Novel Selective Approach to Terminally Substituted [n]Dendralenes

Article abstract of DOI:10.1002/ejoc.201801522

Dendralenes are simple alkenes with cross-conjugated double bonds that are frequently synthesized due to being potentially valuable building blocks for the synthesis of more complex structures. The synthetic approaches to dendralenes are based on the cross-coupling reactions of electrophilic and nucleophilic synthons derived from geminally substituted ethylene. Our novel methodology for the synthesis of only terminally substituted [3]- and [4]dendralenes, as well as 2,3-disubstituted buta-1,3-dienes, involves the preparation of 1,2-disubstituted cyclobutenes from readily available 2-bromocyclobutanone and the subsequent thermal ring-opening reactions.

Full text of DOI:10.1002/ejoc.201801522

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Title: Novel approach to only terminally substituted [n]dendralenes
Authors: Peter Polák and tomas tobrman
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10.1002/ejoc.201801522
European Journal of Organic Chemistry
FULL PAPER
Novel approach to only terminally substituted [n]dendralenes
Peter Polák[a] Tomáš Tobrman[a]*
Abstract: Dendralenes are simple alkenes with cross-conjugated
double bonds that are frequently synthesized due to being potentially
valuable building blocks for the synthesis of more complex structures.
The synthetic approaches to dendralenes are based on the cross-
coupling reactions of electrophilic and nucleophilic synthones derived
from geminally substituted ethylene. Our novel methodology for the
synthesis of only terminally substituted [3]- and [4]dendralenes, as
well as 2,3-disubstituted buta-1,3-dienes, involves the preparation of
of bromoenol phosphates[19] in organic synthesis, we envisioned
that our novel approach to the synthesis of [n]dendralenes could
use 2-bromocyclobutanone as the starting compound. In the first
step, the 2-bromocyclobutanone is converted to the phosphate 1,
then disubstituted cyclobutenes 3 is prepared and, finally, cross-
conjugated double bonds are obtained by the electrocyclic ring-
opening reaction of cyclobutene (Scheme 1, route B). The
designed synthetic route possesses several interesting features
from practical point of view. 2-Bromocyclobutanone,[20] and 2,2-
1,2-disubstituted cyclobutenes from
readily available 2-
bromocyclobutanone and the subsequent thermal ring-opening
reactions.
dibromocyclobutanone[21]
are
easily
preparable
from
commercially available cyclobutanone. The synthesis of 1,2-
diarylcyclobut-1-enes includes the McMurry reaction,[22] inter-[23]
and intramolecular[24] nucleophilic substitution, ring contraction,[25]
and
isomerization,[26]
although
readily
available
2-
Introduction
bromocyclobutenyl phosphates have not previously been used for
their synthesis. The cyclobutene derivatives 3 should have better
stability, compared to some unsubstituted dendralenes, allowing
to use them as bench-stable precursors for the dendralene
synthesis. Electrocyclic ring-opening reactions is a well known
concept that has been extensively reviewed.[27] The electrocyclic
ring-opening reaction of cyclobutenes was intensively studied[28]
and used[29] mainly for the preparation of mono- or
oligosubstituted 1,3-butadienes. Besides of the other
disubstituted butadienes available by the cyclobutene ring
opening reaction, 2,3-disubstituted buta-1,3-dienes are rarely
prepared by this reaction. The reported examples count only
The acyclic molecules with cross-conjugated double bonds
known as dendralenes form a significant group of compounds that
have been intensively studied with respect to their properties,
reactivity, and preparation.[1] Among all the polysubstituted
[n]dendralenes, the synthesis of unsubstituted and terminally
substituted [n]dendralenes remains the most difficult task since
[3]-, [5]-, and [7]dendralenes are unstable exhibiting half-lifes of
10, 25, and 63 hours affording the Diels-Alder dimerization
products.2 In the case of [4]-, [6]-, [8]dendralenes the
docomposition was slower but still observable.[2] The
unsubstituted or only terminally substituted [n]dendralenes with
five or more cross-conjugated ethylene units are usually prepared
by means of cross-couplings between nucleophilic and
electrophilic ethylene templates (Scheme 1, route A).[2,3] From a
synthetic point of view, dendralenes with four cross-conjugated
double bonds are synthesized by the Suzuki reaction,[4] Stille
coupling,[5] addition reactions,[6] cycloaddition,[7] isomerization
processes,[8] and other reactions.[9] The preparation of
[3]dendralenes with terminal substitution can be achieved via
carbopalladation[10] or isomerization reactions.[11] The two double
bonds system with cross-conjugated carbon-substituents is
represented by the 2,3-disubstituted buta-1,3-dienes scaffold.
These substances can be prepared by means of allene
carbopalladation,[10] palladium-catalyzed allylic substitution,[12] the
Suzuki[13] and Kumada[14] reactions, oxidative cross-coupling
reactions,[15] elimination reactions,[16] samarium-catalyzed
compounds with substituents connected via
a heteroatom
spacer.[30] Moreover, only a limited number of papers on the
synthesis of unsubstituted[31] and trisubstituted [3]dendralenes[29e]
via electrocyclic ring-opening reaction of cyclobutene were
published. However, to the best of our knowledge no report on a
general method for the synthesis of only terminally disubstituted
2,3-disubustituted buta-1,3-dienes [3]-, [4]dendralenes bearing
carbon substituents, starting from readily available cyclobutanone
and using the electrocyclic ring-opening reaction have been
published. Therefore, we decided to explore the synthetic
potential of designed procedure.
dimerization of acetophenones,[17] and other reactions.[18]
However, based on our previous investigations of the application
.
[a]
Ing. Peter Polák, assoc. prof. Tomáš Tobrman,
Department of Organic Chemistry, University of Chemistry and
Technology, Prague,
Technická 5, 166 28 Prague 6, Czech Republic
E-mail: tomas.tobrman@vscht.cz
Supporting information for this article is given via a link at the end of
the document.
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10.1002/ejoc.201801522
European Journal of Organic Chemistry
FULL PAPER
Scheme 1. Synthetic approaches to dendralenes.
Table 1. The Negishi reaction of phosphates 2 with 4-tolylzinc chloride.
Results and Discussion
The synthesis of the phosphate
1
began with 2-
bromocyclobutanone, which was transformed into 2,2-
dibromocyclobutanone, before the Perkow reaction gave
phosphate 1. Based on our previous work,[19a] we expected that
the introduction of the first substituents by means of the bromine
replacement could be performed with the Suzuki reaction using
either boronic acids or boronates. Indeed, it was found that the
reported conditions[19a] were sufficient for the introduction of the
aryl substituents (Table 2). Thus, we focused our attention on the
optimization of the Negishi reaction involving phosphates 2 (Table
1). Despite the tremendous progress that has been made in
relation to the cross-coupling reactions of aryl and alkenyl
phosphates,32 the Negishi reaction involving cyclobutenyl
phosphates has not previously been reported. At the beginning of
our work, we considered only diethyl phosphate, since it exhibits
better atom economy when compared to diphenyl phosphate.
However, it soon became clear that the phosphate 2a does not
couple with 4-methylphenylzinc chloride using palladium and
nickel catalysts in dry tetrahydrofuran (THF) at 75 °C (Table 1,
entries 1 and 2). The addition of 1.0 equiv. of aluminum chloride
increased the rate of conversion of the phosphate 2a into the
product 3aa to 93%. The product 3aa was isolated at a 89% yield,
while the nickel catalysts remained unfruitful (Table 1, entries 35).
The complete conversion of 2a was achieved using 4 mol % of
DPPF and the RuPhos ligand, although the isolated yields of 3aa
were low (Table 1, entries 6 and 7). PdCl2(DPEPhos) gave the
best yield of cyclobutene 3aa (Table 1, entry 8). The use of 2
mol % of the catalyst resulted in the complete conversion of the
phosphate 2a, although the isolated yield of 3aa decreased to
83% (Table 1, entry 9). At this point, we briefly explored the
reactivity of the other unsubstituted cyclic phosphates 2bd under
the developed conditions. The cyclobutenyl phosphate 2b
showed complete conversion into 3ba, but the isolated yield was
only 67% (Table 1, entry 10). The cyclopentenyl phosphate 2c
exhibited poor conversion into the product 3ca with 4-tolylzinc
chloride in the presence of AlCl3 and a PdCl2DPEPhos catalyst
(Table 1, entry 11), while the reaction using PdCl2DPPF resulted
in the 90% conversion of 2c (Table 1, entry 12). The ring
enlargement made to the cyclohexenyl phosphate 2d along with
the optimized conditions afforded the product 3da in an 80%
isolated yield (Table 1, entry 13). No superior results were
obtained during the AlCl3-free Negishi reaction with other
catalysts, including PdCl2(SPhos)2, PdCl2DPPF, PdCl2DPEPhos,
NiCl2DPPP, and NiCl2(PCy3)2 (Table 1, note d). The observed
reactivity is in good agreement with our previous results,[19c] which
prompted us to propose that AlCl3 coordinates with the phosphate
moiety, thereby enhancing its reactivity during the Negishi
reaction. In some cases, the large differences observed between
the rate of conversion and the isolated yield (Table 1, entries 4, 5,
7, and 10) were attributed to the McKenna-type degradation[33] of
the starting phosphates.
Entry
1
2
Catalyst
Conversion (%)[a]
3aa, <5
[b]
2a,
2a
2a
2a
2a
2a
2a
2a
2a
2b
2c
2c
2d
PdCl2(SPhos)2
[b]
2
NiCl2(PCy3)2
3aa, <5
3
PdCl2(SPhos)2/AlCl3
NiCl2(PCy3)2/AlCl3
NiCl2DPPP/AlCl3
3aa, 93 (89[e]
3aa, 100 (0[e]
3aa, 100 (0[e]
)
)
)
4
5
6
PdCl2(RuPhos)2/AlCl3
PdCl2DPPF/AlCl3
3aa, 100 (82[e]
3aa, 100 (65[e]
3aa, 100 (92[e]
3aa, 100 (83[e]
)
)
)
)
7
8
PdCl2DPEPhos/AlCl3
[c]
9
PdCl2DPEPhos/AlCl3
PdCl2DPEPhos/AlCl3
PdCl2DPEPhos/AlCl3
[d]
[d]
10
11
12
13
3ba, 100 (67[e]
)
3ca, 50 (38[e]
3ca, 90 (55[e]
)
)
[d]
PdCl2DPPF/AlCl3
[d]
PdCl2DPEPhos/AlCl3
3da, 100 (80[e]
)
[a] The reactions were performed on a 0.30 mmol scale, and the conversion was
determined by means of 1H NMR. [b] The reaction was stirred for 24 h at 75 °C.
A 2 mol % catalyst loading was used.
performed with the following catalysts, PdCl2(SPhos)2, PdCl2DPPF,
PdCl2DPEPhos, NiCl2DPPP, and NiCl2(PCy3)2, without AlCl3 in dry THF at
75 °C, although no superior results were obtained. [e] Isolated yield.
