Prototropic rearrangement of 2-propynyl(methyl)amino, 2-propynyloxy, and 2-propynylsulfanyl derivatives of hetarenes under conditions of phase-transfer catalysis: Mechanism and limitations

Article abstract of DOI:10.1023/B:RUJO.0000003185.14527.cd

2-Propynyl derivatives of N-methylaniline, phenol, benzenethiol, 2-pyridinethiol, 2-pyrimidinethiol, and 1,3-benzoxazole-2-thiol were synthesized. Under conditions of phase-transfer catalysis, phenyl 2-propynyl sulfide is converted into allenyl phenyl sul

Full text of DOI:10.1023/B:RUJO.0000003185.14527.cd

Russian Journal of Organic Chemistry, Vol. 39, No. 7, 2003, pp. 963 967. Translated from Zhurnal Organicheskoi Khimii, Vol. 39, No. 7, 2003,
pp. 1024 1028.
Original Russian Text Copyright
2003 by Rubina, Fleisher, Abele, Popelis, Lukevits.
Prototropic Rearrangement of 2-Propynyl(methyl)amino,
2-Propynyloxy, and 2-Propynylsulfanyl Derivatives of Hetarenes
under Conditions of Phase-Transfer Catalysis:
Mechanism and Limitations
K. Rubina, M. Fleisher, E. Abele, Yu. Popelis, and E. Lukevits
Latvian Institute of Organic Synthesis, Aizkraukles 21, Riga, LV-1006, Latvia
e-mail: kira@osi.lv
Received November 30, 2002
Abstract 2-Propynyl derivatives of N-methylaniline, phenol, benzenethiol, 2-pyridinethiol, 2-pyrimidine-
thiol, and 1,3-benzoxazole-2-thiol were synthesized. Under conditions of phase-transfer catalysis, phenyl
2-propynyl sulfide is converted into allenyl phenyl sulfide and phenyl 1-propynyl sulfide. The rearrangement
mechanism was studied by the AM1 quantum-chemical method.
Rearrangement of 1-alkynes into 2-alkynes was
usually effected in the systems KOH/EtOH [1, 2],
KOEt/EtOH [3], t-BuOK/DMSO [4], and t-BuOK or
EtONa/Me2SO4 [5]. As a rule, the triple bond migra-
tion process is reversible. For example, 2-alkynes are
readily converted into 1-alkynes in the presence of
t-BuLi [6] or BuLi/Et2O [7]. However, both reactions
require a polar solvent or organolithium base to be
used. Ogawa et al. [8] described rearrangement of
2-propynyl sulfides into the corresponding allenes by
the action of potassium bis(trimethylsilyl)amide. Most
recently, Florio et al. [9] reported on the Wittig
rearrangement of 2-propynyl ethers in the presence of
butyllithium in THF. Kobychev et al. [10] performed
a quantum-chemical study of noncatalytic acetylene
allene rearrangement of the XCH2C CH systems
where X = H, Me, NMe2, OMe, F, SMe.
of the rearrangement of phenyl 2-propynyl sulfide into
allenyl phenyl sulfide and phenyl 1-propynyl sulfide,
which occurs during the phase-transfer reaction,
was studied by the AM1 quantum-chemical method.
2-Propynyl(methyl)amino-, 2-propynyloxy-, and
2-propynylsulfanyl-substituted hetarenes were suc-
cessfully synthesized in a two-phase system liquid
solid (Scheme 1, Table 1).
The alkylation of benzenethiol (I) with 2-propynyl
bromide in the system solid K2CO3 18-crown-6
benzene at room temperature afforded a mixture of
phenyl 2-propynyl sulfide (VII, yield 86%) and
phenyl 1-propynyl sulfide (IX, yield 5%). By the
reaction of benzenethiol with 2-propynyl bromide in
the system KOH 18-crown-6 benzene at room tem-
perature (reaction time 1 h) we obtained terminal
acetylene VII in 52% yield. Phenyl 2-propynyl sulfide
(VII) reacted with solid KOH under conditions of
phase-transfer catalysis, yielding 60% of allene VIII
and 40% of phenyl 1-propynyl sulfide (IX). Phenol
(II) failed to react with BrCH2C CH in the system
The goal of our present study was to synthesize
2-propynyl and allenyl derivatives of aromatic and
heteroaromatic thiols, alcohols, and amines under
conditions of phase-transfer catalysis. The mechanism
Scheme 1.
I III, VII XI, Ar = phenyl; IV, XII, Ar = 2-pyridyl; V, XIII, Ar = 2-pyrimidyl; VI, XIV, Ar = 2-benzoxazolyl;
I, IV IX, XII XIV, X = S; II, X, X = O; III, XI, X = NCH3.
1070-4280/03/3907-0963$25.00 2003 MAIK Nauka/Interperiodica

