A Novel Bornane Synthesis by an Old Idea
J . Org. Chem., Vol. 67, No. 11, 2002 3685
tions in synthesis, e.g., both inter- and intramolecular
C-C connections, especially cycloaddition reactions. Chiral
spirodiene building blocks should be accessible. Reactions
with transition-metal complexes, e.g., carbonyls, can
easily be imagined. Emphasis should be laid on the
utilization of the thionoester function in 8, which, to the
best of our knowledge, seems not have been investigated
in the past. The first objective for further research,
however, should be the elaboration of reaction conditions
for a controlled, more selective solvolysis of Raasch’s
cycloadduct 2, to form either 7 or 8 (Scheme 2). As yet,
this is the weak point of our approach. Perhaps, cyclo-
adducts of 1 with other thiocarbonic acid derivatives, i.e.,
thiophosgene equivalents, would be a better choice.
Cl
2
(500 mL). This solution was added dropwise to a suspen-
2 2 2
sion of Hg(OAc) (318.7 g, 1.00 mol) in CH Cl (1 L) at room
temperature and stirred overnight. The solvent was removed
in a rotary evaporator, and diethyl ether (1 L) was added to
the remaining dark mixture of organic liquid and mercury
salts. The mixture was filtrated, and the dark solid residue
washed with diethyl ether (3 × 70 mL). The combined filtrates
were concentrated in vacuo, and the remaining brown liquid
distilled in a 15 cm Vigreux column at reduced pressure (water
aspirator). After a forerun (30-35 °C (11 Torr), 25.01 g) with
6
a mixture of acetic acid and acetic acid anhydride (IR
spectrum), the main fraction (58.56 g) was distilled at 92-96
°
C/11 Torr, consisting mainly of the spirodiene 10b, contami-
nated by minor amounts of acetic acid (anhydride). To remove
these impurities, the distillate was diluted with diethyl ether
(500 mL) and washed with saturated NaHCO
3
solution (2 ×
1
00 mL) and then with water (2 × 100 mL). After being dried
with MgSO , the ether solution was concentrated in a rotary
4
Exp er im en ta l Section
evaporator, and the remaining liquid was distilled in vacuo
water aspirator) to yield 50.66 g (49%) of 10b with bp 85-92
°C (11 Torr). Redistillation using a 20 cm Vigreux column gave
(
Gen er a l P r oced u r es. Spiro[2.4]hepta-4,6-diene (1) was
1
8
prepared according to a literature procedure. Thiophosgene
>97%) and 2-chloroacrylonitrile (99%) were commercial prod-
-1
bp 84-86 °C (11 Torr): IR (film) 1690 (CdO) cm . Anal. Calcd
for C10 (164.2): C 73.15, H 7.37. Found: C 72.92, H 7.44.
The liquid that remained after distillation of 10b was distilled
further, using an oil pump. The slightly yellow distillate (26.11
g) with bp 82-85 °C (0.01 Torr) proved to be a mixture of the
cis and trans diastereoisomers of 9b with a minor amount of
(
12 2
H O
ucts and used without further purification. Diethyl ether,
benzene, and n-pentane were dried by refluxing over sodium
and subsequent distillation. Ethanol was dried with sodium.
For chromatographic separations, silica 60, 40-63 µm, was
used. For elution, predried petroleum ether (PE) was distilled
1
(
bp 40-65 °C); ethyl acetate (EA) was dried over CaCl
2
,
10b ( H NMR spectrum). A part of the mixture (2.7 g) was
distilled, and kept dry over 4 Å molecular sieves. Melting
points were not corrected.
subjected to chromatography on silica (250 g, gravity column).
Elution with PE/EA (15:1) gave 0.34 g of spirodiene 10b. On
further elution with PE/EA (4:1) the two diastereoisomers of
3
′,3′-Dich lor osp ir o(cyclop r op a n e-1,7′-[2]t h ia b icyclo-
2.2.1]h ep t[5]en e) (2). To a solution of thiophosgene (11.5 g,
.10 mol) in dry n-pentane (40 mL), protected from atmo-
9
b were separated (0.86 and 0.74 g), in addition to a middle
[
0
fraction consisting of a mixture of the two compounds (0.64
g). Data for the first eluted diastereomer trans-9b: IR (film)
spheric moisture and cooled in an ice bath was added dropwise
with magnetic stirring 1 (13.0 g, 0.14 mol) in dry diethyl ether
-
1
1
730 (CdO) cm . Anal. Calcd for C12
16 4
H O (224.3): C 64.27,
H 7.19. Found: C 64.27, H 7.25. Data for the second eluted
(20 mL). After 2 h the ice bath was removed, and the light red
-
1
diastereomer cis-9b: IR (film) 1725 (CdO) cm . Anal. Calcd
for C12 (224.3): C 64.27, H 7.19. Found C 63.93, H 7.21.
