6,6-Dimethyl-2-(2-iodoethoxymethyl)bicyclo[3.1.1]hept-2-ene 15
The tosylate of 14 (24.5 g, 70 mmol) was dissolved in AnalaR
acetone (250 cm3) and to the mixture NaI (64.5 g, 0.43 mol) was
added. The mixture was stirred at room temperature for 5 h
and refluxed overnight. The precipitate was filtered off and the
acetone was removed under reduced pressure. Dichloro-
methane (200 cm3) and H2O (200 cm3) were added to the resi-
due, the layers were separated and the aqueous layer was
extracted with dichloromethane (2 × 100 cm3). The organic
fractions were combined, washed with saturated aqueous
sodium thiosulfate (2 × 150 cm3), dried (MgSO4) and the
solvent was evaporated to give 15 (21.8 g, 100%) as a dark red
liquid which was distilled using the Kugelrohr to yield a clear
colourless liquid, bp 80–100 ЊC at 0.1 mmHg; δH 0.83 (3 H, s,
methyl-H), 1.14–1.19 (1 H, d, J 8.9, methylene-H), 1.28 (3 H,
s, methyl-H), 2.03–2.49 (5 H, m), 3.22–3.29 (2 H, t, J 6.8,
methylene-H), 3.62–3.69 (2 H, t, J 6.8, methylene-H), 3.89 (2 H,
s, allylic-H), 5.46–5.52 (1 H, m, olefinic-H); δC 3.1, 20.9, 26.1,
31.2, 31.4, 37.9 (quaternary-C), 40.7, 43.1, 70.1, 73.5, 120.3,
150.0; m/z 306 (Mϩ, 12%), 191 (14), 185 (13), 155 (14), 151 (15),
136 (37), 135 (100), 121 (10), 107 (22), 93 (55), 91 (27), 79 (61),
57 (10) (Found: Mϩ, 306.0467. C12H19OI requires M, 306.0481).
m/z (relative intensity), 150 (1), 135 (6), 117 (4), 107 (43), 91
(37), 79 (100), 77 (46), 65 (18), 53 (18), 51 (70), 45 (22), 39 (55),
29 (35), 27 (44); peak no. 338, benzoic acid; peak no. 375, 6,6-
dimethylbicyclo[3.1.1]heptane-2-spiro-3Ј-oxacyclopentane 17,
180 (Mϩ) (1), 165 (3), 154 (5), 137 (9), 107 (21), 95 (25), 91 (28),
82 (28), 79 (37), 77 (29), 67 (43), 55 (39), 41 (100), 39 (53), 29
(28), 27 (44); peak no. 540, 6,6-dimethyl-2-(2-phenylethoxy-
methyl)bicyclo[3.1.1]hept-2-ene 19, 195 (3), 136 (11), 119 (16),
105 (79), 91 (100), 79 (35), 77 (36), 65 (17), 55 (12), 41 (46), 27
(23). The benzene was evaporated and the resulting solid was
dissolved in ether (50 cm3) and extracted with NaOH (2 ,
2 × 20 cm3). The ether was evaporated to yield a liquid (1.03 g)
from which the cyclised and aromatic products were isolated by
column chromatography eluting with 5% ethyl acetate in light
petroleum, to yield two main fractions (0.19 g; 10% 17, 5%
18 and 0.14 g, 7.4% 19). 6,6-Dimethylbicyclo[3.1.1]heptane-2-
spiro-3Ј-oxacyclopentane 17; δH 0.88 (3 H, s, methyl-H), 1.14–
1.25 (4 H; methyl-H and 1 H, methylene-H), 1.65–1.93 (8 H, m),
2.15–2.25 (1 H, m), 3.45–3.80 (4 H, m); m/z 181 (MHϩ, 100%),
167 (45), 103 (18), 151 (13), 139 (11), 123 (16), 105 (6), 95 (5), 57
(45) (Found: MHϩ, 181.1586. C12H21O requires M, 181.1592).
