Intramolecular cyclization of phenol derivatives with C{double bond, long}C double bond in a side chain

Article abstract of DOI:10.1016/j.jorganchem.2006.05.060

Intramolecular cyclization of phenol derivatives with C{double bond, long}C double bond on a side chain was examined using copper and silver catalyst. For example, 2-allylphenol (1a) was converted to 2,3-dihydro-2-methylbenzofuran (2a) in 70% yield using Cu(OTf)₂ or in 90% yield using AgClO₄. This catalysis was applied to cyclization of 2-allylphenol derivatives, 2-(3-butenyl)phenol, benzoic acids with C{double bond, long}C double bond, 2-allyl-N-tosylaniline, and 2-(3-butenyloxy)phenol. Furthermore, allyl phenyl ether was converted to 2a via Claisen rearrangement and cyclization.

Full text of DOI:10.1016/j.jorganchem.2006.05.060

Journal of Organometallic Chemistry 692 (2007) 691–697
www.elsevier.com/locate/jorganchem
Intramolecular cyclization of phenol derivatives with C@C double
bond in a side chain
*
Yoshihiko Ito , Risa Kato, Kentaro Hamashima, Yohei Kataoka, Yohei Oe,
Tetsuo Ohta, Isao Furukawa
Department of Molecular Science and Technology, Faculty of Engineering, Doshisha University, Kyotanabe, Kyoto 610-0394, Japan
Received 1 March 2006; received in revised form 12 May 2006; accepted 17 May 2006
Available online 30 August 2006
Abstract
Intramolecular cyclization of phenol derivatives with C@C double bond on a side chain was examined using copper and silver cat-
alyst. For example, 2-allylphenol (1a) was converted to 2,3-dihydro-2-methylbenzofuran (2a) in 70% yield using Cu(OTf)2 or in 90% yield
using AgClO4. This catalysis was applied to cyclization of 2-allylphenol derivatives, 2-(3-butenyl)phenol, benzoic acids with C@C double
bond, 2-allyl-N-tosylaniline, and 2-(3-butenyloxy)phenol. Furthermore, allyl phenyl ether was converted to 2a via Claisen rearrangement
and cyclization.
Ó 2006 Elsevier B.V. All rights reserved.
Keywords: Intramolecular addition; Copper; Silver; 2,3-Dihydrobenzofuran; 3,4-Dihydro-2H-1-benzopyrane; 3,4-Dihydro-2H-1,5-benzodioxepin
1. Introduction
species tested, Cu(OTf)2, Cu(ClO4)2 Æ 6H2O, CuOTf Æ C6H6,
AgOTf, AgClO4, AlCl3, and FeCl3 showed some catalytic
activities under standard conditions (in CHCl3, 60 °C,
48 h). Interestingly, for copper and silver complexes, tri-
flates and perchlorates showed catalytic activity, while tet-
rafluoroborates did not work as a catalyst. Other metal
triflates (Zn(OTf)2, NaOTf, Bu4N(OTf), Sn(OTf)2,
Yb(OTf)3, La(OTf)3) and other metal halides (CuCl2,
CuBr2, AgCl, ZnCl2, LiCl, PbCl2, SnCl2 Æ 2H2O) showed
no catalytic activity (see Table 1).
As oxygen containing heterocyclic compounds, such as
2,3-dihydrobenzofuran [1], 3,4-dihydro-2H-1-benozopy-
rane [2], 3,4-dihydro-2H-1,5-benzodioxepin [3], are found
as a moiety of some biologically active materials, syntheses
of these compounds under neutral conditions have been
focused on [4–6]. We have already found the intramolecu-
lar cyclization of 2-allylphenol and related compounds
using ruthenium catalysts [7,8]. Although this reaction gave
cyclic products in good to excellent yields, ruthenium com-
pounds are relatively expensive, and the TON was not sat-
isfactory. In the course of this research, we found that the
copper and silver compounds also catalyze this cyclization
efficiently and described the results here [9].
Catalyst
Solvent / 60 oC / 48 h
O
OH
1a
2a
2. Results and discussion
2.1. Copper catalyst
At first, catalytically active metal species were searched
for cyclization of 2-allylphenol (1a). Among various metal
Solvent effect was examined using Cu(OTf)2, and repre-
sentative results are listed in Table 2. Using nonpolar or
less polar solvent promoted the reaction well, while polar
*
Corresponding author. Tel.: +81 75 753 5664; fax: +81 75 753 5668.