[c]
[d]
The Negishi reaction was also
The optimized reaction conditions for the substitution of the
phosphate moiety were used to verify the feasibility of the
proposed methodology (Table 2). Thus, the bromoenol phosphate
1
was treated with arylboronic acids, and the arylated
cyclobutenyl phosphates were prepared in almost quantitative
yields (Table 2, entries 17). The Suzuki reaction proceeded with
the electron rich and poor acids with the same results, and the
sensitive functional groups, for instance, the keto or nitrile groups,
were tolerated (Table 2, entries 3 and 5). It is worth noting that the
2-thienyl and 1-pyrenyl substituents were also introduced in high
yields (Table 2, entries 4 and 7). The prepared phosphates 2a,ej
were mixed with arylzinc chlorides and the aluminum chloride
promoted the Negishi reaction, which was performed with
outstanding results (Table 2, entries 15). In two cases, the
introduction of bithiophenyl 3jf and the pyrenyl ring 3jg was
performed, which afforded -conjugated molecules in high
isolated yields (Table 2, entries 6 and 7). Finally, the obtained
cyclobutenes 3aaaf,jg were used for the thermal ring-opening
reactions. The ring-opening reactions were performed in xylene
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10.1002/ejoc.201801522
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at 150°C, and quantitative conversion was obtained within several
hours. A lower reaction temperature led to the incomplete
conversion of the starting cyclobutenes 3aaaf,jg. When the ring-
opening reaction was performed in decalin at 200 °C the yield of
the compound 4aa significantly dropped due to side reactions
(Table 2, entry 1). On the other hand, The 2,3-disubstituted buta-
1,3-dienes 4aaae were isolated in almost quantitative yields
(Table 2, entries 15). Surprisingly, the cyclobutene with a
bithiophene substituent failed to give the expected product, and
the formation of a complex reaction mixture was observed (Table
2, entry 6). Yet, the cyclobutene 3jg smoothly opened to give
buta-1,3-diene with cross-conjugated pyrene units 4jg (Table 2,
entry 7).
Table 2. The preparation of cross-conjugated systems with two double bonds.
Entry
1
2, Yield[a] (%), R
3, Isolated yield (%)
4 Isolated yield (%)
4aa, 92 (43[b]
)
2a, 97,
3aa, 92,
2
4ab, 92
2e, 95,
3ab, 93,
3ac, 94,
3ad, 96,
3ae, 95,
3
4
5
6
4ac, 98
2f,96,
4ad, 93
2g, 94,
4ae, 95
2h, 95,
[a]
2i, 96,
3jf, 90,
7
4jg, 81
3jg, 84,
2j, 91,
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[a] Decomposition of the starting compound was observed. [b] The reaction was performed in decalin at 200 °C.
high isolated yields. The biscyclobutenes were also opened,
thereby affording the [4]dendralenes 4mm,an,np,aq,nr
substituted at the terminal positions in moderate isolated yields. It
is worth noting that the tricyclobutene 3ms failed to give the
expected product and a complex reaction mixture was instead
formed under the tested conditions. We expect that the formed
[6]dendralene is unstable under the tested conditions and hence
undergoes thermally induced side reactions. The same reactivity
was observed in the case of the cyclobutene 3kh, where
decomposition was found to be the main reaction pathway. With
the cyclobutene 3 in our hands (Scheme 2), we selected
illustrative examples and tested their behavior during the thermal
ring-opening reaction (Scheme 3). The cyclobutenes with alkenyl
Encouraged by the obtained results, we expected to extend the
developed methodology to the regioselective synthesis of [3]- and
[4]dendralenes (Scheme 2). In this case, the introduction of the
alkenyl or cyclobutenyl moiety would be a crucial step. We were
pleased to observe that the Suzuki reaction involving the alkenyl
fragment 2k,l proceeded with high isolated yields. Surprisingly,
the Suzuki reaction involving the vinylboronic acid
neopentylglycol ester proceeded well, although the formed 2-
vinylcyclobutenyl phosphate was unstable and decomposed
during the isolation by flash chromatography. Additionally, the
cyclobutenyl boronates were smoothly coupled with the enol
phosphate 1, as can be seen from the prepared compounds 2m,n. fragments were transformed to the [3]dendralenes 4ki,kj,lk,ll in
The Negishi reaction involving the substituted enol phosphates
turned out to be difficult in the case of the cycloalkenylzinc
chlorides 3kh. Aromatic as well as cyclobutenyl substituents were
introduced in high isolated yields. The methodology hence allows
access to the substituted cyclobutenes with a heteroaromatic ring
3go and the tricyclobutene 3ms. The prepared compounds
3aq,ms were chosen in order to illustrate the stability of the
cyclobutenes. We were pleased to discover that the tested
compounds were sufficiently stable that they could be stored at
room temperature under an air atmosphere for several months.
high isolated yields. The biscyclobutenes were also opened,
thereby affording the [4]dendralenes 4mm,an,np,aq,nr
substituted at the terminal positions in moderate isolated yields. It
is worth noting that the tricyclobutene 3ms failed to give the
expected product and a complex reaction mixture was instead
formed under the tested conditions. We expect that the formed
[6]dendralene is unstable under the tested conditions and hence
undergoes thermally induced side reactions. The same reactivity
was observed in the case of the cyclobutene 3kh, where
decomposition was found to be the main reaction pathway.
Scheme 2. The preparation of the alkenyl cyclobutenes.
With the cyclobutene 3 in our hands (Scheme 2), we selected
illustrative examples and tested their behavior during the thermal
ring-opening reaction (Scheme 3). The cyclobutenes with alkenyl
fragments were transformed to the [3]dendralenes 4ki,kj,lk,ll in
Scheme 3. Thermal cyclobutene-opening reaction of the substituted
cyclobutenes.
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10.1002/ejoc.201801522
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Mass spectra were measured on ZAB-SEQ (VG Analytical). The dry and
degassed solvents were prepared by PureSolv MD7; silica gel (Merck,
Silica Gel 60, 40-63 m) was used for column chromatography.
Cyclopentenyl diethyl phosphate (2c) and cyclohexenyl diethyl phosphate
(2d) were prepared following the literature procedure.[34] BuLi (2.5 M
solution in hexane) and other compounds were purchased. Concentration
of BuLi was determined by titration using menthol and 1,10-phenanthroline
before use. Concentration of organozinc reagents was determined by
titration using iodine.
In principle, the developed methodology is not limited to the
synthesis of simple disubstituted cyclobutenes. In order to
demonstrate the modularity and versatility of our methodology, we
have chosen the representative example of molecule 4mt with
two cross-conjugated parts connected via a spacer (Scheme 4).
To achieve the synthesis of compound 4mt, the previously
prepared phosphate 2m was treated with organozinc reagent 5,
thereby affording cyclobutene 3mt in a 92% isolated yield. The
prepared compound 3mt was heated to 150 °C in dry xylene, and
the formed dendralene 4mt bearing two cross-conjugated parts
connected by a 1,4-phenylene spacer was obtained in a 65%
isolated yield in two steps from the phosphate 2m.
General procedure for the preparation of diethyl 2-substituted
cyclobutenyl phosphates 2
Toluene (4 mL/mmol) was added to
a mixture of diethyl 2-
bromocyclobuten-1-yl phosphate (1.0 equiv.) (1), boronic acid or boronic
ester (1.3 equiv.), palladium acetate (1 mol %) and RuPhos (2 mol %). The
reaction mixture was stirred for 1 min at ambient temperature, and then
1M K3PO4 (3 equiv.) was added at once. The reaction mixture was stirred
for 18 h at 60 °C. The reaction mixture was diluted with ether, washed with
1M KOH, water and brine then dried over MgSO4. Column
chromatography (silica gel) afforded pure products.
Diethyl
2-(4-methoxyphenyl)-cyclobuten-1-yl
phosphate (2a):
Prepared from diethyl 2-bromocyclobuten-1-yl phosphate (1) (2.85 g, 10
mmol), 4-methoxyphenylboronic acid (1.98 g, 13 mmol), Pd(OAc2) (22.5
mg, 1 mol.%), RuPhos (93.3 mg, 2 mol%), 1M K3PO4 (30 mL),
hexane/EtOAc (3:1→ 2:1, Rf = 0.2), 97% yield (3.03 g), yellow viscous
liquid. 1H NMR (300 MHz, CDCl3): δ = 7.387.31 (m, 2H), 6.896.82 (m,
2H), 4.284.15 (m, 4H), 3.81 (s, 3H), 2.912.87 (m, 2H), 2.402.36 (m,
2H), 1.37 (td, J = 7.1, 1.1 Hz, 6H). 13C NMR (75MHz, CDCl3): δ 158.5,
132.9 (d, J = 7.9 Hz), 127.3, 125.9 (d, J = 1.3 Hz), 120.7 (d, J = 10.8 Hz),
113.7, 64.4 (d, J = 6.0 Hz), 55.2, 31.0 (d, J = 2.7 Hz), 20.9, 16.1 (d, J = 6.7
Hz). HRMS (ESI) [M+H]+ calcd for C15H21O5P: 313.11994, found:
313.11946.
Scheme 4. The preparation of the cross-conjugated fragments connected via a
1,4-phenylene spacer.
Conclusions
Diethyl 2-(4-fluorophenyl)-cyclobuten-1-yl phosphate (2e): Prepared
from diethyl 2-bromocyclobuten-1-yl phosphate (1) (0.570 g, 2 mmol), 4-
fluorophenylboronic acid (0.364 g, 2.6 mmol), Pd(OAc)2 (4.5 mg, 1 mol %),
RuPhos (18.7 mg, 2 mol %), 1M K3PO4 (6 mL), hexane/EtOAc (3:1→2:1,
Rf = 0.3), 95% yield (0.570 g), yellow viscous liquid. 1H NMR (300 MHz,
CDCl3): δ = 7.417.33 (m, 2H), 7.056.96 (m, 2H), 4.294.14 (m, 4H),
2.932.89 (m, 2H), 2.412.36 (m, 2H), 1.38 (td, J = 7.1, 0.9 Hz, 6H). 13C
NMR (75MHz, CDCl3): δ = 161.6 (d, J = 246.9 Hz), 134.5 (dd, J = 7.4, 2.6
Hz), 129.1 (dd, J = 3.3, 1.3 Hz), 127.6 (d, J = 7.9 Hz), 120.0 (d, J = 11.0
Hz), 115.3 (d, J = 21.7 Hz), 64.5 (d, J = 5.6 Hz), 31.1 (d, J = 2.5 Hz), 20.9,
16.1 (d, J = 6.5 Hz). 19F NMR (CDCl3): δ = -114.59 (m). HRMS (APCI)
[M+H]+ calcd for C14H18FO4P: 301.09995, found: 301.10013.
To summarize, we have developed a novel methodology for the
synthesis of [3]- and [4]dendralenes, as well as 2,3-disubstituted
buta-1,3-dienes,
which
utilizes
readily
available
2-
bromocyclobutanone that is transformed into diethyl bromoenol
phosphates. The subsequent Suzuki reaction along with the
aluminum chloride-promoted Negishi reaction was used to
change the bromine and phosphate moieties. The prepared
cyclobutenes showed excellent stability and no signs of their
decomposition were observed within 6 months. The cyclobutenes
were opened in dry xylene at 150 °C, thereby affording 2,3-
disubstituted buta-1,3-dienes as well as terminally disubstituted
[3]- and [4]dendralenes. The attempts to prepare [6]dendralenes
were unsuccessful. The methodology is also suitable for the
preparation of alkenes with cross-conjugated substituents
connected via a spacer. Further studies involving the application
of the developed methodology to the synthesis of higher
dendralenes are ongoing in our laboratory.
Diethyl 2-(4-acetylphenyl)-cyclobuten-1-yl phosphate (2f): Prepared
from diethyl 2-bromocyclobuten-1-yl phosphate (1) (0.285 g, 1 mmol), 2-
(4-acetylphenyl)-5,5-dimethyl-1,3,2-dioxaborinane (0.302 g, 1.3 mmol),
Pd(OAc)2 (2.25 mg, 1 mol %), RuPhos (9.33 mg, 2 mol %), 1M K3PO4 (3
mL), hexane/EtOAc (3:1 → 2:1, Rf = 0.3), 96% yield (0.311 g), yellow
viscous liquid. 1H NMR (300 MHz, CDCl3): δ = 7.937.87 (d, J = 8.4 Hz,
2H), 7.477.42 (d, J = 8.4 Hz, 2H), 4.294.16 (m, 4H), 2.972.91 (m, 2H),
2.57 (s, 3H), 2.462.41 (m, 2H), 1.38 (td, J = 7.1, 1.1 Hz, 6H). 13C NMR
(75MHz, CDCl3): δ = 197.4, 138.3 (d, J = 8.0 Hz), 137.2, 135.1, 128.5,
125.9, 120.0 (d, J = 10.4 Hz), 64.7 (d, J = 5.8 Hz), 31.4 (d, J = 2.5 Hz),
26.5, 20.8, 16.1 (d, J = 5.8 Hz). HRMS (APCI) [M+H]+ calcd for C16H21O5P:
325.11994, found: 325.12013.
