Annulative synthesis of benzofurans from general alkenyl sulfoxides and phenols via pummerer/sigmatropic cascade

Article abstract of DOI:10.1246/bcsj.20180321

In addition to ketene dithioacetal monoxides that were specially designed and have been used so far, general alkenyl sulfoxides of moderate reactivity have now become applicable as substrates in the trifluoroacetic anhydride-mediated annulation with pheno

Full text of DOI:10.1246/bcsj.20180321

Advance Publication Cover Page
Annulative Synthesis of Benzofurans from General Alkenyl Sulfoxides and Phenols via
Pummerer/Sigmatropic Cascade
Mitsuki Hori, Tomoyuki Yanagi, Kei Murakami, Keisuke Nogi, and Hideki Yorimitsu*
Advance Publication on the web December 1, 2018
doi:10.1246/bcsj.20180321
© 2018 The Chemical Society of Japan
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Publication manuscripts.

Annulative Synthesis of Benzofurans from General Alkenyl Sulfoxides and Phenols
via Pummerer/Sigmatropic Cascade
Mitsuki Hori, Tomoyuki Yanagi, Kei Murakami, Keisuke Nogi, and Hideki Yorimitsu*
Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502 Japan
E-mail: < yori@kuchem.kyoto-u.ac.jp s>
Abstract
In addition to ketene dithioacetal monoxides that were
Although the interrupted Pummerer/sigmatropic cascade
is an instructive method for the construction of a benzofuran
scaffold, a methylsulfanyl group intrinsically remains at the 2
position and further manipulations are required to remove or
transform this unit. To further extend the utility and versatility
of this cascade, expansion of applicable alkenyl sulfoxides
should be required. Although Hendrickson tried the annulation
with cyclohexenyl sulfoxides, the yields of the products were
generally less than 50%.4a According to these considerations,
we decided to apply general alkenyl sulfoxides to the
interrupted Pummerer/sigmatropic cascade (Scheme 1b).
specially designed and have been used so far, general alkenyl
sulfoxides of moderate reactivity have now become applicable
as substrates in the trifluoroacetic anhydride-mediated
annulation with phenols for the shorter-step and
transition-metal-free synthesis of benzofurans having diverse
substituents. The improved method enabled concise formation
of furan-fused complex polycyclic skeletons, which culminates
in the two-step synthesis of dioxa[8]helicene. The modest
reactivity of alkenyl sulfoxides has allowed isolation of
dihydrobenzofurans as intermediates, which unveiled two
interesting phenomena: (i) the initial cyclization reflects the
stereochemistry and steric environment of alkenyl sulfoxides
and (ii) the aromatization by the departure of alkanethiol is the
rate-determining step.
Results and Discussion
In view of the reaction mechanism, the α-sulfanyl group
of KDM would stabilize cationic intermediate B by resonance
effect. We thus envisioned that an aryl ring at the α position in
place of sulfanyl group would make a similar stabilization
effect. As expected, 1,2-diphenylvinyl sulfoxide 2a smoothly
underwent the reaction with 4-tert-butylphenol (1a) to afford
benzofuran 3aa in 86% yield under similar conditions of the
previous report (Table 1, entry 1). With this encouraging result,
we further tested various alkenyl sulfoxides 2.8 β-Unsubstituted
alkenyl sulfoxide 2b also underwent the reaction (entry 2).
Chloro and ethoxycarbonyl groups at the β positions were
compatible with the reaction albeit in moderate yields of
products 3ac and 3ad (entries 3 and 4). In contrast, an
ethoxycarbonyl group at the α position totally suppressed the
reaction: a trace amount of benzofuran 3ae was obtained from
sulfoxide 2e (entry 5). This result demonstrates the necessity of
stabilization on the α position. Gratifyingly, alkyl substituents
were found to be sufficient for the stabilization of the cationic
charge, and benzofurans 3af–ah were obtained in high yields
from the corresponding 1-alkyl-2-phenylvinyl sulfoxides 2f–h
(entries 6–8). Acyclic as well as cyclic 1,2-dialkylvinyl
sulfoxides 2i and 2j were also applicable to furnish 3ai and 3aj
in 86% and 89% yields, respectively (entries 9 and 10). Instead
of alkyl chains, phenyl substituent on the sulfur atom of 2j' did
not retard the reaction resulting in the formation of 3aj (entry
11). When α-unsubstituted alkenyl sulfoxide 2k was employed,
the corresponding 2-sulfanyl-2,3-dihydrobenzofuran 4ak was
obtained in an anti-selective manner (entry 12, vide infra for
mechanistic discussion). As described in Scheme 4, departure
of dodecanethiol uneventfully proceeded by simply heating
with TsOH. The reaction of phenyl vinyl sulfoxide (2l) also
provided 2,3-dihydrobenzofuran 4al selectively (entry 13). The
absence of the α substituent would destabilize the intermediary
oxonium cation, and the departure of thiols would be retarded.
Predictably, trisubstituted vinyl sulfoxide 2m was converted to
the corresponding 2-sulfanyl-2,3-dihydrobenzofuran 4am
(entry 14).
Keywords: Pummerer/sigmatropic cascade, alkenyl
sulfoxide, benzofuran
Introduction
Sulfoxides are ubiquitous organosulfur compounds, and
widely utilized in organic synthesis as synthetic intermediates,
chiral auxiliary, ligands, and so on.1 Among sulfoxide-based
organic synthesis, extended Pummerer reactions are emerging
as valuable methods for C–H functionalizations of aryl and
alkenyl sulfoxides without the use of any metal catalysts.2
As a part of our investigations about the development of
Pummerer-based transformations,2g,2h,3,4 we developed the
annulative synthesis of benzofurans from ketene dithioacetal
monoxides (KDM) and phenols by means of trifluoroacetic
anhydride (TFAA) (Scheme 1a).5 First, KDM and phenol
undergo TFAA-mediated interrupted Pummerer reaction to
form S–O-bonded sulfonium A. Via cation-accelerated [3,3]
sigmatropic rearrangement,6,7 a C–C bond is constructed to
generate cationic species B. Subsequent cyclization and
departure of methanethiol from C furnish benzofuran.
(a) With KDM (previous work)
O
Me
OH
O
S
TFAA
SMe
+
SMe
R
R
KDM
interrupted
Pummerer
reaction
TFAA
Me
– MeSH
O
O
O
SMe
SMe
S
SMe
SMe
[3,3]
SMe
H
H
R
H
R
R
C
A
B
(b) With general alkenyl sulfoxides (this work)
R3
TFAA
O
OH
O
S
R1
+
R1
– R3SH
R2
R2
R1 = aryl, alkyl, H
Scheme 1. Pummerer annulation for synthesis of benzofurans

Table 1. Scope of alkenyl sulfoxides 2
Table 2. Scope of phenols 1
OH
OH
R1
O
R2
O
1
1.2 equiv TFAA
R3
+
tBu
1a 1.2 equiv
tBu
R1
O
2 S
R3
CH2Cl2
25 °C, 0.5 h
1.2 equiv TFAA
3
R4
R
+
3
and/or
O
R3
O
CH2Cl2
25 °C, 0.5 h
1 S
R4
phenol 1
R
SR1
R2
R2
2
R3
entry
tBu
sulfoxide 2
product (%)
O
2
R3 R4
4
R4
O
OH
entry
1
sulfoxide 2
product (%)
O
Me
Ph
S
Ph
Ph
R
O
R
Ph
Me
Ph
S
Ph
1
2
3
1b (R = Cl)
1c (R = Br)
1d (R = I)
3ba: 64%
3ca: 80%
3da: 73%
(Z)-2a
(Z)-2a
(Z)-2a
Ph
tBu
tBu
Ph
3aa: 86%
(Z)-2a
O
S
O
O
O
Me
Me
C12H25
S
Ph
Me
Ph
4
5
F3C
1e (R = CF3)
1f (R = OMe)
Ph
3ef: 41%a)
R
R
Ph
(E)-2f’
2
3
4
2b (R = H)
3ab: 65%
3ac: 46%
3ad: 50%
2c (R = Cl, E)
O
2d (R = CO2Et, E/Z = 17/83)
2j
MeO
O
O
C12H25
Ph
S
CO2Et
3fj: 86%
5
CO2Et
tBu
Ph
Ph
Ph
(Z)-2e
3ae: trace
O
OH
Ph
O
O
6
(Z)-2a
C12H25
Ph
S
R
Ph
R
1g
tBu
Ph
3ga: 76%
3af: 81%
3ag: 83%
3ah: 84%
6
7
8
2f (R = Me, Z )
2g (R = Bu, Z )
iPr
O
Ph
2h (R = CH2Ph, E/Z = 30/70)
iPr
OH
3ha
Ph
O
O
7
+
C12H25
Pr
S
Bu
(Z)-2a
9
Bu
O
tBu
Ph
1h
Pr
2i (isomeric ratio = 42/58)
3ai: 72%
Ph
3ha’
iPr
O
O
R
S
3ha+3ha’: 87% (11/1)
tBu
OH
OH
O
Ph
8
9
3aj: 89%
3aj: 89%
2j (R = C12H25
)
(Z)-2a
10
11
2j’ (R = Ph)
Ph
3ia: 89%
O
1i
O
O
SC12H25
C12H25
Ph
S
12
13
14
tBu
Ph
4ak: 70%
2k (E/Z = 9/91)
2j
(syn/anti = 1/18)
O
O
1j
O
SPh
Ph
S
OH
tBu
3jj: 63%b)
2l
4al: 76%
a) at 40 °C for 2.5 h. b) 3 equiv of 2j and 3 equiv of TFAA.