E-mail address: yoshi@sbchem.kyoto-u.ac.jp (Y. Ito).
0022-328X/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2006.05.060

692
Y. Ito et al. / Journal of Organometallic Chemistry 692 (2007) 691–697
Table 1
Table 3
a
Effect of various metal species on intramolecular cyclization of 2-
allylphenola
Intramolecular cyclization of 2-allylphenol derivatives with Cu(OTf)2
Entry
Substrate
Yieldb (%)
Entry
Catalyst
Yieldb (%)
R=
1
2
3
4c
5
6
7
8
9
a
Cu(OTf)2
Cu(ClO4)2 Æ 6H2O
Cu(BF4)2 Æ 6H2O
CuOTf Æ C6H6
AgOTf
AgClO4
AgBF4
AlCl3
FeCl3
70
51
0
42
7
58
0
29
7
1
2
3
4
5
6
a
1a
1b
1c
1d
1e
1f
H
70
89
76
55
19
0
6-CH3
6-OCH3
4-OCH3
6-Cl
6-NO2
Reaction conditions: substrate (1.0 mmol), CHCl3 (1.5 mL), Cu(OTf)2
(5 mol%), 60 °C, 48 h, under Ar.
b
Determined by 1H NMR using internal standard (dibenzy ether)
Reaction conditions: 1a (1.0 mmol), catalyst (10 mol%), CHCl3
(1.5 mL), 60 °C, 48 h, under Ar.
method.
b
Yield was determined by 1H NMR using internal standard (dibenzyl
ether) method.
favorable than at 4-position. This can be explained that
the substituents at 6-position prevent the coordination of
hydroxy group to copper atom, and the cyclization
smoothly proceeds without coordination of hydroxy group
to catalyst (see mechanistic consideration). In case of 1d,
more electron rich hydroxy group coordinates to copper
stronger than that in 1a. Therefore, the yield of 2d was
lower than that of 2a.
2-(3-Butenyl)phenol (3) was converted to 3,4-dihydro-2-
methyl-2H-1-benzopyran (4) in good yield for shorter reac-
tion time by Cu(OTf)2 than by ruthenium catalyst system
(72% isolated yield; RuCl3 Æ nH2O (10 mol%), AgOTf
(30 mol%), Cu(OTf)2 (50 mol%), 80 °C, 48 h in CH3CN).
c
20 mol% of catalyst was used.
Table 2
a
Effect of solvent on intramolecular cyclization of 1a with Cu(OTf)2
Entry
Solvent (mL)
Yieldb (%)
1
2c
3
4
5
6
a
CHCl3 (1.5)
70
33
33
55
59
53
CH2Cl2 (1.5)
n-hexane (1.5)
Benzene (1.5)
Toluene (1.5)
Cyclohexane (1.5)
Reaction conditions: 1a (1.0 mmol), Cu(OTf)2 (10 mol%), 60 °C, 48 h,
under Ar.
b
Yield was determined by 1H NMR using internal standard (dibenzyl
ether) method.
Cu(OTf)2 (5 mol%)
c
At reflux temperature.
benzene / 24 h / reflux
O
OH
4
3
solvent (THF, DMSO, CH3CN, DMF, CH3OH, and
C2H5OH) retarded the reaction to give no product at all.
Especially, substrate1a was converted to 2a in chloroform
in 70% yield.
85% (NMR yield)
2-Allylaniline derivatives were also tested for this catal-
ysis, and 2-allyl-N-tosylaniline (5) was found to be a sole
reactive substrate among tested. That is, compound 5
was converted to cyclic product 6 in 54% yield by
Cu(OTf)2, while 2-allylaniline and 2-allylacetanilide did
not react in toluene at reflux in the presence of Cu(OTf)2.
This applicability of 2-allylaniline derivatives is similar
for cyclization by ruthenium catalyst.
Cu(OTf)2
CHCl3 / 60 oC / 48 h
O
OH
R
R
1
2
Effect of substituent on phenyl ring of 2-allylphenol was
then examined (Table 3). Substrates 1b and 1c, having
methyl or methoxy at 6-position, smoothly reacted to give
2,3-dihydrobenzofuran derivatives in 89% and 76% yield,
respectively. On the other hand, 2-allyl-4-methoxyphenol
(1d) was converted to 2d in 55% yield. In case of substrates
1e and 1f, which have chloride or nitro group at 6-position,
reactions were sluggish to give products in far low yields.
