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Helvetica Chimica Acta – Vol. 93 (2010)
Yield: 48 mg (15%). Yellow oil. 1H-NMR (CDCl3): 7.18 (d, J ¼ 2.7, 1 H); 7.00 (d, J ¼ 8.5, 1 H); 6.88 (dd,
J ¼ 2.7, 8.5, 1 H); 4.98 (s, 1 H); 4.89 (s, 1 H); 4.42 (d, J ¼ 10.8, 1 H); 3.85 (s, 3 H); 3.60 (ddd, J ¼ 4.3, 9.5,
11.0, 1 H); 3.55, 3.00 (2s, 3 H); 2.29 (m, 2 H); 1.82 (s, 3 H); 0.68 (s, 3 H). 13C-NMR (CDCl3): 207.1 (s);
159.2 (s); 152.1 (s); 139.2 (s); 132.2 (s); 129.9 (d); 116.9 (d); 112.1 (d); 110.1 (t); 99.9 (s); 55.9 (q); 51.0
(q); 49.1 (q); 48.2 (s); 46.1 (d); 37.1 (d); 30.0 (t); 23.7 (q); 19.1 (q).
Compound 4b was followed by rel-(1R,2aS,8bS)-2,2a,4,8b-tetrahydro-4,4,6-trimethoxy-1-methyl-1-
(1-methylethenyl)cyclobuta[a]naphthalen-3(1H)-one (3b; Rf 0.31). Yield: 141 mg (44%). Yellow oil.
1H-NMR (CDCl3): 7.21 (d, J ¼ 2.7, 1 H); 6.99 (d, J ¼ 8.5, 1 H); 6.82 (dd, J ¼ 2.7, 8.5, 1 H); 4.75 (br. s, 2 H);
4.00 (d, J ¼ 11.0, 1 H); 3.84 (s, 3 H); 3.66 (ddd, J ¼ 6.2, 10.0, 11.0, 1 H); 3.57, 3.00 (2s, 3 H); 2.70 (dd, J ¼
6.2, 12.5, 1 H); 2.08 (dd, J ¼ 10.0, 12.5, 1 H); 1.62 (s, 3 H); 1.21 (s, 3 H). 13C-NMR (CDCl3): 207.1 (s);
159.2 (s); 148.1 (s); 136.1 (s); 130.1 (s); 128.2 (d); 114.3 (d); 111.1 (t); 109.5 (d); 100.0 (s); 55.1 (q); 52.1
(q); 52.0 (d); 49.1 (q); 47.2 (s); 38.4 (d); 31.1 (t); 30.9 (q); 22.1 (q).
1
3.3. Photocycloaddition of 5a. Irradiation for 3 h led to total conversion (monitoring by H-NMR)
with formation of a 1:2 mixture of 1:1 photoproducts 7 and 6a. CC (SiO2; pentane/2 :1) afforded first
trans-3-(3,3-dimethylbut-1-yn-1-yl)-5,5-dimethyl-2-(3-methyl-2-methylidenebut-3-en-1-yl)cyclohexanone
(7; Rf 0.64). Yield: 23 mg (8%). Light yellow oil. 1H-NMR (CDCl3): 5.10 (s, 1 H); 5.07 (s, 1 H); 5.01 (s,
1 H); 4.98 (s, 1 H); 3.05 (ddd, J ¼ 5.0, 5.1, 7.3, 1 H); 2.80 (dd, J ¼ 6.9, 14.1, 1 H); 2.68 (dd, J ¼ 7.5, 14.1,
1 H); 2.59 (m, 1 H); 2.36 (d, J ¼ 13.6, 1 H); 2.14 (m, 1 H); 1.90 (s, 3 H); 1.85 (m, 1 H), 1.70 (d, J ¼ 13.8,
1 H); 1.13 (s, 3 H); 1.08 (s, 9 H); 0.96 (s, 3 H). 13C-NMR (CDCl3): 212.8 (s); 145.1 (s); 142.4 (s); 114.0 (t);
113.0 (t); 92.3 (s); 78.2 (s); 52.2 (t); 51.0 (d); 41.3 (t); 36.0 (s); 31.5 (d); 31.2 (t); 31.0 (q); 30.2 (q); 29.5 (q);
27.4 (s); 21.5 (q). EI-MS: 286 (20, Mþ), 41 (100).
The second fraction consisted of rel-(1R,6R,7R)-6-(3,3-dimethylbut-1-yn-1-yl)-4,4,7-trimethyl-7-(1-
methylethenyl)bicyclo[4.2.0]octan-2-one (6a; Rf 0.43). Yield: 80 mg (28%). White crystals. M.p. 658.
