Phase-vanishing method applied to condensation reactions using TiCl4

Article abstract of DOI:10.1016/j.jfluchem.2017.02.009

The phase-vanishing (PV) method using perfluorohexanes as the phase screen was applied to the aldol condensation using TiCl₄ as the Lewis acid. A special test tube was used, in which an interface between the fluorous and organic layers was stirred, and cyclohexanone was treated with two equivalents of benzaldehyde derivatives under PV conditions to afford corresponding 2,6-dibenzylidencyclohexanone in good yields. The formyl-methylenation of ketones with triethylamine using TiCl₄ was also demonstrated by the PV method.

Full text of DOI:10.1016/j.jfluchem.2017.02.009

Accepted Manuscript
Title: Phase-vanishing method applied to condensation
reactions using TiCl4
Authors: Yusuke Adachi, Kenji Kuniyoshi, Hiroshi Matsubara
PII:
S0022-1139(17)30008-8
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.jfluchem.2017.02.009
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6-2-2017
7-2-2017
Please cite this article as: Yusuke Adachi, Kenji Kuniyoshi, Hiroshi Matsubara, Phase-
vanishing method applied to condensation reactions using TiCl4, Journal of Fluorine
Chemistryhttp://dx.doi.org/10.1016/j.jfluchem.2017.02.009
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1
Phase-vanishing method applied to condensation reactions using TiCl4
Yusuke Adachi, Kenji Kuniyoshi, Hiroshi Matsubara* matsu@c.s.osakafu-u.ac.jp
Department of Chemistry, Graduate School of Science, Osaka Prefecture University, Sakai,
Osaka 599-8531, Japan
*Corresponding author.

2
Graphical abstract
The phase-vanishing method using perfluorohexanes as the phase screen was applied to the
aldol condensation and formyl-methylenation using TiCl4.

3
Highlights


The phase-vanishing (PV) method was applied to the aldol reaction using TiCl4.
A test tube in which an interface between fluorous and organic layers can be stirred was
prepared.


By using this test tube, PV reactions with TiCl4 were promoted.
Formyl-methylenation of ketones with TiCl4–NEt3 was performed by the PV method.

4
Abstract
The phase-vanishing (PV) method using perfluorohexanes as the phase screen was applied to
the aldol condensation using TiCl4 as the Lewis acid. A special test tube was used, in which an
interface between the fluorous and organic layers was stirred, and cyclohexanone was treated
with two equivalents of benzaldehyde derivatives under PV conditions to afford
corresponding 2,6-dibenzylidencyclohexanone in good yields. The formyl-methylenation of
ketones with triethylamine using TiCl4 was also demonstrated by the PV method.
Keywords: Phase-vanishing method; Fluorous solvent; Aldol reaction; Titanium
tetrachloride; Formyl-methylenation

5
1. Introduction
Generally, highly fluorinated compounds (fluorous compounds) are not miscible with most
organic solvents and water, affording another phase (fluorous phase) [1]. In addition, densities
of these solvents are typically greater than those of organic liquids. By utilizing the unique
properties of fluorous compounds, a synthetically convenient triphasic system was developed
[2]: a phase-vanishing (PV) method, in which fluorous solvents, such as FC-72
(perfluorohexanes) and Galden HT-135 (polyperfluoroalkyl ethers), serve as a phase screen to
connect two separated layers to steadily transport reagents to a substrate-bearing organic layer
[3]. The feasibility of the PV method was first demonstrated by the bromination of alkenes
with molecular bromine [4] and the demethylation of methoxy groups with BBr3 [4]. Various
reactions have been conducted by our group [5] and other groups [6]. For example, a
Grignard-type reaction using a quadraphasic PV system comprising a 1:1 mixture of Galden
HT135 and HT200 [7], iodomethane (or iodoethane), magnesium, diethyl ether, and carbonyl
compounds, was demonstrated [5f]. In this method, alkyl magnesium iodide reagents
successfully generated in situ react with carbonyl compounds, affording the desired products
in good yields. Recently, another PV method has been developed by our group, where
gaseous reagents, e.g. acetylene [8] and hydrogen sulfide [9], obtained from calcium carbide
and phosphorus pentasulfide, respectively, were simultaneously used in several organic
reactions, affording the desired products in good yields. In addition, in these methods, the
passive diffusion of water into the fluorous solvent was exploited to gradually evolve these
gaseous reagents. Therefore, this method is advantageous for reactions requiring gases as it
avoids the use of a high-pressure apparatus, e.g. regulators and gas cylinders. The PV method
is simple and facile for controlling the heat evolved during exothermic reactions using a
common test tube without the need for cooling equipment and dropping funnels. Typical
reagents utilized in PV systems, e.g. Br2, BBr3, SnCl4, and CH2I2, are denser than fluorous
media (ρ > 1.7 g cm−3); next, the use of titanium chloride (TiCl4) is examined. TiCl4 is not
only a simple, common, and cost-effective, but also a versatile, reagent [10,11]. A majority of
applications with this reagent involve its use as a Lewis acid. Several useful transformations
and coupling, including Friedel–Crafts, Diels–Alder, and Mukaiyama reactions, have been
achieved using TiCl4. With the use of TiCl4, low reaction temperatures or slow addition is
required, which can be solved via the use of the PV method. Moreover, the density of TiCl4 is
1.73 g cm−3; hence, TiCl4 is used in the PV method (Scheme 1).

