Synthesis
1. In a dry reaction flask, dissolve 2,5-dichloro-2,5-dimethylhexane (10 g, 54.7 mmol) in toluene (270 mL) and stir until completely dissolved.
2. slowly add anhydrous aluminum trichloride (5.47 g, 41 mmol) to the above solution in batches over 15 minutes, taking care to control the addition rate to avoid intense exotherm.
3. After the addition, the reaction was continued with stirring for 10 minutes, and the progress of the reaction was monitored by thin layer chromatography (TLC, unfolding agent: hexane) to confirm the completion of the reaction.
4. Under cooling in an ice bath, slowly add water dropwise (~10 min) to quench the unreacted aluminum trichloride, taking care to control the rate of dropwise acceleration to avoid intense exotherm.
5. The reaction mixture is extracted with toluene (250 mL) and the organic layer is separated.
6. The organic layer was filtered through a silica gel pad (40 g) and eluted with toluene to remove possible polar impurities.
7. The organic phases were combined and concentrated to dryness under reduced pressure to afford the crude product 1,1,4,4,6-pentamethyl-1,2,3,4-tetrahydronaphthalene (11 g, 97% yield).
8. The product was characterized by nuclear magnetic resonance hydrogen spectroscopy (1H NMR): δ 1.29 (s, 6H), 1.28 (s, 6H), 1.69 (s, 4H), 2.32 (s, 3H), 7.22 (d, 1H), 7.12 (s, 1H), 6.97 (dd, 1H).
References
[1] Journal of Organic Chemistry, 1991, vol. 56, # 15, p. 4706 - 4713
[2] Journal of Organic Chemistry, 2001, vol. 66, # 17, p. 5772 - 5782
[3] Bioorganic and Medicinal Chemistry Letters, 2002, vol. 12, # 23, p. 3467 - 3470
[4] Patent: US2004/10033, 2004, A1. Location in patent: Page/Page column 11
[5] Patent: WO2003/106446, 2003, A1. Location in patent: Page 19-20
