR (600 MHz, CDCl 3 ) dC (ppm): 182.73; 164.22; 151.91; 150.54; 145.97; 135.39; 132.30; 131.45; 130.05; 129.58; 129.47; 129.31; 129.09; 128.61; 128.51; 128.32; 128.18; 128.15; 128.07; 127.19; 126.89; 126.84; 126.77; 125.87; 125.74; 106.30; 105.15; 104.80; 91.55; 91.21; 78.10; 77.63; 77.57; 71.40. IR (KBr) 3855, 3446, 2924, 1654, 1608, 1578, 1507, 1456, 1358, 1297, 1181, 1116, 1098, 1025 . Experimental detailsAll hydrogen atoms were positioned geometrically and refined using a riding model, with C-H = 0.95 Å, U iso (H)= 1.2 U eq (C) for the aromatic H, with O-H = 0.84 Å U iso (H)= 1.5 U eq (O) for the hydroxy H and with U iso (H) = 1.5 U eq (C) for methylene H atoms. The hydroxy groups were allowed to rotate with a fixed angle whilst the methylene group C-H distance was allowed to refine to best fit the experimental electron density [HFIX 147 and HFIX 24 in SHELXL97 [2]]. DiscussionPlants are an invaluable resource when used in combination with traditional environmental knowledge, researches have the opportunity to investigate and expand on this important resource. With the cataloging of various traditional medicines, scientific investigations into their combinations and active ingredients can be undertaken by the scientific community. Huang-qin (Scutellaria baicalensis Georgi) one such traditional Chinese herb has been listed in the Chinese pharmacopeia [1]. Its active ingredients have shown medicinal promise against tuberculosis, fevers, ulcers, cancers, and inflammation. One of these active components known as Baicalein was used to further functionalize the molecule by the exchange of a hydroxy with a benzyloxy moiety. The title molecule consists of a hydroxy (C5 and C6) and benzyloxy (C7) substituted flavone, the g-benzopyrone backbone including the hydroxy and carbon (C71) atom of the benzyloxy substituents was seen to be essentially planar with an r.m.s deviation of 0.0444 Å (central plane). The maximum deviation above the mean plane was observed for the carbon (C71) atom of the benzyloxy substitutent with a distance of 0.105(2) Å. The phenyl of the benzyloxy moiety was disordered ove...