Experimental Section
All reactions were performed under an argon atmosphere. NMR spectra
were measured on a Varian Gemini 300 (1H, 300.07 MHz; 13C, 75.46 MHz),
or a Bruker DRX 500 Avance (1H, 500.13 MHz) spectrometer at 298 K.
Diethyl 2-(2-thienyl)-cyclobuten-1-yl phosphate (2g): Prepared from
diethyl 2-bromocyclobuten-1-yl phosphate (1) (0.285 g, 1 mmol), 5,5-
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10.1002/ejoc.201801522
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dimethyl-2-(thiophen-2-yl)-1,3,2-dioxaborinane (0.255 g, 1.3 mmol),
Pd(OAc)2 (2.25 mg, 1 mol %), RuPhos (9.33 mg, 2 mol %), 1M K3PO4 (3
mL), hexane/EtOAc (3:1, Rf = 0.35), 94% yield (0.271 g), brownish viscous
liquid. 1H NMR (300 MHz, CDCl3): δ = 7.227.18 (m, 1H), 6.996.94 (m,
2H), 4.284.14 (m, 4H), 2.972.90 (m, 2H), 2.462.39 (m, 2H), 1.37 (td, J
= 7.1, 1.0 Hz, 6H). 13C NMR (75MHz, CDCl3): δ = 135.2 (d, J = 1.7 Hz),
132.9 (d, J = 7.7 Hz), 126.8, 124.6, 123.7, 115.4 (d, J = 11.0 Hz), 64.6 (d,
J = 6.0 Hz), 31.8 (d, J = 2.6 Hz), 22.0, 16.1 (d, J = 6.7 Hz). HRMS (APCI)
[M+H]+ calcd for C12H17O4PS: 289.06579, found: 289.06581.
Diethyl
2-(cycloheptene-1-yl)-cyclobuten-1-yl
phosphate
(2l):
Prepared from diethyl 2-bromocyclobuten-1-yl phosphate (1) (1.71 g, 6
mmol), 1-cycloheptenyl-5,5-dimethyl-1,3,2-dioxaborinane (1.62 g, 7.8
mmol), Pd(OAc)2 (13.5 mg, 1 mol %), RuPhos (56 mg, 2 mol %), 1M K3PO4
(18 mL), hexane:EtOAc (3:1, Rf = 0.35), 91% yield (1.64 g), yellow viscous
liquid. 1H NMR (300 MHz, CDCl3): δ = 5.74 (t, J = 6.8 Hz, 1H), 4.15 (quint,
J = 7.5 Hz, 4H), 2.70 (brs, 2H), 2.492.41 (m, 2H), 2.192.04 (m, 4H),
1.751.65 (m, 2H), 1.541.40 (m, 4H), 1.33 (tt, J = 7.2, 1.0 Hz, 6H). 13C
NMR (75MHz, CDCl3): δ = 138.1 (d, J = 1.5 Hz), 132.0 (d, J = 8.2 Hz),
129.9 (d, J = 1.3 Hz), 124.9 (d, J = 10.3 Hz), 64.2 (d, J = 5.8 Hz), 32.4,
30.0 (d, J = 2.5 Hz), 29.7, 28.3, 26.9, 26.6, 21.0, 16.0 (d, J = 6.6 Hz).
HRMS (APCI) [M+H]+ calcd for C15H25O4P: 301.15632, found: 301.15631.
Diethyl 2-[4-(2-cyanoprop-2-yl)phenyl]-cyclobuten-1-yl phosphate
(2h): Prepared from diethyl 2-bromocyclobuten-1-yl phosphate (1) (0.285
g, 1 mmol), [4-(1-cyano-1-methylethyl)phenyl]boronic acid (0.246 g, 1.3
mmol), Pd(OAc)2 (2.25 mg, 1 mol %), RuPhos (9.33 mg, 2 mol %), 1M
K3PO4 (3 mL), Hexane:EtOAc (3:1 → 2:1, Rf = 0.2), 95% yield (0.332 g),
yellow viscous liquid. 1H NMR (300 MHz, CDCl3): δ = 7.41 (s, 4H),
4.284.15 (m, 4H), 2.942.89 (m, 2H), 2.432.37 (m, 2H), 1.70 (s, 6H),
1.38 (td, J = 7.2, 1.0 Hz, 6H). 13C NMR (75MHz, CDCl3): δ = 139.8, 135.9
(d, J = 7.9 Hz), 132.4, 126.5, 125.1, 124.4, 120.1 (d, J = 10.7 Hz), 64.6 (d,
J = 6.1 Hz), 37.0, 31.2 (d, J = 2.6 Hz), 29.0, 20.8, 16.1 (d, J = 6.6 Hz).
HRMS (APCI) [M+H]+ calcd for C18H24NO4P: 350.15157, found:
350.15170.
Diethyl 2-(2-(4-tolyl)cyclobutene-1-yl)cyclobutene-1-yl phosphate
(2m): Prepared from diethyl 2-bromocyclobuten-1-yl phosphate (1) (0.855
g,
3
mmol), 2-(2-(4-methylphenyl)cyclobutenyl)-5,5-dimethyl-1,3,2-
dioxaborinane (0.999 g, 3.9 mmol), Pd(OAc)2 (6.8 mg, 1 mol %), RuPhos
(28 mg, 2 mol %), 1M K3PO4 (9 mL), hexane:EtOAc (3:1, Rf = 0.2), 88%
yield (0.920 g), yellow solid, the product partially decomposed upon
storage in a refrigerator for 1 week. However, it can be stored in a freezer
at -20 °C for several weeks without decomposition, m.p. 4648 °C. 1H
NMR (300 MHz, CDCl3): δ = 7.29 (d, J = 8.0 Hz, 2H), 7.11 (d, J = 8.0 Hz,
2H), 4.18 (p, J = 7.4 Hz, 4H), 2.87 (brs, 2H), 2.742.63 (m, 4H), 2.49 (q, J
= 2.4 Hz, 2H), 2.33 (s, 3H), 1.37 (tt, J = 7.1, 0.8 Hz, 6H). 13C NMR (75MHz,
CDCl3): δ = 138.3 (d, J = 1.2 Hz), 136.88, 136.84 (d, J = 8.0 Hz), 132.9,
129.8 (d, J = 1.8 Hz), 128.9, 125.9, 118.3 (d, J = 10.8 Hz), 64.5 (d, J = 6.0
Hz), 32.1 (d, J = 2.8 Hz), 27.5, 27.0, 23.8, 21.3, 16.1 (d, J = 6.7 Hz). HRMS
(ESI) [M+H]+ calcd for C19H25O4P: 349.15632, found: 349.15560.
Diethyl 2-(6-methoxynapht-2-yl)-cyclobuten-1-yl phosphate (2i):
Prepared from diethyl 2-bromocyclobuten-1-yl phosphate (1) (0.285 g, 1
mmol), 2-(6-methoxynaphthalen-2-yl)-5,5-dimethyl-1,3,2-dioxaborinane
(0.351 g, 1.3 mmol), Pd(OAc)2 (2.25 mg, 1 mol %), RuPhos (9.33 mg, 2
mol %), 1M K3PO4 (3 mL), hexane:EtOAc (3:1, Rf = 0.3), 96% yield (0.348
g), yellow crystalline solid, m.p. 5961 °C. 1H NMR (300 MHz, CDCl3): δ =
7.747.59 (m, 4H), 7.167.06 (m, 2H), 4.324.18 (m, 4H), 3.91 (s, 3H),
2.992.93 (m, 2H), 2.522.46 (m, 2H), 1.39 (td, J = 7.1, 0.8 Hz, 6H). 13C
NMR (75MHz, CDCl3): δ = 157.7, 154.7 (d, J = 7.8 Hz), 133.6, 129.4, 128.7,
128.4 (d, J = 1.5 Hz), 126.8, 125.2, 124.1, 121.3 (d, J = 10.7 Hz), 119.0,
105.9, 64.5 (d, J = 5.9 Hz), 55.3, 31.2 (d, J = 2.5 Hz), 20.9, 16.1 (d, J = 6.5
Hz). HRMS (APCI) [M+H]+ calcd for C19H23O5P: 363.13559, found:
363.13546.
Diethyl
2-(2-(4-fluorophenyl)cyclobuten-1-yl)cyclobuten-1-yl
phosphate (2n): Prepared from diethyl 2-bromocyclobuten-1-yl
phosphate (1) (0.855 g, 3 mmol), 2-(2-(4-fluorophenyl)cyclobutenyl)-5,5-
dimethyl-1,3,2-dioxaborinane (1.02 g, 3.9 mmol), Pd(OAc)2 (6.8 mg, 1
mol %), RuPhos (28 mg, 2 mol %), 1M K3PO4 (9 mL), hexane:EtOAc (3:1,
Rf = 0.2), 92% yield (0.971 g), yellow viscous liquid, product partially
decomposed upon storage in refrigerator for 1 week. However it can be
stored at -20 °C for several weeks without decomposition. 1H NMR (300
MHz, CDCl3): δ = 7.397.31 (m, 2H), 7.036.94 (m, 2H), 4.244.11 (m,
4H), 2.88 (brs, 2H), 2.732.61 (m, 4H), 2.492.42 (m, 2H), 1.37 (td, J =
7.1, 1.0, 6H). 13C NMR (75MHz, CDCl3): δ = 161.8 (d, J = 247.2 Hz), 137.3
(dd, J = 8.1, 0.6 Hz), 137.0 (d, J = 1.2 Hz), 131.9 (d, J = 3.3 Hz), 130.3 (t,
J = 2.0 Hz), 127.5 (d, J = 7.8 Hz), 117.9 (d, J = 10.8 Hz), 115.1 (d, J = 21.8
Hz), 64.5 (d, J = 6.2 Hz), 32.1 (d, J = 2.5 Hz), 27.6, 26.9, 23.7, 16.1 (d, J
= 6.6 Hz). 19F NMR (CDCl3): δ = -114.85 (m). HRMS (ESI) [M+Na]+ calcd
for C18H22FO4P: 375.11320, found: 375.11352.
Diethyl 2-(7-tert-butylpyrene-1-yl)-cyclobuten-1-yl phosphate (2j):
Prepared from diethyl 2-bromocyclobuten-1-yl phosphate (1) (1.43 g, 5
mmol), 7-tert-butylpyren-1-yl boronic acid (1.97 g, 6.5 mmol), Pd(OAc)2
(11.3 mg, 1 mol %), RuPhos (46.7 mg, 2 mol %), 1M K3PO4 (15 mL),
hexane/DCM (9:1→ hexane:EtOAc 3:1 → 2:1, Rf = 0.3), 91% yield (2.10
g), dark-yellow solid, m.p. 8083 °C. 1H NMR (300 MHz, CDCl3): δ = 8.57
(d, J = 8.4 Hz, 1H), 8.21 (s, 2H), 8.117.97 (m, 5H), 4.294.15 (m, 4H),
3.163.10 (m, 2H), 3.943.89 (m, 2H), 1.59 (s, 9H), 1.35 (td, J = 7.1, 1.0
Hz, 6H). 13C NMR (75MHz, CDCl3): δ = 149.0, 135.8 (d, J = 7.4 Hz), 131.3,
130.7, 130.3, 127.8, 127.7 (d, J = 1.2 Hz), 127.5, 127.3, 127.2, 125.6,
124.90, 124.88, 124.5, 123.1, 122.4, 122.1, 121.0 (d, J = 10.8 Hz), 64.6 (d,
J = 6.1 Hz), 35.1, 31.9, 34.4 (d, J = 2.5 Hz), 24.5, 16.1 (d, J = 6.6 Hz).
