I. Okamoto et al. / Tetrahedron Letters 42 (2001) 2987–2989
2989
H
OMe O
H
OMe O
OMe O
H
H
H
SC
5
5
SC
+
SC
R2
R2
R2
EDA complex A
OMe
OMe
B
OMe
contact ion radical pairs (CIP)
C
Me
Me
O
O
O
OH
radical-radical
coupling
H
2
x C
2
2
R4
R1
R4
R1
R3 R2
R3 R2
6
Scheme 2. Proposed mechanism for the formations of 2,2%-binaphthols 6.
OMe O
2. (a) Sankaram, A. V. B.; Srinivasarao, A.; Sidhu, G. S.
Phytochemistry 1976, 15, 237–238; (b) Gunaherath, G. M.
K. B.; Gunatilaka, A. A. L.; Sultanbawa, M. U. S.;
Balasubramaniam, S. Phytochemistry 1983, 22, 1245–1247;
a
b
c
5b
6b
2
2
9
7%
95%
98%
Me
(
c) Gunaherath, G. M. K. B.; Gunatilaka, A. A. L.;
O
Thomson, R. H. J. Chem. Soc., Perkin Trans. 1 1988,
407–410.
3. BuLock, J. D.; Allport, D. C. J. Chem. Soc. 1960, 654–
Scheme 3. Reagents: (a) SnCl at 100°C in dichloromethane;
4
(
b) 65% HNO ; (c) MgBr ·6H O.
3
2
2
662.
or nitromethane can work as an electron acceptor or a
dehydrogenation reagent in the aryl–aryl coupling reac-
tion, and in non-oxidizing solvents such as
dichloromethane or benzene, SC can work as both
Lewis acid and oxidant.
4. (a) Bringmann, G.; Walter, R.; Weirich, R. Angew. Chem.,
Int. Ed. Engl. 1990, 29, 977–991; (b) Pu, L. Chem. Rev.
1998, 98, 2405–2494; (c) Doussot, J.; Guy, A.; Ferroud, C.
Tetrahedron Lett. 2000, 41, 2545–2547; (d) Matumoto, T.;
Imai, S.; Yamamoto, N. Bull. Chem. Soc. Jpn. 1988, 61,
9
11–919; (e) Kashiwagi, Y.; Ono, H.; Osa, T. Chem. Lett.
A possible mechanism for the formation of 6 in the
reaction of 5 with SC is as follows. It is unclear whether
1993, 81–84; (f) Poutsma, M. L.; Dyer, C. W. J. Org.
Chem. 1982, 47, 3367–3377; (g) Bao, J.; Wulff, W. D.;
Dominy, J. B.; Fumo, M.; Grant, E. B.; Rob, A. C.;
Whicomb, M. C.; Yeung, S.-M.; Ostrander, R. L.; Rhein-
gold, A. L. J. Am. Chem. Soc. 1996, 118, 3392–3405.
. (a) Nakamura, S.; Ishihara, K.; Yamamoto, H. J. Am.
Chem. Soc. 2000, 122, 8131–8140; (b) Baul, T. B. Bull. Soc.
Chim. Fr. 1991, 128, 454–456.
5
6
s-type or p-type complexes were formed, but 1-naph-
thols 5 can form EDA complexes A with a 1:1 donor–
acceptor ratio by the addition of SC, as shown in
Scheme 2. Thermal dissociation of complex A into
contact ion radical pairs of aryl radical cation B and
5
6
7
7
stannic species is expected, but the resulting radical
cation itself does not seem to react because of the
results listed in entries 10–13. Therefore, we suggest
that deprotonation from B and the formation of the
neutral radical C cause the coupling reaction to proceed
in our system.
. (a) Bruggermann, K.; Kochi, J. K. J. Org. Chem. 1992, 57,
2956–2960; (b) Bruggermann, K.; Czernuszewicz, R. S.;
Kochi, J. K. J. Phys. Chem. 1992, 96, 4405–4414.
. (a) Kochi, J. K. In Comprehensive Organic Synthesis;
Trost, B. M., Fleming, I., Eds.; Pergamon: Oxford, 1991;
Vol. 7, Chapter 7.4, pp. 849–889; (b) Rathore, R.; Kochi,
J. K. J. Org. Chem. 1996, 61, 627–639; (c) Zhu, D.; Kochi,
J. K. Organometallics 1999, 18, 161–172; (d) Sankarara-
man, S.; Haney, W. A.; Kochi, J. K. J. Am. Chem. Soc.
Finally, we have established a biomimetic synthesis of
3
,3%-biplumbagin (2; mp 212–214°C) from the corre-
sponding binaphthol 6b through the reaction sequences
mentioned (Scheme 3). Physical data for the synthetic
compound 2 were identical with those of the natural
1987, 109, 5235–5249; (e) Miyashi, T.; Kamata, M.;
2
Mukai, T. J. Am. Chem. Soc. 1986, 108, 2755–2757.
. (a) Hannan, R. L.; Barber, R. B.; Rapoport, H. J. Org.
Chem. 1979, 44, 2153–2158; (b) Wurm, G.; Goebler, B.
Arch. Pharm. 1989, 322, 569–572.
. (a) Clowes, G. A. J. Chem. Soc. (C) 1968, 1, 2519–2526;
(b) Scholl, R.; Seer, C.; Weitzenb o¨ ck, R. Ber. Dtsch.
Chem. Ges. 1910, 43, 2202–2209.
product.
8
9
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