Efficient Multigram Approach to Acetylenes and CF3-ynones Starting from Dichloroalkenes Prepared by Catalytic Olefination Reaction (COR)

Article abstract of DOI:10.1002/ejoc.202000531

A novel approach to terminal acetylenes based on catalytic olefination reaction COR of arylaldehydes to form dichloroalkenes followed by treatment with nBuLi was elaborated. This method is atom economical and displays high yields and effectivity. The corresponding alkynes can be prepared in up to 97 % yield. One pot procedure towards CF₃-ynones was elaborated to provide these products in up to 87 % yield starting from dichloroalkenes.

Full text of DOI:10.1002/ejoc.202000531

European Journal of Organic Chemistry
Accepted Article
Accepted Article
Title: Efficient multi gram approach to acetylenes and CF3-ynones
starting from dichloroalkenes prepared by catalytic olefination
reaction (COR)
Authors: Vasiliy Muzalevskiy, Zoia Sizova, Alexey Shastin, Valentine
G. Nenajdenko, and Arstan I. Diusenov
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using the Digital Object Identifier (DOI) given below. The VoR will be
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To be cited as: Eur. J. Org. Chem. 10.1002/ejoc.202000531
Link to VoR: https://doi.org/10.1002/ejoc.202000531
01/2020

10.1002/ejoc.202000531
European Journal of Organic Chemistry
Efficient multi gram approach to acetylenes and CF3-ynones starting from
dichloroalkenes prepared by catalytic olefination reaction (COR)
Vasiliy M. Muzalevskiy,a Zoia A. Sizova,a Arstan I. Diusenov,a Alexey V. Shastin,b
and Valentine G. Nenajdenko,a,*
[a]
Dr. Vasiliy M. Muzalevskiy, Mr. Arstan I. Diusenov, Dr. Zoia A. Sizova, Prof. Dr. Valentine G.
Nenajdenko, Department of Chemistry, Lomonosov Moscow State University, 119899 Moscow,
Russia. E-mail: nenajdenko@org.chem.msu.ru. http://www.chem.msu.ru/rus/chair/org_w/os/welcome.html
[b]
Dr. Alexey V. Shastin, Institute of Problems of Chemical Physics, Russian Academy of
Sciences, 142432 Chernogolovka, Russia.
Abstract
A novel approach to terminal acetylenes based on catalytic olefination reaction COR of
arylaldehydes to form dichloroalkenes followed by treatment with n-BuLi was elaborated. High
yields, effectiveness and atom economy of the method were shown. The corresponding alkynes
can be prepared by this method in up to 97% yield. One pot procedure towards CF3-ynones was
elaborated to give these products in up to 87% yield starting from dichloroalkenes.
Key Topic — Fluorinated compounds
Keywords: olefination, alkenes, alkynes, fluorine, ketones
Introduction
Dichloroalkenes are highly attractive building blocks which can be modified by many ways.1
Literature approaches to the dichloroalkenes are mostly based on various modifications of the
Wittig reaction (phosphorous ylides prepared from CCl4-PPh3, 2 CBrCl3-PPh3, 3 CHCl3-PPh3-t-
7 , 8
9
BuOK, 4 , 5 , 6 CCl4-P(NMe2)3
and CBrCl3-P(NMe2)3 systems), the Wittig-Horner reaction
((EtO)2P(O)CCl2Li10) and -elimination reaction in -trichloromethyl carbinol acetates RCH(OAc)-
13
CCl3 (rarely sulphonates) promoted by treatment with various reducing reagents (Zn,11 In,12 SmI2
,
16
Pb/Al,14 RMgBr,15 CrCl2 ).
Few decades ago a novel catalytic reaction (COR or Nenajdenko-Shastin olefination) was
elaborated in our laboratory.17,18 COR is a transformation of N-unsubstituted hydrazones into
alkenes under treatment with polyhalogenated alkanes in the presence of a base (usually
ammonia or ethylenediamine) and catalytic amounts of copper salts.19 The reaction has a broad
synthetic scope to open robust access to both alkyl and aryl substituted haloalkenes, including
fluorinated ones20 and functionalized alkenes (Scheme 1).21 It should be noted, that COR has a
very simple experimental procedure, which does not require using of organometallic or toxic
organophospourous compounds, affordable price and availability of starting materials. High yields
and stereoselectivity are distinct advantages of the reaction.
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10.1002/ejoc.202000531
European Journal of Organic Chemistry
Scheme 1. Synthetic scope of the catalytic olefination reaction.
,-Unsaturated CF3-ketones have a great synthetic utility in the synthesis of various fluorinated
heterocyclic compounds.22 Using CF3-ynones as building blocks, we have succeeded to prepare
various fluorinated heterocycles such as diazepines23, pyrimidines24, thiophenes25, triazoles26,
pyrazoles27, 1,3-oxazinoquinolines28. During last decades we have permanent interest to study
,-unsaturated CF3-ketones and demand highly efficient and cost affordable procedure to
synthesize CF3-ynones.