O
S
O
SC12H25
Ph
C12H25
We then checked the scope with respect to phenols (Table
2). Owing to the absence of transition metal catalysts, chloro,
bromo, and iodo substituents were intact during the reaction
and benzofurans 3ba–da were obtained in moderate to good
yields (entries 1–3). The reaction of electron-deficient
4-trifluoromethylphenol (1e) was not efficient, and the coupling
products, 3ef and 2-sulfanyl-2,3-dihydrobenzofuran 4ef, were
obtained in 24% and 28% NMR yields, respectively. Increasing
the reaction temperature to 40 °C promoted the departure of
methanethiol to provide 3ef albeit in moderate yield (entry 4).
Ph
tBu
2m
4am: 73%

On the other hand, electron-rich 4-methoxyphenol (1f)
uneventfully reacted with 2j to furnish 3fj in 86% yield (entry
5). An ortho-substituent did not hamper the reaction:
2-phenylphenol (1g) underwent the reaction with 2a to yield
3ga (entry 6). The reaction of 3-isopropylphenol (1h)
1,2-aryl shifts on cyclic O,S-acetals induced by BF3·Et2O were
reported by Procter.4g
O
2 equiv TsOH·H2O
tBu
toluene, 120 °C, 3 h
O
Ph
3ak: 92%
SC12H25
proceeded in
a
regioselective fashion to provide
tBu
6-isopropylbenzofuran 3ha as a major product (entry 7).
2-Naphthol (1i) was also smoothly converted to naphthofuran
O
Ph
1.2 equiv BF3·Et2O
CH2Cl2, 25 °C, 5 h
Ph
4ak (syn/anti = 1/18)
tBu
3ia
in
high
yield
(entry
8).
Gratifyingly,
2,7-dihydroxynaphthalene (1j) underwent the annulation with
alkenyl sulfoxide 2j twice, affording 3jj in one pot (entry 9).
Such cyclohexane-fused product is difficult to synthesize by the
previous method using KDM, which clearly demonstrates the
advantage of the present protocol.
3ab: 43%
Scheme 4. Departure of dodecanethiol from 4ak with or
without 1,2-phenyl shift
To gain insight into the reaction mechanism, especially
the deprotonative cyclization process, we tried to identify
reaction intermediates. A mixture of 1a and (E)-2f' reacted with
TFAA at –20 °C, and the reaction was quenched by methanolic
This concise construction of polycyclic skeletons
culminates in the two-step synthesis of dioxa[8]helicene
(Scheme 2). Treatment of naphthalenediol 1j with 2 equivalents
of alkenyl sulfoxide 2n derived from β-tetralone provided
tetrahydro-7,12-dioxa[8]helicene 3jn in 39% yield. Following
oxidation with DDQ furnished desired 7,12-dioxa[8]helicene
(5)3h in 34% yield over two steps.
KOH in
2-sulfanyl-2,3-dihydrobenzofuran
3
min. As
a
result,
4af'
a
96% yield of
was obtained
accompanied by a 4% yield of benzofuran 3af (Scheme 5a).
This implies that the departure of alkanethiol would be the
rate-determining step of the present annulation. The sluggish
departure would stem from the milder reactivity of alkenyl
sulfoxides than KDM. Indeed, the use of KDM invoked facile
departure of methanethiol even when the instant quench was
applied. The electron donation of the α-methylsulfanyl group
on KDM would facilitate the departure event.
OH
O
O
C12H25
S
3.0 equiv TFAA
+
CH2Cl2
40 °C, 1 h
O
OH
2n 2.0 equiv
3jn: 39%
1j
O
S
O
SMe
O
1.2 equiv 1a
Me
Me
1.2 equiv TFAA
Me
tBu
(a)
(b)
(c)
+
3af
3.3 equiv DDQ
Ph
CH2Cl2
4%a)
Ph
(E)-2f’
benzene
4af’: 96%a)
–20 °C, 3 min,
then KOH/MeOH
reflux, 4 h
(syn/anti = 1/18)
O
5: 86%
O
O
(34% from 1j)
SMe
Me
Me
Ph
S
same as above
Me
Scheme 2. Synthesis of 7,12-dioxa[8]helicene 5.
tBu
+
3af
Ph
9%a)
4af’: 74%a)
2f’ (E/Z = 1/18)
During the course of the investigation, we found that
acetonitrile as the solvent suppressed the departure of
alkanethiols. Treatment of 1a and (Z)-2a with TFAA in
acetonitrile stereoselectively furnished syn-4aa in 64% yield
accompanied by a 16% yield of 3aa. The lower reaction
temperature (0 °C) and the shorter reaction time (10 min) were
found to be effective for the formation of 4aa; the product was
obtained in 90% yield (Scheme 3). Acetonitrile might decrease
the acidity of the reaction system and disturb protonation of the
sulfanyl group.
(syn/anti = 4.7/1)
O
1.2 equiv 1d
O
Me
Ph
S
SMe
Ph
1.2 equiv TFAA
Ph
+
3da
I
CH2Cl2
Ph
8%
–20 °C, 3 min,
then KOH/MeOH
4da: 55% (syn)
(Z)-2a
Scheme
5.
Stereospecific
2-sulfanyl-2,3-dihydrobenzofurans 4. a) NMR yield.
synthesis
of
O
S
It is noteworthy that the formation of 4af' proceeded in a
diastereoselective fashion, and the anti-form was obtained
preferentially (Scheme 5a). In contrast, under the same
conditions, the use of (Z)-2f' afforded syn-4af' as the major
product (Scheme 5b). A similar trend was observed with the
reaction of (Z)-2a with 1d, and syn-4da was obtained in a
diastereoselective manner (Scheme 5c). The configuration of
syn-4da was confirmed by X-ray crystallographic analysis10 as
well as NMR analyses.
1.2 equiv 1a
O
Me
Ph
SMe
Ph
1.2 equiv TFAA
Ph
+
3aa
tBu
CH3CN
Ph
4aa: 90%
5%
0 °C, 10 min
(Z)-2a
Scheme 3. Synthesis of 2-sulfanyl-2,3-dihydrobenzofuran 4aa
in CH3CN.
2-Sulfanyl-2,3-dihydrobenzofuran 4ak obtained from
α-unsubstituted alkenyl sulfoxide 2k (Table 1, entry 12) could
be converted to the corresponding benzofuran 3ak with the aid
of TsOH in hot toluene (Scheme 4).9 Interestingly, when 4ak
was treated with Lewis acidic BF3·Et2O instead of TsOH in
CH2Cl2 at 25 °C, 1,2-phenyl shift proceeded concomitantly
with the departure of dodecanethiol to furnish
2-phenylbenzofuran 3ab albeit in moderate yield. Similar
A description on these cyclization processes is depicted in
Scheme 6 with (E)-2f' as a model substrate. Interrupted
Pummerer reaction and subsequent [3,3] sigmatropic
rearrangement would proceed with retention of the
stereochemistry affording intermediate D. Although the C1–C2
bond of D is potentially rotative, deprotonative cyclization
would occur faster to afford anti-4af' selectively. Through a

similar fast deprotonative cyclization, (Z)-2f' would be
converted to syn-4af' reflecting the (Z)-configuration of the
alkenyl sulfoxide.
spectra were determined on a Bruker micrOTOF II
spectrometer. Melting points were determined on a Stanford
Research Systems MPA100 melting point apparatus. PTLC
analyses were performed on commercial aluminium sheets
bearing
a 0.25-mm layer of Merck Silica gel 60F254.
O
1a
TFAA
Me
O
S
Me
H
Me
S
Purification was done by column chromatography using silica
gel (Wakosil® C-300) and preparative TLC using silica gel
(Merck 60PF254).
S
O
Me
Me C1
Me
H
[3,3]
H
interrupted
Pummerer
reaction
C2
Ph
H
D
Ph
Ph
All reactions were performed under nitrogen atmosphere.
Dehydrated acetonitrile, benzene, toluene and DMSO were
purchased from Wako Pure Chemical Industries, Ltd. and
stored under nitrogen atmosphere. Dehydrated CH2Cl2 were
purchased from KANTO CHEMICAL CO., INC. and stored
under nitrogen atmosphere. Unless otherwise noted, materials
obtained from commercial suppliers were used without further
purification. Alkenyl sulfoxides 2j'4a and 2l11 were prepared
according to the literature.
tBu
rotation of
C1–C2 bond
(E)-2f’
tBu
deprotonative
cyclization
fast
slow
Me
Me
MeS
O
O
O
MeS
Me
S
H
Me
Ph
syn-4af’
H
Ph
H
tBu
H
Ph
tBu
tBu
anti-4af’
major
deprotonative
cyclization
minor
Scheme 6. Description on stereospecific formation of 4af'
General Procedure for Oxidation of Alkenyl Sulfides
to Alkenyl Sulfoxides (GP1): m-Chloroperbenzoic acid
(contains ca. 30% H2O, 1.0 equiv) was added to a solution of
an alkenyl sulfide in CH2Cl2 (0.10 M) portionwise at 0 °C. The
resulting solution was stirred and gradually warmed to room
temperature. Progress of the oxidation was checked by TLC.