HRMS (APCI) [M+H]+ calcd for C28H31O4P: 463.20327, found: 463.20359.
General procedure for the preparation of 1,2-disubstituted
cyclobutenes 3
A solution of freshly prepared and titrated arylzinc chloride·LiCl reagent
(1.5 equiv.) was added to a mixture of 2-arylcyclobutene-1-yl phosphate 2,
PdCl2DPEPhos complex (4 mol %). Then a solution of AlCl3 in dry THF
(0.5M) was added. The reaction mixture was stirred for indicated time
period at 50 °C. Then the reaction mixture was diluted with ether (40 mL)
and quenched with 1M solution of tartaric acid or Rochelle salt in water (10
mL). The mixture was stirred for 20 minutes then the organic phase was
washed with brine and dried over MgSO4. Column chromatography
(silicagel) afforded the final products.
Diethyl 2-(cyclohexen-1-yl)-cyclobuten-1-yl phosphate (2k): Prepared
from diethyl 2-bromocyclobuten-1-yl phosphate (1) (0.855 g, 3 mmol), 1-
cyclohexenyl-5,5-dimethyl-1,3,2-dioxaborinane (0.741 g, 3.9 mmol),
Pd(OAc2) (6.8 mg, 1 mol %), RuPhos (28.0 mg, 2 mol %), 1M K3PO4 (9
mL), hexane:EtOAc (3:1, Rf = 0.35), 97% yield (0.834 g), yellow viscous
liquid. 1H NMR (300 MHz, CDCl3): δ = 5.61 (brs, 1H), 4.17 (quint, J = 7.5
Hz, 4H), 2.73 (brs, 2H), 2.342.36 (m, 2H), 2.152.04 (m, 4H), 1.681.52
(m, 4H), 1.36 (tt, J = 7.1, 0.8 Hz, 6H). 13C NMR (75MHz, CDCl3): δ =132.2
(d, J = 8.4 Hz), 131.3 (d, J = 1.5 Hz), 124.4 (d, J = 1.0 Hz), 123.9 (d, J =
10.4 Hz), 64.3 (d, J = 6.0 Hz), 30.3 (d, J = 2.3 Hz), 26.2, 25.2, 22.3, 22.2,
20.3, 16.1 (d, J = 6.5 Hz). HRMS (APCI) [M+H]+ calcd for C14H23O4P:
287.14067, found: 287.14055.
1-(4-Methoxyphenyl)-2-(4-methylphenyl)cyclobutene (3aa): Prepared
from diethyl 2-(4-methoxyphenyl)-cyclobuten-1-yl phosphate (2a) (0.625 g,
2 mmol), 4-methylphenylzinc chloride•lithium chloride (6.67 mL, 3.0 mmol,
0.45M), PdCl2DPEPhos (57.3 mg, 4 mol %), AlCl3 (4 mL, 2.0 mmol, 0.5M),
the reaction mixture was stirred for 14 h, hexane→hexane/DCM
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201801522
European Journal of Organic Chemistry
FULL PAPER
(9:1)→hexane/EtOAc (20:1, Rf = 0.4), 92% yield (0.461 g), white crystalline
solid, m.p. 7475 °C. 1H NMR (300 MHz, CDCl3): δ = 7.517.38 (m, 4H),
7.13 (d, J = 8.0 Hz, 2H), 6.896.82 (m, 2H), 3.82 (s, 3H), 2.74 (s, 4H), 2.35
(s, 3H). 13C NMR (75MHz, CDCl3): δ = 158.8, 137.4, 136.9, 136.6, 133.7,
129.2, 129.0, 127.3, 125.9, 113.6, 55.2, 26.7, 26.6, 21.3. HRMS (APCI)
[M+H]+ calcd for C18H18O: 251.14304, found: 251.14297.
chloride (2.3 mL, 1.13 mmol, 0.49M), PdCl2DPEPhos (21.5 mg, 4 mol %),
AlCl3 (1.5 mL, 0.75 mmol, 0.5M), the reaction mixture was stirred for 18.5
h, hexane→hexane/DCM (9:1, Rf = 0.5), 90% yield (0.320 g), bright yellow
crystalline solid, m.p. 82 °C decomp. 1H NMR (300 MHz, CDCl3): δ =
8.278.20 (m, 3H), 8.16 (d, J = 8.0 Hz, 1H), 8.088.01 (m, 4H), 7.12 (dq,
J = 5.2, 1.1 Hz, 1H), 6.996.95 (m, 2H), 6.90 (dd, J = 5.2, 3.7 Hz, 1H), 6.77
(d, J = 3.8 Hz, 1H), 3.253.19 (m, 2H), 3.073.01 (m, 2H), 1.59 (s, 9H).
13C NMR (75MHz, CDCl3): δ = 149.1, 137.5, 137.4, 137.2, 136.5, 134.5,
131.5, 131.2, 130.9, 130.7, 127.74, 127.73, 127.67, 127.5, 127.3, 125.8,
125.7, 125.4, 124.9, 124.5, 124.2, 123.7, 123.6, 123.1, 122.44, 122.39,
35.2, 31.9, 31.1, 27.8. HRMS (APCI) [M+H]+ calcd for C32H26S2:
475.15487, found: 475.15522.
1-(3-Trifluoromethylphenyl)-2-(4-methoxyphenyl)cyclobutene (3ab):
Prepared from diethyl 2-(4-methoxyphenyl)-cyclobuten-1-yl phosphate
(2a) (0.234 g, 0.75 mmol), 3-trifluoromethylphenylzinc chloride•lithium
chloride (1.13 mmol, 2.56 mL, 0.44M), PdCl2DPEPhos (21.5 mg, 4 mol %),
AlCl3 (1.5 mL, 0.75 mmol, 0.5M), the reaction mixture was stirred for 15 h,
hexane→hexane/DCM (9:1)→hexane/EtOAc (20:1, Rf = 0.6), 93% yield
(0.213 g), white crystalline solid, m.p. 4143 °C. 1H NMR (300 MHz,
CDCl3): δ = 7.747.66 (m, 2H), 7.507.38 (m, 4H), 6.916.84 (m, 2H), 3.83
(s, 3H), 2.77 (s, 4H). 13C NMR (75MHz, CDCl3): δ = 159.4, 140.5, 137.1,
134.8, 130.8 (q, J = 32.2 Hz), 128.9 (q, J = 1.2 Hz), 128.7, 128.5, 127.4,
124.2 (q, J = 272.5 Hz), 123.6 (q, J = 3.8 Hz), 122.6 (q, J = 3.8 Hz), 113.8,
55.3, 27.0, 26.5. 19F NMR (CDCl3): δ = -63.29 (s). HRMS (APCI)
[M+H]+ calcd for C18H15F3O: 305.11478, found: 305.11510.
1-(1-Pyrenyl)-2-(7-tert-butyl-1-pyrenyl)cyclobutene (3jg): Prepared
from diethyl 2-(7-tert-butylpyrene-1-yl)-cyclobuten-1-yl phosphate (2j)
(0.925 g, 2.0 mmol), 1-pyrenylzinc chloride•lithium chloride (6.52 mL, 3.0
mmol, 0.46M,), PdCl2DPEPhos (57.3 mg, 4 mol %), AlCl3 (4.0 Ml, 2.0 mmol,
0.5M), the reaction mixture was stirred for 19 h, hexane→hexane/DCM
(9:1, Rf = 0.5), 84% yield (0.858 g), bright yellow crystalline solid, m.p.
168172 °C. 1H NMR (300 MHz, CDCl3): δ = 8.34 (d, J = 9.8 Hz, 1H), 8.29
(d, J = 9.2 Hz, 1H), 8.212.17 (m, 1H), 8.13 (dd, J = 7.5, 1.3 Hz, 1H),
8.077.87 (m, 11H), 7.70 (d, J = 9.3 Hz, 1H), 7.68 (d, J = 9.4 Hz, 1H), 3.45
(s, 4H), 1.54 (s, 9H). 13C NMR (75MHz, CDCl3): δ = 148.9, 141.7, 141.4,
131.8, 131.5, 131.3, 131.2, 130.8, 130.7, 130.6, 128.0, 127.8, 127.5,
127.41, 127.37, 127.3, 127.23, 127.18, 126.1, 125.8, 125.7, 125.3, 125.1,
125.0, 124.91, 124.88, 124.83, 124.7, 124.5, 123.1, 122.3, 122.2, 35.1,
31.8, 31.2, 31.1. HRMS (APCI) [M+H]+ calcd for C40H30: 511.24203, found:
511.24220.
1-(4-Methoxyphenyl)-2-(4-tert-
butyldimethylsilyloxyphenyl)cyclobutene (3ac): Prepared from diethyl
2-(4-methoxyphenyl)cyclobuten-1-yl phosphate (2a) (0.234 g, 0.75 mmol),
4-(tert-butyldimethylsilyloxy)phenylzinc chloride•lithium chloride (2.74 mL,
1.12 mmol, 0.41M), PdCl2DPEPhos (21.5 mg, 4 mol %), AlCl3 (1.5 mL,
0.75 mmol, 0.5M), the reaction mixture was stirred for 15 h,
hexane→hexane/DCM (9:1)→Hexane/EtOAc (20:1, Rf = 0.5), 94% yield
(0.237 g), clear viscous liquid. 1H NMR (300 MHz, CDCl3): δ = 7.507.43
(m, 2H), 7.427.36 (m, 2H), 6.896.82 (m, 2H), 6.816.75 (m, 2H), 3.82 (s,
3H), 2.71 (s, 4H), 0.98 (s, 9H), 0.21 (s, 6H). 13C NMR (75MHz, CDCl3): δ
= 158.7, 154.9, 136.35, 136.31, 129.8, 129.4, 127.3, 127.1, 119.8, 113.6,
55.3, 26.7, 26.6, 25.7, 18.2, 4.4. HRMS (APCI) [M+H]+ calcd for
C23H30O2Si: 367.20878, found: 367.20961.
1-(1-Cycloheptenyl)-2-(1-cyclohexenyl)cyclobutene (3kh): Prepared
from diethyl 2-(cyclohexen-1-yl)-cyclobuten-1-yl phosphate (2k) (0.215 g,
0.75 mmol), cycloheptene-1-ylzinc chloride•lithium chloride (2.39 mL, 1.12
mmol, 0.47M), PdCl2DPEPhos (21.5 mg, 4 mol %), AlCl3 (1.5 mL, 0.75
mmol, 0.5M), the reaction mixture was stirred for 18 h, hexane (Rf = 0.9),
26% yield (0.045 g), clear oil. 1H NMR (300 MHz, CDCl3): δ = 5.85 (t, J =
6.7 Hz, 1H), 5.705.65 (m, 1H), 2.382.31 (m, 6H), 2.242.08 (m, 6H),
1.801.71 (m, 2H), 1.671.42 (m, 8H). 13C NMR (75MHz, CDCl3): δ =
141.8, 139.7, 138.7, 134.4, 130.4, 125.5, 32.7, 30.4, 28.7, 27.2, 27.0, 26.9,
1-(4-Methoxyphenyl)-2-(4-cyanophenyl)cyclobutene (3ad): Prepared
from diethyl 2-(4-methoxyphenyl)-cyclobuten-1-yl phosphate (2a) (0.469 g,
1.5 mmol), 4-cyanophenylzinc chloride•lithium chloride (4.50 mL, 2.25
mmol, 0.50M), PdCl2DPEPhos (43.0 mg, 4 mol %), AlCl3 (3.0 mL, 1.5
mmol, 0.5M), the reaction mixture was stirred for 13 h,
hexane→hexane/DCM (9:1)→hexane/EtOAc (20:1, Rf = 0.5), 96% yield
(0.377 g), white crystalline solid, m.p. 106107 °C. 1H NMR (300 MHz,
CDCl3): δ = 7.57 (s, 4H), 7.467.40 (m, 2H), 6.916.85 (m, 2H), 3.84 (s,
3H), 2.812.73 (m, 4H). 13C NMR (75MHz, CDCl3): δ = 159.6, 143.0, 140.5,
134.5, 132.2, 128.3, 127.6, 126.2, 119.2, 113.9, 110.0, 55.3, 27.3, 26.3.
