Helvetica Chimica Acta – Vol. 93 (2010)
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Then, AcOEt (10 ml) was added. The catalyst was filtered off, and the solvent evaporated. The resulting
mixture was separated by CC (SiO2 (10 g), hexane/AcOEt 100 :0 ! 95 :5): 1 (0.077 g, conversion 81%)
and 13a/13b ca. 1.14 :1 (by 1H-NMR; 0.137 g, 23% (yield based on converted 1)).
(3R,3aS,7aR)-1,3,3a,6,7,7a-Hexahydro-1,1,5-trimethyl-3-[(1E)-prop-1-en-1-yl]isobenzofuran (13a):
1H-NMR (500 MHz)1): 1.17 (s, Me(9)); 1.22 (s, Me(8)); 1.44 (dddd, J(4a,4e) ¼ 13.3, J(4a,3aa) ¼ 13.3,
J(4a,5a) ¼ 11.0, J(4a,5e) ¼ 6.2, HaꢀC(4)); 1.61 – 1.67 (m, HeꢀC(4)); 1.65 (br. s, Me(10)); 1.68 (ddd,
J(3’,2’) ¼ 6.5, J(3’,1’) ¼ 1.6, J(3’,1) ¼ 0.4, Me(3’)); 1.81 (ddd, J(3aa,4a) ¼ 13.3, J(3aa,7a) ¼ 6.8, J(3aa,4e) ¼
4.2, HaꢀC(3a)); 1.85 – 1.98 (m, CH2(5)); 2.44 – 2.51 (m, HꢀC(7a)); 3.88 (dd, J(1,7a) ¼ 9.7, J(1,1’) ¼ 7.8,
HꢀC(1)); 5.19 – 5.23 (m, HꢀC(7)); 5.41 (ddq, J(1’,2’) ¼ 15.1, J(1’,1) ¼ 7.8, J(1’,3’) ¼ 1.6, HꢀC(1’)); 5.59
(dqd, J(2’,1’) ¼ 15.1, J(2’,3’) ¼ 6.5, J(2’,1) ¼ 0.7, HꢀC(2’)). 13C-NMR (125 MHz)1): 17.69 (q, C(3’));
22.01(t, C(4)); 23.55 (q, C(10)); 24.04 (q, C(9)); 30.07 (t, C(5)); 31.00 (q, C(8)); 45.73 (d, C(7a)); 46.02 (d,
C(3a)); 81.97 (s, C(3)); 84.41 (d, C(1)); 119.31 (d, C(7)); 127.77 (d, C(2’)); 132.59 (d, C(1’)); 135.45 (s,
C(6)). HR-MS: 206.1691 (Mþ, C14H22Oþ; calc. 206.1665).
(3S,3aS,7aR)-1,3,3a,6,7,7a-Hexahydro-1,1,5-trimethyl-3-[(1E)-prop-1-en-1-yl]isobenzofuran (13b):
1H-NMR (500 MHz)1): 1.20 (s, Me(8)); 1.22 (s, Me(9)); 1.31 (dddd, J(4a,3aa) ¼ 12.8, J(4a,4e) ¼ 12.5,
J(4a,5a) ¼ 11.0, J(4a,5e) ¼ 6.0, HaꢀC(4)); 1.66 (dd, J(3’,2’) ¼ 6.5, J(3’,1’) ¼ 1.6, Me(3’)); 1.68 (br. s,
Me(10)); 1.63 – 1.72 (m, HeꢀC(4)); 1.77 (ddd, J(3aa,4a) ¼ 12.8, J(3aa,7a) ¼ 7.3, J(3aa,4e) ¼ 4.1, Haꢀ
C(3a)); 1.84 – 1.91 (m, CH2(5)); 3.03 – 3.09 (m, HꢀC(7a)); 4.38 (dd, J(1,7a) ¼ 9.0, J(1,1’) ¼ 8.6, HꢀC(1));
5.09 – 5.13 (m, HꢀC(7)); 5.29 (ddq, J(1’,2’) ¼ 15.1, J(1’,1) ¼ 8.6, J(1’,3’) ¼ 1.6, HꢀC(1’)); 5.54 (dqd,
J(2’,1’) ¼ 15.1, J(2’,3’) ¼ 6.5, J(2’,1) ¼ 0.7, HꢀC(2’)). 13C-NMR (125 MHz)1): 17.73 (q, C(3’)); 22.65 (t,
C(4)); 23.74 (q, C(10)); 23.85 (q, C(9)); 27.27 (q, C(8)); 29.31 (t, C(5)); 42.07 (d, C(7a)); 45.27 (d, C(3a));
80.26 (d, C(1)); 81.34 (s, C(3)); 119.69 (d, C(7)); 127.38 (d, C(2’)); 132.43 (d, C(1’)); 134.38 (s, C(6)). HR-
MS: 206.1691 (Mþ, C14H22Oþ; calc. 206.1665).
