Grignard Reaction

1. Grignard Reagent Formation

1. Flame-dry a round bottom flask equipped with a magnetic stir bar.
2. Add magnesium (Mg, 1.1 equiv.) to the round bottom flask.
3. Add a small amount of iodine (I₂, a few crystals). Addition of iodine is to help remove any MgO on the surface of the Mg. Removing MgO allows for Mg and the aryl/alkyl halide to come in contact and react. Sonication or addition of methyl iodide or 1,2-dibromoethane can also help with initiation.
4. Cool the reaction mixture to 0 °C with an ice-water bath
5. Slowly add a THF (1 M) solution of allyl bromide (1 equiv.) to the round bottom flask with magnesium.
6. After adding the solution of allyl bromide, stir the reaction mixture for 3 h at room temperature.

2. Nucleophilic Addition

1. In a separate flame-dried round bottom flask, add trans-cinnamaldehyde (0.85 equiv.) and THF (0.5 M with respect to trans-cinnamaldehyde) and cool to 0 °C.
2. Slowly add the THF solution of the Grignard reagent (allyl-magnesium bromide) to the trans-cinnamaldehyde solution.
3. After the addition, warm the reaction mixture to room temperature by removing the ice-water bath and stir for 4 h.
   1. Monitor the reaction progress via TLC by looking for the disappearance of trans-cinnamaldehyde.
4. After reaction completion, cool the mixture to 0 °C with an ice-water bath.
5. Slowly quench the reaction with a saturated aqueous solution of ammonium chloride (NH₄Cl).
6. Transfer the mixture into a separatory funnel and extract the aqueous layer with ethyl acetate 3x.
7. Combine the organic layers and wash with water and brine (a saturated aqueous solution of NaCl).
8. Dry the organic layer with anhydrous MgSO₄, filter, and evaporate the solvent via rotatory evaporation.
9. Purify the crude residue via flash column chromatography.