Synthesis of naphthalene derivatives via a novel gallium trichloride catalyzed cross-coupling of epoxides with alkynes

Article abstract of DOI:10.1055/s-2002-33530

Gallium trichloride catalyzes the tandem ring opening of epoxides and cyclization with alkynes to generate naphthalene derivatives with complete regio control.

Full text of DOI:10.1055/s-2002-33530

LETTER
1553
Synthesis of Naphthalene Derivatives via a Novel Gallium Trichloride
Catalyzed Cross-Coupling of Epoxides with Alkynes
N
G
aphthalene
D
eriv
a
atives via
C
n
a
talyzed
C
ro
a
ss-Couplin
p
gof
E
poxid
a
es
w
ith
A
lk
t
ynes hy S. Viswanathan, Chao-Jun Li*
Department of Chemistry, Tulane University, New Orleans, LA 70118, USA
Fax +1(504)8655596; E-mail: CJLi@Tulane.Edu
Received 20 June 2002
Epoxides can be readily obtained by the epoxidation of
the corresponding olefin derivatives. Vinyl and aryl ep-
Abstract: Gallium trichloride catalyzes the tandem ring opening
of epoxides and cyclization with alkynes to generate naphthalene
derivatives with complete regio control.
5
oxides, when treated with lewis acids, can be converted
6
into the desired , -unsaturated aldehydes in situ. To
Key words: gallium trichloride, naphthalene, alkyne, epoxide
start the study, styrene epoxide was mixed with 1-phenyl-
1
-butyne in methylene chloride with a catalytic amount of
7
gallium trichloride and the mixture was allowed to reflux
for 21 hours. TLC showed the complete disappearance
of the alkyne. After column chromatography on silica gel,
Polysubstituted aromatic compounds play an important
role in the chemical and pharmaceutical industries. These
extended aromatic systems also find extensive uses in the
production of optical and electronic materials. Recently,
there has been considerable interest in synthesizing naph-
thalene derivatives and other extended aromatic systems,
which are extremely useful benzenoid compounds for bi-
ological studies and material applications. The most im-
portant synthetic routes to such compounds are the
1
-phenyl-2-ethyl-naphthalene was isolated in 48% yield.
The rest of the starting material was attributed to a
competing polymerization reaction. When the reaction
was carried out in chloroform under reflux, the yield in-
creased by 6%. Subsequently, various epoxides were
treated with different aromatic alkynes under the standard
conditions (Table 1).
1
annulation via Fischer carbenes (the Dötz reaction) and
Only one regioisomer was obtained in each case. The re-
giochemistry of the reaction was confirmed by the reac-
tion between styrene oxide and 1-ethynyl naphthalene,
which resulted in the formation of 1,1-binaphthalene as
the only product (Table 1, entry 5). The regiochemistry
for other substituted naphthalenes was established by
comparing the NMR data with the compounds prepared
the palladium catalyzed cyclization of alkynes with aryl-
silyl triflates via in situ generation of highly reactive ben-
2
zynes. Another method of synthesis is based on the
3
cyclopropane shift type reaction. Very recently, we re-
ported a novel synthesis of polysubstituted naphthalene
derivatives via a novel cyclization reaction between
alkynes and carbonyl compounds catalyzed by gallium
4
4
and characterized in our earlier report. When the reaction
trichloride. In order for the reaction to work the carbonyl
between 1-phenyl-1-butyne 2c and 1b was tried with
InCl and In(OTf) , although product 3h was observed
compound has to be a , -unsaturated aldehyde or ketone.
We envisioned an alternative method involving an in situ
epoxide isomerization to these unstable , -unsaturated
aldehydes followed by in situ cyclization with alkynes.
Herein we wish to report a unique coupling between ep-
oxides and alkynes resulting in naphthalene derivatives
with complete regiocontrol of all substituents and in rea-
sonably good yields (Equation 1).
3
3
from the TLC experiment, a significant amount of the
starting alkyne was still present even after 21 hours of re-
fluxing in chloroform. It should be noted that in the case
of styrene oxide, it is the hydrogen that migrates, whereas
in the case of stilbene oxide it is the phenyl group that mi-
grates to generate the , -unsaturated aldehydes. Table 1
also shows that the yields were slightly better with stil-
bene oxides than with styrene oxides. As the same prod-
ucts were obtained by using gallium trichloride catalyzed
cyclization between the aromatic alkynes and the corre-
4
sponding phenyl acetaldehydes, it indicated that the ep-
oxides underwent isomerization to form , -unsaturated
aldehydes in situ before reacting with the alkynes.
We believe that either gallium trichloride or the hydro-
lyzed form, which is gallium hydroxide dichloride, could
act both as a Lewis acid and an alkyne activator. Our re-
cent works on gallium trichloride supports this conten-
Equation 1
4,8
tion. In the first step, gallium hydroxide dichloride
catalyzes the isomerization of epoxide to , -unsaturated
aldehyde. Subsequently, the gallium salt catalyzes the re-
gioselective electrophilic addition of the aldehyde-Lewis
Synlett 2002, No. 9, Print: 02 09 2002.
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Georg Thieme Verlag Stuttgart · New York
ISSN 0936-5214

