Experiment 1: Synthesis of a Flavone This experiment will illustrate a multistep synthetic sequence and will constitute a three-step process. The first step of the synthesis will involve a simple benzoylation of 2-hydroxyacetophenone. The second step is a Baker-Venkataraman rearrangement to provide the ß-diketone 3, which upon treatment with acid leads to cyclization to form the target molecule 4. Note that the final compound is a heterocycle. Reaction Sequence: OH O Things to know: ● 1 2-Benzoyloxyacetophenone (2): . O Ph CI ● pyridine ● Acylation mechanism ● Büchner funnel-vacuum filtration Things to know: ● ● Ph 0 0 2 KOH heat recrystallization from MeOH (hot; cold) Structural Determination (m.p. IR, GC-MS and NMR) Dissolve 2-hydroxyacetophenone (1) (2.72 g, 20.0 mmol) in pyridine (5 mL), add benzoyl chloride (4.22 g, 30,0 mmol) by Pasteur pipette and then fit the flask with a calcium chloride drying tube. Swirl the flask and some heat will be evolved. Allow the reaction to stand for 20 min, or until no further heat is evolved, and then pour the entire contents of the flask into a mixture of 3% HC1¹ (-120 mL) and crushed ice (~40 g). Once all the ice has melted, collect the precipitated solids by vacuum filtration. Wash the product with ice-cold methanol (~5 mL) and then water (~5 ml). Dry at the pump for 20 min² and then recrystallize the crude product from methanol (~5 mL). Record a mp, IR, GC-MS and NMR spectrum on the product. Enolate & Acyl transfer mechanism Pyridine's role? ● Büchner funnel-vacuum filtration Structural Determination (Crude ¹H NMR and m.p.) OH OO 3 Ph ACOH MacBook Pro H₂SO4 o-Hydroxydibenzoylmethane (3): Dissolve 2 (2.40 g, 10 mmol) in pyridine (8 mL) in a 50 mL beaker and heat the solution to 50 °C on a steam bath. Add crushed KOH pellets (~0.85 g) and stir the resulting mixture with a glass rod. During this time a yellow precipitate of the potassium salt of 3 should form. Cool the mixture to room temperature and cautiously add 10% aqueous acetic acid solution (15 mL). Collect the product by suction filtration and dry at the pump for a few minutes. Record the yield, a ¹H NMR spectrum and the melting point. Use the crude product directly in the next step. Page < 1 This HCl solution should be made up immediately prior to the lab session in which it will be used. 2 Occasionally use a spatula to break up the filter cake to ensure thorough drying. O O Ph 4 1 > of 2