HRMS (APCI) [M+H]+ calcd for C18H15NO: 262.12264, found: 262.12263.
26.1, 25.6, 25.5, 22.8, 22.3. HRMS (APCI) [M+H]+ calcd for C17H24
229.19508, found: 229.19520.
:
1-(Cyclohexen-1-yl)-2-(7-tert-butylpyren-1-yl)cyclobutene
(3ki):
Prepared from diethyl 2-(cyclohexene-1-yl)cyclobuten-1-yl phosphate (2k)
(0.287 g, 1.0 mmol), 7-tert-butylpyrene-1-ylzinc chloride•lithium chloride
(3.0 mL, 1.5 mmol, 0.50M), PdCl2DPEPhos (28.7 mg, 4 mol %), AlCl3 (2.0
mL, 1.0 mmol, 0.50M), the reaction mixture was stirred for 12.5 h, hexane,
(Rf = 0.55) 93% yield (0.364 g), yellow foam. 1H NMR (300 MHz, CDCl3):
δ = 8.29 (d, J = 9.4 Hz, 1H), 8.21 (d, J = 7.7 Hz, 2H), 8.04 (d, J = 10.7 Hz,
4H), 7.86 (d, J = 7.7 Hz, 1H), 5.915.85 (m, 1H), 2.95 (s, 2H), 2.812.74
(m, 2H), 2.192.09 (m, 2H), 1.811.70 (m, 2H), 1.59 (s, 9H), 1.541.45 (m,
2H), 1.371.23 (m, 2H). 13C NMR (75MHz, CDCl3): δ = 149.0, 143.9, 136.1,
134.6, 133.8, 131.3, 131.0, 130.1, 127.5, 127.26, 127.22, 127.18, 125.85,
125.80, 125.75, 124.7, 124.2, 123.1, 122.2, 122.0, 35.2, 31.9, 30.5, 26.2,
25.8, 25.6, 22.3, 22.2. HRMS (APCI) [M+H]+ calcd for C30H30: 391.24203,
found: 391.24220.
1-(4-Methoxyphenyl)-2-(1-naphtyl)cyclobutene (3ae): Prepared from
diethyl 2-(4-methoxyphenyl)cyclobuten-1-yl phosphate (2a) (0.234 g, 0.75
mmol), 1-naphtylzinc chloride•lithium chloride (2.54 mL, 1.12 mmol,
0.44M), PdCl2DPEPhos (21.5 mg, 4 mol %), AlCl3 (1.5 mL, 0.75 mmol,
0.5M) the reaction mixture was stirred for 16.5 h, hexane→hexane/DCM
(9:1)→hexane/EtOAc (20:1, Rf = 0.3), 95% yield (0.204 g), white crystalline
solid, m.p. 8385 °C. 1H NMR (300 MHz, CDCl3): δ = 8.03 (d, J = 8.4 Hz,
1H), 7.89 (d, J = 8.0 Hz, 1H), 7.82 (d, J = 7.8 Hz, 1H), 7.57-7.45 (m, 3H),
7.447.36 (m, 1H), 7.167.09 (m, 2H), 6.746.68 (m, 2H), 3.75 (s, 3H),
3.022.91 (m, 4H). 13C NMR (75MHz, CDCl3): δ = 158.9, 140.2, 135.7,
135.5, 133.7, 130.3, 128.3, 127.6, 127.4, 126.5, 125.9, 125.8, 125.5, 125.4,
113.4, 55.2, 30.3, 26.6. HRMS (APCI) [M+H]+ calcd for C21H18O:
287.14304, found: 287.14327.
1-(1-Cyclohexenyl)-2-(4-methoxyphenyl)cyclobutene (3kj): Prepared
from diethyl 2-(cyclohexen-1-yl)cyclobuten-1-yl phosphate (2k) (0.430 g,
1.5 mmol), 4-methoxyphenylzinc chloride•lithium chloride (5.0 mL, 2.25
mmol, 0.45M), PdCl2DPEPhos (43.0 mg, 4 mol %), AlCl3 (3.0 mL, 1.5
mmol, 0.5M), the reaction mixture was stirred for 14 h,
hexane→hexane/DCM (9:1, Rf = 0.45), 66% yield (0.238 g), clear oil. 1H
NMR (300 MHz, CDCl3): δ = 7.357.28 (m, 2H), 6.886.81 (m, 2H),
5.885.82 (m, 1H), 3.81 (s, 3H), 2.632.57 (m, 2H), 2.522.47 (m, 2H),
1-(5-(2,2’-Bithienyl))-2-(7-tert-butyl-1-pyrenyl)cyclobutene
Prepared from diethyl 2-(7-tert-butylpyrene-1-yl)cyclobuten-1-yl
phosphate (2j) (0.347 g, 0.75 mmol), 5-(2,2’-bithienyl)zinc chloride•lithium
(3jf):
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10.1002/ejoc.201801522
European Journal of Organic Chemistry
FULL PAPER
2.252.12 (m, 4H), 1.661.58 (m, 4H). 13C NMR (75MHz, CDCl3): δ =
158.4, 139.4, 135.8, 134.3, 129.9, 128.3, 125.5, 113.4, 55.2, 27.1, 26.7,
25.6, 22.7, 22.3. HRMS (APCI) [M+H]+ calcd for C17H20O: 241.15869,
found: 241.15888.
thienyl)cyclobuten-1-yl phosphate (2g) (0.216 g, 0.75 mmol), 2-(3-
trifluoromethylphenyl)cyclobutene-1-ylzinc chloride•lithium chloride (3.88
mL, 1.13 mmol, 0.29M), PdCl2DPEPhos (21.5 mg, 4 mol %), AlCl3 (1.5 mL,
0.75 mmol, 0.5M), the reaction mixture was stirred for 18 h, hexane (Rf =
0.60), 65% yield (0.162 g), greenish crystalline solid, m.p. 7880 °C. 1H
NMR (300 MHz, CDCl3): δ = 7.66 (s, 1H), 7.55 (d, J = 7.1 Hz, 1H),
7.487.37 (m, 2H), 7.25 (dd, J = 4.4, 1.2 Hz, 1H), 7.036.97 (m, 2H),
2.982.92 (m, 2H), 2.862.75 (m, 6H). 13C NMR (75MHz, CDCl3): δ =
139.2, 138.5, 136.4, 136.1, 135.2, 131.4, 130.5 (q, J = 32.1 Hz), 129.4 (q,
J = 1.1 Hz), 128.6, 127.2, 125.8, 125.7, 124.2 (q, J = 272.5 Hz), 123.5 (q,
J = 3.8 Hz), 123.2 (q, J = 4.0 Hz), 28.9, 28.4, 27.4. 19F NMR (CDCl3): δ =
-63.32 (s). HRMS (APCI) [M+H]+ calcd for C19H15F3S: 333.09193, found:
333.09197.
1-Cycloheptenyl-2-(4-(morpholin-4-ylmethyl)phenyl)cyclobutene
(3lk): Prepared from diethyl 2-(cyclohepten-1-yl)-cyclobuten-1-yl
phosphate (2l) (0.601 g, 2 mmol), 4-(morpholin-4-ylmethyl)phenylzinc
chloride•lithium chloride (10.0 mL, 3.0 mmol, 0.30M), PdCl2DPEPhos
(57.3 mg, 4 mol %), AlCl3 (4.0 mL, 2.0 mmol, 0.5M), the reaction mixture
was stirred for 16 h, hexane/EtOAc (3:1→2:1, Rf = 0.50), 78% yield (0.505
g), yellow viscous liquid. 1H NMR (300 MHz, CDCl3): δ = 7.26 (s, 4H,
overlapping with CHCl3), 6.02 (t, J = 6.8 Hz, 1H), 3.743.67 (m, 4H), 3.48
(s, 2H), 2.622.58 (m, 2H), 2.532.48 (m, 2H), 2.472.41 (m, 4H),
2.392.33 (m, 2H), 2.24 (q, J = 4.1 Hz, 2H), 1.821.73 (m, 2H), 1.581.48
(m, 4H). 13C NMR (75MHz, CDCl3): δ = 141.7, 141.5, 136.1, 135.7, 135.6,
131.3, 128.7, 126.9, 67.0, 63.2, 53.6, 32.6, 29.8, 28.7, 26.9, 26.8, 26.3,
26.1. HRMS (APCI) [M+H]+ calcd for C22H29NO: 324.23219, found:
324.23258.
1-(2-(4-Methylphenyl)cyclobutene-1-yl)-2-(7-tert-butylpyren-1-
yl)cyclobutene
(3mm):
Prepared
from
diethyl
2-(2-(4-
methylphenyl)cyclobuten-1-yl)cyclobuten-1-yl phosphate (2m) (0.385 g,
1.0 mmol), 7-tert-butylpyren-1-ylzinc chloride•lithium chloride (3.0 mL, 1.5
mmol, 0.50M), PdCl2DPEPhos (28.6 mg, 4 mol %), AlCl3 (2.0 mL, 1.0
mmol, 0.5M), the reaction mixture was stirred for 12.5 h,
hexane→hexane/DCM (9:1, Rf = 0.35), 91% yield (0.412 g), bright yellow
crystalline solid, m.p. 150154 °C. 1H NMR (300 MHz, CDCl3): δ = 8.45 (d,
J = 9.3 Hz, 1H), 8.20 (s, 2H), 8.128.00 (m, 4H), 7.91 (d, J = 8.3 Hz, 1H),
7.35 (d, J = 7.1 Hz, 2H), 7.08 (d, J = 7.7 Hz, 2H), 3.15 (brs, 2H), 3.113.04
(m, 2H), 2.60 (brs, 2H), 2.31 (s, 3H), 2.21 (brs, 2H), 1.59 (s, 9H). 13C NMR
(75MHz, CDCl3): δ = 149.0, 141.7, 140.7, 138.1, 137.0, 134.0, 133.1,
132.3, 131.3, 130.9, 130.3, 128.8, 128.3, 127.4, 127.2, 126.2, 125.7, 125.6,
124.8, 124.1, 123.1, 122.2, 122.0, 35.2, 31.9, 31.5, 29.7, 27.4, 27.1, 21.3.
HRMS (APCI) [M+H]+ calcd for C35H32: 453.25768, found: 453.25799.
1-Cycloheptenyl-2-(4-(methoxymethyl)phenyl)cyclobutene
(3ll):
Prepared from diethyl 2-(cyclohepten-1-yl)-cyclobuten-1-yl phosphate (2l)
(0.601 g, 2.0 mmol), 4-(methoxymethyl)phenylzinc chloride•lithium
chloride (6.10 mL, 2.99 mmol, 0.49M), PdCl2DPEPhos (57.3 mg, 4 mol %),
AlCl3 (4.0 mL, 2.0 mmol, 0.5M), the reaction mixture was stirred for 17 h,
hexane→hexane/DCM (9:1, Rf = 0.30), 73% yield of a mixture with 15
mol % of 4,4’-bis(methoxymethyl)biphenyl (0.451 g), yellow liquid. 1H NMR
(300 MHz, CDCl3): δ = 7.347.27 (m, 4H), 6.02 (t, J = 6.6 Hz, 1H), 4.44 (s,
2H), 3.40 (s, 3H), 2.632.58 (m, 2H), 2.532.48 (m, 2H), 2.382.32 (m,
2H), 2.282.20 (m, 2H), 1.821.73 (m, 2H), 1.571.47 (m, 4H). HRMS
(APCI) [M+H]+ calcd for C19H24O: 269.18999, found: 269.18998.