Tricyclic ether 18; the 1H NMR of 18 was badly overlapped by
that of 17 and, except for the two methyl singlets at 0.79 and
1.33 ppm, could not be distinguished with any confidence; δC
20.9, 25.8 (2 × CH3), 31.3, 32.3 (2 × CH2), 37.7 (C), 40.2, 40.7,
40.9, 51.3 (4 × CH), 53.4, 66.7, 80.4 (3 × CH2). 6,6-Dimethyl-
2-(2-phenylethoxymethyl)bicyclo[3.1.1]hept-2-ene 19; δH 0.85
(3 H, s, methyl-H), 1.15–1.20 (1 H, d, J 8.6, methylene-H), 1.30
(3 H, s, methyl-H), 2.10–2.48 (5 H, m), 2.86–2.98 (2 H, t, J 7.2),
3.57–3.67 (2 H, t, J 7.3), 3.89 (2 H, s, allylic-H), 5.45–5.52 (1 H,
s, olefinic-H), 7.20–7.40 (5 H, m, arom-H); δC 21.0, 26.2
(2 × CH3), 31.5, 31.2, 36.4 (3 × CH2), 38.0 (quaternary-C),
40.9, 43.3 (2 × CH), 70.8, 73.7 (2 × CH2), 119.6 (olefinic-C),
126.1, 127.2, 128.3, 128.7, 128.9 (6 × arom-C), 145.5 (olefinic-
C); m/z 257 (MHϩ, 10%), 239 (12), 213 (5), 195 (14), 181 (27),
167 (24), 155 (9), 135 (100), 123 (10), 105 (23), 93 (40), 79 (10),
58 (54), 56 (38) (Found: MHϩ, 257.1913. C18H25O requires M,
257.1905). The alkaline fractions were neutralised with excess
acid and the mixture was extracted with ether to give benzoic
acid (1.21 g).
1-[2-(6,6-Dimethylbicyclo[3.1.1]hept-2-en-2-ylmethoxy)ethyl]-
cyclohexa-2,5-diene-1-carboxylic acid 16
Ammonia (500 cm3) was added to benzoic acid (2.5 g, 20.4
mmol) to which Li (0.45 g, 65.2 mmol) was added portionwise
causing the solution to turn blue. This mixture was left stirring
for 30 min followed by the addition of 6,6-dimethyl-2-(2-iodo-
ethoxymethyl)bicyclo[3.1.1]hept-2-ene 15 (7.5 g, 24.5 mmol)
dissolved in dry THF (5 cm3), causing the solution to turn
brown. The NH3 was allowed to evaporate, ice was added to
the residue followed by aqueous NaOH (2 , 100 cm3) and di-
chloromethane (100 cm3). The layers were separated and the
dichloromethane fraction was extracted with NaOH (100 cm3),
the alkaline fractions were combined and neutralised with
excess HCl. The product was extracted with ether (3 × 100
cm3), the ethereal extracts were combined, dried (MgSO4) and
the solvent was evaporated yielding a dark oil (5.18 g; 4.56 g,
74%, 16 and 0.28 g, 11% dihydrobenzoic acid and 0.34 g, 14%
unreacted benzoic acid); δH (signals for 16 only) 0.81 (3 H, s,
Tin hydride mediated cyclisation of iodide 15
6,6-Dimethyl-2-(2-iodoethoxymethyl)bicyclo[3.1.1]heptane 15
(0.5 g, 1.63 mmol) and tributyltin hydride (0.52 g, 1.8 mmol)
were dissolved in benzene (5 cm3) and added to a 1 cm diameter
13C NMR tube. The tube was capped and irradiated with light
from a 125 W medium pressure Hg lamp for 2.5 h at room
temperature and 3.5 h at 70–90 ЊC. Analysis of the reaction
