Crystal structure of 3-bromo-4,6-dibenzyloxy-2-hydroxy acetophenone, C22H19BrO4

Abstract

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.