The most convenient approach to the synthesis of CF3-ynones is a trifluoroacetylation of
acetylenic carbanions by CF3CO2Et. As a rule, lithium acetylides are used for this aim prepared by
treatment of terminal acetylenes with strong lithium bases. One of the most general literature
approaches to the terminal acetylenes is Corey-Fuchs reaction, which is a two-step transformation
of aldehydes by chain extension to acetylene. The first step is a Wittig olefination of aldehyde with
CBr4 and PPh3 (or PPh3 and Zn) to form dibromoalkene.29 The second step is a conversion of the
prepared dibromoalkene into acetylene by treatment with n-BuLi. 30 Discovered in early 70-s,
Corey-Fuchs reaction became of one of the most reliable and universal approach towards terminal
acetylenes.31 In spite high synthetic utility, this method has one significant drawback – low atom
economy.32
We envisioned that dichloroalkenes can be used as starting materials for more efficient synthesis
of acetylenes. From that point of view this would be a valuable alternative for Corey-Fuchs
reaction. In this manuscript we report a systematical investigation of conversion of aldehydes into
acetylenes through the intermediate formation of dichloroalkenes using COR as well as one-pot
synthesis of CF3-ynones.
Results and discussion
Literature synthesis of dichloralkenes based on COR demands to use excess of CCl4 (up to 5
equivalents).18 We decided here to optimize synthesis of dichloroalkenes. It was proposed that
inverse order of reagents addition can provide excess of CCl4 if a solution of an in situ prepared
hydrazone is slowly added to a mixture of carbon tetrachloride (or other polyhaloalkane), aqueous
ammonia and CuCl in DMSO (see experimental part for details). This simple trick allows creating a
substantial excess of polyhaloalkane in respect to hydrazone in each moment of time.33 Using
inverse order of reagent addition, a set of dichloroalkenes was synthesized in up to 88% (Scheme
2). Inverse order of reagent addition allowed to decrease dramatically the amount of both copper
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10.1002/ejoc.202000531
European Journal of Organic Chemistry
catalyst (2 mol% of CuCl) and CCl4 (2 equivalents). Moreover, this advanced procedure provided
significantly higher yields of dichloroalkenes. For example, we succeeded to improve yield of most
problematic alkene 3e from 26%18 to 60%. Another improvement of the inversed procedure is a
successful scaling of the reaction to a multi-gram value. Thus, the reaction can be carried out in up
to 0.2 mol scale to produce up to 30-35 g of alkenes at one batch. It should be noted, that more
reactive CBrCl3 can give even better yields (77% compared to 69% for 3f). However, CCl4 is a
reagent of choice due to its lower price (158 $ for 500 g of CBrCl3, ~10 $ for 1 kg of CCl4).
Scheme 2. Synthesis of dichloroalkenes 3 using the inverse order addition.
The inversed procedure is also applicable for olefination of ketones. Due to lower electrophilicity of
ketones comparing to aldehydes, two step procedure was applied staring from the corresponding
hydrazones 5. Treatment of hydrazones 5 with CBrCl3 led to tetrasubstituted alkenes 6 in up to
74% yield (Scheme 3).
Scheme 3. Synthesis of dichloroalkenes from ketones.
Next, we shifted our attention to the synthesis of terminal acetylenes 7 starting from
dichloroalkenes 3 (Scheme 4). It should be noted, that only very rare examples of conversion of
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10.1002/ejoc.202000531
European Journal of Organic Chemistry
dichloroalkenes into acetylenes can be found in the literature.10a,11c,34 We found that treatment of
dichloroalkenes 3 with two equivalents of n-BuLi at -70 C followed by acidic work up led to
terminal acetylenes 7 in high yields. For example, alkyne 7b was isolated in 97% yield.
Scheme 4. Synthesis of acetylenes 7 from dichloroalkenes 3.
It should be noted, that the yield of acetylenes 7 calculated on two steps is very high. For example,
the total yield of 7b is 74%, which is slightly better then in the literature (55%35 and 71%36).
However, the proposed here approach has several advantages. One of the major disadvantages
of the Corey-Fuchs reaction is large excess of phosphorous reagents. In turn, the reaction left a
stoichiometric amount of triphenylphosphine oxide having high molecular weight. Isolation of target
product and separation of Ph3PO from the reaction mixture can be tricky especially in the case of
a large scale synthesis.30 In contrast, COR results in formation of nontoxic symmetrical azines,
NH4Cl and molecular nitrogen (Scheme 1). Another very important advantage is a greater value of
atom economy of COR (0.55 for 3b), comparing 0.29 for 3b using Corey-Fuchs reaction. At last,
the most significant advantage of COR is a much lower cost of all starting materials. Indeed,
hydrazine monohydrate, carbon tetrachloride, aqueous ammonia are industrial compounds
produced in up to hundreds million tons (NH3) per year. Since that, their prices are dramatically
lower than those of CBr4 and PPh3 (Scheme 5). Lower molecular weights of COR reagents make
COR is even more beneficial. Thus, total cost of all reagents for the synthesis of alkynes in 0.2 mol
scale by Corey-Fuchs method is about 115 $, while COR requires 21$. As a result, total cost of all
reagents in our approach to acetylenes is about almost 6 times lower than in Corey-Fuchs reaction.