6
2. Results and discussion
As the model reaction, the PV method was applied to the aldol condensation of
cyclohexanone with benzaldehyde in the presence of TiCl4 [12]. Table 1 summarizes the
results obtained. First, FC-72 (4.5 mL) was placed in a test tube (14 mm  130 m, Fig. 2
test tube A) under argon, and TiCl4 (1.1 equiv.) was slowly introduced. As a result, heavier
TiCl4 sank to the bottom, forming two layers. Next, a CH2Cl2 (5 mL) solution containing
cyclohexanone (1, 2.0 mmol) and benzaldehyde (2a, 2.0 mmol) was added; this solution
floated above the FC-72 layer, forming a triphasic system (Fig. 1, photograph A).
The test tube was then left without stirring at 23 °C. The TiCl4 layer disappeared after 2 h,
affording two layers, and the top layer gradually turned dark red. However, the reaction was
not complete at this stage. After 12 h, an insoluble solid was observed around the surface
between the fluorous and organic layers (Fig. 1, photograph B). The reaction mixture in the
organic layer was quenched with water and extracted with dichloromethane. The organic
phase was collected and washed with brine, dried over sodium sulfate, filtered, and
concentrated in vacuo, affording dialkenylated product 2,6-bis(benzylidene)cyclohexanone
(4a) in 38% yield (measured by 1H-NMR) and not the desired product
2-benzylidenecyclohexanone (3a) (entry 1). As the aldol reaction did not cease at the
formation of mono-substituted ketone 3a, our synthetic target was changed to the
disubstituted product 4a. However, the use of two equivalents of 2a afforded 4a in a similar
1
yield of 36% (entry 2). H-NMR analysis confirmed the presence of significant amounts of
unreacted 1 and 2a in the reaction mixture, indicating that the insoluble solid formed at the
fluorous–organic interface during the reaction possibly suppresses the diffusion of TiCl4 to the
organic layer [13]. A special test tube was then developed in which the interface could be
stirred (Fig. 2, test tube B). However, the aldol reaction did not efficiently proceed in test tube
B, affording the product in lower yields than, or yields similar to, those observed for the
products in the usual test tube (16% and 35%; entries 3 and 4). The inner diameter of test tube
B at the interface was reduced to locate a stirring bar, which decreased the diffusion of TiCl4
to the organic layer. As such, another type test tube in which the surface can be stirred was
prepared according to the study reported by Iskra (Figure 2, test tube C) [6d]. In the middle of
the test tube (30 mm from the bottom), a glass grid was installed (Fig. 3), and a magnetic
stirrer bar [14] was placed on the grid, efficiently stirring the interface. In addition, the glass
grid did not obstruct the diffusion of TiCl4. This test tube was effective in promoting the aldol
reaction; the desired product was almost quantitatively obtained in 6 h (entry 5). Decreasing
the reaction time to 3 h led to a slightly decreased product yield (entry 6). Reducing the TiCl4

