Reaction Steps
To powdered anhydrous aluminum chloride (13.7 g, 0.10 mol) under nitrogen is added dry dichloromethane (30 ml). Mesityl oxide (20.0 g, 0.20 mol) in dichloromethane (75 ml) is then added with stirring over 30 minutes and the mixture is heated under reflux for 1 hour. Penta-1,3-diene (mixture of isomers) (70.0 g, 1.03 mol) in dichloromethane (300 ml) is added dropwise over 6 hours. The mixture is then stirred overnight at room temperature. Liquid paraffin (100 ml) and 10% hydrochloric acid (200 ml) is added and the mixture is steam distilled for 3 hours. The steam distillate is extracted with ether (5×75 ml) and the product worked up as usual. The residue is distilled to give a liquid, b.p. 52°-54° at 1 mm Hg (15.0 g, 0.09 mol, 45%), shown by GLC [column (A), 120° C.] to consist of two components in the proportions ca. 13:87 in order of increasing retention time. These were separated by preparative GLC [column (B), 130° C.]: trans-4-acetyl-3,5,5-trimethylcyclohexene (6) (Found: C, 79.6; H, 10.75. C11H18O requires C, 79.5; H, 10.85%); m/e 166 (M+, 33%), 123 (100), 109 (39), 107 (33), 81 (39), 69 (33), 67 (27), 55 (27), 43 (82) and 41 (50); π9.17-8.86 (9H, 4 overlapping lines, 3- and 5-Me), 8.60-8.04 (2H, m, 6-H2), 7.87 (3H, s, Ac), 7.90-7.30 (2H, m with br s overlapping, 3- and 4-H), and 4.54br (2H, s, 1- and 2-H); νmax. (film) 1 710 (Ac) and 695 cm-1 (cis--CH=CH); cis-4-acetyl-3,5,5-trimethylcyclohexene (5) (Found: C, 79.55; H, 10.8%); m/e 166 (M+, 4%), 138 (39), 123 (95), 109 (11), 107 (23), 81 (12), 69 (8), 67 (9), 55 (12), 53 (11), 43 (100) and 41 (23); π9.18-8.89 (9H, 3 overlapping lines, 3- and 5-Me), 8.68-8.18 (2H, m, 6-H2), 7.97 (3H, s, Ac), 7.70-7.30 (2H, m, 4- and 3-H), and 4.86-4.16 (2H, m, 1- and 2-H); νmax. (film) 1 170 (Ac), and 1 692 and 710 cm-1 (cis--CH=CH).
