A novel rearrangement of arylvinylidenecyclopropanes to naphthalene derivatives catalyzed by Lewis acids or Br?nsted acids

Article abstract of DOI:10.1055/s-2005-871565

Arylvinylidenecyclopropanes undergo a novel rearrangement in the presence of Lewis acids or Br?nsted acids to give the corresponding naphthalene derivatives in good to high yields under mild conditions. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2005-871565

LETTER
1869
A Novel Rearrangement of Arylvinylidenecyclopropanes to Naphthalene
Derivatives Catalyzed by Lewis Acids or Brønsted Acids
A
N
ovel Rearrang
u
e
ment of
A
ry
a
lvinylidene
n
c
yclopropan
g
es to
N
aphth
-
alene De
C
r
ivatives ai Xu,a Ming Ma,a Le-Ping Liu,b Min Shi*a
a
School of Chemistry & Pharmaceutics, East China University of Science and Technology, 130 Meilong Road, Shanghai 200237,
P. R. China
Fax +86(21)64166128; E-mail: Mshi@pub.sioc.ac.cn
b
State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences,
354 Fenglin Lu, Shanghai 200032, P. R. China
Received 4 May 2005
conditions, 2a was obtained in lower yields (Table 1, en-
tries 4, 7, and 8). A prolonged reaction time is required in
the presence of Lewis acids Yb(OTf)3 and Sc(OTf)3 to
give 2a in 58% and 41% yields, respectively (Table 1,
entries 5 and 6). Brønsted acid TfOH (10 mol%) is also
fairly effective in this reaction giving 2a in moderate yield
(42%) at room temperature and in high yield (94%) at
80 °C (Table 1, entries 10 and 11). At 80 °C, TsOH is as
effective as TfOH (Table 1, entry 9). Examination of
solvent effects revealed that DCE is the best solvent for
this novel rearrangement (Table 1, entries 12–18).
Abstract: Arylvinylidenecyclopropanes undergo a novel rear-
rangement in the presence of Lewis acids or Brønsted acids to give
the corresponding naphthalene derivatives in good to high yields
under mild conditions.
Key words: arylvinylidenecyclopropanes, Lewis acids, Brønsted
acids, naphthalene derivatives, rearrangement
Thermal and photochemical skeletal conversions of
vinylidenecyclopropanes 1 have attracted much attention
from mechanistic, theoretical, spectroscopic, and synthet-
ic viewpoints.1,2 Vinylidenecyclopropanes 1 also undergo
a variety of unique addition reactions with electrophiles to
give novel products, sometimes along with the formation
of cyclopropane ring-opened products.3
Next, we carried out the reaction with a variety of deriva-
tives of 1 in the presence of Sn(OTf)2 under the optimized
conditions. As can be seen from Table 2, the correspond-
ing rearranged products 2, naphthalene derivatives, were
obtained in good to high yields (Table 2, entries 1–8). For
vinylidenecyclopropanes 1g (R3 = R4 = aliphatic group)
and 1h (R3 = aliphatic group, cis/trans = 1:1), 2g and 2h
were obtained in good yields (Table 2, entries 6 and 7).
For vinylidenecyclopropanes 1i (R2 = aliphatic group, cis/
trans = 1:1), the corresponding naphthalene derivative 2i
was formed in 50% yield as the sole product (Table 2,
entry 8).
Recently, we have been investigating the Lewis acid cat-
alyzed ring-opening reactions of methylenecyclopropanes
(MCPs), another series of highly strained but readily
accessible molecules. Thus far, we have found that the
cyclopropane ring of MCPs can be opened by alcohols
and other nucleophiles in a different, novel manner to give
the corresponding homoallylic derivatives in good yields
under mild conditions in the presence of Lewis acids.4,5
Therefore, we attempted to examine the Lewis acid cata-
lyzed reaction of 1 with a variety of nucleophiles under
similar conditions. In this paper, we wish to report the
Lewis acid or Brønsted acid catalyzed rearrangement of
arylvinylidenecyclopropanes 1 to the corresponding
naphthalene derivatives 2 in good to high yields under
mild conditions.6
1
Their structures were determined by H and 13C NMR
spectroscopic data as well as HRMS or microanalyses.
Based on the above results and our previous investigations
on the Lewis acid catalyzed ring-opening reaction of
MCPs,4,5 a plausible mechanism for the rearrangement of
arylvinylidenecyclopropanes 1 in the presence of either
Lewis acids or Brønsted acids is outlined in Scheme 1.
The coordination of 1 to the Lewis acid6 or the addition of
1 with a Brønsted acid initially gave 1-cyclopropylvinyl
cation A, a vinyl group stabilized cyclopropyl cation,8
which results in the formation of cyclopropane ring-
opened cationic intermediate B, which is stabilized by the
aromatic R3 group in most cases.3l The intramolecular
Friedel–Crafts reaction produces the cyclized intermedi-
ate C. The rearrangement of C affords the intermediate D.
The 1,4-proton shift along with release of Lewis acid or
deprotonation gives the corresponding intermediate E.
The 1,3-proton shift produces the thermodynamically
favored naphthalene derivatives 2;9 this is the driving
force in this reaction moving the equilibrium towards the
formation of the naphthalene derivatives 2 (Scheme 1).
Initial examination using diphenylvinylidenecyclopro-
pane (1a) as the substrate in the presence of a variety of
Lewis acids or Brønsted acids, revealed that a novel rear-
rangement took place to give 2-methyl-1,4-diphenylnaph-
thalene (2a) under various conditions. While the reaction
with Sn(OTf)2 (10 mol%) as a Lewis acid in DCE, at room
temperature was sluggish, the reaction proceeded smooth-
ly under reflux (80 °C) to give 2a in 92% yield after four
hours (Table 1, entries 2 and 3). Using other Lewis acids
such as Zr(OTf)4, Cu(OTf)2, and BF3·OEt2 under identical
SYNLETT 2005, No. 12, pp 1869–1872
0
1
.0
8
.2
0
0
5
Advanced online publication: 22.06.2005
DOI: 10.1055/s-2005-871565; Art ID: U13305ST
© Georg Thieme Verlag Stuttgart · New York

