Notes
J . Org. Chem., Vol. 64, No. 4, 1999 1389
1
1
85.36, 140.40, 135.79, 134.91, 134.72, 132.54, 132.10, 130.53,
30.01, 129.90, 125.82, 125.27, 122.26.
6
-Vin yl-1,4-p h en a n th r en equ in on e (5). Compound 5 was
obtained from 4 following method B for 5 h, after flash chroma-
1
tography (eluent, CH
δ 9.48 (broad s, 1H, H
and H ), 6.97 (dd, 1H, J ) 11.0 and 18.0 Hz), 6.95 (m, 2H),
2
Cl
2
/hexane 50:50), in 40% yield: H NMR
5
), 8.18 (s, 2H, H
9
and H10), 7.81 (m, 2H,
H
7
8
5
.98 (d, 1H, J ) 18.0 Hz), 5.46 (d, 1H, J ) 11.0 Hz).
Helicen ebisqu in on e (M)-1. Compound (M)-1 was obtained
from 5 and 3 equiv of (+)-2 following method A at 4 Kbar for 7
d, after flash chromatography (eluent, CH Cl ), in 22% yield:
2
2
1
mp >300 °C; H NMR δ 8.27 (d, 2H, J ) 8.3 Hz), 8.09 (d, 2H, J
F igu r e 1. Endo approaches of vinylarenes on the s-cis
conformation of sulfinylquinone (+)-2.
)
)
2
8.3 Hz), 7.84 (s, 2H), 6.98 (d, 2H, J ) 10.1 Hz), 6.87 (d, 2H, J
+
10.1 Hz); EI-MS m/z (%) 338 (M , 100), 282 (48), 256 (75),
10 4
00 (38), 100 (26); HRMS (EI) calcd for C22H O 338.05791,
According to the model proposed for (SS)-p-tolylsulfi-
found 338.05859.
1-Br om o-4-br om om eth yln a p h th a len e (7). A mixture of
commercially available 1-bromo-4-methylnaphthalene (6) (1 g,
nylquinone cycloadditions,9
b-d,g
the (M) absolute config-
uration of helicenes (-)-1 and (-)-10 must result from
the endo approach of the vinylarene toward the less
encumbered face of the quinone, which bears the lone
electron pair at sulfur in the s-cis conformation of (+)-2
A in Figure 1). Although the formation of helicene (+)-
4 with (P) configuration is not easy to rationalize, an
inspection of molecular models revealed an unfavorable
interaction between the OMe group at C-4 of approaching
3 and the sulfinylic oxygen of (+)-2 (B in Figure 1),
which could be responsible for the inversion of the π-facial
diastereoselectivity observed. A likely evolution of an
s-trans conformation of (+)-2 from the less sterically
demanding face could be the origin of this result.
In summary, a direct and easy access to enantioen-
riched helicenebisquinones (M)-1 and antipodal (M)- and
4
.5 mmol), N-bromosuccinimide (966 mg, 5.4 mmol), and benzoyl
peroxide (73 mg, 0.3 mmol) in CCl (15 mL) was refluxed for 3
h. After workup and crystallization (hexane), compound 7 was
obtained in 85% yield: mp 102-104 °C; H NMR δ 8.32 and
4
1
(
1
8
.15 (2m, 2H), 7.70 (m, 2H), 7.66 and 7.39 (AB system, 2H, J )
13
7.5 Hz), 4.92 (s, 2H); C NMR δ 133.24, 132.31, 132.05, 129.47,
127.95, 127.79, 127.50, 127.36, 124.41, 124.12, 30.93. Anal. Calcd
for C11
2
1
H
8
Br
.56; Br, 46.98.
-Br om o-4-vin yln a p h th a len e (8). A solution of 7 (1.14 g,
.8 mmol) and PPh (1 g, 3.8 mmol) in 50 mL of acetone was
2
: C, 44.31; H, 2.71; Br, 47.02. Found: C, 44.58; H,
1
3
3
refluxed for 4 h. After evaporation of the solvent, the crude
phosphonium bromide was obtained. To a mixture of 17.9 mL
of formaldehyde (37% aqueous solution) and 3.8 mmol of the
above obtained phosphonium bromide in H
added a solution of 1.43 g of NaOH in H
the mixture was extracted with CH Cl . After workup and flash
2 2
chromatography (eluent, hexane), compound 8 was obtained as
a colorless liquid in 89% yield: H NMR δ 8.29 and 8.12 (2m,
2
O (10 mL) was slowly
O (7 mL). After 3 h,
2
(
P)-10 is reported. Our synthesis features their prepara-
tion using sulfinylquinone (+)-2 to effect the asymmetric
Diels-Alder reactions with vinylarenes in a highly
stereoselective manner.
1
2H), 7.58 (m, 2H), 7.78 and 7.45 (AB system, 2H, J ) 8.0 Hz),
7.58 (dd, 1H, J ) 11.3 and 17.2 Hz), 5.80 (dd, 1H, J ) 1.6 and
1
1
1
7.2 Hz), 5.54 (dd, 1H, J ) 1.6 and 11.3 Hz); 13C NMR δ 135.14,
33.24, 131.75, 131.47, 129.45, 127.29, 126.70, 126.36, 123.71,
23.52, 122.43, 117.36.