After completion of the reaction, saturated aqueous NaHCO3
was added to the reaction mixture and the resulting solution
was extracted with CH2Cl2 (30 mL × 3). The combined organic
layer was dried over Na2SO4 and concentrated under a reduced
pressure. The residue was purified by silica gel
chromatography with an eluent (hexane/EtOAc = 1/1) to give
the corresponding alkenyl sulfoxide.
Procedure for Preparation of Alkenyl Sulfoxides 2a
and 2f': Procedures described in the previous report12 were
used with some modifications. The synthesis of 2a is
representative. A 200-mL Schlenk tube was charged with
TEMPO (0.31 g, 2.0 mmol, 0.10 equiv), methyl mercaptan
sodium salt (ca. 15% in water, 11 mL, 24 mmol, 1.2 equiv) and
DMSO (100 mL). Diphenylacetylene (3.4 g, 20 mmol) was
then added and the resulting mixture was stirred at 85 °C for
2.5 h. After cooling the mixture, water (100 mL) was added and
the resulting biphasic solution was extracted with a mixture of
hexane/AcOEt (v/v = 40/1, 100 mL × 3). The combined organic
layer was washed with brine, dried over Na2SO4, and
On the other hand, (Z)-rich sulfoxide 2k preferably
provided the anti-form of 2-sulfanyl-2,3-dihydrofuran 4ak
(Table 1, entry 12). The absence of the α substituent would
facilitate rotation of the C1–C2 bond of intermediate E
(Scheme 7). The fast bond rotation leads E to E' to relieve the
steric repulsion between the thionium unit and the phenyl ring,
anti-4ak was thus obtained as the major product even from
(Z)-rich sulfoxide 2k.
O
1a
TFAA
C12H25
O
S
C12H25
Ph
C12H25
S
H
S
O
H
HC1
H
Ph
[3,3]
Ph
interrupted
Pummerer
reaction
C2
H
H
E
H
(Z)-2k
tBu
rotation of
C1–C2 bond
tBu
unfavorable
deprotonative
cyclization
fast
H
H
O
H
O
C12H25
S
H
O
C12H25
S
S
H
Ph
C12H25
Ph
tBu
Ph
syn-4ak
minor
tBu
H
H
anti-4ak
major
tBu
deprotonative
cyclization
E’
favorable
Scheme 7. Description on favorable formation of anti-4ak
concentrated under
a
reduced pressure to give
Conclusion
(Z)-1,2-diphenylvinyl methyl sulfide with some impurities.
Subsequent oxidation in accordance with GP1 provided (Z)-2a
(3.3 g, 14 mmol, 70%) as a white solid. With the same
procedures, (Z)-rich alkenyl sulfoxide 2f' was prepared.
General Procedure for Synthesis of Benzofurans
(GP2): The synthesis of 3aa is representative. A 10-mL
Schlenk flask was charged with 4-tert-butylphenol (1a, 36 mg,
0.24 mmol), 2a (49 mg, 0.20 mmol), and CH2Cl2 (2 mL). TFAA
(34 µL, 0.24 mmol) was added at 25 °C, and the resulting
mixture was stirred for 30 min. The mixture was filtered
through a pad of alumina and concentrated under reduced
We succeeded in applying general alkenyl sulfoxides to
the annulative synthesis of benzofurans via interrupted
Pumemrer/sigmatropic cascade. The improved method enabled
concise formation of furan-fused complex polycyclic skeletons,
which culminates in the two-step synthesis of
7,12-dioxa[8]helicene. The milder reactivity of alkenyl
sulfoxides than KDM has allowed isolation of
2-sulfanyl-2,3-dihydrobenzofurans, which unveiled the
aromatization by the departure of alkanethiol is the
rate-determining
step.
The
stereochemistry
proved that
of
the
2-sulfanyl-2,3-dihydrobenzofurans
pressure. Purification by preparative TLC (hexane/CH2Cl2
=
deprotonative cyclization reflects the configuration of the C–C
double bond and steric environment of alkenyl sulfoxides.
5/1) provided 3aa (56 mg, 0.17 mmol, 86%) as a white solid.
Synthesis of 7,12-dioxa[8]helicene
5 (Scheme 2):
According to GP2, 5,6,13,14-tetrahydro-7,12-dioxa[8]helicene
(3jn, 32 mg, 0.078 mmol, 39%) was synthesized from 1j (32
mg, 0.20 mmol) and 2n (0.14 g, 0.40 mmol, 2.0 equiv). A
solution of 3jn (39 mg, 0.095 mmol) and DDQ (70 mg, 0.31
mmol) in benzene (10 mL) was refluxed for 4 h. After cooling
the reaction mixture to room temperature, the mixture was
filtered through a pad of silica gel and concentrated under
reduced pressure. The residue was washed with hexane (30
mL) to give 5 (34 mg, 0.082 mmol, 86%) as a white solid.
Experimental
1
Instrumentation and Chemicals. H NMR (600 MHz)
and 13C NMR (151 MHz) spectra were taken on a JEOL
ECA-600 or JEOL ECZ-600 spectrometer. Chemical shifts (δ)
are reported in parts per million in CDCl3 relative to residual
1
CHCl3 at 7.26 ppm for H and relative to CDCl3 at 77.16 ppm
for 13C, and in dichloromethane-d2 relative to CDHCl2 at 5.32
ppm for 1H and relative to CD2Cl2 at 53.84 ppm for 13C. Mass

Procedure
for
Synthesis
of
6.83 (s, 1H), 2.57 (ddd, J = 13.2, 10.2, 6.0 Hz, 1H), 2.40 (ddd,
J = 13.2, 10.2, 6.0 Hz, 1H), 1.69–1.75 (m, 1H), 1.56–1.63 (m,
1H), 1.22–1.36 (m, 18H), 0.88 (t, J = 6.9 Hz, 3H); 13C NMR
(CDCl3) δ 144.79, 129.98, 129.73, 129.22, 128.62, 122.47,
51.77, 32.04, 29.72 (2C), 29.62, 29.47, 29.43, 29.25, 28.61,
22.83, 21.38, 14.25. HRMS (APCI-MS, positive): m/z =
355.1861. Calcd for C20H3235ClOS: 355.1857 [M+H]+.
2-Ethoxycarbonyl-1-phenylvinyl dodecyl sulfoxide (2d,
E/Z = 17:83): 2-Ethoxycarbonyl-1-phenylvinyl dodecyl sulfide
was synthesized via procedures similar in the previous report15
and was oxidized into 2d according to GP1. Orange oil. The
configuration of the olefin moiety was determined by NOESY
analysis. 1H NMR (CDCl3) δ 7.40–7.46 (m, 5H), 6.61 (s, 0.17 ×
1H), 6.31 (s, 0.83 × 1H), 4.26 (q, J = 7.2 Hz, 0.83 × 2H),
4.07–4.14 (m, 0.17 × 2H), 2.90–2.99 (m, 0.83 × 2H), 2.55 (ddd,
J = 14.6, 8.7, 4.6 Hz, 0.17 × 1H), 2.34 (ddd, J = 14.6, 8.7, 4.6
Hz, 0.17 × 1H), 1.74–1.86 (m, 2H), 1.33 (t, J = 7.2 Hz, 0.83 ×
3H), 1.21–1.52 (m, 18H), 1.15 (t, J = 7.2 Hz, 0.17 × 3H), 0.88
(t, J = 7.2 Hz, 3H); 13C NMR (CDCl3) for the major isomer δ
164.52, 131.83, 130.01, 129.52, 128.88, 128.33, 122.89, 61.55,
54.96, 32.05, 29.75 (2C), 29.69, 29.50, 29.48, 29.39, 28.78,
23.70, 22.83, 14.34, 14.25. HRMS (APCI-MS, positive): m/z =
393.2462. Calcd for C23H37O3S: 393.2458 [M+H]+.
2-Methylsulfanyl-2,3-dihydrobenzofuran 4aa in CH3CN
Solvent (Scheme 3): A 10-mL Schlenk flask was charged with
1a (36 mg, 0.24 mmol), 2a (48 mg, 0.20 mmol), and
acetonitrile (2 mL). Trifluoroacetic anhydride (34 µL, 0.24
mmol) was added at 0 °C, and the resulting mixture was stirred
for 10 min. The mixture was filtered through a pad of alumina
and concentrated under reduced pressure. Purification by
preparative TLC (hexane/CH2Cl2 = 20/1) provided 4aa (67 mg,
0.18 mmol, 90%) as colorless oil.
Conversion of 2-Sulfanyl-2,3-dihydrobenzofuran 4ak
to Benzofuran 3ak by TsOH (Scheme 4): To a solution of 4ak
(88 mg, 0.19 mmol) in toluene (2 mL), TsOH·H2O (76 mg,
0.40 mmol) was added. The mixture was heated in an oil bath
at 120 °C for 3 h, and then was allowed to cool to room
temperature. The mixture was filtered through a pad of alumina
and concentrated under reduced pressure. Purification by
preparative TLC (hexane/CH2Cl2= 20/1) provided 3ak (45 mg,
0.18 mmol, 92%) as pale yellow oil.
