H. R. El-Seedi et al. / Tetrahedron Letters 43 (2002) 3301–3304
3303
struct synthetic intermediates of naturally occurring
complicated molecules, is under way.
Acknowledgements
The authors are very grateful to the Japan Society for
the Promotion of Science for a fellowship to H.R.E.
and generous financial support from Tokubetsu
Kenkyuin Shorei-hi (Grant in Aid for Scientific
Research P 00168).
References
1
. (a) Shizuri, Y; Shigemori, H.; Suyama, K.; Nakamura,
K.; Okuno, Y.; Ohkubo, M.; Yamamura, S. In Studies
in Natural Products Chemistry; Att-ur-Rahman, Ed.;
Elsevier Science, 1991; pp. 159–173; (b) Yamamura, S;
Nishiyama, S. Synlett 2002, 533–543.
Scheme 1.
OH
O
4
14
1
2
. Related investigations employing phenol derivatives: (a)
Gates, B. D.; Dalidowicz, P.; Tebben, A.; Wang, S.;
Swenton, J. S. J. Org. Chem. 1992, 57, 2135–2143; (b)
Shizuri, Y.; Nakamura, K.; Yamamura, S. J. Chem.
Soc., Chem. Commun. 1985, 530–531; (c) Chiba, K.;
Fukuda, M.; Kim, S.; Kitano, Y.; Tada, M. J. Org.
Chem. 1999, 64, 7654–7656.
cat. TsOH
OMe
15
[O]
12
3. Anodic oxidation of other naphthols, has been unsuc-
cessful until now, owing to high oxidation potentials
Scheme 2.
and/or production of complicated mixtures.
. Compound 8: IR (film) 3068, 1596 cm ; l (CDCl3)
tions (all of the entries in Table 1 were completed
within ca. 2 h). The acquisition of 12 in high yields
−1
4
H
1
3
.47 (3H, d, J=6.8 Hz), 3.54 (1H, dq, J=8, 6.8 Hz),
.95 (3H, s), 5.19 (1H, d, J=8 Hz), 5.94 (2H, s), 6.60
(
entries 7 and 8) indicated that the electrolytic condi5-
tions had a comparable acidity to those of Lewis acids,
(
1H, s), 6.77 (1H, d, J=8 Hz), 6.90 (1H, dd, J=2, 8
Hz), 6.94 (1H, d, J=2 Hz), 7.43 (2H, complex), 7.91
1H, dd, J=1.5, 7.2 Hz) and 8.17 (1H, dd, J=1.5, 7.2
Hz). lC (CDCl ) 18.8, 47.1, 55.6, 92.2, 99.7, 100.7, 106.3,
which effected efficient migration under mild conditions
5
b
6
(
ex. 0°C to room temp., 1–4 h). It is still unclear at
(
this stage why only 4 afforded such migration, which
was not observed in the case of 5.
3
1
1
1
07.8, 119.3, 120.7, 121.1, 122.3, 122.7, 124.7, 125.3,
25.7, 135.1, 147.2, 147.5, 147.7 and 150.1. Compound
7
In addition, the dimeric derivatives 13 and 17 were
0: lH (CDCl ) 1.56 (1H, m), 1.65 (1H, m), 1.91 (1H,
3
obtained (entries 8, 9, 11 and 12): the radical dimeriza-
tion of A produced 13, which experienced further oxi-
dation, leading to 17. The dimers were effectively
produced, when the reaction without nucleophiles was
undertaken in high concentrations (entry 12). Relatively
m), 2.12 (1H, m), 3.49 (1H, dt, J=1.5, 6.4 Hz), 3.78
2H, complex), 3.89 (3H, s), 6.11 (1H, d, J=6.8 Hz),
.68 (1H, s), 7.47 (2H, ddd, J=1.5, 4.8, 6.8 Hz), 7.96
1H, d, J=8.0 Hz) and 8.20 (1H, d, J=8.0 Hz). Com-
(
6
(
pound 11: lH (CDCl ) 1.56 (1H, m), 1.65 (1H, m), 1.91
3
mild anodic oxidation condition and the stabilizing7
(1H, m), 2.12 (1H, m), 3.49 (1H, dt, J=1.5, 6.4 Hz),
factor of the phenyl residue enabled the isolation of 13,
3
.78 (2H, complex), 3.98 (3H, s), 6.11 (1H, d, J=6.8
Hz), 6.68 (1H, s), 7.47 (2H, dq, J=1.5, 6.8 Hz), 7.96
1H, d, J=7.8 Hz) and 8.20 (1H, d, J=8.8 Hz). Com-
which was not obtained by the usual chemical
8
oxidations.
(
−
1
pound 12: IR (film) 1663 and 1593 cm ; l (CDCl3)
In conclusion, anodic oxidation of 4-methoxy-1-naph-
thol was undertaken. The cation B, electrolytically gen-
erated, reacted with nucleophiles to give the
corresponding benzofuran derivatives, 8–11. Upon
using 4, the C-glycoside 12 was characteristically
obtained. The appropriate control of the oxidation
conditions effectively produced the dimers 13 and 17
possessing different oxidation stages.
H
1
(
4
.70 (1H, m), 1.98 (2H, complex), 2.52 (1H, m), 3.92
1H, dq, J=6.8, 7.3 Hz), 4.04 (1H, dq, J=5.9, 7.3 Hz),
.98 (1H, t, J=8.3 Hz), 7.01 (1H, s), 7.72 (2H, ddd,
J=2.0, 4.9, 7.3 Hz) and 8.06 (2H, ddd, J=2.0, 2.4, 4.9
Hz). Compound 13: lH (CDCl ) 3.98 (6H, s), 6.71 (2H,
3
s), 7.57 (4H, m), 8.18 (2H, dd, J=2.4, 7.3 Hz) and 8.28
(2H, dd, J=2.4, 7.3).
. (a) Suzuki, K.; Matsumoto, T.; Hosoya, T. J. Synth.
Org. Chem. Jpn. 1995, 53, 1045–1054; (b) Kometani, T.;
Kondo, H.; Fujimori, Y. Synthesis 1988, 1005–1007.
5
Further investigation of naphthols possessing addi-
tional substituents, which open up a possibility to con-