Scheme 5. Comparison of total reagents cost for Corey-Fuchs reaction and COR.
Finally, we tested possibility to use lithium acetylides formed in situ by treatment of
dichloroalkenes 3 by n-BuLi for trifluoroacetylation with CF3CO2Et at -70 C. As a result, CF3-
ynones can be synthesized by this one-pot approach very efficiently to give target products in
good to high yield (Scheme 6). The transformation was successfully carried out in up to 0.1 mol
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10.1002/ejoc.202000531
European Journal of Organic Chemistry
scale to yield up to 20 g of CF3-ynones in a single load. It should be noted, that the yields of
alkynes 7, obtained by this procedure, are comparable or even higher of those in the synthesis
from terminal acetylenes.27b,37 So, the method is a valuable alternative to the known analogues.
Scheme 6. One pot synthesis of CF3-ynones from dichloroalkenes 3.
Conclusions
In conclusion, we investigated transformation of arylaldehydes into acetylenes through the two
step procedure using COR with inverse addition of the reagents for the synthesis of starting
dichloroalkenes. Comparing to Corey-Fuchs reaction the proposed approach has several
advantages such as higher atom economy, 6 times lower cost and low toxicity of the reaction
wastes. Based on dichloroalkenes a versatile one pot procedure towards CF3-ynones was
elaborated.
Experimental part
General remarks. NMR spectra were recorded in CDCl3 at 600.1, 400.1 (1H), 150.9, 100.6 (13C)
and 376.3 (19F) MHz respectively. Chemical shifts (δ) in ppm are reported with the use of the
1
13
19
residual chloroform signals (7.25 for H and 77.0 for C) as internal reference. The F chemical
shifts were referenced to C6F6, (-162.9 ppm). HRMS (ESI-TOF) spectra were measured with an
Orbitrap Elite instrument. TLC analysis was performed on “Merck 60 F254” plates. All reagents
were of reagent grade and were used as such or distilled prior to use. Melting points were
determined on an Electrothermal 9100 apparatus.
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European Journal of Organic Chemistry
Synthesis of dichloroalkenes 3 (general procedure, 0.2 mol scale): First step (preparation of
hydrazone 2 solution). Erlenmeyer flask was charged with N2H4xH2O (0.21 mol, 10.5 mL), DMSO
(50 mL) and solution of corresponding arylaldehyde 1 (0.2 mol) in DMSO (150 mL) was added at
stirring for 0.5-1 min and the reaction mixture was kept at room temperature for 3-4 h to form
solution of corresponding hydrazone 2. Second step (performing of the COR). 500 mL one-necked
round bottom flask equipped with stirring bar and plugged with rubber septum (with needle used
as a nitrogen outlet) was charged with DMSO (150 mL), polyhalogenalkane (0.4 mol, CCl4
(method A) or CBrCl3 (method B)), NH3(aq.) (0.4 mol, 32 mL, 25% aqueous solution), CuCl (0.4 g,
0.004 mol, 2 mol%) and the mixture thus obtained was stirred for 1-2 min at cold water bath
(~10 °C) to form clear deep blue solution. Next, a solution of hydrazone 2 was added in small
portions (~10 mL) during 0.5-1 h in such a rate, allowing to consume most of hydrazone from the
previous portion (N2 gas evolution ceased). After addition of the last portion of hydrazone the
reaction mixture was stirred overnight and then poured into aqueous HCl (1200-1500 mL, 0.5 M).
Organic layer was separated and water phase was extracted with CH2Cl2 (3x100 mL). Combined
extracts were washed with water (2x200 mL), dried over Na2SO4 and volatiles were evaporated in
vacuo. The residue was purified by vacuum distillation or by passing through short silica gel pad
using hexane and appropriate hexane–CH2Cl2 mixtures as an eluent. *After addition of about a
half of the hydrazone, additional NH3(aq.) (0.2 mol, 16 mL, 25% aqueous solution) was added
because of the gradual evolution of NH3 from the reaction mixture.