1H-NMR (CDCl3): 4.83 (br. s, 1 H); 4.59 (s, 1 H); 2.95 (dd, J ¼ 9.5, 9.8, 1 H); 2.30 (d, J ¼ 14.8, 1 H); 2.21
(dd, J ¼ 9.8, 10.8, 1 H); 2.06 (dd, J ¼ 1.3, 14.8, 1 H); 1.91 (d, J ¼ 12.8, 1 H); 1.89 (dd, J ¼ 9.5, 10.8, 1 H);
1.63 (dd, J ¼ 1.5, 12.8, 1 H); 1.67 (s, 3 H); 1.35 (s, 3 H); 1.17 (s, 9 H); 1.03 (s, 3 H); 1.02 (s, 3 H). 13C-NMR
(CDCl3): 210.8 (s); 150.3 (s); 109.6 (t); 92.4 (s); 82.6 (s); 51.4 (t); 48.5 (s); 45.2 (d); 42.6 (s); 41.9 (t); 35.3
(s); 32.7 (t); 31.7 (q); 31.1 (q); 27.9 (s); 26.3 (q); 23.7 (t); 18.7 (q). EI-MS: 286 (9, Mþ), 205 (100).
X-Ray Crystal-Structure Determination of 6a1). Pale colorless blocks (0.36 ꢁ 0.17 ꢁ 0.05 mm) from
hexane, C20H30O, Mr 286.44, monoclinic, space group P2(1)/c; Z ¼ 4, a ¼ 15.942(3) ꢄ, b ¼ 9.1199(1) ꢄ,
c ¼ 12.1515(19) ꢄ, b ¼ 90.944(3)8; V¼ 1766.5(5) ꢄ3, Dx ¼ 1.077 g cmꢂ3
.
3.4. Photocycloaddition of 5a at Low Degree of Conversion. Irradiation for 60 min and subsequent
CC as described above afforded 3-[2-(tert-butyl)-4-methyl-4-(1-methylethenyl)cyclobut-1-en-1-yl]-5,5-
1
dimethylcyclohex-2-en-1-one (8; Rf 0.30). Yield: 6 mg (2%). Light yellow oil. H-NMR (CDCl3): 5.90
(br., 1 H); 4.82 (s, 1 H); 4.80 (s, 1 H); 2.41 (d, J ¼ 14.5, 1 H); 2.27 (d, J ¼ 1.4, 2 H); 2.22 (s, 2 H); 2.14 (d,
J ¼ 14.5, 1 H); 1.71 (s, 3 H); 1.38 (s, 3 H); 1.12 (s, 9 H); 1.035 (s, 3 H), 1.032 (s, 3 H). 13C-NMR (CDCl3):
199.9 (s); 155.3 (s); 149.4 (s); 142.5 (s); 142.2 (s); 126.3 (d); 110.2 (t); 50.9 (t); 47.5 (s); 42.5 (t); 40.1 (t);
33.5 (s); 33.4 (s); 29.4 (q); 28.1 (q); 23.4 (q); 18.4 (q). EI-MS: 286 (40, Mþ), 229 (100).
1
3.5. Photocycloaddition of 5b. Irradiation for 3 h led to total conversion (monitoring by H-NMR)
with formation of a 1:2 mixture of 1:1 photoproducts 9 and 6b. CC (SiO2; pentane/Et2O 2 :1) afforded
first rel-(4aR,8aR)-3,4,4a,5,8,8a-hexahydro-3,3,6,7-tetramethyl-4a-(phenylethynyl)naphthalen-1(2H)-
1
one (9; Rf 0.61). Yield: 55 mg (18%). Light yellow oil. H-NMR (CDCl3): 7.30 – 7.28 (m, 2 H); 7.24 –
7.22 (m, 3 H); 2.42 (dd, J ¼ 1.2, 5.2, 1 H); 2.30 (dd, J ¼ 1.0, 5.0, 1 H); 2.27 (br. s, 2 H); 2.20 (d, J ¼ 12.8,
1 H); 2.18 (dd, J ¼ 2.0, 12.8, 1 H); 2.04 (d, J ¼ 12.8, 1 H); 2.01 (dd, J ¼ 2.0, 13.0, 1 H); 1.69 (s, 3 H); 1.64
(d, J ¼ 13.0, 1 H); 1.62 (s, 3 H); 1.21 (s, 3 H); 1.07 (s, 3 H). 13C-NMR (CDCl3): 209.7 (s); 131.7 (d); 128.7
(d); 126.9 (d), 124.1 (s); 123.0 (s); 122.7 (s); 91.3 (s); 85.3 (s); 54.3 (t); 52.3 (d); 49.3 (t); 48.9 (s); 48.5 (t);
35.7 (s); 33.1 (q); 28.7 (q); 27.0 (q); 18.7 (q); 18.5 (q). EI-MS: 306 (51, Mþ), 168 (100).
The second fraction consisted of rel-(1R,6R,7R)-4,4,7-trimethyl-6-(phenylethynyl)-7-(1-methylethe-
nyl)bicyclo[4.2.0]octan-2-one (6b; Rf 0.36). Yield: 67 mg (22%). White crystals. M.p. 1448. 1H-NMR
(CDCl3): 7.36 – 7.34 (m, 2 H); 7.26 – 7.24 (m, 3 H); 4.88 (br. s, 1 H); 4.64 (s, 1 H); 3.11 (dd, J ¼ 9.3, 10.5,
1
)
CCDC-764276 and -764277 contain the supplementary crystallographic data for 6a and 6b,