1870
G.-C. Xu et al.
LETTER
Table 1 Rearrangement of Diphenylvinylidenecyclopropane (1a) to 2-Methyl-1,4-diphenylnaphthalene (2a) in the Presence of a Variety of
Lewis Acids or Brønsted Acids7
Lewis acid (10 mol%)
solvent
2a
1a
Entry
1
Solvent
Lewis acid (0.1 equiv)
none
Temperature (°C)
Time (h)b
Yield (%)a 2a
c
ClCH2CH2Cl
ClCH2CH2Cl
ClCH2CH2Cl
ClCH2CH2Cl
ClCH2CH2Cl
ClCH2CH2Cl
ClCH2CH2Cl
ClCH2CH2Cl
ClCH2CH2Cl
ClCH2CH2Cl
ClCH2CH2Cl
CH3CH2OH
THF
80
25
80
80
80
80
80
80
80
80
25
78
66
80
80
80
80
80
120
120
4
–
2
Sn(OTf)2
Sn(OTf)2
Zr(OTf)4
Yb(OTf)3
Sc(OTf)3
Cu(OTf)2
BF3·OEt2
TsOH
51
92
81
58
41
41
71
92
94
42
34
83
87
65
63
3
4
4
5
9
6
50
4
7
8
4
9
4
10
11
12
13
14
15
16
17
18
TfOH
4
TfOH
10
10
25
4
Sn(OTf)2
Sn(OTf)2
Sn(OTf)2
Sn(OTf)2
Zr(OTf)4
Yb(OTf)3
Zr(OTf)4
Toluene
CH3CN
4
CH3CN
4
c
CH3CN
50
4
–
Toluene
68
a Isolated yields.
b Until all of the starting material 1 was consumed.
c No reaction occurred.
δ–
Interestingly, for diphenylvinylidenecyclopropane (1j),
naphthalene derivative 2j was formed in good yield under
identical conditions by eliminating one propene molecule
(Scheme 2); currently, its reaction mechanism remains
obscure.
R3
–
R3
R3
Lewis acid
or Bronsted acid
R1
LA(H)
LA(H)
R1
R2
R1
R2
+
δ+
R2
DCE, 80 °C
A
B
R2'
R2'
R2'
In conclusion, we have found a novel rearrangement of
arylvinylidenecyclopropanes 1 to the corresponding
naphthalene derivatives 2, in the presence of Lewis acids
R1
R1
R1
–LA(H+)
[1,4]-H
H
R3
H
R3
–
R3
–
LA
H
LA
H
H
(H)
H
(H)
D
C
E
R2'
R1
Sn(OTf)2
[1,3]-H
DCE, 80 °C
R3
Lewis acid or Bronsted acid-mediated rearrangement
1j
2j, 50%
Scheme 2 Rearrangement of diphenylvinylidenecyclopropane (1j)
Scheme 1 Plausible mechanism for the rearrangement of arylvinyl-
idenecyclopropanes 1 in the presence of Lewis acid or Brønsted acid.
in the presence of Lewis acid Sn(OTf)2 in DCE at 80 °C.7
Synlett 2005, No. 12, 1869–1872 © Thieme Stuttgart · New York

