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mixture of diastereoisomers) as an oil. Treatment of esters 5a with 1 ml of 2n HCl in 5 ml of THF gave 334 mg of
a crude mixture. Chromatography afforded 292 mg (1.40 mmol) of 6a (97%) as a colorless oil. IR: 1720.
1H-NMR: 1.49 (s, 3 H); 1.50 ± 1.80 (m, 3 H); 2.25 (ddd, J 13.0, 6.0, 6.0, 1 H); 2.40 ± 2.70 (m, 2 H); 7.11 (d, J
1.0, 1 H); 7.38 (br. s, 1 H). 13C-NMR: 13.9; 19.5; 20.2; 27.9; 34.1; 41.1; 60.6; 120.5; 125.1; 136.8; 139.3; 176.1. GC/
.
MS: 208 (M ). Anal. calc. for C12H16O3 (208.26): C 69.21, H 7.74; found: C 69.23, H 7.76.
Data of 4a: Major isomer: 1H-NMR: 0.91 (t, J 7.0, 3 H); 1.09 (s, 3 H); 1.25 (t, J 7.0, 3 H); 1.20 ± 1.75 (m,
6 H); 2.05 ± 2.45 (m, 3 H); 2.64 (t, J 7.0, 2 H); 2.55 ± 2.75 (m, 1 H); 2.86 (d, J 5.0, 1 H); 3.01 (d, J 5.0, 1 H);
4.00 ± 4.30 (m, 2 H); 5.96 (br. s, 1 H). 13C-NMR: 13.4; 13.9; 19.3; 21.3; 22.3; 28.6; 32.1; 33.3; 36.3; 48.1; 51.4; 60.3;
.
63.1; 122.1; 134.3; 174.2. GC/MS: 298 (M ). Anal. calc. for C16H26O3S: C 64.39, H 8.78; found: C 64.37, H 8.77.
Minor isomer: 1H-NMR: 0.93 (t, J 7.0, 3 H); 1.07 (s, 3 H); 1.26 (t, J 7.0, 3 H); 1.20 ± 1.75 (m, 6 H); 2.34 (d, J
6.0, 1 H); 2.05 ± 2.45 (m, 3 H); 2.65 (t, J 7.0, 3 H); 2.55 ± 2.75 (m, 1 H); 2.88 (d, J 6.0, 1 H); 4.00 ± 4.30 (m,
2 H); 6.02 (d, J 1.0, 1 H). 13C-NMR: 13.4; 13.9; 20.1; 21.4; 22.4; 29.4; 32.1; 34.1; 36.3; 47.9; 50.2; 60.3; 62.3;
.
118.7; 134.5; 174.2. GC/MS: 298 (M ). Anal. calc. for C16H26O3S (298.44): C 64.39, H 8.78; found: C 64.38, H
8.79.
Ethyl (4,5,6,7-Tetrahydro-4-methyl-2-benzofuran-4-yl)acetate (6b). A mixture of 2.00 g (6.70 mmol) of 3b
and 1.90 g (10.00 mmol) of Me3SSO4Me in 30 ml of CH2Cl2 and 30 ml 50% aq. NaOH was heated at 488 for 24 h.
Workup as for 4a produced 1.70 g (5.40 mmol) of crude ethyl {8-[(butylsulfanyl)methylidene]-5-methyl-1-
oxaspiro[2.5]oct-5-yl}acetate (4b) as a viscous oil. NMR Analysis showed the presence of two diastereoisomers
in a ratio of ca. 4 :3. Filtration of oxiranes 4b through a SiO2 pad converted them to ethyl [1-(butylsulfanyl)-
1,3,4,5,6,7-hexahydro-4-methyl-2-benzofuran-4-yl]acetate (5b; 1.60 g, 5.10 mmol, 94%; mixture of diaster-
eoisomers) as a liquid. A mixture of 5b and 3 ml of 2n HCl in 5 ml of THF was stirred at r.t. for 3 h and then
saturated with CaCO3. The layers were separated, the aq. portion extracted with Et2O, and the combined org.
solns. washed, dried, and evaporated. Flash chromatography of the residue provided 1.05 g (4.70 mmol) of liquid
6b (92%). IR: 1718. 1H-NMR: 1.22 (t, J 7.0, 3 H); 1.36 (s, 3 H); 1.50 ± 1.90 (m, 2 H); 2.52 (s, 2 H); 2.45 ± 2.55
(m, 2 H); 4.10 (q, J 7.0, 2 H); 7.08 (d, J 1.0, 1 H); 7.24 (br. s, 1 H). 13C-NMR: 14.0; 19.5; 19.6; 29.0; 32.0; 36.3;
.
47.1; 59.8; 120.3; 129.6; 136.7; 137.7; 171.3. GC/MS: 222 (M ). Anal. calc. for C13H18O3 (222.28): C 70.24, H 8.16;
found: C 70.26, H 8.18.