mixture by GC–MS indicated that all the iodide had been
consumed; peak no. 306, 2-(ethoxymethyl)-6,6-dimethylbicyclo-
[3.1.1]hept-2-ene 20, m/z (relative intensity), 136 (12), 119 (29),
105 (16), 93 (33), 92 (46), 91 (100), 79 (31), 77 (52), 59 (82), 41
(69), 31 (49), 29 (46), 27 (43), 18 (19); peak no. 373, 6,6-
dimethylbicyclo[3.1.1]heptane-2-spiro-3Ј-oxacyclopentane 17
(MS as above). The reaction contents were transferred to a
round-bottomed flask and saturated aqueous KF (10 cm3) was
added and the mixture was stirred for 3 days. The polymeric tin
fluoride was filtered off and the layers were separated. The
aqueous layer was extracted with ether and the ethereal extracts
were combined, dried (MgSO4) and the solvent was evaporated
2
3
19
HO2C
17
16
18
1
4
11
12
7
13
6
5
8
15 10
14
O
9
16
methyl-H), 1.10–1.16 (1 H, d, J 8.4, 14-H), 1.24 (3 H, s,
methyl-H), 1.90–2.05 (2 H, t, J 7.2, 7-H), 1.95–2.43 (5 H, m),
2.59–2.75 (2 H, m, 4-H), 3.34–3.44 (2 H, t, J 7.3, 8-H), 3.75–
3.83 (2 H, m, 9-H), 5.40–5.50 (1 H, m, 11-H), 5.80–5.98 (4 H, m,
2,3,5,6-H). A small amount of the title compound was isol-
ated after two successive purification steps by column chroma-
tography, to give essentially pure material as a viscous oil;
δC 21.0, 26.0, 26.2 (3 × 4,17,18-C), 31.3, 31.5 (2 × 12,14-C),
38.0 (16-C), 38.7 (7-C), 41.0, 41.3 (2 × 13,15-C), 46.1 (1-C),
66.0 (8-C), 73.8 (9-C), 119.7 (11-C), 126.0, 126.6 (4 × 2,3,5,6-
C), 145.4 (10-C), 180.2 (19-C); m/z 302 (Mϩ, 2%), 195 (4), 151
(28), 134 (58), 119 (36), 107 (39), 105 (68), 93 (51), 92 (52), 91
(100), 79 (64), 77 (46) (Found: Mϩ, 302.1884. C19H26O3 requires
M, 302.1882).
1
yielding an orange liquid which, when analysed by H NMR,
still contained some tin residues. The liquid was distilled using a
Kugelrohr (80–100 ЊC, 1 mmHg) giving a clear colourless liquid
(0.114 g, 8% 20, 31% 17); δH 0.83 (3 H, s, methyl-H, 20), 0.86
(3 H, s, methyl-H, 17), 1.12–1.30 (11 H, m; 4 H, 17 and 7 H, 20),
1.70–1.94 (8 H, m, 17), 2.02–2.45 (6 H, m; 1 H, 17 and 5 H, 20),
3.38–3.75 (6 H, m; 4 H, 17 and 2 H, 20), 3.78–3.82 (2 H,
m, allylic-H, 20), 5.40–5.50 (m, 1 H, olefinic-H, 20); δC 23.5,
25.1, 27.2, 28.7, 28.9, 38.8 (quaternary-C), 40.4, 43.4, 47.9
(quaternary-C), 51.2, 66.2, 80.4 (minor signals due to 20 were
Radical fragmentation of carboxylic acid 16
Carboxylic acid 16 (2.12 g, 7.0 mmol) was refluxed in benzene
for 5 days with portionwise addition of dibenzoyl peroxide
(3 × 0.2 g, 30% wt overall). GC–MS; peak no. 297, (tentatively
identified as the 6-endo product 18; see Results and discussion),
2080
J. Chem. Soc., Perkin Trans. 1, 1998