5. Interaction of (þ)-Car-2-ene (1) with 4-Methoxybenzaldehyde on K10 Clay. To a suspension of K10
clay (2.5 g) in CH2Cl2 (8 ml) 4-methoxybenzaldehyde (0.50 g, 3.68 mmol) was added. Then, a soln. of 1
(0.500 g, 3.68 mmol) in CH2Cl2 (7 ml) was added dropwise. The mixture was stirred for 1.5 h at r.t. Then,
Et2O (5 ml) was added. The catalyst was filtered off, and the solvent evaporated. The resulting mixture
was separated by CC (SiO2 (10 g), hexane/AcOEt 100 :0 ! 85 :15): 1 (0.112 g, conversion 78%), 17
(0.049 g, 5%), and 16a/16b ca. 7:1 (by 1H-NMR; 0.313 g, 31%); yields are based on converted 1.
Note that aromatic aldehydes are stable on K10 clay because they were isolated in unchanged form
from reaction mixtures in all of their transformations with carenes. Since the large amounts of aldehydes
hindered product separation, they were taken in a smaller ratio than for reactions with (2E)-but-2-enal.
4-(4-Methoxyphenyl)-2,2,6-trimethyl-3-oxabicyclo[3.3.1]non-6-ene (17): [a]1D9 ¼ þ74 (c ¼ 0.9). 1H-
and 13C-NMR: identical with those reported in [15].
(3S,3aS,7aR)-1,3,3a,6,7,7a-Hexahydro-3-(4-methoxyphenyl)-1,1,15-trimethylisobenzofuran (16a):
1H-NMR (600 MHz)1): 1.30 (s, Me(9)); 1.41 (s, Me(8)); 1.62 (dddd, J(4a,3aa ¼ 13.1, J(4a,4e) ¼ 12.8,
J(4a,5a) ¼ 9.5, J(4a,5e) ¼ 7.0, HaꢀC(4)); 1.67 (br. s, Me(10)); 1.74 (ddddd, J(4e,4a) ¼ 12.8, J(4e,3aa) ¼ 4.3,
J(4e,5a) ¼ 4.3, J(4e,5e) ¼ 3.0, J(4e,7a) ¼ 0.5, HeꢀC(4)); 1.96 (ddd, J(3aa,4a) ¼ 13.1, J(3aa ,7a) ¼ 6.9,
J(3aa,4e) ¼ 4.3, HaꢀC(3a)); 1.97 – 2.01 (m, CH2(5)); 2.62 – 2.68 (m, HꢀC(7a)); 3.78 (s, MeO); 4.54 (d,
J(1,7a) ¼ 10.1, HꢀC(1)); 5.17 (br. d, J(7,7a) ¼ 4.6, HꢀC(7)); 6.86 (d, J ¼ 8.6, HꢀC(3’), HꢀC(5’)); 7.27
(d, J ¼ 8.6, HꢀC(2’), HꢀC(6’)). 13C-NMR (151 MHz)1): 21.91 (t, C(4)); 23.45 (q, C(10)); 24.06 (q, C(9));
30.06 (t, C(5)); 31.03 (q, C(8)); 46.42 (d, C(3a)); 48.46 (d, C(7a)); 55.08 (q, C(7’)); 82.24 (s, C(3)); 85.01
(d, C(1)); 113.55 (d, C(3’), C(5’)); 118.66 (d, C(7)); 127.18 (d, C(2’), C(6’)); 134.31 (s, C(1’)); 136.16 (s,
C(6)); 158.83 (s, C(4’)). HR-MS: 272.1770 (Mþ, C18H24O2þ ; calc. 272.1771).
(3R,3aS,7aR)-1,3,3a,6,7,7a-Hexahydro-3-(4-methoxyphenyl)-1,1,5-trimethylisobenzofuran (16b): For
the minor product 16b, we revealed only the following signals in the 1H-NMR spectrum: 1H-NMR
(500 MHz)1): 1.32 (s, Me(8)); 1.35 (s, Me(9)); 1.47 (m, Me(10)); 1.79 – 1.84 (m, CH2(5)); 1.91 – 1.97 (m,
HꢀC(3a)); 3.14 – 3.20 (m, HꢀC(7a)); 3.76 (s, MeO); 4.75 – 4.78 (m, HꢀC(7)); 5.08 (d, J(1,7a) ¼ 9.2,
HꢀC(1)); 6.76 (d, J ¼ 8.6, HꢀC(3’), HꢀC(5’)); 7.10 (d, J ¼ 8.6, HꢀC(2’), HꢀC(6’)). 13C-NMR
(125 MHz)1): 22.60 (t, C(4)); 23.60 (q, C(10)); 23.87 (q, C(9)); 27.02 (q, C(8)); 28.66 (t, C(5)); 43.24 (d,
C(7a)); 45.08 (d, C(3a)); 54.83 (q, C(7’)); 80.85 (d, C(1)); 81.35 (s, C(3)); 112.96 (d, C(3’), C(5’)); 120.46
(d, C(7)); 128.04 (d, C(2’), C(6’)); 133.14 (s, C(1’)); 133.68 (s, C(6)); 158.30 (s, C(4’)). HR-MS: 272.1770
(Mþ, C18H24Oþ2 ; calc. 272.1771).