These results suggest that the reaction is mainly controlled
by nucleophilic attack by hydroxy group of phenol because
the substrates with electron-donating group showed higher
reactivity than the substrates with electron-withdrawing
group. At the same time, substituents at 6-position were
2.2. Silver catalyst
Silver perchlorate was used for survey of solvent. Reac-
tion of 1a proceeded smoothly in dichloromethane and
Cu(OTf)2 (5 mol%)
N
Ts
Toluene / 24 h / reflux
NHTs
6
5
54% yield

Y. Ito et al. / Journal of Organometallic Chemistry 692 (2007) 691–697
693
chloroform. Reproducibility was not good in benzene, tol-
uene, hexane, or cyclohexane at lower than 60 °C because
of low solubility of silver perchlorate in such solvent. Using
ethanol, acetonitrile, DMSO, DMF, and THF retarded the
reaction at all.
At higher reaction temperature, yields of 2a became bet-
ter, and reaction time could be shortened (entries 10, 11,
115, and 16). Interestingly, loading a lower amount of
AgClO4 as a catalyst from 10 mol% to 5 mol% increased
the yield of the product 2a (entries 7, 12, and 17). This
observation indicates that the catalyst might decompose
the product 2a (see Table 4).
resulted no reaction. In case of CIO4À and OTfÀ, coordina-
tion ability of these counter anions weakens the coordina-
tion by phenolic oxygen to promote the reaction efficiently.
This reaction was retarded by adding phosphine (PPh3,
dppe, BINAP) or amine (pyridine). Silver catalyst may pro-
mote the reaction using only one or two coordination sites.
Therefore, these additives are seemed to block the coordi-
nation sites. When using (R)-BINOL as an additive, cycli-
zation reaction proceeded smoothly, but no enantiomeric
excess of the product was observed (see Table 5).
2-(3-Butenyl)phenol (3) was subjected for this reaction
to be converted to 3,4-dihydro-2-methyl-2H-1-benzopyran
(4) in good yield by using AgClO4 or AgOTf. Interestingly,
loading 3 mol% of AgOTf gave the product 4 in almost
similar yield as that (80%) by the reaction using 5 mol%
of AgOTf, while using 3 mol% AgClO4 resulted lower yield
(74%) of the product 4 than that using 5 mol% catalyst
(81%).
Next, several silver compounds were investigated as a
catalyst for this cyclization. Silver perchlorate and silver
trifluoromethanesulfonate catalyzed the reaction effi-
ciently, while silver tetrafluoroborate, silver trifluoroace-
tate, and silver hexafluorophosphate did not catalyze the
reaction. Sunderrajan et al. reported the effect of distance
between silver atom and counter anion on the formation
of silver–olefin complex. In their report, as the distances
between silver and counter anion (0.225 nm in AgO-
COCF3 < 0.233 nm in AgBF4 < 0.237 nm in AgOTf)
became longer, it was easier to form silver–olefin complexes
[10]. Tendency of the formation of silver–olefin complex
might be affected for the catalytic activity. Furthermore,
coordination ability of counter anion seems to influence
the catalyticÀactivity. That is, a silver cation, which has
AgOTf (3 mol%)
toluene / 24 h / reflux
O
OH
4
3
82% (NMR yield)
3,4-Dihydro-2H-1,5-benzodioxepin structure is impor-
tant framework in Strobilurin I and K that exhibit antifun-
gul activities and cytostatic activities [11]. Therefore, our
catalyst system was applied to the reaction of 2-(3-butenyl-
oxy)phenol (7). Friedel–Crafts type product 9 was formed
selectively by acid (entry 1). Silver triflates showed no cata-
lytic activity, while Cu(OTf)2 gave some extent of the
desired product 8 accompanied with 9. This indicates that
the benzene ring in 7 is fairly nucleophilic, compared with
the nucleophilicity of oxygen atom in hydroxy group. Addi-