Conversion of Dihydrobenzofuran 4ak to Benzofuran
3ab by BF3·Et2O via 1,2-phenyl shift (Scheme 4): To a
solution of 4ak (91 mg, 0.20 mmol) in CH2Cl2 (2 mL),
BF3·Et2O (30 µL, 0.24 mmol) was added. The mixture was
stirred at 25 °C for 5 h. After the reaction, saturated aqueous
NaHCO3 (10 mL) was added and the resulting mixture was
extracted with AcOEt (10 mL × 3). The combined organic layer
was washed with brine, dried over Na2SO4, and concentrated
under reduced pressure. Purification by preparative TLC
(hexane/CH2Cl2 = 20/1) provided 3ab (22 mg, 0.086 mmol,
43%) as a white solid.
Procedure for Short-Time Reaction (Scheme 5): The
synthesis of 4da (Scheme 5c) is representative. A solution of
4-iodophenol (53 mg, 0.24 mmol) and 2a (48 mg, 0.20 mmol)
in CH2Cl2 (5 mL) was placed in a flask. TFAA (34 µL, 0.24
mmol) was then added at –20 °C. After 3 min, a KOH solution
in MeOH (0.5 M, 4 mL) was added at –20 °C with stirring.
Water (15 mL) was then added and the resulting biphasic
solution was extracted with EtOAc (15 mL × 3). The combined
organic layer was washed with brine, dried over Na2SO4, and
concentrated under reduced pressure. Purification by
preparative TLC (hexane/CH2Cl2 = 10/1) provided 4da (49 mg,
0.11 mmol, 55%) as a white solid.
(Z)-1-Ethoxycarbonyl-2-phenylvinyl dodecyl sulfoxide
(2e): Via procedures similar in the previous report,15
(Z)-1-ethoxycarbonyl-2-phenylvinyl dodecyl sulfide was
synthesized, and oxidized into 2e according to GP1. Yellow
1
solid. m.p. = 52.5–54.3 °C. H NMR (CDCl3) δ 8.10 (s, 1H),
7.49–7.51 (m, 2H), 7.40–7.44 (m, 3H), 4.35–4.44 (m, 2H), 3.58
(ddd, J = 12.6, 9.6, 5.4 Hz, 1H), 3.12 (ddd, J = 12.6, 7.2, 9.6 Hz,
1H), 1.67–1.77 (m, 2H), 1.43 (t, J = 7.8 Hz, 3H), 1.24–1.47 (m,
18H), 0.88 (t, J = 6.9 Hz, 3H); 13C NMR (CDCl3) δ 163.29,
148.62, 135.41, 132.48, 131.24, 130.83, 128.68, 62.15, 52.51,
32.04, 29.74 (2C), 29.66, 29.50 (2C), 29.31, 28.95, 23.87,
22.83, 14.41, 14.25. HRMS (APCI-MS, positive): m/z =
393.2462. Calcd for C23H37O3S: 393.2458 [M+H]+.
Dodecyl (Z)-1-methyl-2-phenylvinyl sulfoxide (2f): Via
procedures similar in the previous report,12 dodecyl
(Z)-1-methyl-2-phenylvinyl sulfide was synthesized, and
oxidized into 2f according to GP1. White solid. m.p. =
1
51.8–53.0 °C. H NMR (CDCl3) δ 7.34 (t, J = 7.2 Hz, 2H),
7.25–7.30 (m, 3H), 6.92 (s, 1H), 2.89 (dt, Jd = 13.2, Jt = 7.2 Hz,
1H), 2.62 (dt, Jd = 13.2, Jt = 7.2 Hz, 1H), 2.20 (s, 3H),
1.62–1.68 (m, 2H), 1.23–1.41 (m, 18H), 0.88 (t, J = 7.2 Hz,
3H); 13C NMR (CDCl3) δ 142.01, 135.20, 134.59, 129.45,
128.50, 128.24, 51.77, 32.04, 29.73 (2C), 29.65, 29.47 (2C),
29.29, 28.89, 23.26, 22.82, 14.24, 13.76. HRMS (APCI-MS,
positive): m/z = 335.2411. Calcd for C21H35OS: 335.2403
[M+H]+.
1-Methyl-2-phenylvinyl methyl sulfoxide (2f', E/Z =
26:74): (For E isomer): Yellow oil. 1H NMR (CDCl3) δ
7.38–7.40 (m, 4H), 7.31–7.34 (m, 1H), 7.14 (d, J = 1.4 Hz, 1H),
2.62 (s, 3H), 2.15 (d, J = 1.4 Hz, 3H); 13C NMR (CDCl3) δ
141.31, 134.82, 130.42, 129.36, 128.72, 128.47, 39.12, 11.26.
HRMS (APCI-MS, positive): m/z = 181.0688. Calcd for
C10H13OS: 181.0682 [M+H]+. (For Z isomer): Yellow solid. 1H
NMR (CDCl3) δ 7.34–7.37 (m, 2H), 7.29–7.32 (m, 1H), 7.22 (d,
J = 7.1 Hz, 2H), 6.91 (s, 1H), 2.62 (s, 3H), 2.24 (d, J = 1.7 Hz,
3H); 13C NMR (CDCl3) δ 142.91, 134.67, 134.42, 129.43,
128.54, 128.37, 37.69, 13.05. HRMS (APCI-MS, positive): m/z
= 181.0691. Calcd for C10H13OS: 181.0682 [M+H]+.
Characterization Data
(Z)-1,2-Diphenylvinyl methyl sulfoxide (2a): White
solid. m.p. = 90.5–94.3 °C. H NMR (CDCl3) δ 7.59–7.61 (m,
2H), 7.37–7.45 (m, 8H), 7.19 (s, 1H), 2.46 (s, 3H); 13C NMR
(CDCl3) δ 144.83, 139.07, 134.43, 134.05, 130.01, 129.45,
129.02, 128.99, 128.55, 128.51, 37.92. HRMS (APCI-MS,
positive): m/z = 243.0845. Calcd for C15H15OS: 243.0838
[M+H]+.
1
Dodecyl 1-phenylvinyl sulfoxide (2b): Dodecyl
1-phenylvinyl sulfide was synthesized via procedures similar in
the previous report13 and was oxidized into 2b according to
1
GP1. Orange oil. H NMR (CDCl3) δ 7.35–7.41 (m, 5H), 6.02
(s, 1H), 5.99 (s, 1H), 2.61 (ddd, J = 12.8, 10.2, 6.0 Hz, 1H),
2.36 (ddd, J = 12.8, 10.2, 6.0 Hz, 1H), 1.71–1.77 (m, 1H),
1.55–1.61 (m, 1H), 1.21–1.36 (m, 18H), 0.87 (t, J = 7.2 Hz,
3H); 13C NMR (CDCl3) δ 152.57, 134.33, 129.40, 129.22,
126.74, 117.25, 51.81, 32.03, 29.71 (2C), 29.61, 29.44 (2C),
29.25, 28.63, 22.80, 21.59, 14.23. HRMS (APCI-MS, positive):
m/z = 321.2249. Calcd for C20H33OS: 321.2247 [M+H]+.
(E)-2-Chloro-1-phenylvinyl dodecyl sulfoxide (2c):
Via procedures similar in the previous report,14
(E)-2-chloro-1-phenylvinyl dodecyl sulfide was synthesized,
and oxidized into 2c according to GP1. Yellow oil. H NMR
(CDCl3) δ 7.41–7.47 (m, 3H), 7.36 (dd, J = 7.9, 1.7 Hz, 2H),
(Z)-1-Butyl-2-phenylvinyl dodecyl sulfoxide (2g): Via
procedures
similar
in
the
previous
report,12
(Z)-1-butyl-2-phenylvinyl dodecyl sulfide was synthesized, and
oxidized into 2g according to GP1. Colorless oil. The
configuration of the olefin moiety was confirmed by NOESY
1

analysis. 1H NMR (CDCl3) δ 7.34 (t, J = 7.2 Hz, 2H),
7.25–7.29 (m, 3H), 6.86 (s, 1H), 2.84 (dt, Jd = 12.8, Jt = 7.2 Hz,
1H), 2.68–2.69 (m, 1H), 2.58 (dt, Jd = 12.8, Jt = 7.2 Hz, 1H),
2.39–2.46 (m, 1H), 1.62–1.69 (m, 4H), 1.46–1.50 (m, 2H),
1.22–1.37 (m, 18H), 0.98 (t, J = 7.5 Hz, 3H), 0.88 (t, J = 7.2 Hz,
3H); 13C NMR (CDCl3) δ 146.65, 134.83, 133.42, 129.46,
128.51, 128.11, 52.55, 32.05, 31.60, 29.74 (2C), 29.66, 29.48
(2C), 29.28, 28.82, 25.93, 23.36, 22.83, 22.69, 14.25, 14.12.
HRMS (APCI-MS, positive): m/z = 377.2876. Calcd for
C24H41OS: 377.2873 [M+H]+.