LETTER
Rearrangement of Arylvinylidenecyclopropanes to Naphthalene Derivatives
1871
Table 2 Lewis Acid Sn(OTf)2-Catalyzed Rearrangement of a Variety of Arylvinylidenecyclopropanes 1 in DCE at 80 °C7
R
R3
R1
Sn(OTf)2
R2
R3
DCE, 80 °C
R2
R4
1
R4
2
Entry
1
R1, R2
R3, R4
Time (h)
10
Yield (%)a
2
C6H5, C6H5
p-MeC6H4, H
1b
Me
2b, 80
2c, 61
2
3
C6H5, C6H5
p-MeOC6H4, H
1c
10
10
OMe
p-MeC6H4, p-MeC6H4
C6H5, H
Me
1d
Me
2d, 91
4
5
p-MeOC6H4, p-MeOC6H4
C6H5, H
1e
10
10
OMe
MeO
2e, 70
p-FC6H4, p-FC6H4
C6H5, H
F
1f
F
2f, 80
6
7
8
C6H5, C6H5
–(CH2)4–
1g
10
10
10
2g, 42
2h, 85
2i, 50
C6H5, C6H5
C6H5, Me (cis/trans = 1:1)
1h
Me, C6H5 (cis/trans = 1:1)
C6H5, H
1i
a Isolated yields.
or Brønsted acids, in good to high yields.10 A plausible
reaction mechanism has been discussed. The novelty in
this paper is the efficient and cascade formation of
naphthalene derivatives 2 catalyzed by Lewis acids or
Brønsted acids under mild conditions. Efforts are under-
way to elucidate the mechanistic details of this reaction
and to disclose the scope and limitations of this trans-
formation.
Acknowledgment
We thank the State Key Project of Basic Research (Project 973)
(No. G2000048007), Shanghai Municipal Committee of Science
and Technology, Chinese Academy of Sciences (KGCX2-210-01),
and the National Natural Science Foundation of China for financial
support (20472096, 203900502, and 20272069).
Synlett 2005, No. 12, 1869–1872 © Thieme Stuttgart · New York

1872
G.-C. Xu et al.
LETTER
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Figure 1
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(10) Typical reaction procedure for the rearrangement of
diarylvinylidenecyclopropanes: To a solution of
diarylvinylidenecyclopropane 1d (64 mg, 0.2 mmol) in DCE
(2.0 mL) was added Sn(OTf)2 (8 mg, 0.02 mmol), the
reaction mixture was stirred for 10 h at 80 °C (monitored by
TLC). After the starting materials (diarylvinylidenecyclo-
propans 1) were consumed, the solvent was removed under
reduced pressure and the residue was subjected to flash
column chromatography to give the desired product 2d (58
mg, 91%) as a colorless liquid. 2-Methyl-1-phenyl-4-(para-
methylphenyl)-7-methylnaphthalene (2d): colorless oil; IR
(CH2Cl2): 3053, 3023, 2954, 2923, 2855, 1620, 1600, 1516,
1507, 1440, 1381, 1362, 1029, 883, 824, 760, 703, 526
cm–1; 1H NMR (300 MHz, CDCl3): d = 2.22 (3 H, s, CH3),
2.34 (3 H, s, CH3), 2.45 (3 H, s, CH3), 7.15–7.22 (2 H, m,
Ar), 7.28–7.31 (5 H, m, Ar), 7.40–7.53 (5 H, m, Ar), 7.82
(1 H, d, J = 8.7 Hz, Ar); 13C NMR (75 MHz, CDCl3): d =
20.9, 21.3, 21.8, 125.4, 125.8, 126.9, 126.9, 128.4, 128.4,
128.8, 128.9, 130.0, 130.2, 132.7, 133.4, 135.2, 136.8,
137.0, 138.0, 139.2, 140.0; MS (EI): m/z (%) = 322 (100)
[M+], 307 (10.3), 292 (7.6), 229 (3.8), 215 (5.1), 91 (1.7);
HRMS (MALDI): m/z calcd for C25H23 (M+ + 1), 323.1794;
found, 323.1786.
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Synlett 2005, No. 12, 1869–1872 © Thieme Stuttgart · New York