tion of phosphine improved the selectivity. Among biden-
tate phosphines used, diphosphines with larger bite angles
increased the selectivity of 8. Triphenylphosphine was the
À
BF4 or PF6 as a counter anion, is strongly coordinated
by oxygen atom and C@C double bond of substrate 1a,
Table 4
a
Intramolecular cyclization of 2-allylphenol (1a) with AgClO4
Entry
Solvent (mL)
Temperature (°C)/time (h)
Yieldb of 2a (%)
1
2
3c
CH2Cl2 (1.5)
CH2Cl2 (1.5)
CH2Cl2 (4.5)
Reflux/24
Reflux/48
Reflux/48
60
50
27 (40)
4
5
6
7c
CHCl3 (1.5)
CHCl3 (1.5)
CHCl3 (1.5)
CHCl3 (4.5)
40/48
1 (60)
62
54
Reflux/24
Reflux/48
Reflux/24
81
8
10
11
12c
Benzene (1.5)
Benzene (1.5)
Benzene (1.5)
Benzene (4.5)
40/48
60/48
Reflux/24
Reflux/24
2 (23)
<65
70
Table 5
Effect of catalysts on intramolecular cyclization of 2-allylphenol (1a)a
77
Entry
Catalyst (mol%)
Time (h)
Yieldb of 2a (%)
13
14
15
16
17c
18d
a
Toluene (1.5)
Toluene (1.5)
Toluene (1.5)
Toluene (1.5)
Toluene (4.5)
Toluene (4.5)
40/48
60/48
80/48
Reflux/24
Reflux/24
Reflux/24
5 (33)
<63
58
66
90
1
2
3
4
5
6
7
8
9
a
AgBF4 (5)
AgOCOCF3 (5)
AgPF6 (5)
AgOTf (5)
AgOTf (3)
AgOTf (2)
AgOTf (2)
AgClO4 (5)
AgClO4 (3)
24
24
24
24
24
24
40
24
24
0 (86)
0 (92)
0 (74)
84
77 (3)
86
73 (13)
83 (1)
90
Reaction conditions: 1a (1.0 mmol), solvent (1.5 mL), AgClO4
(10 mol%), under Ar.
b
Determined by 1H NMR analysis using internal standard (dibenzyl
77 (3)
ether) method and figures in parenthesis showed yield of recovered
starting material.
Reaction condition; 2-allylphenol (1a, 3 mmol), toluene (4.5 mL),
c
Reaction conditions: 1a (3.0 mmol), solvent (4.5 mL), AgClO4
reflux, under Ar.
b
Determined by 1H NMR analysis using internal standard (dibenzyl
(5 mol%), under Ar.
d
Reaction conditions: 1a (3.0 mmol), solvent (4.5 mL), AgClO4
ether) method, and figures in parenthesis were yield of recovered starting
material.
(3 mol%), under Ar.

694
Y. Ito et al. / Journal of Organometallic Chemistry 692 (2007) 691–697
best among the additives used. The amount of PPh3 largely
influenced the selectivity and reactivity. Using 2.2 equiv. of
PPh3 to copper atom resulted the best selectivity of 1.32
ratio of 8/9, while adding less amount of PPh3 decreased
the selectivity, and employing 3 equiv. of PPh3 made the
reaction sluggish. Other monodentate phosphines resulted
in low reactivity with low selectivity at all (see Table 6).
2.3. Mechanistic consideration
Plausible reaction mechanism is postulated in Scheme 1.
At first, carbon–carbon double bond is activated by coor-
dination to Lewis acidic copper (II) center. Then oxygen
or nitrogen atom attacks to carbon–carbon double bond
coordinated to copper intramolecularly to give alkylcopper
intermediate B and trifluoromethanesulfonic acid (TfOH).
This alkylcopper intermediate B is hydrolyzed by TfOH
to afford product and Cu(OTf)2. As electron withdrawing
groups (Cl, NO2) decreased the yields of the products,
nucleophilic attack by oxygen atom is included in the
mechanism. Coordination of hydroxy group to copper
atom prevents the reaction in some extent, because 6-posi-
tion substituents increased the yield of the products. There-
fore, intermediate A is written as a copper–olefin complex
without coordination by oxygen of substrate. But the weak
coordination by oxygen atom of substrate to copper as a
bidentate fashion is still possible.
O
OH
7
O
catalyst
O
OH
+
benzene / 24 h / reflux
O
9
8
For obtaining seven-membered ring selectively, sub-
strate 10, in which ortho position was blocked by methyl
substituent, was used for this reaction. Copper(II) triflate
catalyzed the cyclization of 10 efficiently to give the desired
product 11 in 85% yield even in 3 h.
