Reaction Steps
To a stirred suspension of lithium aluminium hydride (LAH, 4.63 g, 122 mmol) in THF (100 mL) was added dropwise between 3-5° C. within a period of 1 h a solution of ethyl 2,5-dimethyl-3-methylenehexanoate (22.5 g, 122 mmol) in THF (500 mL), and the resulting reaction mixture was stirred for 3 h under reflux. With cooling in an ice-bath, water (5.00 mL) was added dropwise, followed by 15% aq. NaOH solution (5.00 mL) and again water (15.0 mL). After stirring for further 30 min at room temp, the formed precipitate was filtered off by suction with the aid of a sintered funnel, and washed with Et2O (100 mL). The combined filtrates were evaporated under reduced pressure, and the resulting residue was purified by silica-gel flash chromatography (pentane/Et2O, 8:2, Rf=0.18) to provide 2,5-dimethyl-3-methylenehexan-1-ol (13.6 g, 79%) as a colourless odoriferous liquid. IR (neat): ν=3332 (s, ν O—H), 1462 (w, δa, CH3), 1366 (w, δs, CH3), 1026 (s, ν C—O), 891 (s, δ C═H) cm−1. 1H NMR (CDCl3): δ=0.90 (d, J=6.5 Hz, 6H, 5-Me2), 1.05 (d, J=7.0 Hz, 3H, 2-Me), 1.69 (br. s, 1H, OH), 1.79 (sept, J=7.0 Hz, 1H, 5-H), 1.91 (dd, J=7.0, 1.5 Hz, 2H, 4-H2), 2.32 (sext, J=6.5 Hz, 1H, 2-H), 3.45-3.59 (m, 2H, 1-H2), 4.86 (d, J=1.5 Hz, 1H, 1′-HE), 4.87 (d, J=1.5 Hz, 1H, 1′-HZ) ppm. 13C NMR (CDCl3): δ=16.4 (q, 2-Me), 22.3/22.6 (2q, 5-Me2), 26.2 (d, C-5), 41.6 (d, C-2) 44.8 (t, C-4), 65.9 (t, C-1), 110.7 (d, C-1′), 150.1 (s, C-3) ppm. MS (EI): m/z (%)=142 (5) [M+], 124 (3) [M+-CH3], 111 (28) [M+-CH3O], 83 (86) [C6H11+], 69 (100) [C5H9+]. Odour description: very pleasant and fresh green-rosy note with natural slightly agrestic-earthy aspects and “vert de lilas”-like facets of lilac, hyacinth and peony.