0.09 × 2H), 2.75 (ddd, J = 13.9, 7.4, 5.7 Hz, 0.91 × 1H),
1.72–1.80 (m, 2H), 1.25–1.49 (m, 18H), 0.88 (t, J = 6.9 Hz,
3H); 13C NMR (CDCl3) for major isomer δ 139.19, 135.82,
134.12, 129.84, 129.48, 128.76, 54.45, 32.03, 29.73 (2C), 29.66,
29.47 (2C), 29.33, 28.95, 22.82, 22.65, 14.24. HRMS
(APCI-MS, positive): m/z = 321.2241. Calcd for C20H33OS:
321.2247 [M+H]+.
Cyclohexylidene(phenyl)methyl dodecyl sulfoxide
(2m): Cyclohexylidene(phenyl)methyl dodecyl sulfide was
synthesized via procedures similar in the previous report4a and
was oxidized into 2m according to GP1. White solid. m.p. =
66.7–68.0 °C. 1H NMR (CD2Cl2) δ 7.36–7.40 (m, 3H),
7.16–7.28 (brs, 2H), 2.65–2.71 (m, 2H), 2.43 (ddd, J = 12.6,
9.0, 6.0 Hz, 1H), 2.29 (ddd, J = 12.6, 9.0, 6.0 Hz, 1H),
1.99–2.12 (m, 2H), 1.77–1.82 (m, 1H), 1.45–1.62 (m, 7H),
1.26–1.36 (m, 18H), 0.88 (t, J = 6.9 Hz, 3H); 13C NMR
(CD2Cl2) δ 152.41, 135.71, 132.27, 131.53, 128.27, 128.20,
51.68, 34.03, 32.34, 31.10, 30.03 (2C), 29.94, 29.78, 29.76,
29.64, 29.27, 28.76, 28.69, 26.77, 23.39, 23.11, 14.28. HRMS
(APCI-MS, positive): m/z = 389.2878. Calcd for C25H41OS:
389.2873 [M+H]+.
3,4-Dihydronaphthalen-2-yl dodecyl sulfoxide (2n):
3,4-Dihydronaphthalen-2-yl dodecyl sulfide was synthesized
via procedures similar in the previous report4a and was oxidized
into 2n according to GP1. Yellow solid. m.p. = 43.3–44.0 °C.
1H NMR (CDCl3) δ 7.21–7.25 (m, 2H), 7.16–7.18 (m, 2H),
7.06 (s, 1H), 2.92–3.01 (m, 2H), 2.69–2.79 (m, 2H), 2.54–2.59
(m, 1H), 2.37–2.42 (m, 1H), 1.64–1.77 (m, 2H), 1.25–1.47 (m,
18H), 0.88 (t, J = 6.9 Hz, 3H); 13C NMR (CDCl3) δ 141.73,
135.63, 132.12, 129.77, 129.13, 127.85, 127.64, 127.21, 51.53,
32.04, 29.73 (2C), 29.66, 29.51, 29.47, 29.35, 28.93, 28.01,
22.83, 22.23, 20.33, 14.25. HRMS (APCI-MS, positive): m/z =
347.2403. Calcd for C22H35OS: 347.2403 [M+H]+.
1-Benzyl-2-phenylvinyl dodecyl sulfoxide (2h, E/Z =
30:70): Via procedures similar in the previous report,16 (Z)-rich
1-benzyl-2-phenylvinyl dodecyl sulfide was synthesized and
oxidized into 2h according to GP1. Yellow solid. The
configuration of the olefin moiety was confirmed by NOESY
1
analysis. H NMR (CDCl3) δ 7.42 (d, J = 7.2 Hz, 0.30 × 2H),
7.39 (s, 0.30 × 1H), 7.29–7.37 (m, 6H), 7.28 (d, J = 7.8 Hz,
0.70 × 2H), 7.23 (d, J = 7.8 Hz, 0.30 × 2H), 7.20 (d, J = 7.2 Hz,
0.70 × 2H), 6.65 (s, 0.70 × 1H), 4.06 (d, J = 16.8 Hz, 0.30 ×
1H), 4.00 (d, J = 16.5 Hz, 0.70 × 1H), 3.84 (d, J = 16.8 Hz,
0.30 × 1H), 3.82 (dd, J = 16.5, 1.8 Hz, 0.70 × 1H), 2.82 (ddd, J
= 13.2, 7.2 Hz, 6.6 Hz, 0.70 × 1H), 2.64 (ddd, J = 13.2, 10.5,
6.0 Hz, 0.30 × 1H), 2.59 (dt, Jd = 13.2, Jt = 7.8 Hz, 0.70 × 1H),
2.46 (ddd, J = 13.2, 9.6, 4.8 Hz, 0.30 × 1H), 1.62–1.76 (m, 2H),
1.22–1.34 (m, 18H), 0.88 (t, J = 6.6 Hz, 3H); 13C NMR
(CDCl3) for the major isomer δ 145.85, 138.30, 136.06, 134.51,
129.86, 129.48, 128.90, 128.49, 128.35, 126.91, 52.60, 32.31,
32.06, 29.75 (2C), 29.66, 29.49 (2C), 29.26, 28.79, 23.40,
22.84, 14.26. HRMS (APCI-MS, positive): m/z = 411.2720.
Calcd for C27H39OS: 411.2716 [M+H]+.
Dodecyl 4-nonen-5-yl sulfoxide (2i, isomeric ratio =
42:58): Dodecyl 4-nonen-5-yl sulfide was synthesized via
procedures similar in the previous report4a and was oxidized
1
into 2i according to GP1. Colorless oil. H NMR (CDCl3) δ
5-tert-Butyl-2,3-diphenylbenzofuran (3aa): White solid
1
6.13 (t, J = 7.5 Hz, 0.42 × 1H), 5.83 (t, J = 7.5 Hz, 0.58 × 1H),
2.84 (ddd, J = 13.9, 8.1, 4.6 Hz, 0.58 × 1H), 2.68 (ddd, J = 14.6,
8.4, 5.0 Hz, 0.42 × 1H), 2.45–2.56 (m, 0.42 × 1H, 0.58 × 2H),
2.33–2.39 (m, 1H), 2.17–2.24 (m, 0.42 × 2H, 0.58 × 1H),
2.04–2.14 (m, 1H), 1.25–1.70 (m, 26H), 0.90–0.95 (m, 6H),
0.88 (t, J = 6.9 Hz, 3H); 13C NMR (CDCl3) mixture of isomers
δ 143.28, 142.26, 135.51, 133.72, 52.38, 52.24, 32.05, 31.83,
31.26, 30.26, 30.19, 29.74, 29.68, 29.51, 29.48, 29.40, 29.36,
29.00, 28.92, 25.32, 24.98, 23.27, 22.90, 22.84, 22.83, 22.63,
22.42, 22.38, 14.25, 14.09, 13.98, 13.91, 13.79 (nine of the
aliphatic signals contain overlapping). HRMS (APCI-MS,
positive): m/z = 343.3028. Calcd for C21H43OS: 343.3029
[M+H]+.
1-Cyclohexenyl dodecyl sulfoxide (2j): 1-Cyclohexenyl
dodecyl sulfide was synthesized via procedures similar in the
previous report4a and was oxidized into 2j according to GP1.
Colorless oil. 1H NMR (CDCl3) δ 6.41–6.42 (m, 1H),
2.62–2.70 (m, 2H), 2.26–2.30 (m, 1H), 2.20–2.24 (m, 2H),
2.03–2.08 (m, 1H), 1.68–1.81 (m, 3H), 1.60–1.67 (m, 3H),
1.25–1.46 (m, 18H), 0.87 (t, J = 6.9 Hz, 3H); 13C NMR
(CDCl3) δ 140.91, 132.70, 51.10, 32.03, 29.73 (2C), 29.66,
29.50, 29.46, 29.35, 28.92, 25.67, 22.81, 22.47, 22.36, 22.16,
20.58, 14.23. HRMS (APCI-MS, positive): m/z = 299.2403.
Calcd for C18H35OS: 299.2403 [M+H]+.
(56 mg, 0.17 mmol, 86%). m.p. = 136.2–137.7 °C. H NMR
(CDCl3) δ 7.66 (d, J = 7.1 Hz, 2H), 7.50–7.55 (m, 6H), 7.44 (t,
J = 7.1 Hz, 2H), 7.30–7.34 (m, 3H), 1.39 (s, 9H); 13C NMR
(CDCl3) δ 152.40, 150.91, 146.26, 133.22, 131.00, 129.98,
129.93, 129.15, 128.52, 128.33, 127.69, 127.13, 122.85, 117.86,
116.10, 110.58, 34.95, 32.01. HRMS (APCI-MS, positive): m/z
= 326.1669. Calcd for C24H22O: 326.1665 [M]+.
5-tert-Butyl-2-phenylbenzofuran (3ab): White solid (33
mg, 0.13 mmol, 65%). m.p. = 102.5–105.1 °C. 1H NMR
(CDCl3) δ 7.86 (d, J = 8.2 Hz, 2H), 7.59 (s, 1H), 7.43–7.46 (m,
3H), 7.35–7.37 (m, 2H), 7.00 (s, 1H), 1.40 (s, 9H); 13C NMR
(CDCl3) δ156.18, 153.29, 146.13, 130.85, 129.04, 128.90,
128.51, 125.00, 122.40, 117.23, 110.58, 101.64, 34.87, 32.00.