2.4. Claisen rearrangement and intramolecular cyclization of
allyl phenyl ether
Allyl phenyl ether (11) has been known to be con-
verted to 2,3-dihydro-2-methylbenzofuran (2a) in moder-
ate to good yields using heterogeneous catalyst, [12]
In(III), [13] or Mo(CO)6 [14]. We also tested the reaction
of 11 using our catalysts and found that 11 was
converted to 2a in moderate yield using Cu(OTf)2 or sil-
ver catalysts. GC-mass analysis of the reaction mixture
using Cu(OTf)2 in chloroform revealed that it was a mix-
ture of substrate 12, product 2a, and 2-allylphenol (1a).
O
O
O
Cu(OTf)2 (5 mol%)
benzene / 3 h / reflux
OH
11
85% yield
10
Table 6
Cyclization of 7a
Entry
Catalyst (mol%)
Additive (mol%)
Recoveryb of 7 (%)
Yieldb of 8 (%)
Yieldb of 9 (%)
Ratio of 8/9
1
2
3
4c
TfOH (10)
AgOTf (5)
0
100
0
0
0
60
0
0
0
0
86
0
0
20
70
35
0
76
100
0
0
68
0
0
Cu(OTf)2 (5)
Cu(OTf)2 (10)
Cu(OTf)2 (10)
Cu(OTf)2 (10)
Cu(OTf)2 (10)
Cu(OTf)2 (10)
Cu(OTf)2 (10)
Cu(OTf)2 (10)
Cu(OTf)2 (10)
Cu(OTf)2 (10)
Cu(OTf)2 (10)
Cu(OTf)2 (10)
Cu(OTf)2 (10)
Cu(OTf)2 (10)
Cu(OTf)2 (10)
Cu(OTf)2 (10)
Cu(OTf)2 (10)
25
22
41
17
24
46
48
54
7
67
67
59
20
57
40
40
41
0
68
54
40
13
28
59
10
0
0.37
0.33
0.69
0.85
0.42
1.15
1.20
1.32
100
Dppm (10)
Dppe (10)
Dppp (10)
PPh3 (10)
PPh3 (20)
PPh3 (21)
PPh3 (22)
PPh3 (30)
P(OPh)3 (22)
P(4-FC6H4)3 (22)
PPh2Cy (22)
P(4-MeC6H4)3 (22)
P(2-MeC6H4)3 (22)
P(4-MeOC6H4)3 (12)
P(4-MeOC6H4)3 (20)
P(4-MeOC6H4)3 (22)
5c,d
6c
7c
8c
9c
10c
11c,d
12c
13c
14c
15c
16c
17c
18c
19c
a
Trace
40
40
16
36
26
12
0
0
0.74
1.00
1.23
1.29
0.44
1.20
Reaction conditions: 7 (1.0 mmol), catalyst, additive, benzene (2.0 mL), reflux, 24 h.
Determined by 1H NMR using internal standard (dibenzyl ether) method.
In toluene for 48 h.
b
c
d
In toluene for 72 h.

Y. Ito et al. / Journal of Organometallic Chemistry 692 (2007) 691–697
695
Cu(OTf)2
( )
X
n
( )
n
XH
Cu2+ OTf-
( )
n
( )
n
Cu2+
2OTf -
X
X
H
H+OTf-
B
A
Scheme 1. Possible mechanism for the intramolecular cyclization reaction with Cu(OTf)2.
Therefore, the reaction proceeded through 1a by Claisen
3.2. Intramolecular cyclization
rearrangement.
Typical procedure: to two-necked flask were added a
solution of substrates (1.0 mmol) in solvent (1.5 mL) and
Cu(OTf)2 (0.05 mmol), and the resulting mixture was stir-
ring under reflux for 24 h under argon atmosphere. After
the reaction, solvent was removed in vacuum, and distilled
water and dibenzyl ether were added to the residue.
Organic materials were extracted with chloroform. Analy-
sis of the crude mixture containing internal standard was
analyzed by 1H NMR to determine the yield of the
product.
O
O
12
2a
Cu(OTf)2 (5 mol%) in CHCl3, at reflux, 48 h
Cu(OTf)2 (5 mol%) in benzene, at reflux, 48 h 50%
AgOTf (5 mol%) in CHCl3, at reflux, 48 h
AgClO4 (5 mol%) in CHCl3, at reflux, 24 h
14%
54%
64%
3.3. 2,3-Dihydro-2-methylbenzofuran (2a)
3. Experimental
3.1. General
1H NMR(CDCl3) d 1.46 (3H, d, J = 6.4, CH3), 2.81
(1H, dd, J = 14.4, 7.2, CH2), 3.30 (1H, dd, J = 14.4, 7.2,
CH2), 4.88–4.94 (1H, m, CH), 6.75 (1H, d, J = 7.6, Ar),
6.82 (1H, t, J = 7.6, Ar), 7.10 (1H, t, J = 7.6, Ar), 7.15
(1H, d, J = 7.6, Ar). GC–MS (m/z) 134.
