Trans Acetic Acid 5-isopropyl-2-methyl Cyclohex-2-enyl Ester (Trans Carvyl Acetate)

To a red solution of Li₂PdCl₄, prepared in situ by mixing LiCl (30.8 mg, 0.72 mmol) and PdCl₂ (43 mg, 0.24 mmol) in 20 mL of AcOH stirred at 85°C, was added Cu(OAc)₂ (4 g, 20 mmol) and stirred for 30 mn. Then the reaction mixture was cooled to room temperature and the limonene 1 (1 g, 7.3 mmol) was added [1]. the evolution of the reaction was followed by GC. Once the reaction was finished, a mixture of hexane/ether (1:1, 30mL) was added and the solution was stirred for 30 min. the organic phase was separated and the remaining acetic acid phase was diluted with saturated NaCl (10mL) and extracted with hexane/ether (1:1, 3x30 mL). The combined extracts were neutralized with a saturated solution of NaHCO₃, dried over MgSO₄. Removal of the solvent under reduced pressure and purification of the residue by flash chromatography, using hexane/ether (9:1) as eluent, gave the compound 2 (86%) as a colorless oil [2,3].

IR (cm^-1) 3080(C-H, sp²) 1740(C=O) 1640(C=C) 1240(C-O).

1H NMR (400 MHz, CDCl3) 1.63(1H, ddd, J6ax, 5 13, J6ax, 6eq 11.2, J6ax, 1 4.2Hz, 6ax-H)1.68(3H, s, 9-CH3) 1.72(3H, s, 10-CH3) 1.83(1H, m, 4ax-H) 1.95(1H, ddd, J6eq, 6ax 11.2, J6eq, 1 2.6 and J6eq, 5 4.2Hz, 6eq-H) 2.07(3H, s, 12-CH3) 2.21(1H, m, 4eq-H) 2.32(1H, m, J5, 6ax 13, J5, 6eq 4.2, J5, 4ax 11.2 and J5, 4eq 4.2Hz, 5-CH) 4.72(2H, d, J 19 Hz, 8-CH2) 5.26(1H, dd, J1, 6ax 4.2 and J1, 6eq 2.6Hz, 1-CH) 5.73(1H, m, 3-CH).

¹³C NMR (100 MHz, CDCl₃) 20.6 and 20.8(CH₃, C-9 and C-10) 21.3(CH₃, C-12) 30.9 and 33.7(CH₂, C-4 and C-6) 70.6(CH, C-1), 109.2(CH₂, C-8) 127.8(CH, C-3) 130.9(C-7) 148.6(C-2) 170.7(C-11).