1-Chloro-4-(2,2-dichlorovinyl)benzene (3a). Obtained from 4-chlorobenzaldehyde 1a (28.2 g,
1
0.20 mol) and CCl4 (40 mL, 0.40 mol). Colorless oil, yield 30.96 g (75%). H NMR (400.1 MHz,
CDCl3):  6.81 (s, 1H, CH=CCl2), 7.30 (d, 2Н, Ar, 3JHH = 8.3 Hz), 7.49 (d, 2Н, Ar, 3JHH = 8.4 Hz). 1H
NMR data of 3a are in agreement with those in the literature.38
1-(2,2-Dichlorovinyl)-4-methoxybenzene (3b). Obtained from 4-methoxybenzaldehyde 1b
1
(27.20 g, 0.20 mol) and CCl4 (40 mL, 0.40 mol). Colorless oil, yield 30.862 g (76%). H NMR
(400.1 MHz, CDCl3):  3.82 (s, 3H, MeO), 6.78 (s, 1H, CH=CCl2), 6.89 (d, 2Н, Ar, 3JHH = 8.9 Hz),
7.49 (d, 2Н, Ar, 3JHH = 8.9 Hz). 1H NMR data of 3b are in agreement with literature.39
1-(2,2-Dichlorovinyl)-4-methylbenzene (3c). Obtained from 4-methylbenzaldehyde 1c (24.00 g,
1
0.20 mol) and CCl4 (40 mL, 0.40 mol). Colourless oil; yield 32.918 g (88%). H NMR (400.1 MHz,
CDCl3):  2.35 (s, 3H, OCH3), 6.82 (s, 1H, CH=CCl2), 7.18 (d, 2Н, Ar, 3JHH = 8.2 Hz), 7.43 (d, 2Н,
Ar, 3JHH = 8.2 Hz). 1H NMR data of 3c are in agreement with those in the literature.40
1-(tert-Butyl)-4-(2,2-dichlorovinyl)benzene (3d). Obtained from 4-(tert-butyl)benzaldehyde 1d
1
(32.45 g, 0.20 mol) and CCl4 (40 mL, 0.40 mol). Colorless oil, yield 34.780 g (76%). H NMR
3
(400.1 MHz, CDCl3):  1.34 (s, 9H, t-Bu), 6.84 (s, 1H, CH=CCl2), 7.41 (d, 2Н, Ar, JHH = 8.5 Hz),
7.50 (d, 2Н, Ar, 3JHH = 8.5 Hz). 1H NMR data of 2c are in agreement with those in the literature. 41
4-(2,2-Dichlorovinyl)-N,N-dimethylaniline (3e). Obtained from 4-(dimethylamino)benzaldehyde
1e (29.84 g, 0.20 mol) and CCl4 (40 mL, 0.40 mol). White solid, mp 70-71 °C, yield 26.002 g (60%).
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10.1002/ejoc.202000531
European Journal of Organic Chemistry
3
1H NMR (400.1 MHz, CDCl3):  2.98 (s, 6H, NMe2), 6.67 (d, 2Н, Ar, JHH = 8.9 Hz), 6.72 (s, 1H,
CH=CCl2), 7.46 (d, 2Н, Ar, 3JHH = 8.9 Hz). 1H NMR data of 2c are in agreement with those in the
literature.42
1-(2,2-Dichlorovinyl)-4-fluorobenzene (3f). Obtained from 4-fluorobenzaldehyde 1f (12.47 g,
0.10 mol) and CCl4 (20 mL, 0.20 mol), method A or from 4-fluorobenzaldehyde 1f (18.60 g, 0.15
mol) and CBrCl3 (59.4 g, 0.30 mol) method B. Colorless oil, yield 13.155 g (69%, A) or 22.04 g
(77%, B). Purified by passing through silica gel pad (A) or by vacuum distillation (b.p. = 95-97 °C /
5 Torr). 1H NMR (400.1 MHz, CDCl3):  6.81 (s, 1H, CH=CCl2), 7.05 (pseudo-t, 2Н, Ar, 3JHH ~ 8-9
3
4
1
Hz), 7.51 (pseudo-d, 2Н, Ar, JHH ~ 8-9 Hz, JHF ~ 5-6 Hz). H NMR data of 3f are in agreement
with l those in the literature.43
1-(2,2-Dichlorovinyl)-4-(trifluoromethyl)benzene
(3g).
Obtained
from
4-
trifluoromethylbenzaldehyde 1g (17.44 g, 0.10 mol) and CCl4 (20 mL, 0.20 mol). Colorless oil,
1
1
yield 15.682 g (81%). H NMR (400.1 MHz, CDCl3):  6.89 (s, 1H, CH=CCl2), 7.63 (s, 4Н, Ar). H
NMR data of 2c are in agreement with those in the literature.44
(4-(2,2-Dichlorovinyl)phenyl)(methyl)sulfane (3h). Obtained from 4-(methylthio)benzaldehyde
1h (22.8 g, 0.15 mol) and CBrCl3 (60 g, 0.20 mol) Brownish crystals, mp 57-58 °C, yield 26.2 g
(80%). 1H NMR (600 MHz, CDCl3):  2.48 (s, 3H, SMe), 6.79 (s, 1H, CH=CCl2), 7.22 (d, 2Н, Ar,
3JHH = 8.4 Hz), 7.46 (d, 2Н, Ar, 3JHH = 8.4 Hz). 1H NMR data of 3h are in agreement with those in
the literature.39
2,4-Dichloro-1-(2,2-dichlorovinyl)benzene (3i). Obtained from 2,4-dichlorobenzaldehyde 1i
(35.00 g, 0.20 mol) and CCl4 (40 mL, 0.40 mol). Colorless crystals, mp 49-50 °C (lit.45 47-48 °C),
yield 29.549 g (61%). 1H NMR (400.1 MHz, CDCl3):  6.97 (s, 1H, CH=CCl2), 7.26 (dd, 1Н, Ar, J =