Proton nuclear magnetic resonance (1H NMR) spectra
were measured using a JEOL JNM A-400 (400 MHz) spec-
trometer using tetramethylsilane as the internal standard.
IR spectra were measured on a Shimadzu IR-408 spec-
trometer. Mass spectral (GC–MS) data were recorded on
a Shimadzu QP2000A instrument. Melting points were
measured on a Yanako Model MP and were not corrected.
Substrates purchased were used without further purifica-
tion. Solvents were purified according to the literature
method, and stored under argon.
2-Allyl-4-methoxyphenol (1d), [15] 2-allyl-6-chlorophe-
nol (1e), [16] 2-allyl-6-nitrophenol (1f), [17] 2-(3-butenyl)-
phenol (3), [18] 2-allylaniline, [19] N-(2-allylphenyl)acetam-
ide, [20] 2-allyl-N-tosylaniline (5), [21] 2-(3-butenyl-
oxy)phenol (7), [22] and 2-(3-butenyloxy)-3-methylphenol
(10) [23] were prepared according to the literature method.
3.4. 2,3-Dihydro-2,7-dimethylbenzofuran (2b)
1H NMR(CDCl3) d 1.47 (3H, d, J = 6.4, CH3), 2.20
(3H, s, CH3), 2.81 (1H, dd, J = 15.2, 7.6, CH2), 3.30 (1H,
dd, J = 15.2, 7.6, CH2), 4.86–4.94 (1H, m, CH), 6.73 (1H,
d, J = 7.6, Ar), 6.92 (1H, d, J = 7.6, Ar), 6.98 (1H, d,
J = 7.6, Ar). GC–MS (m/z) 148.
3.5. 2,3-Dihydro-7-methoxy-2-methylbenzofuran (2c)
1H NMR(CDCl3) d 1.51 (3H d, J = 6.0, CH3), 2.84 (1H,
dd, J = 15.2, 7.6, CH2), 3.32 (1H, dd, J = 15.2, 7.6, CH2),

696
Y. Ito et al. / Journal of Organometallic Chemistry 692 (2007) 691–697
3.87 (3H, s, OCH3), 4.93–5.02 (1H, m, CH), 6.72–6.81 (3H,
m, Ar). GC–MS (m/z) 164.
(1H, m, OCHHCH2), 4.20–4.31 (1H, m, CH), 4.40–4.48
(1H, m, OCHHCH2), 6.81–6.91 (3H, m, Ar). GC–MS
(m/z) 178.
3.6. 2,3-Dihydro-5-methoxy-2-methylbenzofuran (2d)
Acknowledgements
1H NMR(CDCl3) d 1.43 (3H, d, J = 6.79, CH3), 2.77
(1H, dd, J = 15.2, 7.6, CH2), 3.25 (1H, dd, J = 15.2, 7.6,
CH2), 3.73 (3H, s, OCH3), 4.83–4.91 (1H, m, CH),
6.61–6.67 (2H, m, Ar), 6.73 (1H, d, J = 2.4, Ar). GC–MS
(m/z) 164.
This work was partially supported by Doshisha Univer-
sity’s Research Promotion Fund, and a Grant to RCAST
at Doshisha University from the Ministry of Education,
Culture, Sports, Science and Technology, Japan. This work
was supported by Grant-in-Aid for Scientific Research on
Priority Areas (No. 16033259, ‘‘Reaction Control of Dy-
namic Complexes’’) from Ministry of Education, Japan.
3.7. 7-Chloro-2,3-dihydro-2-methylbenzofuran (2e)
1H NMR(CDCl3) d 1.51 (3H, d, J = 6.4, CH3), 2.89
(1H, dd, J = 16.0, 7.6, CH2), 3.41 (1H, dd, J = 16.0, 8.8,
CH2), 5.07–5.16 (1H, m, CH), 6.77 (1H, d, J = 8.8, Ar),
8.06–8.16 (2H, m, Ar). GC–MS (m/z) 179.
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