7
amount marginally affected the product yield (entry 7). Finally, decreasing the reaction time
to 5 h also afforded an excellent yield of 4a (>98%, entry 8); hence, entry 8 is chosen as the
optimal reaction conditions for the PV aldol reaction.
Using the optimized conditions, the substrate scope was explored with various aldehydes.
Methoxybenzaldehydes underwent the aldol reaction to afford desired products almost
quantitatively (Table 2, entries 3 and 4), while 4-tolualdehyde afforded the coupling product
in a somewhat lower yield (Table 2, entry 2). The yield obtained for fluorobenzaldehyde was
slightly less than those obtained for methoxybenzaldehydes. On the other hand,
4-cyanobenzaldehyde afforded the corresponding bisbenzylidene product in significantly
lower yield (Table 2, entry 6).
Table 3 summarizes the general scope of ketones. Cyclic ketones, e.g. cyclopentanone
(1b) and 2-tetralone (1c), afforded the desired products 4g and 4h, respectively, in moderate
yields [15]. On the contrary, acyclic ketones did not undergo the aldol reaction.
To exclusively prepare monoalkenylated ketones, the Mukaiyama aldol reaction [16] was
examined using the PV system (Table 4). Thus, siloxycyclohexene 5 was treated with 2a in
the presence of TiCl4. However, dialkenylated product 4a was always obtained as the major
product. Perhaps, mono-alkenylated product 3a generated in situ would rapidly undergo the
second alkenylation under PV conditions. Typically, the Mukaiyama aldol reaction is carried
out at low temperature, e.g. 78 °C; hence, the PV reaction was conducted with lowering
temperature. Unfortunately, decreasing the reaction temperature to 10 °C suppressed the
diffusion of TiCl4, resulting in no product formation.
Next, the formyl-methylenation of ketones with triethylamine in the presence of TiCl4
[17] using the PV system was performed (Table 5). The reaction conditions were initially
screened using benzophenone (6a) as the starting substrate: 6a (1.0 mmol) and triethylamine
(4.0 mmol) were treated with TiCl4 (4.0 mmol) using the test tube C at 23 °C for 1 day,
affording desired 3,3-diphenylacrolein (7a) in 46% yield (entry 1). A large amount of
unreacted substrate (54%) was recovered from the reaction mixture, and trace amount of
product 8a from the McMurry coupling [18] was obtained. Extending the reaction time led to
the increased yield of 7a to 75%, with the decreased amount of the unreacted ketone (entries
2–3). Reducing the amounts of TiCl4 and triethylamine led to decreased product yield (entry
4). With increasing reaction temperature from 23 to 30 °C with a shorter reaction time (2
days), the product yield was improved to 85% (entry 5); the generality of the reaction under
these conditions was investigated.
Benzophenones bearing electron-donating or electron-withdrawing groups afforded the

8
desired products in moderate yields, except substrate 6d (entries 1–6). Fluorenone (6g)
afforded corresponding acrolein 7g in 25%, while anthrone (6h) was unreacted, with
considerable recovery under this condition (entries 7 and 8). On the other hand, benzaldehyde
(2a) formed a complex mixture, with the desired product in trace amounts, and a trace amount
of the unreacted substrate was recovered (entry 9).
3. Conclusion
The PV method was applied to reactions involving TiCl4. By the use of a simple test tube
for the PV system, low yields of products were obtained because of the generation of an
insoluble solid during reactions, which obstructed the diffusion of TiCl4. However, by using a
special test tube in which interface between fluorous and organic layers was stirred, the
reactions were promoted to afford products. Using this test tube, the cross-aldol reaction, as
well as formyl-methylenation, was successfully conducted in the PV system. The PV method
described here, which employs the special test tube, can also be extended to enable other
reactions, where insoluble solids are generated during the reaction. Further applications of this
method will be reported in due course.
4. Experimental
4.1. Typical procedure for the aldol reaction of cyclohexane with benzaldehyde in the
presence of TiCl4 using the PV method (Table 1, entry 8)
First, a Pyrex test tube (14 mm × 130 mm) bearing a stirring bar grid (made of glass) located
30 mm from the bottom, was purged with argon. Second, a magnetic stirring bar
(cross-shaped, 10 mm × 10 mm) was located on the grid. Third, TiCl4 (417 mg, 2.2 mmol)
was placed at the bottom of the test tube, and FC-72 (4.5 mL) was slowly added to this test
tube using a syringe; the fluorous layer reached the grid. Subsequently, a solution of
cyclohexanone (196 mg, 2.0 mmol) in dichloromethane (5.0 mL) and benzaldehyde (424 g,
4.0 mmol) were slowly added in that order, forming three layers. A rubber septum was fitted
into the test tube, and the septum was pierced using a needle equipped with an
argon-containing balloon. The test tube was slowly stirred at 25 °C for 5 h ensuring that the
layers were not mixed. After removing FC-72 using a glass pipette, the organic layer was
carefully transferred to a beaker containing water using dichloromethane. The organic layer
was separated, and the aqueous layer was extracted with dichloromethane. The combined

