Synthesis of Chiral Cyclohexenones
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b) Reaction of 20b with p-toluenesulfonic acid: According to procedure III 234 mg of 20b (0.96 mmol)
yielded a mixture (270 mg) which contained 25% 4a, 40% 24b, 13% 24c, and 11% 21b. Compounds
were separated partially by column chromatography (petroleum ether:ethyl acetate¼ 1:1). 8-Methoxy-
3,3-dimethyloct-4-ene-2,6-dione (24a): GLC (180ꢁC): 92%; IR: ꢄꢀ¼ 2829, 2815 (CH3–O), 1711,
1674 (C¼O), 1624 (>C¼C<), 1119 (C–O–C) cmꢂ1; MS: m=z ¼ 199 (<1, Mþ þ H), 183
(<1, Mþ-CH3), 167 (<1, Mþ-CH3–O), 156 (85, Mþ-C2H2O), 139 (1), 128 (18), 111 (20), 96
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(65), 87 (43), 43 (100); H NMR (200MHz, CDCl3): ꢅ ¼ 1.28 (s, 6H, 3-CH3), 2.12 (s, 1-CH3), 2.81
(t, J ¼ 6.3 Hz, 7-CH2), 3.31 (s, CH3–O), 3.67 (t, J ¼ 6.3Hz, 8-CH2), 6.15 (d, J ¼ 16.2Hz, 5-CH),
6.91 (d, J ¼ 16.2Hz, 4-CH) ppm; 13C NMR (50.3 MHz, CDCl3): ꢅ ¼ 24.00 (3-CH3), 26.37 (1-CH3),
41.04 (7-CH2), 51.22 (3-C), 59.31 (CH3–O), 68.08 (8-CH2), 129.31 (5-CH), 150.34 (4-CH), 198.60
(6-C¼O), 209.46 (2-C¼O) ppm; 3,3-Dimethylocta-4,7-diene-2,6-dione (24b): GLC (180ꢁC): 91%;
IR: ꢄꢀ¼ 1712, 1667 (C¼O), 1625, 1612 (>C¼C<) cmꢂ1; MS: m=z ¼ 167 (<1, Mþ þ H), 151
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(<1, Mþ-CH3), 124 (45, Mþ-C2H2O), 109 (100), 107 (5), 95 (8), 81 (12); H NMR (200 MHz,
CDCl3): ꢅ ¼ 1.31 (s, 6H, 3-CH3), 2.14 (s, 1-CH3), 5.86 (dd, J ¼ 10.5, 1.3 Hz, 1H, 8-CH2), 6.29 (dd,
J ¼ 17.5, 1.3 Hz, 1H, 8-CH2), 6.40 (d, J ¼ 16.1Hz, 5-CH), 6.60 (dd, J ¼ 17.5, 10.5 Hz, 7-CH), 7.00
(d, J ¼ 16.1Hz, 4-CH) ppm; 13C NMR (50.3 MHz, CDCl3): ꢅ ¼ 23.97 (3-CH3), 26.40 (1-CH3),
51.37 (3-C), 126.97 (5-CH), 129.67 (8-CH2), 135.50 (7-CH), 151.22 (4-CH), 189.93 (6-C¼O),
209.31 (2-C¼O) ppm; 8-Hydroxy-3,3-dimethyloct-4-ene-2,6-dione (24c): GLC (180ꢁC): 62% 24b
and 29% 21b; MS: m=z ¼ 170 (85), 139 (1, Mþ-C2H5O), 124 (20), 101 (32), 97 (72), 81 (25), 43
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(100); H NMR (200MHz, CDCl3) (simultaneously with 21b): ꢅ ¼ 1.28 (s, 6H, 3-CH3), 2.12 (s, 1-
CH3), 2.82 (t, J ¼ 6.4 Hz, 7-CH2), 3.70 (t, J ¼ 6.4 Hz, 8-CH2) 6.15 (d, J ¼ 16.3Hz, 5-CH), 6.91
(d, J ¼ 16.3Hz, 4-CH) ppm; 13C NMR (50.3 MHz, CDCl3) (simultaneously with 21b): ꢅ ¼ 23.90
(3-CH3), 26.31 (1-CH3), 41.13 (7-CH2), 51.17 (3-C), 65.94 (8-CH2), 129.46 (5-CH), 150.34 (4-CH),
199.00 (6-C¼O), 209.66 (2-C¼O) ppm; 21b: MS: m=z ¼ 226 (<1, Mþ), 211 (<1, Mþ-CH3), 194