1-(2-(4-Fluorophenyl)cyclobuten-1-yl)-2-(6-methoxynaphth-2-
yl)cyclobutene
(3np):
Prepared
from
diethyl
2-(2-(4-
fluorophenyl)cyclobuten-1-yl)cyclobuten-1-yl phosphate (2n) (0.265 g,
0.75 mmol), 6-methoxynaphthylzinc chloride•lithium chloride (2.81 mL,
1.12 mmol, 0.40M), PdCl2DPEPhos (21.5 mg, 4 mol %), AlCl3 (1.5 mL,
0.75 mmol, 0.5M), the reaction mixture was stirred for 18 h,
hexane→hexane/DCM (9:1→hexane:EtOAc 20:1, Rf = 0.45), 62% yield
(0.166 g), greenish crystalline solid, m.p. 173175 °C. 1H NMR (300 MHz,
CDCl3): δ = 7.657.56 (m, 3H), 7.517.46 (m, 1H), 7.377.29 (m, 2H),
1-(2-(4-Methoxyphenyl)cyclobuten-1-y)-2-(3-(trifluoromethyl)phenyl)
cyclobutene
(3an):
Prepared
from
diethyl
2-(4-
methoxyphenyl)cyclobuten-1-yl phosphate (2a) (0.394 g, 1.26 mmol), 2-
(3-(trifluoromethyl)phenyl)cyclobuten-1-ylzinc chloride•lithium chloride
(5.4 mL,1.89 mmol, 0.35M), PdCl2DPEPhos (36.0 mg, 4 mol %), AlCl3 (2.5
mL, 1.25 mmol, 0.5M), the reaction mixture was stirred for 16 h,
hexane→hexane/DCM (9:1, Rf = 0.20), 61% (0.274 g), greenish crystalline
solid, m.p. 109111 °C. 1H NMR (300 MHz, CDCl3): δ = 7.56 (s, 1H), 7.48
(d, J = 7.8 Hz, 1H), 7.447.31 (m, 2H), 7.307.24 (m, 2H), 6.826.77 (m,
2H), 3.79 (s, 3H), 2.78 (s, 4H), 2.772.72 (m, 4H). 13C NMR (75MHz,
CDCl3): δ = 159.1, 142.0, 138.1, 137.0, 136.4, 131.9, 130.4 (q, J = 32.1
Hz), 129.4 (q, J = 1.2 Hz), 128.7, 128.4, 128.0, 124.2 (q, J = 272.3 Hz),
123.2 (p, J = 4.0 Hz), 113.5, 55.3, 28.4, 27.9, 27.2, 26.9. 19F NMR (CDCl3):
δ = -63.36 (s). HRMS (APCI) [M+H]+ calcd for C22H19F3O: 357.14608,
found: 357.14643.
7.137.06 (m, 2H), 6.966.88 (m, 2H), 3.91 (s, 3H), 2.892.74 (m, 8H). 13
C
NMR (75MHz, CDCl3): δ = 161.8 (d, J = 247.1 Hz), 157.8, 141.0, 139.4 (d,
J = 0.6 Hz), 134.6 (d, J = 2.2 Hz), 134.2, 133.8, 132.2 (d, J = 3.4 Hz), 131.3,
129.6, 128.6, 128.2 (d, J = 7.9 Hz), 126.3, 125.4 (d, J = 0.8 Hz), 118.9,
115.1, 114.8, 105.8, 55.3, 28.3, 28.2, 27.15, 27.10. 19F NMR (CDCl3): δ =
-114.65 (m). HRMS (APCI) [M+H]+ calcd for C25H21FO: 357.16492, found:
357.16525.
1-(4-Cyanophenyl)-2-(2-(4-fluorophenyl)cyclobuten-1-yl)cyclobutene
(3nr): Prepared from diethyl 2-(2-(4-fluorophenyl)cyclobuten-1-
yl)cyclobuten-1-yl phosphate (2n) (0.352 g, 1.0 mmol), 4-cyanophenylzinc
chloride•lithium chloride (2.88 mL, 1.50 mmol, 0.52M), PdCl2DPEPhos
(28.6 mg, 4 mol %), AlCl3 (2.0 mL, 1.0 mmol, 0.5M), the reaction mixture
was stirred for 13 h, hexane→hexane/DCM (9:1→hexane:EtOAc 20:1, Rf
= 0.55), 83% yield (0.250 g), greenish crystalline solid, m.p. 119122 °C.
1H NMR (300 MHz, CDCl3): δ = 7.52 (d, J = 7.7 Hz, 2H), 7.36 (d, J = 8.3
Hz, 2H), 7.28 (dd, J = 7.6, 6.0 Hz, 2H), 6.95 (t, J = 8.4 Hz, 2H), 2.802.71
(m, 8H). 13C NMR (75MHz, CDCl3): δ = 162.2 (d, J = 247.5 Hz), 141.9 (d,
J = 0.9 Hz), 139.6, 138.9, 138.5, 133.5 (d, J = 2.2 Hz), 131.83, 131.76 (d,
J = 3.4 Hz), 128.4 (d, J = 8.1 Hz), 126.7, 119.1, 115.1 (d, J = 21.6 Hz),
110.0, 28.5, 28.0, 27.3, 26.8. 19F NMR (CDCl3): δ = -113.42 (m). HRMS
(APCI) [M+H]+ calcd for C21H16FN: 302.13395, found: 302.13397.
1-(4-Methoxyphenyl)-2-(2-(4-methylphenyl)cyclobuten-1-
yl)cyclobutene
(3aq):
Prepared
from
diethyl
2-(4-
methoxyphenyl)cyclobuten-1-yl phosphate (2a) (0.422 g, 1.35 mmol), 2-
(4-methylphenyl)cyclobuten-1-ylzinc chloride•lithium chloride (4.58 mL,
2.43 mmol, 0.53M), PdCl2DPEPhos (38.7 mg, 4 mol %), AlCl3 (2.7 mL,
1.35 mmol, 0.5M), the reaction mixture was stirred for 12.5 h,
hexane→hexane/DCM (9:1, Rf = 0.30), 88% yield (0.360 g), white
crystalline solid, m.p. 146148 °C. 1H NMR (300 MHz, CDCl3): δ =
7.367.27 (m, 4H), 7.08 (d, J = 8.2 Hz, 2H), 6.856.78 (m, 2H), 3.80 (s,
3H), 2.752.71 (m, 8H), 2.33 (s, 3H). 13C NMR (75MHz, CDCl3): δ = 158.8,
140.27, 140.25, 136.8, 134.0, 133.2, 132.8, 129.0, 128.7, 127.9, 126.5,
113.5, 55.2, 28.3, 28.2, 27.11, 27.06, 21.3. HRMS (APCI) [M+H]+ calcd for
C22H22O : 303.17434, found: 303.17453.
1-(2-(4-Fluorophenyl)cyclobuten-1-yl)-2-(2-(4-
1-(2-Thienylcyclobutene-1-y)-2-(3-
methylphenyl)cyclobuten-1-yl)cyclobutene (3ms): Prepared from 2-(2-
(trifluoromethyl)phenyl)cyclobutene (3go): Prepared from diethyl 2-(2-
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10.1002/ejoc.201801522
European Journal of Organic Chemistry
FULL PAPER
(4-methylphenyl)cyclobuten-1-yl)cyclobuten-1-yl phosphate (2m) (0.289 g,
0.75 mmol), 2-(4-fluorophenyl)cyclobuten-1-ylzinc chloride•lithium chloride
(3.55 mL, 1.35 mmol, 0.38M), PdCl2DPEPhos (21.5 mg, 4 mol %), AlCl3
(1.5 mL, 0.75 mmol, 0.5M), the reaction mixture was stirred for 13 h,
hexane (Rf = 0.65), 87% yield (0.223 g), bright yellow crystalline solid, m.p.
146150 °C. 1H NMR (300 MHz, CDCl3): δ = 7.407.33 (m, 2H), 7.30 (d,
J = 8.2 Hz, 2H), 7.12 (d, J = 8.2 Hz, 2H), 7.036.94 (m, 2H), 2.812.72 (m,
4H), 2.69 (m, 8H), 2.34 (s, 3H). 13C NMR (75MHz, CDCl3): δ = 161.8 (d, J
= 247.7 Hz), 141.5, 139.7 (d, J = 0.8 Hz), 137.3, 137.1, 136.2, 134.3 (d, J
= 2.2 Hz), 133.6, 133.2, 132.3 (d, J = 3.5 Hz), 128.8, 128.1 (d, J = 8.0 Hz),
126.5, 115.0 (d, J = 21.4 Hz), 29.7, 29.6, 28.20, 28.17, 27.44, 27.41, 21.3.
19F NMR (CDCl3): δ = -114.78 (m). HRMS (APCI) [M+H]+ calcd for
C25H23F: 343.18566, found: 343.18582.
2-(4-Methoxyphenyl)-3-(4-tert-butyldimethylsilyloxyphenyl)buta-1,3-
diene
(4ac):
Prepared
from
1-(4-methoxyphenyl)-2-(4-tert-
butyldimethylsilyloxyphenyl) cyclobutene (3ac) (0.168 g, 0.5 mmol), the
reaction mixture was stirred for 14 h, hexane→hexane/DCM
(9:1)→hexane/EtOAc (20:1, Rf = 0.5), 98% yield (0.165 g), clear viscous
liquid. 1H NMR (300 MHz, CDCl3): δ = 7.347.22 (m, 4H), 6.826.69 (m,
4H), 5.74 (d, J = 1.8 Hz, 2H), 5.22 (d, J = 1.7 Hz, 2H), 3.77 (s, 3H), 0.96
(s, 9H), 0.17 (s, 6H). 13C NMR (75MHz, CDCl3): δ = 159.0, 155.2, 149.5,
149.4, 133.2, 132.7, 128.51, 128.47, 119.6, 114.4, 114.3, 113.5, 55.2, 25.6,
18.2, -4.4. HRMS (APCI) [M+H]+ calcd for C23H30O2Si : 367.20878, found:
367.20895.
2-(4-Cyanophenyl)-3-(4-methoxyphenyl)buta-1,3-diene
(4ad):
Prepared from 1-(4-methoxyphenyl)-2-(4-cyanophenyl)cyclobutene (3ad)
(0.131 g, 0.5 mmol), the reaction mixture was stirred for 14 h,
hexane→hexane/DCM (9:1)→hexane/EtOAc (20:1, Rf = 0.35), 93% yield
(0.122 g), white crystalline solid, m.p. 5758 °C. 1H NMR (300 MHz,
CDCl3): δ = 7.54 (d, J = 8.3 Hz, 2H), 7.47 (d, J = 8.4 Hz, 2H), 7.307.24
(m, 2H), 6.836.76 (m, 2H), 5.64 (d, J = 1.1 Hz, 1H), 5.53 (d, J = 1.5 Hz,
1H), 5.50 (d, J = 1.1 Hz, 1H), 5.25 (d, J = 1.4 Hz, 1H), 3.77 (s, 3H). 13C
NMR (75MHz, CDCl3): δ = 159.3, 148.6, 148.1, 144.6, 132.0, 131.7, 128.4,
127.9, 118.8, 118.5, 115.4, 113.7, 111.0, 55.2. HRMS (APCI) [M+H]+ calcd
for C18H15NO: 262.12264, found: 262.12276.
