Regioselective Diels-Alder Reaction of 5-hydroxy-1,4-naphthoquinone with Isoprene at Room Temperature; Tetrahydroanthraquinone
Submitted Oct 13, 2015, published Oct 19, 2015
5-hydroxy-1,4-naphthoquinone (Alfa Aesar)
Dichloromethane (Alfa Aesar)
To a stirred solution of 5-hydroxy-1,4-naphthoquinone (2.09 g, 12 mmol) in dichloromethane (160 mL) was added boron triacetate (2.481 g, 13.2 mmol) at room temperature. The reaction mixture was sealed and allowed to stir for approximately fifteen minutes. Isoprene (3.60 mL, 36 mmol) was then added to the flask via syringe. Upon completion (indicated by TLC), the reaction was quenched by addition of saturated aqueous sodium bicarbonate (160 mL). The aqueous layer was extracted with dichloromethane (4 x 100 mL), and the combined organic fractions were washed with water (3 x 100 mL), brine (100 mL), dried over anhydrous magnesium sulfate, and passed through a celite filter. Removal of the solvent by rotary evaporation yielded the product (5-hydroxy-2-methyl-1,4,4a,9a-tetrahydroanthracene-9,10-dione) as a dark-yellow solid (2.48 g, 86%).
1H NMR (400 MHz, CDCl3): 1.72 (s, 3H), 2.15 (d, 1H), 2.32 (d, 1H), 2.42 (d, 1H), 2.56 (d, 1H), 3.27-3.32 (q, 1H), 3.38-3.42 (q, 1H), 5.42 (m, 1H), 12.05 (s, 1H).
13C NMR (100 MHz, CDCl3): 23.46, 25.48, 28.38, 46.02, 46.59, 118.22, 123.91, 136.92, 161.73, 197.24, 205.66.
Melting Point: 110.2-112.1 °C
Hsu, D.; Huang, J. J Org. Chem. 2012, 77, 2659-2666.
Fringuelli, F.; Pizzo, F.; Taticchi, A.; Halls, T. D. J.; Wenkert, E. J. Org. Chem. 1982, 47, 5056-5065.
e.g. Actual NMR spectra (as images or jdx files for interactive spectra), photographs of apparatus, TLC’s or crystals or videos. Please contact the ChemSpider team (ChemSpider-at-rsc.org) for help with this.
Keywords: addition, aromatics/arenes, cycloaddition, Lewis-Acid mediated, regioselective