8.5, 4JHH = 1.9 Hz), 7.42 (d, 1Н, Ar, 4JHH = 1.9 Hz), 7.63 (d, 1Н, Ar, 3JHH = 8.5 Hz). 1H NMR data of
3h are in agreement with those in the literature.39
1-Chloro-2-(2,2-dichlorovinyl)benzene (3j). Obtained from 2-chlorobenzaldehyde 1j (14.11 g,
0.10 mol) and CCl4 (20 mL, 0.20 mol). Pale yellow oil, yield 15.989 g (77%). 1H NMR (400.1 MHz,
CDCl3):  7.04 (s, 1H, CH=CCl2), 7.23-7.30 (m, 2Н, Ar), 7.37-7.42 (m, 1Н, Ar), 7.66-7.70 (m, 1Н,
Ar). 1H NMR data of 2c are in agreement with those in the literature.40
1-(2,2-Dichlorovinyl)-3-methoxybenzene (3k). Obtained from 3-methoxybenzaldehyde 1k (13.73
g, 0.10 mol) and CCl4 (20 mL, 0.20 mol). Colorless oil, yield 15.625 g (77%). 1H NMR (400.1 MHz,
CDCl3):  3.81 (s, 3H, MeO), 6.83 (s, 1H, CH=CCl2), 6.86 (dd, 1Н, Ar, 3JHH = 8.3 Hz, 4JHH = 2.5 Hz),
7.10 (m, 2Н, Ar), 7.28 (t, 1Н, Ar, 3JHH = 7.9 Hz). 1H NMR data of 2c are in agreement with those in
the literature.40
1-(2,2-Dichlorovinyl)-2-methoxybenzene (3l). Obtained from 2-methoxybenzaldehyde 1l (13.63
g, 0.10 mol) and CCl4 (20 mL, 0.20 mol). Colorless oil, yield 15.215 g (75%). 1H NMR (400.1 MHz,
CDCl3):  3.83 (s, 3H, MeO), 6.88 (d, 1Н, Ar, 3JHH = 8.3 Hz), 6.97 (t, 1Н, Ar, 3JHH ~ 7.6 Hz), 7.08 (s,
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European Journal of Organic Chemistry
1H, CH=CCl2), 7.33-7.25 (pseudo-t, 3JHH ~ 7-8 Hz, 1Н, Ar), 7.71 (pseudo-d, 1Н, Ar, 3JHH = 7-8 Hz).
1H NMR data of 2c are in agreement with those in the literature.42
1-(2,2-Dichlorovinyl)-3-nitrobenzene (3m). Obtained from 3-nitrobenzaldehyde 1m (15.17 g,
0.10 mol) and CCl4 (20 mL, 0.20 mol). Slightly yellow solid, mp 53-54 °C, yield 12.00 g (55%). 1H
3
NMR (400.1 MHz, CDCl3):  6.92 (s, 1H, CH=CCl2), 7.55 (pseudo-t, 1Н, Ar, JHH ~ 8.0 Hz), 7.82
(pseudo-d, 1H, Ar, 3JHH ~ 8.0 Hz), 8.16 (ddd, 1Н, Ar, 3JHH = 8.0 Hz, 3JHH = 2.1 Hz, J = 0.8 Hz), 8.42
4
1
(pseudo-t, 1H, Ar, JHH ~ 2 Hz). H NMR data and mp of 3h are in agreement with those in the
literature.39
1-(2,2-Dichlorovinyl)naphthalene (3n). Obtained from 1-naphthaldehyde 1n (15.63 g, 0.10 mol)
1
and CCl4 (20 mL, 0.20 mol). Viscous oil, yield 14.035 g (63%). H NMR (400.1 MHz, CDCl3): 
7.36 (s, 1H, CH=CCl2), 7.57-7.46 (m, 3Н, Ar), 7.64 (d, 1Н, Ar, 3JHH = 7.1 Hz), 7.93-7.82 (m, 3H, Ar).
1H NMR data of 2c are in agreement with those in the literature.41
Synthesis of hydrazones 5. Hydrazones 5 were prepared using procedures reported previously.
Hydrazone 5a was obtained in 86% yield by the reaction with hydrazine hydrate in refluxing
ethanol.18 Hydrazone 5b was prepared in 95% yield by heating of -tetralone with hydrazine
hydrate in neat condition with addition of NEt3.46 The analytical data of hydrazone 5b are in
agreement with literature values.46
(1-(4-Methoxynaphthalen-1-yl)ethylidene)hydrazine (5a). Obtained as a mixture of Z and E
isomers from 1-(4-methoxynaphthalen-1-yl)ethan-1-one 4a (10.0 g, 0.05 mol). Viscous oil, yield
1
9.25 g (86%). H NMR (600.1 MHz, CDCl3):  for the mixture of Z and E isomers:  2.23 (s, 3H,
Me), 2.28 (s, 3H, Me), 3.98 (s, 3H, MeO), 4.00 (s, 3H, MeO), 4.92 (br s, 2H, NH2), 5.37 (br s, 2H,
NH2), 6.78 (d, 3JHH = 7.9 Hz, 2H), 6.85 (d, 3JHH = 7.8 Hz, 2H), 7.22 (d, 3JHH = 7.9 Hz, 2H), 7.34 (d,
3JHH = 7.8 Hz, 2H), 7.45-7.55 (m, 4H), 7.64 (pseudo-d, 3JHH ~ 7-8 Hz, 1H), 8.04 (pseudo-d, 3JHH
~
3
3
13
8 Hz, 1H), 8.30 (pseudo-d, JHH ~ 8 Hz, 1H), 8.33 (pseudo-d, JHH ~ 8 Hz, 1H). C NMR (150.9
MHz, CDCl3) for the mixture of Z and E isomers:  16.4, 25.3, 55.4, 55.5, 103.1, 103.6, 122.2,
122.6, 124.6, 124.97, 125.03, 125.3, 125.65, 125.69, 125.7, 125.77, 125.81, 126.5, 127.3, 129.8,
131.2, 131.7, 148.5, 149.1, 155.3, 155.8. HRMS (ESI-TOF): m/z [M+H]+ Calcd for C13H15N2O+
215.1179; found: 215.1177.