4,5,6,7-Tetrahydro-4-methyl-2-benzofuran-4-carboxylic Acid (7a). Alkaline hydrolysis of 250 mg
(1.20 mmol) of 6a, as described for 7b (vide infra), gave 180 mg (1.00 mmol) of 7a (83%) as a colorless,
.
viscous oil, which solidified on standing (spectra data identical to that reported in [1]). GC/MS: 180 (M ).
Anal. calc. for C10H12O3 (180.20): C 66.65, H 6.71; found: C 66.67, H 6.70.
(4,5,6,7-Tetrahydro-4-methyl-2-benzofuran-4-yl)acetic Acid (7b). A mixture of 500 mg (2.20 mmol) and
10 ml of 25% aq. NaOH was heated at 858 for 3 h. Upon normal work-up 320 mg (1.60 mmol) of 7b (73%) was
obtained. IR: 2400 ± 3600, 1700. 1H-NMR: 1.39 (s, 3 H); 1.55 ± 1.90 (m, 4 H); 2.51 (t, J 6.0, 2 H); 2.57 (s, 2 H);
7.09 (d, J 1.0, 1 H); 7.26 (d, J 1.0, 1 H); 11.2 (br. s, 1 H). 13C-NMR: 19.5; 19.6; 28.9; 32.0; 36.2; 46.9; 120.3;
.
129.5; 136.9; 137.7; 178.1. GC/MS: 194 (M ). Anal. calc. for C11H14O3 (194.23): C 68.02, H 7.27; found: C 68.01,
H 7.25.
2,3,4,4a,5,6-Hexahydro-6-oxonaphthalene-1-carbaldehyde (11). Conversion of 7b to (4,5,6,7-tetrahydro-4-
methyl-2-benzofuran)acetyl chloride (9) and 1-diazo-3-(4,5,6,7-tetrahydro-4-methyl-2-benzofuran-4-yl)propan-
2-one (10) was performed according to a standard procedure ([1] and refs. cit. therein). A soln. of 20 mg
(0.09 mmol) of 10 and a few crystals of Rh2(OAc)4 in 2 ml of CH2Cl2 were stirred at r.t. for 1 h and then worked
up in the usual manner to give 14 mg (0.07 mmol) of 11 (78%). 1H-NMR: 1.27 (s, 3 H); 1.60 ± 2.20 (m, 8 H); 6.18
(d, J 10.0, 1 H); 8.02 (d, J 10.0, 1 H); 10.4 (s, 1 H). 13C-NMR: 16.5; 23.8; 25.7; 36.8; 38.1; 52.1; 130.0; 137.0;
.
189.6. GC/MS: 190 (M ). Anal. calc. for C12H14O2 (176.22): C 75.76, H 7.42; found: C 75.77, H 7.44.
Ethyl 6-Methyl-1,4-dioxaspiro[4.5]decane-6-carboxylate (12a). A mixture of 880 mg (5.0 mmol) of 1a,
340 mg (5.5 mmol) of ethylene glycol, 2 ml of triethoxymethane and 2 drops of conc. H2SO4 was allowed to stand
at r.t. for 18 h. It was filtered through a SiO2 pad and the solvents were evaporated, providing 1.10 g (4.81 mmol)
of 12a (96%). B.p. 106 ± 1078 (4 mm Hg). IR: 1721. 1H-NMR: 1.24 (s, Me 3 H); 1.26 (t, J 7.0, Me 3 H); 1.35 ±
1.70 (m, 6 H); 1.82 ± 1.95 (m, 1 H); 2.06 (ddd, J 13.0, 7.0, 5.0, 1 H); 3.85 ± 4.02 (m, 2 H); 4.15 (q, J 7.0, 3 H).
.
13C-NMR: 13.9; 18.8; 21.3; 23.1; 31.5; 34.4; 50.7; 59.9; 64.3; 65.0; 110.3; 174.5. GC/MS: 228 (M ). Anal. calc. for
C12H20O4 (228.29): C 63.14, H 8.83; found: C 63.11, H 8.85.
Ethyl (6-Methyl-1,4-dioxaspiro[4.5]dec-6-yl)acetate (12b). According to the procedure described above for
1
12a, with 2.00 g (10.0 mmol) of 1b to give 2.40 g (9.90 mmol, 99%) of liquid 12b. IR: 1721. H-NMR: 1.11 (s,
3 H); 1.25 (t, J 7.0, 3 H); 1.40 ± 1.80 (m, 8 H); 2.37 (d, J 14.0, 1 H); 2.39 (d, J 14.0, 1 H); 3.90 ± 4.00 (m,
2 H); 4.10 (q, J 7.0, 3 H). 13C-NMR: 14.0; 19.6; 20.6; 23.2; 30.0; 34.6; 40.0; 41.5; 59.5; 64.6; 111.6; 172.4. GC/
.
MS: 242 (M ). Anal. calc. for C13H22O4 (242.32): C 64.44, H 9.15; found: C 64.42, H 9.16.