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(39, Mþ-CH4O), 180 (25), 167 (15), 149 (15), 135 (17), 121 (18), 107 (24), 100 (100); H NMR
(200 MHz, CDCl3) (simultaneously with 24c): ꢅ ¼ 1.04 (s, 6-CH3), 1.12 (s, 6-CH3), 1.15
(t, J ¼ 6.9 Hz, CH3–CH2–O), 2.44 (t, J ¼ 6.4 Hz, 10-CH2), 2.53–2.62 (m, 4-CH2), 3.32 (s,
CH3–O), 3.47 (m, CH3–CH2–O), 3.53 (t, J ¼ 6.4 Hz, 20-CH2), 5.82 (bs, 2-CH) ppm; 13C NMR
(50.3MHz, CDCl3) (simultaneously with 24c): ꢅ ¼ 15.47 (CH3–CH2–O), 19.04=22.10 (6-CH3),
33.13=38.02 (4-CH2, 10-CH2), 47.13 (6-C), 59.15 (CH3–O), 67.97 (CH3–CH2–O), 70.41 (20-CH2),
81.89 (5-CH), 125.77 (2-CH), 157.49 (3-C), 204.17 (1-C¼O) ppm.
c) Ozonolyses of 8c and decomposition of the ozonide to 20b: According to procedures IVand V 1.90 g
of 8c (8.96 mmol) yielded without purification of the intermediate products after final ball tube
distillation 1.11 g (51%) of the liquid 20b.
d) Reaction of 20b with NaOH=EtOH: To a stirred soln. of 234 mg of 20b (0.96 mmol) in 10cm3 of
ethanol at rt 100 mg of KOH in 3 cm3 of ethanol were added and refluxed about 15min. After that
100 cm3 of diethyl ether were added and the organic layer was washed with H2O, sat. NH4Cl-soln.,
brine, dried (Na2SO4), and concentrated. Purification by column chromatography (petroleum ether:
ethyl acetate ¼ 2:1) yielded 64mg (39%) of 25a and 25mg (16%) of 25b. 2-Methoxymethyl-3,4,4-
trimethylcyclohexa-2,5-dienone (25a): GLC (180ꢁC): 96%; IR: ꢄꢀ¼ 2813 (CH3–O), 1662, 1628
(C¼O), 1624 (>C¼C<), 1105, 1086 (C–O–C) cmꢂ1; MS: m=z ¼ 180 (<1, Mþ), 179 (<1,
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Mþ-H), 165 (100, Mþ-CH3), 150 (30), 135 (20), 122 (12), 105 (10); H NMR (200MHz, CDCl3):
ꢅ ¼ 1.25 (s, 6H, 4-CH3), 2.08 (s, 3-CH3), 3.34 (s, CH3–O), 4.29 (s, CH2–O), 6.20 (d, J ¼ 9.9 Hz,
6-CH), 6.74 (d, J ¼ 9.9 Hz, 5-CH) ppm; 13C NMR (50.3 MHz, CDCl3): ꢅ ¼ 16.10 (3-CH3), 26.47
(4-CH3), 40.84 (4-C), 58.74 (CH3–O), 64.84 (CH2–O), 126.73 (6-CH), 132.20 (2-C), 157.14
(5-CH), 164.88 (3-C), 185.24 (1-C¼O) ppm; 2-Ethoxymethyl-3,4,4-trimethylcyclohexa-2,5-dienone
(25b): GLC (120ꢁC): 82%; IR: ꢄꢀ¼ 2809 (CH3–O), 1664, 1629 (C¼O), 1097 (C–O–C) cmꢂ1; MS:
m=z ¼ 195 (<1, Mþ þ H), 194 (<1, Mþ), 179 (100, Mþ-CH3), 151 (80, Mþ-CH3, –CO), 135 (20),
123 (25), 105 (18), 91 (20); 1H NMR (200MHz, CDCl3): ꢅ ¼ 1.18 (t, J ¼ 7.2 Hz, CH3–CH2–O), 1.24
(s, 6H, 4-CH3), 2.08 (s, 3-CH3), 3.50 (t, J ¼ 7.2 Hz, CH3–CH2–O), 4.32 (s, 2-C–CH2–O), 6.18