Synthesis of dichloroalkenes 6 (general procedure, 0.02 mol scale): 250 mL one-necked
round bottom flask equipped with stirring bar and plugged with rubber septum (with needle used
as a nitrogen outlet) was charged with DMSO (40 mL), NH3(aq.) (0.06 mol, 4.8 mL, 25% aqueous
solution), CuCl (0.2 g, 0.002 mol, 10 mol%), CBrCl3 (0.06 mol, 6 mL) and the mixture thus
obtained was stirred for 1-2 min at cold water bath (~10 °C) to form clear deep blue solution. Next,
solution of corresponding hydrazone 5 (0.02 mol) in DMSO (10 mL) was added in small portions
(~1 mL) during 1 h in such a rate, allowing to consume most of hydrazone from the previous
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10.1002/ejoc.202000531
European Journal of Organic Chemistry
portion (N2 gas evolution ceased). After stirring of the reaction mixture overnight, it was poured
into aqueous HCl (400 mL, 0.5 M), organic layer was separated and water phase was extracted
with CH2Cl2 (3x50 mL). Combined extracts were washed with water (2x50 mL), dried over Na2SO4
and volatiles were evaporated in vacuo. The residue was purified by passing through short silica
gel pad using hexane and appropriate hexane–CH2Cl2 mixtures as an eluent.
1-(1,1-Dichloroprop-1-en-2-yl)-4-methoxynaphthalene
(6a).
Obtained
from
(1-(4-
methoxynaphthalen-1-yl)ethylidene)hydrazine 5a (4.28 g, 0.02 mol). Viscous oil, yield 2.59 g
(49%). 1H NMR (600.1 MHz, CDCl3):  2.31 (s, 3H, Me), 4.03 (s, 3H, MeO), 6.84 (d, 3JHH = 7.8 Hz,
3
3
2H), 7.23 (d, JHH = 7.8 Hz, 2H), 7.52-7.58 (m, 4H), 7.73 (pseudo-d, JHH ~ 7-8 Hz, 1H), 8.37
3
(pseudo-d, JHH ~ 8 Hz, 1H). 13C NMR (150.9 MHz, CDCl3):  23.3, 55.5, 103.4, 118.3, 122.6,
124.4, 125.2, 125.3, 125.8, 127.0, 130.3, 130.8, 135.0, 155.3. HRMS (ESI-TOF): m/z [M+H]+
Calcd for C14H13Cl2O+ 267.0338; found: 267.0328.
1-(Dichloromethylene)-1,2,3,4-tetrahydronaphthalene
(6b).
Obtained
from
(3,4-
dihydronaphthalen-1(2H)-ylidene)hydrazine 5b (4.8 g, 0.03 mol). Viscous oil, yield 4.73 g (74%).
1H NMR (600.1 MHz, CDCl3):  1.78-1.85 (m, 2H, CH2), 2.66-2.73 (m, 4H, 2CH2), 7.15-7.20 (m,
1H), 7.21-7.27 (m, 2H), 7.86-7.91 (m, 1H). 13C NMR (150.9 MHz, CDCl3):  22.7, 30.3, 31.1, 116.2,
125.3, 127.7, 128.0, 128.8, 132.9, 133.9, 140.4. The NMR data of 6b are in agreement with those
in the literature.47
Synthesis of terminal acetylenes 7 (general procedure): Preheated 500 mL three-necked
round bottom flask equipped with thermometer, dropping funnel (with rubber septum) and argon
inlet was purged with argon and then charged with dry THF (125 mL) and corresponding
dichloroalkene 3 (0.1 mol). Thus, obtained solution was cooled to -90°C and n-BuLi (0.205 mol, 82
mL, 2.5 M solution in hexane) was added dropwise keeping temperature below -70…-60 °C. The
reaction mixture was kept at -60...-45 °C for 1h, cooling bath was removed and the reaction
mixture was allowed to warm up to 0…5 °C. Then the reaction mixture was cooled to -20 °C and
HCl (0.25 mol, 125 mL, 2 M aqueous solution) was carefully added for 1 minute. After warming to
room temperature (15-20 °C) organic layer was separated and water phase was extracted with
CH2Cl2 (3x30 mL). Combined extracts were washed with water (50 mL), dried over Na2SO4 and
volatiles were evaporated in vacuo. The residue was purified by passing through short silica gel
pad using hexane and appropriate hexane–CH2Cl2 mixtures as an eluent.