9
organic layers were washed with brine then dried over sodium sulfate, filtered, and
concentrated. The residue was purified by silica-gel column chromatography using
hexane–ethyl acetate (5:1) as the eluent, affording 2,6-dibenzylidenecyclohexanone (4a, 496
1
mg, 90%) [19] as a yellow solid. H-NMR (CDCl3, 400 MHz): δ 7.84 (2H, s, C=CH), 7.48
(4H, d, J = 7.5 Hz, Ar-H), 7.41 (4H, t, J = 7.5 Hz, Ar-H), 7.34 (2H, t, J = 7.2 Hz, Ar-H),
2.94–2.92 (4H, m, C=C-CH2), 1.81–1.75 (2H, m, C=C-CH2-CH2); 13C-NMR (CDCl3, 100
MHz): δ 190.31, 136.95, 136.21, 135.98, 130.41, 128.64, 128.43, 28.49, 23.03.
2,6-Bis(2,5-dimethoxybenzylidene)cyclohexanone (4d)
1H-NMR (400 MHz, CDCl3) δ: 7.93 (2H, s, C=CH), 6.88–6.83 (6H, m, Ar-H), 3.81 (6H, s,
OCH3), 3.79 (6H, s, OCH3), 2.86–2.83 (4H, m, C=C-CH2), 1.78–1.74 (2H, m,
C=C-CH2-CH2). 13C-NMR (100 MHz, CDCl3): δ 190.44, 152.90, 136.91, 132.43, 131.07,
1
125.98, 116.42, 114.50, 111.62, 56.15, 55.89, 28.81, 23.50. IR (KBr): 1663, 1220, 1037 cm .
GC-MS: EI, 70 eV, m/z (rel. int.): 394(M+, 5), 364(24), 363(100), 333(5), 331(7), 317(8),
227(12), 182(5%). HRMS: EI, 70 eV, m/z: calcd. for C24H26O5: 394.1780, found: 394.1776.
4.2. Typical procedure for the formyl-methylenation of benzophenone with triethylamine in the
presence of TiCl4 by the PV method (Table 5, entry 5)
First, a Pyrex test tube (14 mm × 130 mm) bearing a stirring bar grid (made of glass) located
30 mm from the bottom, was purged with argon. Second, a cross-shaped magnetic stirring bar
(10 mm 10 mm) was placed on the grid. Third, TiCl4 (759 mg, 4.0 mmol) was placed at the
bottom of the test tube, and FC-72 (3.5 mL) was slowly added to this test tube using a
syringe; the fluorous layer reached the grid. Subsequently, a solution of benzophenone (182
mg, 1.0 mmol) in dichloromethane (5.0 mL), followed by triethylamine (405 g, 4.0 mmol),
was slowly added in that order, forming three layers. A rubber septum was fitted into the test
tube, and the septum was pierced using a needle equipped with an argon-containing balloon.
The test tube was slowly stirred at 30 °C for 2 days ensuring that the layers were not mixed,
and then it was allowed to cool to ambient temperature. After removing FC-72 using a glass
pipette, the organic layer was carefully transferred to a beaker containing saturated NH4Cl aq
using dichloromethane. The organic layer was separated, and the aqueous layer was extracted
with dichloromethane. The combined organic layers were washed with brine then dried over
sodium sulfate, filtered, and concentrated. The residue was purified by silica-gel column
chromatography using hexane–ethyl acetate (98:4) as the eluent, affording