HRMS (APCI-MS, positive): m/z = 250.1359. Calcd for
C18H18O: 250.1352 [M]+. All the resonances in 1H and 13C
NMR spectra were consistent with the reported values.17
5-tert-Butyl-3-chloro-2-phenylbenzofuran
(3ac):
1
Colorless oil (26 mg, 0.092 mmol, 46%). H NMR (CDCl3) δ
8.14 (d, J = 7.5 Hz, 2H), 7.59 (s, 1H), 7.50 (t, J = 7.5 Hz, 2H),
7.43–7.43 (m, 2H), 7.40 (t, J = 7.5 Hz, 1H), 1.42 (s, 9H); 13C
NMR (CDCl3) δ 151.11, 149.14, 146.89, 129.63, 128.88,
128.76, 127.80, 126.34, 123.76, 115.12, 110.92, 108.27, 35.03,
31.94. HRMS (APCI-MS, positive): m/z = 284.0976. Calcd for
C18H1735ClO: 284.0962 [M]+.
Dodecyl 2-phenylvinyl sulfoxide (2k, E/Z = 9:91): Via
procedures similar in the previous report,12 (Z)-rich dodecyl
2-phenylvinyl sulfide was synthesized, and oxidized into 2k
according to GP1. White solid. 1H NMR (CDCl3) δ 7.47 (d, J =
6.9 Hz, 0.09 × 2H), 7.35–7.42 (m, 0.91 × 5H, 0.09 × 3H), 7.24
(d, J = 15.1 Hz, 0.09 × 1H), 7.08 (d, J = 10.6 Hz, 0.91 × 1H),
6.83 (d, J = 15.1 Hz, 0.09 × 1H), 6.41 (d, J = 10.6 Hz, 0.91 ×
1H), 2.92 (ddd, J = 13.9, 7.4, 5.7 Hz, 0.91 × 1H), 2.78–2.85 (m,
5-tert-Butyl-3-ethoxycarbonyl-2-phenylbenzofuran
(3ad): Pale yellow oil (32 mg, 0.10 mmol, 50%). 1H NMR
(CDCl3) δ 8.13 (s, 1H), 8.02 (d, J = 7.5 Hz, 2H), 7.43–7.51 (m,
5H), 4.42 (q, J = 7.1 Hz, 2H), 1.43 (t, J = 7.1 Hz, 3H), 1.43 (s,
9H); 13C NMR (CDCl3) δ 164.30, 161.00, 152.22, 147.24,
130.24, 129.95, 129.61, 128.16, 126.91, 123.32, 118.91, 110.57,
109.11, 60.68, 35.05, 31.94, 14.34. HRMS (APCI-MS,
positive): m/z = 322.1567. Calcd for C21H22O3: 322.1563 [M]+.

1
All the resonances in 1H and 13C NMR spectra were consistent
with the reported values.18
(56 mg, 0.16 mmol, 80%). m.p. = 131.3–134.5 °C. H NMR
(CDCl3) δ 7.65–7.67 (m, 2H), 7.62 (t, J = 1.2 Hz, 1H),
7.48–7.51 (m, 4H), 7.43–7.46 (m, 3H), 7.32–7.35 (m, 3H); 13C
NMR (CDCl3) δ 152.85, 151.89, 132.41, 132.23, 130.24,
129.79, 129.27, 128.89, 128.63, 128.09, 127.66, 127.19, 122.80,
117.10, 116.24, 112.73. HRMS (APCI-MS, positive): m/z
=348.0144. Calcd for C20H1379BrO: 348.0144 [M]+.
5-Iodo-2,3-diphenylbenzofuran (3da): White solid (55
mg, 0.14 mmol, 73%). m.p. = 162.2–164.8 °C. 1H NMR
(CDCl3) δ 7.80 (d, J = 1.4 Hz, 1H), 7.63–7.65 (m, 2H), 7.60
(dd, J = 8.5, 1.4 Hz, 1H), 7.42–7.50 (m, 5H), 7.31–7.34 (m,
4H); 13C NMR (CDCl3) δ 153.47, 151.47, 133.35, 133.07,
132.23, 130.19, 129.82, 129.28, 128.95, 128.88, 128.64, 128.09,
127.19, 116.77, 113.29, 86.61. HRMS (APCI-MS, positive):
m/z = 396.0007. Calcd for C20H13IO: 396.0006 [M]+.
5-tert-Butyl-2-methyl-3-phenylbenzofuran (3af): Pale
1
yellow oil (42 mg, 0.16 mmol, 81%). H NMR (CDCl3) δ 7.62
(d, J = 1.7 Hz, 1H), 7.53–7.57 (m, 4H), 7.40–7.44 (m, 2H),
7.38 (dd, J = 8.6, 1.7 Hz, 1H), 2.56 (s, 3H), 1.41 (s, 9H); 13C
NMR (CDCl3) δ 152.38, 151.62, 145.88, 133.26, 129.14,
128.93, 128.47, 127.01, 121.53, 117.16, 115.56, 110.18, 34.91,
32.07, 12.97. HRMS (APCI-MS, positive): m/z =264.1519.
Calcd for C19H20O: 264.1509 [M]+.
5-tert-Butyl-2-butyl-3-phenylbenzofuran
(3ag):
1
Colorless oil (51 mg, 0.17 mmol, 83%). H NMR (CDCl3) δ
7.54 (s, 1H), 7.50–7.50 (m, 4H), 7.39–7.41 (m, 2H), 7.34 (d, J
= 8.5 Hz, 1H), 2.84 (t, J = 7.7 Hz, 2H), 1.72–1.77 (m, 2H),
1.37–1.40 (m, 2H), 1.37 (s, 9H), 0.91 (t, J = 7.7 Hz, 3H); 13C
NMR (CDCl3) δ 155.69, 152.34, 145.83, 133.28, 129.29,
128.89, 128.58, 127.03, 121.51, 117.03, 115.64, 110.25, 34.91,
32.06, 30.71, 26.65, 22.57, 13.94. HRMS (APCI-MS, positive):
m/z =306.1976. Calcd for C22H26O: 306.1978 [M]+.
2-Methyl-3-phenyl-5-(trifluoromethyl)benzofuran
1
(3ef): Pale yellow oil (23 mg, 0.082 mmol, 41%). H NMR
(CDCl3) δ 7.84 (s, 1H), 7.48–7.54 (m, 6H), 7.41 (t, J = 7.3 Hz,
1H), 2.57 (s, 3H); 13C NMR (CDCl3) δ 155.51, 153.38, 131.88,
129.07, 128.98, 127.56, 125.46 (q, J = 31.9 Hz), 124.85 (q, J =
272.0 Hz), 120.84 (q, J = 4.4 Hz), 117.35, 117.08 (q, J = 4.4
Hz), 111.36, 111.17, 12.91. HRMS (APCI-MS, positive): m/z =
276.0753. Calcd for C16H11F3O: 276.0757 [M]+.
2-Benzyl-5-tert-butyl-3-phenylbenzofuran
(3ah):
Yellow oil (57 mg, 0.17 mmol, 84%). 1H NMR (CDCl3) δ 7.58
(d, J = 1.4 Hz, 1H), 7.49–7.54 (m, 4H), 7.39–7.41 (m, 2H),
7.36 (dd, J = 8.6, 1.4 Hz, 1H), 7.28–7.31 (m, 2H), 7.21–7.26 (m,
3H), 4.20 (s, 2H), 1.37 (s, 9H); 13C NMR (CDCl3) δ 152.92,
152.72, 146.04, 138.19, 132.90, 129.28, 129.02, 128.72, 128.63,
128.40, 127.37, 126.66, 122.00, 118.60, 115.93, 110.58, 34.94,
33.05, 32.05. HRMS (APCI-MS, positive): m/z =340.1822.
Calcd for C25H24O: 340.1822 [M]+.
8-Methoxy-1,2,3,4-tetrahydrodibenzo[b,d]furan (3fj):
Orange oil (35 mg, 0.17 mmol, 86%). H NMR (CDCl3) δ 7.28
1
(d, J = 8.2 Hz, 1H), 6.87 (d, J = 2.7 Hz, 1H), 6.79 (dd, J = 8.2,
2.7 Hz, 1H), 3.84 (s, 3H), 2.72 (tt, J = 6.0, 2.1 Hz, 2H), 2.60 (tt,
J = 6.0, 2.1 Hz, 2H), 1.91–1.95 (m, 2H), 1.82–1.86 (m, 2H);
13C NMR (CDCl3) δ 155.80, 155.14, 149.35, 129.55, 113.11,
111.20, 111.09, 101.73, 56.13, 23.70, 23.08, 22.83, 20.64.