1-Chloro-4-ethynylbenzene (7a). Obtained from dichloroalkene 3a (10.35 g, 0.05 mol). Pale
brown solid, mp 42-44 °C, yield 5.33 g (78%). 1H NMR (400.1 MHz, CDCl3):  3.09 (s, 1H, C≡CH),
3
3
1
7.29 (d, 2Н, Ar, JHH = 8.4 Hz), 7.41 (d, 2Н, Ar, JHH = 8.4 Hz). H NMR data of 7a are in
agreement with those in the literature. 48
1-Methoxy-4-ethynylbenzene (7b). Obtained from dichloroalkene 3b (30.45 g, 0.15 mol). Beige
solid, mp 28-30 °C, yield 19.2 g (97%). 1H NMR (400.1 MHz, CDCl3):  2.99 (s, 3H, MeO), 3.80 (s,
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3
1
1H, C≡CH), 6.83 (d, 2Н, Ar, JHH = 8.8 Hz), 7.42 (d, 2Н, Ar, JHH = 8.8 Hz). H NMR spectrum of
7b are in agreement with those in the literature.49
1-(tert-Butyl)-4-ethynylbenzene (7c). Obtained from dichloroalkene 3d (23.0 g, 0.1 mol).
1
Colourless oil, yield 14.5 g (92%). H NMR (400.1 MHz, CDCl3):  1.30 (s, 9H, t-Bu), 3.02 (s, 1H,
C≡CH), 7.33 (d, 2Н, Ar, 3JHH = 8.4 Hz), 7.42 (d, 2Н, Ar, 3JHH = 8.4 Hz). 1H NMR data of 7d are in
agreement with those in the literature. 50
Synthesis of CF3-ynones 8 (general procedure): Preheated 500 mL three-necked round bottom
flask equipped with thermometer, dropping funnel (with rubber septum) and argon inlet was
purged with argon and then charged with dry THF (125 mL) and corresponding dichloroalkene 3
(0.1 mol). Thus obtained solution was cooled to -90°C and n-BuLi (0.205 mol, 82 mL, 2.5 M
solution in hexane) was added dropwise keeping temperature below -70…-60 °C. The reaction
mixture was kept at -60...-45 °C for 1h, cooling bath was removed and the reaction mixture was
allowed to warm up to 0…5 °C. Then the reaction mixture was cooled to -90 °C and CF3CO2Et
(15.6 g, 0.11 mol) was quite rapidly added for 1-2 minutes. Cooling bath was removed and the
reaction mixture was allowed to warm up to 0…5 °C. Then the reaction mixture was cooled to -
20 °C and HCl (0.25 mol, 125 mL, 2 M aqueous solution) was carefully added for 1 minute. After
warming to room temperature (15-20 °C) organic layer was separated and water phase was
extracted with CH2Cl2 (3x30 mL). Combined extracts were washed with water (50 mL), dried over
Na2SO4 and volatiles were evaporated in vacuo. The residue was purified by vacuum distillation or
by passing through short silica gel pad using hexane and appropriate hexane–CH2Cl2 mixtures as
an eluent.
4-(4-Chlorophenyl)-1,1,1-trifluorobut-3-yn-2-one (8a). Obtained from dichloroalkene 3a (10.35 g,
0.05 mol). Purified by passing through short silica gel pad (hexane–CH2Cl2 3:1). Pale yellow
crystals, m.p. 40-42 °C, yield 7.49 g (64%). 1H NMR (400.0 MHz, CDCl3):  7.43 (d, 3JHH = 8.5 Hz,
2H), 7.61 (d, 3JHH = 8.5 Hz, 2H). The NMR data are in agreement with previously reported.27b
1,1,1-Trifluoro-4-(4-methoxyphenyl)but-3-yn-2-one (8b). Obtained from dichloroalkene 3b (20.3
g, 0.1 mol). Purified by passing through short silica gel pad (hexane–CH2Cl2 3:1). Pale yellow oil
yield 19.92 g (87%). 1H NMR (400.1 MHz, CDCl3):  3.87 (s, 3H, OCH3), 6.94 (d, 3JHH = 8.9 Hz, 2H,
Ar), 7.63 (d, 3JHH = 8.9 Hz, 2H, Ar). The NMR data are in agreement with previously reported.27b
1,1,1-Trifluoro-4-p-tolylbut-3-yn-2-one (8c). Obtained from dichloroalkene 3c (9.35 g, 0.05 mol).