1-{4-[2-(4-Fluorophenyl)cyclobutenyl]phenyl}-2-[2-(4-methylphenyl)
cyclobutenyl]cyclobutene(3mt):
methylphenyl)cyclobuten-1-yl)cyclobuten-1-yl phosphate (2m) (0.385 g,
1.0 mmol), 4-(2-(4-(fluorophenyl)cyclobuten-1-yl)phenyl)zinc
Prepared
from
2-(2-(4-
chloride•lithium chloride (3.0 mL, 1.5 mmol, 0.50M), PdCl2DPEPhos (28.6
mg, 4 mol %), AlCl3 (2.0 mL, 1.0 mmol, 0.5M), the reaction mixture was
stirred for 14 h, hexane (Rf = 0.25), 92% yield (0.386 g), bright yellow
crystalline solid, m.p. 176180 °C. 1H NMR (300 MHz, CDCl3): δ =
7.507.24 (m, 8H), 7.09 (d, J = 7.9 Hz, 2H), 7.036.95 (m, 2H), 2.76 (s,
8H), 2.75 (s, 4H), 2.33 (s, 3H). 13C NMR (75MHz, CDCl3): δ = 162.0 (d, J
= 247.2 Hz), 141.4, 140.1, 138.3 (d, J = 1.8 Hz), 137.6, 137.1, 135.4, 135.1,
134.6, 133.9, 133.2, 132.5 (d, J = 3.4 Hz), 128.7, 127.8 (d, J = 8.0 Hz),
126.6, 126.5, 125.6, 115.2 (d, J = 21.3 Hz), 28.4, 28.3, 27.2, 27.0, 26.6,
21.4. 19F NMR (CDCl3): δ = -114.23 (m). HRMS (APCI) [M+H]+ calcd for
C31H27F: 419.21696, found: 419.21708.
2-(4-Methoxyphenyl)-3-(1-naphthyl)buta-1,3-diene (4ae): Prepared
from 1-(4-methoxyphenyl)-2-(1-naphthyl)cyclobutene (3ae) (0.143 g, 0.5
mmol), the reaction mixture was stirred for 18 h, hexane→hexane/DCM
(9:1)→hexane/EtOAc (20:1, Rf = 0.4), 95% yield (0.136 g), white crystalline
solid, m.p. 7576 °C. 1H NMR (300 MHz, CDCl3): δ = 8.118.04 (m, 1H),
7.897.78 (m, 2H), 7.527.40 (m, 6H), 6.966.88 (m, 2H), 5.50 (d, J = 1.8
Hz, 1H), 5.415.38 (m, 1H), 5.195.17 (m, 1H), 4.81 (d, J = 1.4 Hz, 1H),
3.84 (s, 3H). 13C NMR (75MHz, CDCl3): δ = 159.1, 149.9, 148.8, 139.7,
133.60, 133.55, 131.9, 129.8, 128.2, 127.7, 126.9, 126.1, 125.8, 125.6,
125.3, 120.2, 117.7, 113.5, 55.3. HRMS (APCI) [M+H]+ calcd for C21H18O:
287.14304, found: 287.14329.
General procedure for the synthesis of alkenes 4 by opening of the
cyclobutene ring.
A solution of 1,2-disubstituted cyclobutene 3 in xylene (10 mL/mmol) was
stirred at 150 °C. After the reaction was complete, the majority of xylene
was evaporated and the resultant mixture was subjected to column
chromatography (silica gel) affording the final product 4.
2-(1-Pyrenyl)-3-(7-tert-butyl-1-pyrenyl)buta-1,3-diene (4jg): Prepared
from 1-(1-pyrenyl)-2-(7-tert-butyl-1-pyrenyl)cyclobutene (3jg) (0.255 g, 0.5
mmol), the reaction mixture was stirred for 20 h. After the reaction mixture
was cooled to ambient temperature, about half of xylene was evaporated
on vacuum and the mixture was diluted with hexane. The pure product
precipitated immediately and filtration afforded 0.206 g (81%) of the pure
product as a white crystalline solid, m.p. 264 °C (decomp.). 1H NMR (300
MHz, CDCl3): δ = 8.49 (d, J = 9.1 Hz, 1H), 8.45 (d, J = 9.1 Hz, 1H),
8.348.09 (m, 14H), 8.04 (t, J = 7.7 Hz, 1H), 5.435.38 (m, 2H), 5.225.17
(m, 2H), 1.61 (s, 9H). 13C NMR (75MHz, CDCl3): δ = 149.4, 149.3, 136.7,
136.5, 131.4, 131.3, 131.1, 130.9, 130.7, 130.5, 129.4, 129.2, 127.71,
127.65, 127.58, 127.53, 127.45, 127.43, 127.38, 127.29, 127.26, 126.0,
125.6, 125.4, 125.2, 125.0, 124.91, 124.88, 124.80, 124.6, 124.4, 123.1,
122.4, 122.3, 122.03, 121.97, 35.3, 32.0. HRMS (APCI) [M+H]+ calcd for
C40H30: 511.24203, found: 511.24215.
2-(4-Methoxyphenyl)-3-(4-methylphenyl)buta-1,3-diene
(4aa):
Prepared from 1-(4-methoxyphenyl)-2-(4-methylphenyl)cyclobutene (3aa)
(0.250 g, 1.0 mmol), the reaction mixture was stirred for 14 h,
hexane→hexane/DCM (9:1→hexane:EtOAc 20:1, Rf = 0.4), 92% yield
(0.230 g), white crystalline solid, m.p. 3638 °C. 1H NMR (300 MHz,
CDCl3): δ = 7.367.25 (m, 4H), 7.07 (d, J = 8.4 Hz, 2H), 6.836.76 (m, 2H),
5.52 (d, J = 1.8 Hz, 1H), 5.47 (d, J = 1.7 Hz, 1H), 5.28 (d, J = 1.8 Hz, 1H),
5.24 (d, J = 1.7 Hz, 1H), 3.77 (s, 3H), 2.30 (s, 3H). 13C NMR (75MHz,
CDCl3): δ = 159.0, 149.8, 149.3, 137.24, 137.19, 132.7, 128.9, 128.5,
127.2, 115.2, 114.5, 113.5, 55.2, 21.1. HRMS (APCI) [M+H]+ calcd for
C18H18O: 251.14304, found: 251.14319.
2-(4-Methoxyphenyl)-3-(3-trifluoromethylphenyl)buta-1,3-diene (4ab):
Prepared
from
1-(3-trifluoromethylphenyl)-2-(4-
2-Cyclohexene-1-yl-3-(7-tert-butylpyrene-1-ylbuta-1,3-diene
(4ki):
methoxyphenyl)cyclobutene (3ab) (0.152 g, 0.5 mmol), the reaction
mixture was stirred for 15 h, hexane→hexane/DCM (9:1, Rf = 0.35), 92%
yield (0.140 g), clear viscous liquid. 1H NMR (500 MHz, CDCl3): δ = 7.66
(s, 1H), 7.53 (d, J = 7.5 Hz, 1H), 7.48 (d, J = 7.7 Hz, 1H), 7.37 (t, J = 7.7
Hz, 1H), 7.327.28 (m, 2H), 6.836.79 (m, 2H), 5.58 (d, J = 1.2 Hz, 1H),
5.50 (d, J = 1.5 Hz, 1H), 5.41 (d, J = 1.2 Hz, 1H), 5.23 (d, J = 1.7 Hz, 1H),
3.78 (s, 3H). 13C NMR (75MHz, CDCl3): δ = 159.3, 148.9, 148.6, 141.0,
132.2, 130.8 (q, J = 1.4 Hz), 130.6 (q, J = 32.4 Hz), 128.6, 124.17 (q, J =
3.8 Hz), 124.12 (q, J = 270.8 Hz), 124.17 (q, J = 3.9 Hz), 124.07 (q, J =
3.9 Hz), 117.4, 115.5, 113.7, 55.2. 19F NMR (CDCl3): δ = -63.14 (s). HRMS
(APCI) [M+H]+ calcd for C18H15F3O: 305.11478, found: 305.11525.
Prepared from 1-(cyclohexene-1-yl)-2-(7-tert-butylpyren-1-yl)cyclobutene
(3ki) (0.195 g, 0.5 mmol), the reaction mixture was stirred for 16 h, hexane
(Rf=0.45), 98% yield (0.191 g), yellow viscous liquid. 1H NMR (300 MHz,
CDCl3): δ = 8.34 (d, J = 9.2 Hz, 1H), 8.228.17 (m, 2H), 8.117.99 (m, 4H),
7.84 (d, J = 8.0 Hz, 1H), 5.955.89 (m, 1H), 5.78 (d, J = 2.1 Hz, 1H), 5.44
(d, J = 1.9 Hz, 1H), 5.13 (d, J = 1.5 Hz, 1H), 4.76 (d, J = 1.8 Hz, 1H),
2.382.29 (m, 2H), 2.102.01 (m, 2H), 1.741.52 (m, 13H). 13C NMR
(75MHz, CDCl3): δ = 153.3, 149.0, 148.3, 137.4, 137.3, 131.2, 130.8,
130.2, 128.5, 127.31, 127.26, 127.20, 126.7, 125.4, 124.9, 124.2, 123.1,
122.2, 122.0, 119.6, 114.4, 35.2, 32.0, 28.0, 25.6, 22.9, 22.2. HRMS
(APCI) [M+H]+ calcd for C30H30: 391.24203, found: 391.24234.
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201801522
European Journal of Organic Chemistry
FULL PAPER
2-(1-Cyclohexenyl)-3-(4-methoxyphenyl)buta-1,3-diene
(4kj):
124.14 (two overlapping quartets), 119.7, 119.0, 117.3, 114.5, 113.5, 55.2.
19F NMR (CDCl3): δ = -63.04 (s). HRMS (APCI) [M+H]+ calcd for
C22H19F3O: 357.14608, found: 357.14660.
Prepared from 1-(1-cycohexenyl)-2-(4-methoxyphenyl)cyclobutene (3kj)
(0.120 g, 0.5 mmol), the reaction mixture was stirred for 17 h,
hexane→hexane/DCM (9:1, Rf=0.55), 72% yield (0.087 g), clear viscous
liquid. 1H NMR (300 MHz, CDCl3): δ = 7.357.29 (m, 2H), 6.866.79 (m,
2H), 5.745.69 (m, 1H), 5.44 (d, J = 1.8 Hz, 1H), 5.225.20 (m, 1H), 5.09
(d, J = 1.8 Hz, 1H), 5.025.00 (m, 1H), 3.80 (s, 3H), 2.262.18 (m, 2H),
2.041.95 (m, 2H), 1.711.60 (m, 2H), 1.581.47 (m, 2H). 13C NMR
(75MHz, CDCl3): δ = 159.0, 151.3, 149.3, 135.3, 133.0, 128.8, 127.5,
113.4, 112.5, 111.6, 55.2, 25.8, 22.8, 22.1. HRMS (APCI) [M+H]+ calcd for
C17H20O: 241.15869, found: 241.15878.
2-(4-Fluorophenyl)-3,4-dimethylene-5-(6-methoxynaphthyl)hexa-1,5-
diene (4np): Prepared from 1-(2-(4-fluorophenyl)cyclobuten-1-yl)-2-(6-
methoxynaphth-2-yl)cyclobutene (3np) (0.178 g, 0.5 mmol), the reaction
mixture was stirred for 24 h, hexane→hexane/DCM (9:1, Rf=0.40), 66%
yield (0.118 g), yellow crystalline solid, m.p. 9194 °C. 1H NMR (300 MHz,
CDCl3): δ = 7.67 (d, J = 2.8 Hz, 1H), 7.65 (d, J = 3.0 Hz, 1H), 7.61 (d, J =
1.3 Hz, 1H), 7.42 (dd, J = 8.5, 1.8 Hz, 1H), 7.327.25 (m, 2H), 7.187.11
(m, 2H), 7.036.94 (m, 2H), 5.50 (d, J = 1.7 Hz, 1H), 5.36 (d, J = 1.5 Hz,
1H), 5.345.29 (m, 4H), 5.23 (d, J = 1.7 Hz, 1H), 5.17 (d, J = 1.6 Hz, 1H),
3.93 (s, 3H). 13C NMR (75MHz, CDCl3): δ = 162.4 (d, J = 246.2 Hz), 157.8,
149.0, 148.70, 148.66, 148.3, 136.6 (d, J = 3.2 Hz), 135.7, 134.0, 129.6,
129.0 (d, J = 8.2 Hz), 128.7, 126.5, 126.1, 126.0, 119.20, 119.15, 118.9,
115.70 (d, J = 1.1 Hz), 115.65, 114.9 (d, J = 21.4 Hz), 105.7, 55.3. 19F
NMR (CDCl3): δ = -115.59 (m). HRMS (APCI) [M+H]+ calcd for C25H21FO:
357.16492, found: 357.16548.