Sp ir o[2.4]h ep ta -4,6-d ien e-4-m eth a n ol (11). To a stirred
slurry of LiAlH (2.95 g, 77.7 mmol) in dry diethyl ether (50
mL), cooled in an ice bath, was added dropwise a solution of
10b (8.21 g, 50.0 mmol) in dry diethyl ether (50 mL). The ice
bath was removed, and stirring was continued at room
temperature for 24 h. Then, water (5 mL) was added cautiously
with cooling with an ice bath, followed by 15% aqueous sodium
hydroxide solution (5 mL) and finally water (15 mL). The
coarse solid formed was filtered off, washed with tert-butyl
methyl ether (30 mL) and boiled with tert-butyl methyl ether
solution was cooled by means of a dry ice/acetone bath. A white
solid precipitated which was filtered and washed with ice-cold
n-pentane (20 mL), excluding moisture. The white solid was
dried in vacuo with cooling in an ice bath [yield 18.87 g (91%),
16 4
H O
4
3
mp 64-65 °C (lit. mp 61 °C, yield 74%)]. The substance
decomposes on storing and should be used immediately. The
1
H NMR was in agreement with the data given in ref 3.
Eth a n olysis of 2: Eth yl cis-7-Mer ca p tosp ir o[2.4]h ep t-
5
4
-en e-4-ca r boxyla te (7b) a n d O-Eth yl Sp ir o[2.4]h ep ta -
,6-d ien e-4-th ioca r boxyla te (8b): Cycloadduct 2 (3.10 g, 15
mmol) was added portionwise and with magnetic stirring to
dry ethanol (60 mL), chilled in an ice bath. The ice bath was
removed, and stirring was continued for 1 h, whereupon the
yellow solution became dark brown. The solvent was evapo-
rated at reduced pressure at room temperature, finally using
the vacuum of an oil pump. The remaining dark brown oil (2.74
g) was purified by chromatography. Separation of 2.60 g at
silica (250 g) with PE/EA (30:1) gave a brown liquid (8b; 1.78
g, 69%); a second fraction was eluted with PE/EA (20:1),
affording 7b (465 mg, 17%) as a brown oil: IR (film) 3070,
4
(50 mL). The combined ether extracts were dried with MgSO ,
concentrated in vacuo, and distilled in a Kugelrohr apparatus
at 70-75 °C (0.01 Torr), giving a colorless liquid (11; 4.40 g,
72% yield): IR (film) 3330 (br, OH) cm . Anal. Calcd for
-
1
C
8
H
10O (122.2): C 78.65, H 8.25. Found C 78.41, H 8.41.
-Ch lor o-1-h yd r oxym et h ylsp ir o(b icyclo[2.2.1]h ep t -5-
en e-7,1′-cyclop r op a n e)-2-ca r bon itr ile (14a ). 11 (1.83 g,
5.0 mmol) and 2-chloroacrylonitrile (1.75 g, 20.0 mmol) were
2
1
-
1
2
7
1
980, 2935, 2875 (CH), 2560 (SH), 1735 (CdO) cm ; MS (EI,
dissolved in dry benzene (10 mL) and heated to 80 °C with
magnetic stirring for 22 h. The brown reaction mixture was
filtrated over a short silica column and further eluted with
PE/EA (3:2). After evaporation of the solvent under reduced
pressure the residue was recrystallized from diethyl ether/
+
0 eV) m/z (rel intens) 198 (3) [M ], 165 (44), 137 (4), 125 (23),
05 (4), 97.0 (10), 91 (100), 79 (24), 65 (18), 53 (4), 45 (7), 43
(10), 39 (14), 29 (79). Data for 8b: IR (film) 3090, 2985, 2940,
2
1
895, 2870 (CH), 1550 (CdC), 1460, 1440, 1395, 1370, 1285,
-
1
260, 1215 cm ; UV/vis (ethanol) λmax (log ꢀ) 241 (3.86), 257
pentane, giving 2.52 g (80%) of 14a with mp 177-178 °C: IR
(
shoulder, 3.72), 342 (4.10) nm. Anal. Calcd for C10
180.3): C 66.63, H 6.71, S 17.78. Found: C 66.41, H 6.70, S
7.58.
Desu lfu r iza tion of 7b a n d 8b: Eth yl cis+tr a n s-7-
H
12OS
-1
12
(KBr) 3470 (br, OH), 2215 (CN) cm . Anal. Calcd for C11H -
(
1
ClNO (209.7): C 63.01, H 5.77, N 6.68, Cl 16.91. Found C
6
3.16, H 5.84, Cl 16.98, N 6.66.
-Ch lor o-1-h ydr oxym eth ylspir o(bicyclo[2.2.1]h epta n e-
,1′-cyclop r op a n e)-2 -ca r bon itr ile (15). A solution of cy-
2
Acetoxysp ir o[2.4]h ep t-5-en e-4-ca r boxyla te (9b) a n d Eth -
yl Sp ir o[2.4]h ep ta -4,6-d ien e-4-ca r boxyla te (10b). Dry eth-
anol (1 L) was chilled in an ice bath. With magnetic stirring,
cycloadduct 2 (130.0 g, 0.628 mol) was added in portions, and
the solution stirred for 15 h at 0 °C. The solvent was removed
7
cloadduct 14a (6.27 g, 29.9 mmol) in dry ethyl acetate (80 mL)
was charged with palladium/carbon catalyst (300 mg) and
shaken under hydrogen gas at atmospheric pressure. The
catalyst was removed by filtration and the solvent evaporated
under reduced pressure. The remaining white solid (6.05 g,
in a rotary evaporator, and the oily residue diluted with CH
2
-
9
5%) with mp 180-182 °C dec was analytically pure: IR (KBr)
-
1
(18) Kunitake, T.; Ochiai, T. Macromol. Synth. 1985, 9, 61-63.
3490 (br, OH), 2215 (CN) cm . Anal. Calcd for C11H14ClNO