FEATURE ARTICLE
Equatorial Preference in the GaCl3-Promoted Ethenylation of Cyclic Ketones
143
Pyridine (5 mL) and Ac2O (1 mL) were added to (1S*,2R*,6R*)-
2,6-dimethyl-2-ethenyl-1-cyclohexane (136 mg, 0.88 mmol) in
Et2O (5 mL), and the mixture was stirred at r.t. for 1 h. After addi-
tion of sat. NaHCO3 the organic materials were extracted with Et2O,
washed with sat. KHSO4, brine, dried (MgSO4) and concentrated.
The residue was purified by flash column chromatography (hexene:
EtOAc 50:1) to give (1S*,2R*,6R*)-1-acetoxy-2,6-dimethyl-2-
ethenylcyclohexane (131 mg, 76%).
MS (EI) m/z: 166 (M+, 57%), 67 (M+–99, 100%).
HRMS calcd for C11H18O, 166.1358; found, 166.1356.
Since this compound possesses trans-2,6-dimethyl group, the 3-me-
thyl should be axial. The equatorial configuration of the 2-ethenyl
group was determined by NOE between the 2-methyl protons (
1.35) and the 6-axial proton ( 2.72).
(2R*,3S*,6R*)-2-Ethenyl-2,3,6-trimethylcyclohexanone
IR (neat): 2928, 2857, 1769, 1463, 1072 cm–1.
IR (neat): 1711, 1601, 1260, 1453, 1384 cm–1.
1H NMR (400 MHz, CDCl3): = 0.83 (3 H, d, J = 6.8 Hz), 1.07 (3
H, s), 1.02–1.07 (1 H, m), 1.42–1.53 (4 H, m), 1.69–1.83 (2 H, m,
6ax), 2.01 (3 H, s), 4.53 (1 H, d, J = 10.4 Hz, 1ax), 4.92 (1 H, d,
J = 9.6 Hz), 4.96 (1 H, d, J = 17.6 Hz), 5.72 (1 H, dd, J = 17.6, 11.2
Hz).
13C NMR (100 MHz, CDCl3): = 15.6, 18.7, 20.9, 21.0, 32.5, 33.9,
37.6, 41.7, 81.5, 111.6, 146.9, 170.5.
1H NMR (400 MHz, CDCl3): = 0.87 (3 H, d, J = 7.2 Hz), 0.99 (3
H, d, J = 6.4 Hz), 1.08 (3 H, s), 1.43–1.51 (1H, m, 4ax), 1.54–1.62
(1 H, m, 5ax), 1.88–1.95 (1 H, m, 5eq), 2.18–2.25 (2 H, m, 3eq,4eq),
2.80 (1 H, ddq, J = 12.4, 6.4, 6.0 Hz, 6ax), 4.93 (1 H, d, J = 17.6
Hz), 5.11 (1 H, d, J = 10.0 Hz), 6.06 (1 H, dd, J = 17.6, 10.8 Hz).
13C NMR (100 MHz, CDCl3): = 15.0, 15.5, 21.5, 28.6, 31.5, 41.2,
41.6, 56.1, 114.8, 144.6, 214.8. IR (neat) 1711, 1601, 1260, 1453,
1384 cm-1.
MS (EI) m/z: 196 (M+, 3%), 43 (M+–153, 100%).
HRMS calcd for C12H22O2: 196.1463; found: 196.1463.
MS (EI) m/z 166 (M+, 48%), 93 (M+-73, 100%).
The equatorial configuration of the 2-ethenyl group was determined
by NOE between the 2-methyl protons ( 1.07) and the 6-axial pro-
ton ( 1.69-1.83).
HRMS calcd for C11H18O, 166.1358; found,166.1343.
The axial configuration of the 3-methyl group was determined by
NOE between the 3-methyl protons ( 0.87) and the 5-axial proton
(
1.54-1.62). The equatorial configuration of the 2-methyl group
(1S*,2R*,6R*)-1-Acetoxy-2,6-dimethyl-2-ethenylcyclohexane
was determined by NOE between the 2-ethenyl proton ( 6.06) and
the 6-axial proton ( 2.80).
IR (neat): 2934, 1741, 1245 cm–1.
1H NMR (400 MHz, CDCl3): = 0.81 (3 H, d, J = 7.6 Hz), 1.06 (3
H, s), 1.23 (1 H, td, J = 12.4, 4.4 Hz), 1.27–1.32 (1 H, m), 1.40–1.45
(1H, m), 1.54 (1 H, td, J = 13.2, 3.6 Hz), 1.61–1.67 (1 H, m), 1.71
(1 H, td, J = 13.2, 4.4 Hz), 1.87–1.96 (1 H, m), 2.01 (3 H, s), 4.78
(1 H, br. s), 4.92 (1 H, dd, J = 10.8, 1.6 Hz), 4.93 (1 H, dd, J = 17.6,
1.6 Hz), 5.75 (1 H, dd, J = 11.2, 17.6 Hz).
13C NMR (100 MHz, CDCl3): = 18.4, 21.0, 21.2, 22.4, 28.6, 29.3,
30.4, 30.8, 40.7, 111.2, 146.3, 170.5.
MS (EI) m/z: 196 (M+, 0.7%), 43 (M+–153, 100%).
(2S*,3R*,6R*)-3-Butyl-2-ethenyl-2,6-dimethylcyclohexanone
IR (neat): 3083, 1705, 1640, 1456, 996 cm–1.
