1,4-Napthoquinone (>98%, TCI America)

2,3-dimethyl-1,3-butadiene (98%, stabilized with 100 ppm BHT, Alfa Aesar)

Ethanol (200 proof, Pharmco)

To a stirred solution of 1,4-napthoquinone (6.33 g, 40 mmol) in ethanol (100 mL), 2,3-dimethyl-1,3-butadiene (4.95 mL, 44 mmol) was added via syringe. The solution was stirred, heated to 80 °C, and kept under reflux overnight.  After approx. 12 hours at reflux, the reaction mixture was allowed to cool for 15 min before concentrating via rotary evaporation to yield the adduct (1,4,4a,9a-tetrahydro-2,3-dimethyl-9,10-anthracenedione) as a light gray, sand-colored solid (9.52 g, 99%).

Upon taking the reaction off of the heat, the solid crystalline product should begin to crash out. An ice bath may be used to aid in speed of this.

This reaction has been performed from a 2 to 40 mmol scale where each reaction resulted in good yield and purity.

¹H NMR (400 MHz, CDCl₃): δ 8.22 (t, 2H, J = 4.8 Hz), 8.10 (s, 2H), 7.78 (t, 2H, J = 4.4 Hz), 2.45 (s, 6H)

¹³C NMR (100 MHz, CDCl₃): δ 198.34, 134.18, 134.08, 126.81, 123.45, 47.34, 30.66, 18.87

R_f = 0.55 (1:3 EtOAC/Hex)

M.p. 146.2 - 147.1°C

Allen, C. F. H.; Bell, A. Organic Syntheses. 1942, 22, 37-8.