HRMS (APCI-MS, positive): m/z = 202.0993. Calcd for
C13H14O2: 202.0988 [M]+. All the resonances in H and 13C
NMR spectra were consistent with the reported values.19
2,3,7-Triphenylbenzofuran (3ga): White solid (53 mg,
0.15 mmol, 76%). m.p. = 156.9–158.3 °C. H NMR (CDCl3) δ
7.99 (dd, J = 8.2, 1.0 Hz, 2H), 7.67 (dd, J = 8.0, 1.0 Hz, 2H),
7.54–7.57 (m, 4H), 7.49–7.52 (m, 3H), 7.47 (dd, J = 7.8, 1.0 Hz,
1H), 7.44 (td, J = 7.4, 1.0 Hz, 2H), 7.28–7.35 (m, 4H); 13C
NMR (CDCl3) δ 151.26, 150.79, 136.69, 133.00, 131.28,
130.75, 129.99, 129.16, 128.81, 128.58, 128.51, 127.86, 127.78,
127.13, 125.39, 124.41, 123.68, 119.37, 117.80, (one of these
aromatic signals contains overlapping). HRMS (APCI-MS,
positive): m/z = 347.1428. Calcd for C26H19O: 347.1430
[M+H]+.
5-tert-Butyl-2-butyl-3-propylbenzofuran
(3ai):
1
Colorless oil (39 mg, 0.14 mmol, 72%). H NMR (CDCl3) δ
7.43 (s, 1H), 7.31 (d, J = 8.5 Hz, 1H), 7.26 (d, J = 8.5 Hz, 1H),
2.71 (t, J = 7.6 Hz, 2H), 2.59 (t, J = 7.5 Hz, 2H), 1.65–1.69 (m,
4H), 1.35–1.41 (m, 2H), 1.38 (s, 9H), 0.98 (t, J = 7.5 Hz, 3H),
0.94 (t, J = 7.6 Hz, 3H); 13C NMR (CDCl3) δ 154.99, 152.23,
144.98, 129.54, 120.80, 115.19, 114.33, 109.99, 34.80, 32.10,
30.73, 26.25, 25.74, 23.26, 22.53, 14.28, 14.02. HRMS
(APCI-MS, positive): m/z =272.2129. Calcd for C19H28O:
272.2135 [M]+.
1
1
8-tert-Butyl-1,2,3,4-tetrahydrodibenzo[b,d]furan (3aj):
White solid (40 mg, 0.18 mmol, 89%). m.p. = 53.9–55.4 °C. 1H
NMR (CDCl3) δ 7.43 (s, 1H), 7.35 (d, J = 8.8 Hz, 1H), 7.29 (d,
J = 8.8 Hz, 1H), 2.74–2.76 (m, 2H), 2.65–2.67 (m, 2H),
1.94–1.98 (m, 2H), 1.85–1.89 (m, 2H), 1.41 (s, 9H); 13C NMR
(CDCl3) δ 154.27, 152.62, 145.30, 128.57, 120.82, 114.67,
113.00, 110.14, 34.82, 32.08, 23.62, 23.15, 22.88, 20.66.
HRMS (APCI-MS, positive): m/z =228.1512. Calcd for
C16H20O: 228.1509 [M]+. All the resonances in 1H and 13C
NMR spectra were consistent with the reported values.19
5-tert-Butyl-3-phenylbenzofuran (3ak): Pale yellow oil
(45 mg, 0.18 mmol, 92%). 1H NMR (CDCl3) δ 7.84 (d, J = 2.1
Hz, 1H), 7.77 (s, 1H), 7.67 (d, J = 6.9 Hz, 2H), 7.52 (t, J = 6.9
Hz, 2H), 7.50 (d, J = 8.9 Hz, 1H), 7.45 (dd, J = 8.9, 2.1 Hz,
1H), 7.41 (t, J = 6.9 Hz, 1H), 1.42 (s, 9H); 13C NMR (CDCl3) δ
154.19, 146.28, 141.68, 132.49, 129.15, 127.75, 127.51, 126.24,
122.68, 122.57, 116.46, 111.20, 34.99, 32.06. HRMS
(APCI-MS, positive): m/z =251.1422. Calcd for C18H19O:
251.1430 [M+H]+.
6-Isopropyl-2,3-diphenylbenzofuran
/
4-isopropyl-2,3-diphenylbenzofuran (3ha/3ha'
=
11/1):
1
Colorless oil (53 mg, 0.17 mmol, 87%). H NMR (CDCl3) for
major isomer δ 7.65 (dd, J = 8.2, 1.4 Hz, 2H), 7.51 (dd, J = 8.2,
1.4 Hz, 2H), 7.47 (t, J = 8.2 Hz, 2H), 7.45 (d, J = 1.0 Hz, 1H),
7.40–7.43 (m, 2H), 7.28–7.33 (m, 3H), 7.15 (dd, J = 8.2, 1.0 Hz,
1H), 3.07 (sep, J = 6.8 Hz, 1H), 1.35 (d, J = 6.8 Hz, 6H); 13C
NMR (CDCl3) for major isomer δ 154.56, 150.28, 146.67,
133.23, 131.03, 129.88, 129.07, 128.53, 128.32, 128.26, 127.67,
127.01, 122.17, 119.79, 117.59, 108.71, 34.55, 24.52. HRMS
(APCI-MS, positive): m/z = 312.1510. Calcd for C23H20O:
312.1509 [M]+.
2,3-Diphenylnaphtho[2,1-b]furan (3ia): White solid (57
mg, 0.18 mmol, 89%). m.p. = 103.3–106.1 °C. 1H NMR
(CDCl3) δ 7.93 (d, J = 8.2 Hz, 1H), 7.76 (q, J = 8.7 Hz, 2H),
7.55–7.58 (m, 8H), 7.40 (t, J = 7.5 Hz, 1H), 7.25–7.30 (m, 4H);
13C NMR (CDCl3) δ 151.56, 150.24, 134.87, 131.08, 131.03,
130.73, 129.54, 129.09, 128.55, 128.50, 128.35, 127.93, 126.36,
126.12, 124.40, 123.79, 123.22, 119.71, 112.35 (one of these
aromatic signals contains overlapping). HRMS (APCI-MS,
positive): m/z = 320.1192. Calcd for C24H16O: 320.1196 [M]+.
All the resonances in 1H and 13C NMR spectra were consistent
5-Chloro-2,3-diphenylbenzofuran (3ba): White solid
1
(39 mg, 0.13 mmol, 64%). m.p. = 116.0–118.1 °C. H NMR
(CDCl3) δ 7.63–7.66 (m, 2H), 7.41–7.50 (m, 7H), 7.31–7.34 (m,
3H), 7.27–7.30 (m, 1H); 13C NMR (CDCl3) δ 152.49, 152.06,
132.28, 131.82, 130.31, 129.79, 129.27, 128.89, 128.76, 128.64,
128.08, 127.19, 124.97, 119.78, 117.25, 112.25. HRMS
(APCI-MS, positive): m/z =304.0654. Calcd for C20H1335ClO:
304.0649 [M]+.
5-Bromo-2,3-diphenylbenzofuran (3ca): White solid

with the reported values.20
Compound 3jj: White solid (40 mg, 0.13 mmol, 63%).
m.p. > 190 °C (decomp.). H NMR (CDCl3) δ 7.66 (d, J = 8.8
Hz, 2H), 7.53 (d, J = 8.8 Hz, 2H), 3.09 (t, J = 6.6 Hz, 4H), 2.87
(t, J = 6.6 Hz, 4H), 2.00–2.04 (m, 4H), 1.63–1.67 (m, 4H); 13C
NMR (CDCl3) δ 154.22, 152.90, 128.45, 125.11, 123.14,
122.58, 116.37, 110.63, 25.66, 24.26, 24.10, 22.86. HRMS
(APCI-MS, positive): m/z = 317.1539. Calcd for C22H21O2:
317.1536 [M+H]+.
HRMS (APCI-MS, positive): m/z = 452.3112. Calcd for
C30H45OS: 452.3107 [M+H]+.
1
5-tert-Butyl-2-phenylsulfanyl-2,3-dihydrobenzofuran
(4al): Colorless oil (43 mg, 0.15 mmol, 76%). 1H NMR
(CDCl3) δ 7.57–7.58 (m, 2H), 7.32–7.35 (m, 2H), 7.27–7.30 (m,
1H), 7.23 (s, 1H), 7.18–7.19 (m, 1H), 6.79 (d, J = 8.2 Hz, 1H),
6.19 (dd, J = 8.9, 5.5 Hz, 1H), 3.67 (dd, J = 16.5, 8.9 Hz, 1H),
3.19 (dd, J = 16.5, 5.5 Hz, 1H), 1.30 (s, 9H); 13C NMR (CDCl3)
δ 155.97, 144.42, 134.25, 131.89, 129.10, 127.66, 125.56,
125.29, 121.77, 109.60, 89.47, 37.15, 34.49, 31.85. HRMS
(APCI-MS, positive): m/z = 284.1223. Calcd for C18H20OS:
284.1229 [M]+.