1H NMR (400 MHz, CDCl3): = 0.87 (3 H, t, J = 7.6 Hz), 0.99 (3
H, d, J = 6.8 Hz), 1.16 (3 H, s), 1.01–1.18 (2 H, m), 1.19–1.38 (3 H,
m), 1.47–1.61 (2 H, m), 1.88–1.93 (1 H, m), 2.03–2.09 (1 H, m),
2.69 (1 H, ddd, J = 12.4, 6.8, 6.4 Hz, 6ax), 5.01 (1 H, dd, J = 17.6,
1.6 Hz), 5.24 (1 H, dd, J = 10.8, 1.2 Hz), 5.84 (1 H, ddd, J = 17.6,
11.2, 1.2 Hz).
13C NMR (100 MHz, CDCl3): = 14.2, 14.9, 15.1, 22.9, 26.5, 29.9,
30.5, 35.1, 40.7, 46.9, 113.9, 142.2, 215.2.
HRMS calcd for C12H22O2, 196.1463; found, 196.1427.
(2S*,3R*,6R*)-2-Ethenyl-2,3,6-trimethylcyclohexanone
MS (EI) m/z: 208 (M+, 71%), 81 (M+–127, 100%).
IR (neat): 3091, 1704, 1639, 1455, 1414, 985 cm–1.
HRMS calcd for C14H24O, 208.1827; found, 208.1830.
1H NMR (400 MHz, CDCl3): = 0.86 (3 H, d, J = 6.4 Hz), 0.99 (3
H, d, J = 6.4 Hz), 1.17 (3 H, s), 1.30–1.41 (1 H, m), 1.67–1.72 (2 H,
m), 1.73–1.83 (1 H, m, 3ax), 2.00–2.06 (1 H, m), 2.68 (1 H, septet,
J = 6.2 Hz, 6ax), 5.01 (1 H, d, J = 17.6 Hz), 5.22 (1 H, d, J = 11.2
Hz), 5.87 (1 H, dd, J = 17.6, 11.2 Hz).
13C NMR (100 MHz, CDCl3): = 14.1, 15.1, 15.9, 29.5, 35.1, 40.4,
41.4, 55.2, 113.7, 142.0, 215.3.
Anal. calcd for C10H16O: C, 80.71; H, 11.62. Found: C, 80.49; H,
11.77.
The stereochemistry was determined by analogy to the 3-methyl de-
rivatives. The equatorial configuration of the 2-ethenyl group was
determined by NOE between the 2-methyl protons ( 1.16) and the
6-axial proton ( 2.69).
MS (EI) m/z: 166 (M+, 60%), 67 (M+–99, 100%).
(2S*,3S*,6R*)-3-Butyl-2-ethenyl-2,6-dimethylcyclohexanone
IR (neat): 3080, 1706, 1634, 1456, 995 cm–1.
HRMS calcd for C11H18O, 166.1358; found, 166.1346.
1H NMR (400 MHz, CDCl3): = 0.87 (3 H, t, J = 6.4 Hz), 1.03 (3
H, d, J = 6.8 Hz), 1.06–1.17 (2 H, m), 1.18–1.33 (3 H, m), 1.34 (3
H, s), 1.43–1.63 (3H, m), 1.74–1.80 (1 H, m), 1.90–1.98 (1 H, m),
2.00–2.09 (1 H, m), 2.71 (1 H, ddd, J = 10.8, 6.8, 6.4 Hz, 6ax), 5.05
(1 H, dd, J = 17.6, 1.2 Hz), 5.16 (1 H, dd, J = 11.2, 1.6 Hz), 6.28 (1
H, dd, J = 17.6, 11.2 Hz).
The equatorial 3-methyl stereochemistry was determined by ob-
serving the 3-proton with irradiation of the 3-methyl protons, J (3H-
4H) = ca 9.6 Hz. The equatorial configuration of the 2-ethenyl group
was determined by NOE between the 2-methyl protons ( 1.17) and
the 6-axial proton ( 2.68).
(2S*,3S*,6R*)-2-Ethenyl-2,3,6-trimethylcyclohexanone
13C NMR (100 MHz, CDCl3): = 14.2, 15.9, 22.8, 23.0, 23.3, 28.8,
30.0, 30.2, 40.3, 47.0, 54.5, 114.2, 139.6, 215.6.
IR (neat): 1707, 1612 cm–1.
1H NMR (400 MHz, CDCl3): = 0.91 (3 H, d, J = 6.8 Hz), 1.03 (3
H, d, J = 6.4 Hz), 1.35 (3 H, s), 1.49–1.56 (1 H, m), 1.57–1.65 (1 H,
m), 1.91–2.03 (2 H, m), 2.04–2.15 (1 H, m, 3eq), 2.72 (1 H, ddq,
J = 11.6, 6.4, 6.4 Hz, 6ax), 5.06 (1H, d, J = 17.2 Hz), 5.16 (1H, dd,
J = 10.8, 1.2 Hz), 6.27 (1H, dd, J = 17.6, 10.8 Hz).
13C NMR (100 MHz, CDCl3): = 15.8, 16.4, 22.6, 27.6, 30.2, 40.4,
41.8, 54.3, 114.1, 139.5, 215.5.
MS (EI) m/z: 208 (M+, 78%), 81 (M+-127, 100%).
HRMS calcd for C14H24O, 208.1827; found, 208.1831.
The stereochemistry was determined by analogy to the 3-methyl de-
rivatives. The equatorial configuration of the 2-ethenyl group was
determined by NOE between the 2-methyl protons ( 1.34) and the
6-axial proton ( 2.71).
Synthesis 2002, No. 1, 138–145 ISSN 0039-7881 © Thieme Stuttgart · New York