10
1
3,3-diphenylpropenal (7a, 125 mg, 60%) [17,20] as a yellow oil. H-NMR (CDCl3, 500
MHz): δ 9.53 (d, 1H, J = 7.7 Hz, CHO), 7.50–7.30 (m, 10H, Ar-H), 6.60 (d, 1H, J = 8.2 Hz,
13
vinyl-H). C-NMR (CDCl3, 125 MHz): δ 193.57, 162.32, 139.81, 136.78, 130.83, 130.59,
129.55, 128.77, 128.72, 128.44, 127.38.
3,3-Bis(4-cyanophenyl)propenal (7d)
1H-NMR (500 MHz, CDCl3): δ 9.52 (d, 1H, J = 7.7 Hz, CHO), 7.81 (d, 2H, J = 8.5 Hz, Ar-H),
7.70 (d, 2H, J = 8.5 Hz, Ar-H), 7.44–7.40 (m, 4H, Ar-H), 6.66 (d, 1H, J = 7.7 Hz, vinyl-H);
13C-NMR (125 MHz, CDCl3): δ 191.49, 157.15, 142.90, 140.18, 132.79, 132.68, 131.26,
1
129.95, 129.00, 118.02, 117.91, 114.51, 114.14; IR (KBr): 2746, 2225, 1671 cm . GC-MS:
EI, 70 eV, m/z (rel. int.): 258(M+, 91), 257(100), 229(43), 201(21), 175(18), 127(86),
75(16%); HRMS: EI, 70 eV, m/z: calcd. for C17H10N2O: 258.0793, found: 258.0786.
Acknowledgements
This study was partially supported by a Grant-in-Aid for Scientific Research (C) (no.
1681202700) from the Japan Society for the Promotion of Science (JSPS).

11
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(j) M. Tojino, Y. Hirose, M. Mizuno, Tetrahedron Lett. 54 (2013) 7124–7126.

12
[7];1; Galden HT135 and HT200 are polyether-type perfluorinated solvents (Fig. 4), which
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Reagents for Organic Synthesis, second ed., L.A. Paquette, D. Crich, P.L. Fuchs, G.A.
Molander (Eds.), Wiley, Chichester, UK, 2009, vol. 12, pp. 9526–9552;
(b) M. Periasamy, ARKIVOC VII (2002) 151–166.
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A. Mariappan, Tetrahedron Lett. 55 (2014) 3503–3506;
(b) J . Alvarado, A.T. Herrmann, A. Zakarian, J . Org. Chem. 79 (2014) 6206–6220;
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[13];1; White smoke was vigorously evolved after the removal of FC-72 from the reaction,
indicative of the presence of significant amounts of TiCl4 in the solvent.
[14];1; A cross-shaped magnetic stirrer bar was used as it was easy to rotate on the grid.
[15];1; As a considerable amount of unreacted substrates was recovered after the reaction,
the reactivity of these ketones was somehow less than that of cyclohexane. Notably, stable
alkenylation products were obtained from the reaction, with no decomposition as detected
1
by H-NMR or GCMS.

13
[16] (a) T. Mukaiyama, K. Nakamura, K. Banno,;1; Chem. Lett. 2 (1973) 1011–1014; (b) T.
Mukaiyama, Org. Rect. 28 (1982) 203–331.
[17] P. Bharathi, M. Periasamy,;1; Org. Lett. 1 (1999) 857–859.
[18] J .E. McMurry, M.P. Fleming,;1; J . Am. Chem. Soc. 96 (1974) 4708–4709.
[19] M. Singh, N. Raghav,;1; Med. Chem. Res. 23 (2014) 1781–1788.
[20];1; A considerable decrease (25%) in the isolated yield was related to the difficulty in
the separation of the desired product by silica-gel column chromatography.

14
Figure Captions
Fig. 1. PV aldol reaction of cyclohexanone and benzaldehyde with TiCl4. Arrows indicate the phase interface.
(A) A triphasic system: TiCl4, FC-72, and CH2Cl2 solution of cyclohexanone and benzaldehyde (from the
bottom). (B) After 12 h, the TiCl4 layer disappeared, affording two phases, FC-72 and CH2Cl2 phases (from the
bottom), respectively, and a dark red insoluble solid was generated near the interface of the two phases.
Fig. 2. Test tubes for the PV method
Fig. 3. Top view of test tube C (Temporary outer jacket to hold the test tube is also shown.)
Fig. 4. Structure of Galden.®
Scheme 1. Concept of PV method using TiCl4.