Purified by passing through short silica gel pad (hexane–CH2Cl2 3:1). Pale brown oil, yield 7.34 g
(69%). 1H NMR (400.1 MHz, CDCl3):  2.42 (s, 3H, CH3), 7.25 (d, 3JHH = 8.4 Hz, 2H, Ar), 7.57 (d,
3JHH = 8.4 Hz, 2H, Ar). The NMR data are in agreement with previously reported.27b
4-(4-tert-Butylphenyl)-1,1,1-trifluorobut-3-yn-2-one (8d). Obtained from dichloroalkene 3d (9.94
g, 0.043 mol). Purified by passing through short silica gel pad (hexane–CH2Cl2 3:1). Pale yellow
crystals, m.p. 48-50 °C, yield 6.85 g (62%). 1H NMR (400.1 MHz, CDCl3):  1.33 (s, 9H, t-Bu), 7.46
This article is protected by copyright. All rights reserved.

10.1002/ejoc.202000531
European Journal of Organic Chemistry
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3
(d, JHH = 8.3 Hz, 2H, Ar), 7.61 (d, JHH = 8.3 Hz, 2H, Ar). The NMR data and m.p. are in
agreement with previously reported.27b
1,1,1-Trifluoro-4-(4-fluorophenyl)but-3-yn-2-one (8e). Obtained from dichloroalkene 3f (19.1 g,
0.1 mol). Purified by vacuum distillation (b.p. = 84-86 °C / 10 Torr). Colorless oil, yield 11.21 g
1
(52%). H NMR (400.1 MHz, CDCl3):  7.12-7.18 (m, 2H, Ar), 7.67-7.72 (m, 2H, Ar). 19F NMR
(376.3 MHz, CDCl3):  -103.64...-103.56 (m, 1F, ArF), -78.91 (s, 3F, CF3). The NMR data are in
agreement with previously reported.37
1,1,1-Trifluoro-4-(4-(trifluoromethyl)phenyl)but-3-yn-2-one (8f). Obtained from dichloroalkene
3g (19.26 g, 0.08 mol). Purified by vacuum distillation (b.p. = 80-84 °C / 10 Torr). Colorless oil,
yield 16.72 g (79%). 1H NMR (400.1 MHz, CDCl3):  7.71 (d, 3JHH = 8.2 Hz, 2H, Ar), 7.78 (d, 3JHH
=
8.2 Hz, 2H, Ar). 19F NMR (376.3 MHz, CDCl3):  -78.93 (s, 3F, COCF3), -64.46 (s, 3F, ArCF3). The
NMR data are in agreement with previously reported.37
1,1,1-Trifluoro-4-(4-(methylthio)phenyl)but-3-yn-2-one (8g). Obtained from dichloroalkene 3h
(10.85 g, 0.05 mol). Purified by passing through short silica gel pad (hexane–CH2Cl2 3:1). Brown-
1
yellow crystals, m.p. 31-33 °C, yield 4.90 g (40%). H NMR (400.1 MHz, CDCl3):  2.52 (s, 3H,
SCH3), 7.24 (d, 3JHH = 8.4 Hz, 2H, Ar), 7.56 (d, 3JHH = 8.4 Hz, 2H, Ar). The NMR data and m.p. are
in agreement with previously reported.27b
4-(2-Chlorophenyl)-1,1,1-trifluorobut-3-yn-2-one (8h). Obtained from dichloroalkene 3j (9.94 g,
0.043 mol). Purified by passing through short silica gel pad (hexane–CH2Cl2 3:1). Colorless oil,
1
yield 20.0 g (86%). H NMR (400.1 MHz, CDCl3):  7.32-7.37 (m, 1H, Ar), 7.46-7.51 (m, 2H, Ar),
3
19
7.68 (pseudo-d, JHH ~ 8 Hz, 1H, Ar). F NMR (376.3 MHz, CDCl3):  -78.81 (s, CF3). The NMR
data are in agreement with previously reported.37
1,1,1-Trifluoro-4-(2-methoxyphenyl)but-3-yn-2-one (8i). Obtained from dichloroalkene 3l (14.86
g, 0.073 mol). Purified by passing through short silica gel pad (hexane–CH2Cl2 3:1). Colorless oil,
yield 13.41 g (81%). 1H NMR (400.1 MHz, CDCl3):  3.91 (s, 3H, CH3O), 6.94 (pseudo-d, JHH ~ 8
4
Hz, 1H, Ar), 6.97 (td, 3JHH = 7.6 Hz, 4JHH = 0.9 Hz, 1H, Ar), 7.51 (td, 3JHH = 8.0 Hz, JHH = 1.7 Hz,
1H, Ar), 7.55 (dd, 3JHH = 7.6 Hz, 4JHH = 1.7 Hz, 1H, Ar). 19F NMR (376.3 MHz, CDCl3):  -78.69 (s,
CF3). The NMR data are in agreement with previously reported.37
Acknowledgments. This work was supported by Russian Science Foundation (grant no. 18-13-
00136. The authors acknowledge partial support in measuring of NMR from M.V. Lomonosov
Moscow State University Program of Development. The authors acknowledge Thermo Fisher
Scientific Inc., MS Analytica (Moscow, Russia), and personally to Prof. A. Makarov for providing
mass spectrometry equipment for this work.
1 G. Chelucci, Chem. Rev. 2012, 112, 1344-1462.
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