2-(1-Cycloheptenyl)-3-(4-(morpholin-4-ylmethyl)phenyl)buta-1,3-
diene
(4lk): Prepared from 1-cycloheptenyl-2-(4-(morpholin-4-
ylmethyl)phenyl)cyclobutene (3lk) (0.187 g, 0.578 mmol), the reaction
mixture was stirred for 21 h, hexane:EtOAc (3:1)→(2:1, Rf=0.60), 75%
yield (0.140 g), clear viscous liquid. 1H NMR (300 MHz, CDCl3): δ = 7.31
(d, J = 8.1 Hz, 2H), 7.23 (d, J = 8.1 Hz, 2H), 5.90 (t, J = 6.7 Hz, 1H), 5.43
(d, J = 1.8 Hz, 1H), 5.215.19 (m, 2H), 4.98 (d, J = 1.9 Hz, 1H), 3.733.68
(m, 4H), 3.48 (s, 2H), 2.472.40 (m, 4H), 2.362.29 (m, 2H), 2.142.05 (m,
2H), 1.751.65 (m, 2H), 1.461.34 (m, 4H). 13C NMR (75MHz, CDCl3): δ =
152.8, 149.6, 143.8, 139.5, 136.8, 132.4, 128.8, 127.0, 114.5, 112.8, 67.0,
63.2, 53.6, 32.5, 30.5, 28.6, 26.6, 26.4. HRMS (APCI) [M+H]+ calcd for
C22H29NO: 324.23219, found: 324.23261.
2-(4-Methoxyphenyl)-3,4-dimethylene-5-(4-tolyl)hexa-1,5-diene (4aq):
Prepared from 1-(4-methoxyphenyl)-2-(2-(4-methylphenyl)cyclobuten-1-
yl)cyclobutene (3aq) (0.151 g, 0.5 mmol), the reaction mixture was stirred
for 23 h, hexane→hexane/DCM (9:1, Rf=0.40), 65% yield (0.098 g), clear
viscous liquid. 1H NMR (300 MHz, CDCl3): δ = 7.287.19 (m, 4H), 7.11 (d,
J = 8.2 Hz, 2H), 6.876.81 (m, 2H), 5.37 (d, J = 1.8 Hz, 1H), 5.33 (d, J =
1.8 Hz, 1H), 5.275.23 (m, 3H), 5.21 (d, J = 1.8 Hz, 1H), 5.175.15 (m,
2H), 3.82 (s, 3H), 2.35 (s, 3H). 13C NMR (75MHz, CDCl3): δ = 159.2, 149.1,
149.0, 148.9, 148.7, 137.8, 137.2, 133.2, 128.8, 128.5, 127.2, 118.9, 118.8,
115.0, 114.3, 113.4, 55.3, 21.2. HRMS (APCI) [M+H]+ calcd for C22H22O :
303.17434, found: 303.17462.
2-(1-Cycloheptenyl)-3-(4-(methoxmethyl)phenyl)buta-1,3-diene (4ll):
Prepared
from
of
1-cycloheptenyl-2-(4-(morpholin-4-
ylmethyl)phenyl)cyclobutene (3ll) (0.20 g, 0.64 mmol containing
approximately 15 mol.% of 4,4’-bis(methoxymethyl)biphenyl), the reaction
mixture was stirred for 22 h, hexane→hexane/DCM (9:1→4:1, Rf=0.20),
77% yield (0.133 g), clear viscous liquid. 1H NMR (300 MHz, CDCl3): δ =
7.34 (d, J = 7.8 Hz, 2H), 7.25 (d, J = 7.8 Hz, 2H), 5.88 (t, J = 6.7 Hz, 1H),
5.43 (d, J = 1.8 Hz, 1H), 5.22 (d, J = 1.8 Hz, 1H), 5.20 (d, J = 1.9 Hz, 1H),
4.99 (d, J = 1.8 Hz, 1H), 4.44 (s, 2H), 3.39 (s, 3H), 2.362.28 (m, 2H),
2.132.04 (m, 2H), 1.751.64 (m, 2H), 1.481.33 (m, 4H). 13C NMR
(75MHz, CDCl3): δ = 152.7, 149.6, 143.7, 140.1, 137.2, 132.4, 127.4,
127.1, 114.7, 112.8, 74.5, 58.1, 32.4, 30.5, 28.6, 26.6, 26.4. HRMS (APCI)
[M+H]+ calcd for C19H24O: 269.18999, found: 269.19001.
2-(4-Cyanophenyl)-3,4-dimethylene-5-(4-fluorophenyl)hexa-1,5-diene
(4nr): Prepared from 1-(4-cyanophenyl)-2-(2-(4-fluorophenyl)cyclobuten-
1-yl)cycobutene (3nr) (0.151 g, 0.5 mmol), the reaction mixture was stirred
for 24 h, hexane→hexane/DCM (9:1)→hexane/EtOAc (20:1, Rf=0.50),
65% yield (0.098 g), yellow oil. 1H NMR (300 MHz, CDCl3): δ = 7.617.56
(m, 2H), 7.377.31 (m, 2H), 7.247.18 (m, 2H), 7.036.94 (m, 2H), 5.44 (d,
J = 1.2 Hz, 1H), 5.39 (d, J = 1.2 Hz, 1H), 5.355.31 (m, 2H), 5.275.24 (m,
2H), 5.19 (d, J = 1.8 Hz, 1H), 5.16 (d, J = 1.8 Hz, 1H). 13C NMR (75MHz,
CDCl3): δ = 162.5 (d, J = 247.1 Hz), 148.4, 147.94, 147.85, 147.7, 145.1,
136.3 (d, J = 3.5 Hz), 132.0, 129.0 (d, J = 8.0 Hz), 128.0, 119.8, 119.4,
118.8, 118.4, 116.1 (d, J = 1.0 Hz), 115.0 (d, J = 21.3 Hz), 111.2. 19F NMR
(CDCl3): δ = -115.16 (m). HRMS (APCI) [M+H]+ calcd for C21H16FN:
302.13395, found: 302.13399.
2-(7-tert-Butylpyrenyl)-3,4-dimethylene-5-(4-tolyl)hexa-1,5-diene
(4mm): Prepared from 1-(2-(4-methylphenyl)cyclobuten-1-yl)-2-(7-tert-
butylpyrene-1-yl)cyclobutene (3mm) (0.226 g, 0.5 mmol), the reaction
mixture was stirred for 24 h, hexane (Rf=0.50), 50% yield (0.113 g),
yellowish wax. 1H NMR (300 MHz, CDCl3): δ = 8.268.20 (m, 2H), 8.11 (d,
J = 7.7 Hz, 1H), 8.07 (s, 2H), 8.05 (d, J = 8.2 Hz, 1H), 7.95 (d, J = 9.3 Hz,
1H), 7.74 (d, J = 7.8 Hz, 1H), 5.98 (d, J = 1.7 Hz, 1H), 5.55 (d, J = 1.7 Hz,
1H), 5.44 (brs, 1H), 5.40 (d, J = 1.4 Hz, 1H), 5.335.29 (m, 2H), 4.90 (d, J
= 1.8 Hz, 1H), 2.44 (s, 3H), 1.62 (s, 9H). 13C NMR (75MHz, CDCl3): δ =
150.2, 149.5, 149.0, 147.6, 137.9, 137.1, 136.7, 131.2, 130.8, 130.3, 128.9,
128.7, 128.2, 127.4, 127.3, 127.2, 127.1, 125.4, 124.6, 124.1, 123.0, 122.2,
122.1, 120.0, 119.8, 118.8, 115.7, 35.2, 31.9, 21.2. HRMS (APCI)
[M+H]+ calcd for C35H32: 453.25768, found: 453.25801.
2-{4-[2-(4-fluorophenyl)-1-methyleneprop-2-enyl]phenyl}-3,4-
dimethylene-5-(4-methylphenyl)hexa-1,5-diene(4mt): Prepared from
alkene 3mt (0.222 g, 0.53 mmol), the reaction mixture was stirred for 24 h,
hexane (Rf=0.30), 72% yield (0.160 g), slightly yellow wax. 1H NMR (300
MHz, CDCl3): δ = 7.417.28 (m, 4H), 7.277.15 (m, 4H), 7.08 (d, J = 7.9
Hz, 2H), 7.016.91 (m, 2H), 5.58 (d, J = 1.5 Hz, 1H), 5.51 (d, J = 1.5 Hz,
1H), 5.39 (d, J = 1.6 Hz, 1H), 5.36 (d, J = 1.6 Hz, 1H), 5.32 (d, J = 1.4 Hz,
1H), 5.31 (d, J = 1.6 Hz, 1H), 5.305.24 (m, 3H), 5.23 (d, J = 1.7 Hz, 1H),
5.155.13 (m, 2H), 2.35 (s, 3H). 13C NMR (75MHz, CDCl3): δ = 162.4 (d,
J = 246.6 Hz), 149.3, 149.0, 148.9, 148.81, 148.80, 148.76, 139.9, 139.0,
137.7, 137.2, 136.2 (d, J = 3.4 Hz), 129.1 (d, J = 8.0 Hz), 128.8, 127.27,
127.25, 127.1, 118.9, 116.21, 116.15, 116.14, 115.7, 115.13, 115.06 (d, J
= 21.4 Hz), 21.1. 19F NMR (CDCl3): δ = -115.42 (m). HRMS (APCI)
[M+H]+ calcd for C31H27F: 419.21696, found: 419.21713.
2-(4-Methoxyphenyl)-3,4-dimethylene-5-(3-
(trifluoromethyl)phenyl)hexa-1,5-diene (4an): Prepared from 1-(2-(4-
methoxyphenyl)cyclobutene-1-y)-2-(3-(trifluoromethyl)phenyl)cyclobutene
(3an) (0.179 g, 0.5 mmol), the reaction mixture was stirred for 23 h,
hexane→hexane/DCM (9:1, Rf=0.35), 64% yield (0.114 g), clear viscous
liquid. 1H NMR (300 MHz, CDCl3): δ = 7.567.38 (m, 4H), 7.257.20 (m,
2H), 6.886.81 (m, 2H), 5.44 (d, J = 1.4 Hz, 1H), 5.38 (d, J = 1.4 Hz, 1H),
5.355.32 (m, 2H), 5.25 (d, J = 1.9 Hz, 1H), 5.22 (d, J = 1.8 Hz, 1H), 5.21
(d, J = 1.8 Hz, 1H), 5.16 (d, J = 1.5 Hz, 1H), 3.82 (s, 3H). 13C NMR (75MHz,
CDCl3): δ = 159.3, 148.8, 148.5, 148.2, 148.0, 141.4, 132.8, 130.6 (q, J =
1.2 Hz), 130.5 (q, J = 32.1 Hz), 128.6, 128.4, 124.18 (q, J = 272.2 Hz),
Acknowledgments
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10.1002/ejoc.201801522
European Journal of Organic Chemistry
FULL PAPER
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Financial support from specific university research (MSMT No 21-
SVV/2018) and the Grant Agency of the Czech Republic (Grant
No 18-12150S) is gratefully acknowledged.
Keywords: alkenes • cross-coupling • aluminum • C-C bond
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Developed methodology for the
synthesis of terminally substituted [3]-
and [4]dendralenes, as well as 2,3-
disubstituted buta-1,3-dienes, involves
the preparation of 1,2-disubstituted
cyclobutenes from readily available 2-
bromocyclobutanone and the
subsequent thermal ring-opening
reactions.
Synthetic Method*
Peter Polák Tomáš Tobrman*
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Synthetic procedure
Author(s), Corresponding Author(s)*
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