1
554
G. S Viswanathan, C.-J. Li
LETTER
Table 1 Cross-Cyclization Between Epoxides and Alkynes to Generate Naphthalene Derivatives
Entry
Epoxide
Alkyne
Product
Isolated Yield
1
2
3
[%]
O
O
O
O
O
Ph
H
2a
2
a
Ph
1
45
1
1
1
1
a
a
a
a
3a
3b
3c
3d
Ph
Me
2
b
Me
Et
Ph
Ph
Ph
2
3
4
42
54
63
Ph
Et
Pr
2
c
Ph
2
d
Pr
H
5
6
1a
43
58
2
e
3
3
3
e
f
O
O
Ph
H
2a
Ph
Ph
Ph
2
a
Ph
Ph
1
1
b
b
Ph
Me
2
b
Me
7
8
Ph
Ph
67
64
g
O
Ph
Et
Ph
2
c
Et
Ph
1
b
3
h
acid complex to C of the phenyl alkyne. Intramolecular References
2
electrophilic attack of the formed alkenyl cation to the ar-
(
1) (a) Shore, N. E. Chem. Rev. 1988, 88, 1081. (b) Dötz, K. H.
Angew. Chem., Int. Ed. Engl. 1984, 23, 587.
omatic system, followed by elimination of a proton, gen-
erates the cyclization product, which aromatizes to form
the corresponding naphthalene derivatives and regener-
ates the active catalyst gallium hydroxide dichloride9
(
2) (a) Yoshikawa, E.; Radhakrishnan, K. V.; Yamamoto, Y. J.
Am. Chem. Soc. 2000, 122, 7280. (b) Pena, D.; Perez, D.;
Guitian, E.; Castedo, L. J. Am. Chem. Soc. 1999, 121, 5827.
(
c) Radhakrishnan, K. V.; Yoshikawa, E.; Yamamoto, Y.
(
Scheme 1).
Tetrahedron Lett. 1999, 40, 7533. (d) Larock, R. C.; Tian,
Q. J. Org. Chem. 1998, 63, 2002. (e) Feldman, K. S.;
Ruckle, R. E. Jr.; Ensel, S. M.; Weinreb, P. H. Tetrahedron
Lett. 1992, 33, 7101.
(
(
3) Wakasugi, K.; Nishii, Y.; Tanabe, Y. Tetrahedron Lett.
2000, 41, 5937.
4) Viswanathan, G. S.; Wang, M.; Li, C. J. Angew. Chem. Int.
Ed. 2002, 41, 2138.
Synlett 2002, No. 9, 1553–1555 ISSN 0936-5214 © Thieme Stuttgart · New York

LETTER
Naphthalene Derivatives via Catalyzed Cross-Coupling of Epoxides with Alkynes
1555
O
R1
Ph
R1
O
GaCl2
Ga(OH)Cl2
R2
R1
H2O
R1
R1
OGaCl2
O
H
GaCl2
R2
R2
Ph
Ph
R1
Ph
R1
OGaCl2
R2
OGaCl2
R2
H
Ph
Scheme 1 Proposed mechanism for the cross-cyclization between epoxides and alkynes
(
5) For a monograph, see: Raifeld, Y. E.; Raisman, A. M.; Lee,
V. J. Asymmetric Epoxidation: Mechanisms, Techniques,
and Synthetic Applications; CRC: Boca Raton, FL, USA,
(8) Viswanathan, G. S.; Li, C. J. Tetrahedron Lett. 2002, 43,
1613.
(9) Typical experimental procedure: Gallium trichloride (14.0
mg, 0.079 mmol, 10.6 mol%) was added to a solution of 1-
phenyl-1-propyne (2b, 86.9 mg, 0.748 mmol) and trans-
stilbene oxide (1b, 165.8 mg, 0.844 mmol) in CH Cl (4.0
1
999.
6) (a) Li, J.; Li, C. J. Tetrahedron Lett. 2001, 42, 793.
b) Ranu, B. C.; Jana, U. J. Org. Chem. 1998, 63, 8212.
(
(
(
2
2
7) For recent leading examples of GaCl catalyzed reactions,
mL). The solution turned dark brown instantly. The reaction
mixture was refluxed for 15 h then concentrated in vacuo.
Subsequently, the crude mixture was purified by column
chromatography on silica gel with hexane as eluent to give
1-phenyl-2-methylnaphthalene (3g, 147.3 mg, 0.50 mmol,
yield 67%).
3
see: (a) Yonehara, F.; Kido, Y.; Morita, S.; Yamaguchi, M.
J. Am. Chem. Soc. 2001, 123, 11310. (b) Kido, Y.;
Yonehara, F.; Yamaguchi, M. Tetrahedron 2001, 57, 827.
(
2
c) Takaya, J.; Kagoshima, H.; Akiyama, T. Org. Lett. 2000,
, 1577; and references cited therein. (d) Asao, N.; Asano,
T.; Ohishi, T.; Yamamoto, Y. J. Am. Chem. Soc. 2000, 122,
817. (e) Kido, Y.; Yoshimura, S.; Yamaguchi, M.;
4
Uchimaru, T. Bull. Chem. Soc. Jpn. 1999, 72, 1445. (f) Su,
J.; Goodwin, S. D.; Li, X. W.; Robinson, G. H. J. Am. Chem.
Soc. 1998, 120, 12994. (g) Kido, Y.; Yamaguchi, M. J. Org.
Chem. 1998, 63, 8086.
Synlett 2002, No. 9, 1553–1555 ISSN 0936-5214 © Thieme Stuttgart · New York