15
Tables
Table 1 Optimization of conditions for the PV aldol reactiona
Yield (%)b,c
Entry Test-tube 2a (equiv.) TiCl4 (equiv.) Time (h)
3a
4a
38
1
2
3
4
5
6
7
8
A
A
B
B
C
C
C
C
1.0
2.0
2.1
2.0
2.0
2.0
2.0
2.0
1.1
1.1
1.2
1.2
1.1
1.2
0.7
1.1
12
12
5
< 2
< 2
36
d
–
16
d
12
6
–
35
d
–
>98
86
3
5
3
< 2
80
>98 (90)e
d
5
–
a Reaction conditions: FC-72 (4.5 mL), CH2Cl2 (5 mL), cyclohexanone (2.0 mmol) under argon at 23 °C.
b Based on cyclohexanone.
c Determined by 1H-NMR using 1,1,2,2-tetrachloroethane as the internal standard.
d Not detected.
e Isolated yield.

16
Table 2 PV aldol reaction of cyclohexanonea
Entry
R
Yield (%)b
1
2
3
4
5
6
H (2a)
Me (2b)
>98 (90)c
80
OMe (2c)
2,5-OMe (2d)
F (2e)
>98
>98
93 (81)c
CN (2f)
70
a Reaction conditions: cyclohexanone (2.0 mmol), benzaldehydes (4.0 mmol), TiCl4 (2.2 mmol), FC-72 (4.5 mL),
CH2Cl2 (5 mL) in test tube C under argon at 23 °C for 5 h.
b Determined by 1H-NMR using 1,1,2,2-tetrachloroethane as the internal standard.
c Isolated yield.

17
Table 3 PV aldol reaction with benzaldehydea
Entry
1
Substrate
Yield (%)b
74
1b
1c
2
61
c
3
4
–
1d
1e
< 2
a Reaction conditions: ketones (2.0 mmol), benzaldehyde (4.0 mmol), TiCl4 (2.2 mmol), FC-72 (4.5 mL), CH2Cl2
(5 mL) in test tube C under argon at 23 °C for 5h.
b Determined by 1H-NMR using 1,1,2,2-tetrachloroethane as the internal standard.
c Not detected.

18
Table 4 Mukaiyama aldol reaction using the PV methoda
Yield (%)b,c
Entry
5 (equiv.)
Time (h)
3a
13
18
25
4
4a
52
49
53
33
1
2
1.0
1.5
1.9
2.0
2.0
5
5
3
5
4
5d
3
e
e
24
–
–
a Reaction condition: benzaldehyde (1.0 mmol), FC-72 (4.5 mL), CH2Cl2 (5 mL) in test tube C under argon at
23 °C.
b Based on benzaldehyde.
c Determined by 1H-NMR using 1,1,2,2-tetrachloroethane as the internal standard.
d At 10 °C.
e Not detected.

19
Table 5 Optimization of conditions for the formyl-methylenation of benzophenonea
Yield (%)b
Temperature
Entry
Time (day)
Recovery 6a (%)b
(°C)
7a
46
8a
1
2
23
23
23
23
30
1
2
3
3
2
< 2
< 2
< 2
< 2
< 2
54
29
62
3
4c
75
14
50
42
14 (11)d
5
85 (60)d
a Reaction conditions: benzophenone (1.0 mmol), TiCl4 (4.0 mmol), NEt3 (4.0 mmol), FC-72 (4.5 mL), CH2Cl2
(5 mL) in test tube C under argon.
b Determined by 1H-NMR using 1,1,2,2-tetrachloroethane as the internal standard.
c Using TiCl4 (3.0 equiv.) and NEt3 (3.0 equiv.).
d Isolated yield.

20
Table 6 Formyl-methylenation of ketones using the PV methoda
Yield (%)b
Entry
Substrate
R = H (6a)
Recovery 6 (%)b
7
8
< 2c
2
1
2
3
4
5
6
60
62
55
12
66
40
11
9
R = F (6b)
R = Cl (6c)
R = CN (6d)
R = Me (6e)
R = OMe (6f)
12
31
47
49
38
d
–
d
–
d
–
d
7
8
25c
17c
–
6g
6h
d
d
–
–
93
d
9
< 2
–
< 2
2a
a Reaction conditions: ketone (1.0 mmol), TiCl4 (4.0 mmol), NEt3 (4.0 mmol), FC-72 (4.5 mL), CH2Cl2 (5 mL)
in test tube C under argon at 30 °C for 2 days.
b Isolated yield.
c Determined by 1H-NMR using 1,1,2,2-tetrachloroethane as the internal standard.
d Not detected.