5,6,13,14-Tetrahydro-7,12-dioxa[8]helicene
(3jn):
White solid. m.p. > 270 °C (decomp.). 1H NMR (CDCl3) δ 7.89
(d, J = 8.9 Hz, 2H), 7.73 (d, J = 8.9 Hz, 2H), 7.01 (d, J = 7.5
Hz, 2H), 6.88 (t, J = 7.5 Hz, 2H), 6.84 (d, J = 7.5 Hz, 2H), 6.76
(t, J = 7.5 Hz, 2H), 3.03–3.09 (m, 4H), 2.80–2.88 (m, 4H); 13C
NMR (CDCl3) δ 157.01, 154.15, 133.25, 132.74, 128.94,
126.59, 125.41, 124.99, 124.86, 123.90, 122.01, 119.55, 119.47,
110.82, 30.09, 23.32. HRMS (APCI-MS, positive): m/z =
412.1448. Calcd for C30H20O2: 412.1458 [M]+.
5-tert-Butyl-2-dodecylsulfanyl-2-phenyl-2H-spiro[benz
ofuran-3,1'-cyclohexane] (4am): Colorless oil (75 mg, 0.15
1
mmol, 73%). H NMR (CDCl3) δ 7.79 (brs, 2H), 7.54 (d, J =
2.1 Hz, 1H), 7.40 (brs, 2H), 7.33 (t, J = 7.2 Hz, 1H), 7.23 (dd, J
= 8.2, 2.1 Hz, 1H), 6.85 (d, J = 8.2 Hz, 1H), 2.37–2.42 (m, 2H),
2.11 (ddd, J = 12.3, 8.4, 6.6 Hz, 1H), 1.98–2.02 (m, 1H),
1.81–1.86 (m, 2H), 1.69 (d, J = 13.0 Hz, 1H), 1.34 (s, 9H),
1.04–1.38 (m, 24H), 0.88 (t, J = 7.2 Hz, 3H), 0.63 (td, Jt = 13.0,
Jd = 3.0 Hz, 1H); 13C NMR (CDCl3) δ 154.18, 143.63, 139.91,
136.94, 128.00, 127.80, 124.53, 122.84, 110.17, 109.45, 53.91,
35.91, 34.58, 32.07, 31.98, 29.97, 29.77, 29.72, 29.57, 29.50,
29.26, 29.24, 29.11, 29.09, 25.50, 23.47, 22.84, 21.17, 14.27
(two of these signals contains overlapping). HRMS (APCI-MS,
positive): m/z = 521.3814. Calcd for C35H53OS: 521.3812
[M+H]+.
(2R*,3S*)-5-tert-Butyl-2-methylsulfanyl-2,3-diphenyl-2
,3-dihydrobenzofuran
(4aa):
Colorless
oil.
The
stereochemistry was determined by the analogy with that of
4da. The stereochemistry was supported by NMR analysis: no
correlation was observed between the two hydrogen atoms on
C2 and C3 positions in NOESY analysis after reduction21 to the
corresponding 2,3-diphenyl-2,3-dihydrobenzofuran. 1H NMR
(CDCl3) δ 7.68 (d, J = 7.5 Hz, 2H), 7.36–7.41 (m, 5H),
7.30–7.34 (m, 2H), 7.26–7.28 (m, 2H), 7.04 (s, 1H), 6.98 (d, J
= 8.9 Hz, 1H), 4.86 (s, 1H), 1.77 (s, 3H), 1.27 (s, 9H); 13C
NMR (CDCl3) δ 156.16, 144.81, 143.08, 136.48, 130.74,
129.64, 128.51, 128.24, 128.19, 127.84, 126.88, 125.78, 122.48,
109.81, 103.91, 62.81, 34.62, 31.85, 11.86. HRMS (APCI-MS,
positive): m/z = 375.1771. Calcd for C25H27OS: 375.1777
[M+H]+.
(2S*,3S*)-5-tert-Butyl-2-methyl-2-methylsulfanyl-3-ph
enyl-2,3-dihydrobenzofuran (syn-4af'): White solid. m.p. =
93.8–97.7 °C. The stereochemistry was determined by NOESY
analysis. 1H NMR (CDCl3) δ 7.38 (brs, 5H), 7.26 (d, J = 8.2 Hz,
1H), 7.14 (s, 1H), 6.82 (d, J = 8.2 Hz, 1H), 4.73 (s, 1H), 2.04 (s,
3H), 2.02 (s, 3H), 1.28 (s, 9H); 13C NMR (CDCl3) δ 156.12,
144.54, 136.29, 130.00, 129.54, 128.39, 128.19, 125.61, 122.61,
109.77, 99.34, 60.72, 34.61, 31.86, 27.00, 11.19. HRMS
(APCI-MS, positive): m/z = 313.1624. Calcd for C20H25OS:
313.1621 [M+H]+.
(2S*,3R*)-5-tert-Butyl-2-methyl-2-methylsulfanyl-3-ph
enyl-2,3-dihydrobenzofuran (anti-4af'): Colorless oil. The
stereochemistry was determined by NOESY analysis. 1H NMR
(CDCl3) δ 7.24–7.33 (m, 4H), 7.11 (d, J = 1.4 Hz, 1H), 7.05 (d,
J = 6.8 Hz, 2H), 6.82 (d, J = 8.2 Hz, 1H), 4.55 (s, 1H), 2.24 (s,
3H), 1.32 (s, 3H), 1.28 (s, 9H); 13C NMR (CDCl3) δ 156.03,
144.72, 139.44, 130.13, 129.28, 128.56, 127.49, 125.78, 122.88,
109.41, 98.31, 58.98, 34.56, 31.85, 24.25, 11.97. HRMS
(APCI-MS, positive): m/z = 313.1628. Calcd for C20H25OS:
313.1621 [M+H]+.
(2S*,3R*)-5-tert-Butyl-2-dodecylsulfanyl-3-phenyl-2,3-
dihydrobenzofuran (4ak): White solid (1.6 g, 3.5 mmol, 70%).
m.p. = 41.6–42.9 °C. The stereochemistry was determined by
the vicinal coupling constant between the two hydrogen atoms
on C2 and C3 positions. 1H NMR (CDCl3) δ 7.33 (t, J = 7.5 Hz,
2H), 7.26–7.29 (m, 1H), 7.23 (dd, J = 8.2, 2.1 Hz, 1H), 7.19 (d,
J = 7.5 Hz, 2H), 7.05 (d, J = 2.1 Hz, 1H), 6.82 (d, J = 8.2 Hz,
1H), 5.63 (d, J = 5.5 Hz, 1H), 4.42 (d, J = 5.5 Hz, 1H),
2.69–2.79 (m, 2H), 1.61–1.66 (m, 2H), 1.22–1.37 (m, 18H),
1.26 (s, 9H), 0.88 (t, J = 7.2 Hz, 3H); 13C NMR (CDCl3) δ
156.56, 144.64, 142.04, 129.20, 128.96, 127.91, 127.45, 125.90,
122.31, 109.55, 95.71, 55.89, 34.55, 32.07, 31.84, 31.60, 29.97,
29.80, 29.78, 29.73, 29.65, 29.50, 29.32, 29.03, 22.84, 14.27.
(2R*,3S*)-5-Iodo-2-methylsulfanyl-2,3-diphenyl-2,3-di
hydrobenzofuran (4da): White solid (49 mg, 0.11 mmol,
55%). m.p. = 166.6–169.8 °C. The stereochemistry was
1
determined by X-ray crystallographic analysis (Figure S1). H
NMR (CDCl3) δ 7.61–7.63 (m, 2H), 7.57 (dd, J = 7.5, 2.1 Hz,
1H), 7.36–7.42 (m, 5H), 7.32–7.35 (m, 1H), 7.29 (d, J = 2.1 Hz,
1H), 7.24–7.25 (m, 2H), 6.85 (d, J = 9.3 Hz, 1H), 4.84 (s, 1H),
1.76 (s, 3H); 13C NMR (CDCl3) δ 158.34, 142.57, 137.91,
135.71, 134.14, 133.29, 130.59, 128.65, 128.54, 128.36, 128.07,
126.62, 112.99, 104.34, 83.25, 62.26, 11.99. HRMS (APCI-MS,
positive): m/z = 445.0114. Calcd for C21H18IOS: 445.0118
[M+H]+.
7,12-Dioxa[8]helicene (5): White solid. m.p.
=
1
299.9–303.2 °C. H NMR (CDCl3) δ 8.14 (d, J = 8.9 Hz, 2H),
7.97 (d, J = 8.2 Hz, 2H), 7.87 (d, J = 8.2 Hz, 2H), 7.82 (d, J =
8.9 Hz, 2H), 7.66 (d, J = 7.5 Hz, 2H), 7.57 (d, J = 7.5 Hz, 2H),
6.91 (t, J = 7.5 Hz, 2H), 6.39 (t, J = 7.5 Hz, 2H); 13C NMR
(CDCl3) δ 155.85, 153.22, 130.02, 129.80, 128.96, 128.58,
128.27, 127.60, 125.89, 123.94, 123.92, 123.62, 121.81, 119.34,
112.16, 111.31. HRMS (APCI-MS, positive): m/z = 408.1155.
1
Calcd for C30H16O2: 408.1145 [M]+. All the resonances in H
and 13C spectra were consistent with the reported values.3h
Acknowledgement
This work was supported by JSPS KAKENHI Grant
Numbers JP16H04109, JP18H04252, JP18H04409, and
JP18K14212. T.Y. acknowledges JSPS Predoctoral Fellowship.
H.Y. thanks The Mitsubishi Foundation for financial support.
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