Reaction Steps
Under water-free conditions titanium(IV) chloride (91 g, 0.5 mol) in tetrachloromethane (120 ml) are added dropwise within 45 min to tetrahydrofuran at 0° C. The mixture is stirred for another 30 min at this temperature, then 2-Methyl-4-(2,6,6-trimethylcyclohex-1-enyl)butanal 5 (50 g, 0.24 mol) (M. Matsui et al., Agric. Biol. Chem. 50, 1475-1480, 1986) and dimethyl malonate (31.7 g, 0.24 mol) in tetrahydrofuran (50 ml) are added within 15 min at 0° C. followed by dropwise addition of pyridine (76 g) in tetrahydrofuran (240 ml) over 90 min at 0° C. The orange-brown suspension is stirred for 18 h at 25° C., then poured upon ice/water and extracted with tert-butyl methyl ether. The combined organic layers are washed with water and conc. NaCl and dried over MgSO4. After filtration and evaporation of the solvents the crude product (75 g) is short-path-distilled giving 62.5 g 3a at 170° C./0.07 mbar (81% yield, purity>98%). Analytical data: 1H-NMR (400 MHz, CDCl3): δ 0.95 (s, 6 H), 1.1 (d, 3 H), 1.4-1.5 (4H), 1.5-1.6 (2 H), 1.58 (s, 3 H), 1.8-2.0 (2 H), 2.5 (m, 1 H), 3.8 (s, 3 H), 3.85 (s, 3 H), 6.85 (d, 1 H) ppm. 13C-NMR (400 MHz, CDCl3): δ 19.45 (t), 19.55 (q), 19.75 (q), 26.4 (t), 28.5 (q), 32.7 (t), 34.8 (s), 35.7 (d), 36.8 (t), 39.7 (t), 52.1 (q), 52.2 (q), 126.7 (s), 127.1 (s), 136.8 (s), 154.9 (d), 164.4 (s), 166.0 (s). MS (EI): m/z (%) 322 (M+, 10), 307 ([M-15]+, 2), 275 (6), 259 (7), 243 (16), 215 (11), 200 (18), 187 (19), 175 (20), 173 (16), 172 (100), 153 (22), 145 (28), 140 (70), 137 (27), 135 (34), 123 (60), 122 (28), 121 (42), 109 (35), 108 (34), 95 (62), 93 (36), 81 (44), 79 (33), 55 (36), 41 (35). IR (film): 2950 (m), 2926 (m), 2865 (m), 1725 (s), 1642 (w), 1454 (w), 1433 (m), 1363 (w), 1327 (w), 1246 (s), 1221 (s), 1204 (s), 1168 (w), 1104 (w), 1054 (m), 991 (w), 945 (w), 925 (w), 833 (w), 762 (w).