Exp er im en ta l Section
1
,4-Divin yln a p h th a len e (9). Compound 9 was obtained
Melting points were obtained in open capillary tubes and are
1
13
from 8 following method B for 2 h, after flash chromatography
uncorrected. H and C NMR spectra were recorded in CDCl
3
1
(
eluent, hexane), in 65% yield: H NMR δ 8.19 (dd, 2H, J ) 3.2
and 6.4 Hz), 7.66 (s, 2H), 7.57 (dd, 2H, J ) 3.2 and 6.4 Hz), 7.53
dd, 2H, J ) 11.0 and 17.2 Hz), 5.84 (dd, 2H, J ) 1.6 and 17.2
Hz), 5.52 (dd, 2H, J ) 1.6 and 11.0 Hz); C NMR δ 135.51,
34.34, 131.10, 125.86, 124.21, 123.48, 116.99.
Helicen ebisqu in on e (M)-10. Compound (M)-10 was ob-
tained from 9 and 6 equiv of (+)-2 following method A at 4 Kbar
for 4 d, after flash chromatography (eluent, CH Cl ), in 12%
at 300 and 75 MHz, respectively. All reactions were monitored
by thin-layer chromatography that was performed on precoated
sheets of silica gel 60, and flash column chromatography was
done with silica gel 60 (230-400 mesh) from Macherey-Nagel.
Eluting solvents are indicated in the text. The apparatus for
inert atmosphere experiments was dried by flaming in a stream
(
1
3
1
of dry argon. CH
hydrolysis was carried out with water, extractions with CH
Cl , and solvent drying with Na SO . High-pressure reactions
2
Cl
2
was dried over P
2
O
5
. For routine workup,
2
-
2
2
1
yield: mp >300 °C; H NMR δ 8.84 (d, 2H, J ) 8.6 Hz), 8.60 (m,
2H), 8.34 (d, 2H, J ) 8.6 Hz), 7.80 (m, 2H), 6.98 (d, 2H, J ) 10.1
2
2
4
were performed in a Unipress Equipment 101LV 30/16 in
polyethylene vials.
Gen er a l P r oced u r e for High -P r essu r e Diels-Ald er Re-
a ction s, Meth od A. A mixture of excess of (SS)-(2-p-tolylsulfi-
nyl)-1,4-benzoquinone (2) and the corresponding vinylarene (0.1
+
Hz), 6.84 (d, 2H, J ) 10.1 Hz); EI-MS m/z (%) 388 (M , 19), 306
(12), 254 (43), 248 (49), 149 (100), 77 (61). Anal. Calcd for
C
26
H
12
O
4
: C, 80.40; H, 3.11. Found: C, 80.17; H, 3.30.
6-Br om o-1,4-ch r ysen equ in on e (11). A solution of 8 (783
mmol) in dry CH
conditions. After the time required in each case and evaporation
of the solvent, the crude product was obtained.
Gen er a l P r oced u r e for Stille Cr oss-Cou p lin g Rea ction s,
Meth od B. A mixture of the corresponding bromoarene (0.5
3 4
mmol), tributylvinylstannane (1 mmol), Pd(PPh ) (0.02 mmol),
and one crystal of 4-tert-butylcatechol in 10 mL of toluene was
refluxed for 2-5 h under argon in the dark. The mixture was
treated with saturated aqueous KF solution and extracted with
EtOAc. After workup, the crude product was obtained.
2
Cl
2
(1 mL) was submitted to high-pressure
mg, 3.4 mmol) and (()-2 (2.46 g, 10 mmol) in toluene (20 mL)
was refluxed for 2 h. After evaporation of the solvent and
precipitation in MeOH, pure 11 was obtained in 84% yield: mp
1
240-245 °C (MeOH); H NMR δ 9.93 (d, 1H, J ) 0.8 Hz), 9.05
(d, 1H, J ) 8.8 Hz), 8.72 (m, 1H), 8.42 (m, 1H), 8.37 (d, 1H, J )
8.8 Hz), 7.80 (m, 2H), 7.04 and 6.99 (AB system, 2H, J ) 10.1
Hz); 13C NMR δ 187.73, 185.26, 140.99, 136.14, 134.16, 132.26,
131.00, 130.05, 129.74, 129.39, 128.84, 128.35, 128.32, 128.08,
+
127.75, 126.06, 123.71, 123.47; EI-MS m/z (%) 338 (M + 2, 96),
+
336 (M , 95), 257 (100), 254 (22), 200 (35), 175 (24), 149 (19),
6
-Br om o-1,4-p h en a n th r en equ in on e (4). Compound 4 was
obtained from commercially available 1-bromo-4-vinylbenzene
3) and 6 equiv of (()-2 following method A at 4 Kbar for 2 d,
after flash chromatography (eluent, CH Cl /hexane 50:50), in
3% yield: mp 179-180 °C (MeOH); H NMR δ 9.79 (m, 1H),
.18 (d, 1H, J ) 8.6 Hz), 8.13 (dd, 1H, J ) 0.6 and 8.6 Hz), 7.78
9 2
128 (21). Anal. Calcd for C18H BrO : C, 64.29; H, 2.70; Br, 23.49.
Found: C, 64.05; H, 2.91; Br, 23.60.
6-Br om o-1,4-d im etoxych r ysen e (12). A mixture of com-
pound 11 (760 mg, 2.25 mmol) in 150 mL of ethyl ether and
2
sodium dithionite (3.82 g, 22.5 mmol) in 150 mL of H O was
vigorously shaken in a separatory funnel for 10 min. After
separation of the organic layer and workup, the corresponding
crude hydroquinone was obtained and used without further
(
2
2
1
5
8
(
7
dd, 1H, J ) 1.1 and 8.8 Hz), 7.73 (dd, 1H, J ) 1.7 and 8.8 Hz),
.01 and 6.96 (AB system, 2H, J ) 10.2 Hz); 13C NMR δ 187.45,