Toluene → 2-Methyl-4-(propan-2-yl)cyclohex-3-en-1-one

Participants

Reaction Steps

Approximately 20 mg of ZnBr2 (Fisher Certified-not fused) was added to 3 mL of toluene which had been distilled and stored over molecular sieves. The mixture was brought to reflux with vigorous stirring (to disperse the solid zinc bromide) in an apparatus which had been well flushed with nitrogen and equipped with a drying tube. Three quarters of a mixture of 2,3-epoxycarane (150 mg, 0.98 mmol) and 3 mL of toluene was added immediately. After 10 min the remaining one quarter was added over a 10 min period. Forty minutes after initial oxide addition the reaction mixture was cooled, taken up in 30 mL of ether, washed successively with water (2 × 10 mL), saturated NaHCO3 (1 × 10 mL), saturated NaCl (1 × 10 mL) and dried over anhydrous Na2SO4. Partial removal of solvent under reduced pressure afforded an oily residue from which 2-methyl-4-isopropylcyclohex-3-en-1-one (MICO) was isolated by preparative VPC. IR (CCl4) 2975, 1720, 1360, 1200, 1180(d), 970 and 930 reciprocal centimeters; UV (95% EtOH) lambda (max) 290 nm (extinction coefficient = 90.9); NMR (DCCl3) PPM 1.04 (d, 6H, J = 7 Hz, CH3 --C--CH3), 1.14 (d, 3H, J = 7 Hz, CH3 --C--), 2.3 (quintet, 1H, J = 7 Hz), 2.46 (n, M, 4H), 2.88 (br, Q with additional splitting H--C--C=O), 5.37 (n, M, 1H, H--C=C); MS m/e (rel. intensity) 153(4), 152(42), 135(5), 100(65), 109(10), 96(11), 95(100), 81(30), 68(10), 67(25), 55(11). Anal. calcd. for C10H16O: C, 78.89; H, 10.59. Found: C, 79.08; H, 10.41. An IR of the major product of the reaction showed a peak at 1720 reciprocal centimeters, attributed to the presence of a nonconjugated carbonyl. The product MICO exhibited a cool, refreshing menthol fragrance with a slight raspberry note which finds utility for the compound in odorant compositions.

Provenance & Evidence