The alkoxycarbonylation of terpenic olefins which affords the corresponding esters is an elegant synthesis [1-2]. Morover, the metal-complex-catalyzed hydrocarboxylation is among the most extensively investigated processes in homogeneous catalysis[3].
In a flask fitted with a reflux condenser was placed PdCl2 (34 mg, 0.19 mmol), Cu(OAc)2 (1.1 g, 5.5 mmol) and p-Toluenesulfonic acid (PTSA) (69.6 mg, 0.36 mmol), and the atmosphere was replaced with CO/O2 (1:1). 15 ml of methanol were added and the mixture was stirred for 15 min at room temperature under atmospheric pressure of CO/O2. 3-Isopropenyl-6-methyl-cyclohexene, 1, (3.6 mmol ) prepared by pyrolysis of 2-carene at high temperature (>220 °C) was added. The resulting mixture was further stirred at room temperature and at CO/O2 was bubbled in for 5 days. The reaction was monitored by GC (conversion = 94%).
At the end of the reaction, the solvent was removed by rotary evaporation. The residue was purified by using silica gel chromatography column with Hexane/AcOEt (96:4) to afford 2 as colorless oil (46%).
1H-NMR (300 MHz, CDCl3): 5.72 (1H, dd, J1=3.26 Hz/J2=1.31Hz); 3.6 (3H, S, O-CH3); 1.07 (3H, d, J=7.18 Hz, CH3); 1.01(3H, d, J=6.53 Hz, CH3).
13C-NMR (100 MHz, CDCl3): 202.2 (C=O); 172.1 (C=O); 167.4 (=C); 124 (=CH); 51.6 (OCH3); 40.9 (-CH); 39.3 (-CH2); 37.5 (-CH); 30.7 (-CH2); 27.1 (CH2); 19 (CH3); 14.9 (CH3).
M.S: m/z 210 (M+); 151 (59); 109 (42).
Supplementary Material
References
- Naigre, R.; Chenal, T.; Ciprès, I.; Kalck, P.; Daran, J.C.; Vaissermann, J. J. Org. Chem. 1994, 480, 91–102. [CrossRef]
- Chenal, T.; Ciprès, I.; Jenck, J.; Kalck, P.; Peres, Y. J. Mol .Catal. 1993, 78, 351–366. [CrossRef]
- Tkatchenko, I. Comprehensive Organometallic Chemistry; Vol. 8, Pergamon, Oxford, (1982); pp. 101–223. [Google Scholar]
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