964
RUBINA et al.
Table 1. Synthesis and mass spectra of alkynes VII XIV
Initial
comp. no.
Reaction
time, h
Producta
(yield, %)
Mass spectrum,
Ar
X
S
Base
m/z (Irel, %)
I
Ph
K2CO3 (2 equiv)
3.5
VII (86)
IX (5)
VII (52)
VIII (60)
IX (40)
X
X (44)
XI (98)
XIc
XII (95)
XIII (100)
XIV (86)
148 (M+, 36)
148 (M+, 100)
148 (M+, 36)
146 (M+, 27)
148 (M+, 100)
132 (M+, 36)
132 (M+, 36)
145 (M+, 65)
145 (M+, 65)
149 (M+, 57)
150 (M+, 98)
189 (M+, 88)
I
I
Ph
Ph
S
S
KOH (2 equiv)
KOH (2 equiv)
1
24
II
II
III
III
IV
V
Ph
Ph
Ph
Ph
O
O
N
N
S
K2CO3 (2 equiv)
KOH (2 equiv)
K2CO3 (2 equiv)
KOH (2 equiv)
KOH (2 equiv)
KOH (2 equiv)
KOH (2 equiv)
24
7b
16
10
0.25
0.3
0.5
2-Pyridyl
2-Pyrimidyl
2-Benzoxazolyl
S
S
VI
a
Compounds VII, VIII [5], X, and XI [11] have already been reported.
The reaction was initially accompanied by heat evolution; the mixture was then stirred for 5.5 h at room temperature and was heated
b
for 1 h at 50 C.
The product was not isolated.
c
Table 2. 1H NMR spectra of compounds VII XIV in CDCl3, , ppm (J, Hz) (relative to HMDS)
Comp. no.
VII
Ar
XR
CH3
CH
XCH2
CH2
XCH
Ar
Ph
Ph
SCH2C CH
SCH C CH2
2.22 t
(J = 2.5) (J = 2.5)
3.59 d
7.2 7.5 m
7.35 m
VIII
4.97 d
5.94 t
(J = 6.2) (J = 6.2)
IX
X
Ph
Ph
SC CCH3
OCH2C CH
2.08 s
2.95 s
7.34 m
6.98 m,
7.29 m
6.82 m,
7.26 m
7.00 m,
7.18 m,
7.50 m,
8.44 m
6.98 m,
8.51 m
7.26 m,
7.45 m,
7.62 m
2.50 t
(J = 2.1) (J = 2.1)
2.15 t 4.03 d
(J = 2.3) (J = 2.3)
2.18 t 3.95 d
(J = 2.6) (J = 2.6)
4.67 d
XI
Ph
N(CH2C CH)CH3
SCH2C CH
XII
2-Pyridyl
XIII
XIV
2-Pyrimidyl
SCH2C CH
2.18 t
(J = 2.6) (J = 2.6)
2.30 t 4.07 d
(J = 2.8) (J = 2.8)
4.00 d
2-Benzoxazolyl SCH2C CH
solid K2CO3 18-crown-6 benzene. Phenyl 2-propynyl
ether (X) was synthesized in 44% yield in the system
BrCH2C CH solid KOH 18-crown-6 benzene. The
reaction of N-methylaniline (III) with 2-propynyl
bromide in the system K2CO3(or KOH) 18-crown-6
benzene gave 98% of N-methyl-N-(2-propynyl)aniline
(XI) as the only product. 2-Propynyl hetaryl sulfides
XII XIV were readily obtained in 86 100% yield
from the corresponding thiols by treatment with
BrCH2C CH in the system KOH 18-crown-6 ben-
zene at room temperature (reaction time 15 30 min).
Prolonged reaction of alkynes XII XIV with KOH
leads to tarring of the mixture. Spectral parameters of
compounds VII XIV are given in Tables 1 3.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 39 No. 7 2003

PROTOTROPIC REARRANGEMENT OF 2-PROPYNYL(METHYL)AMINO. . .
965
Table 3. 13C NMR spectra of compounds VII XIV in CDCl3, C, ppm
Comp. no.
Ar
XR
C C
XCH2
22.55
Ara
VII
Ph
Ph
SCH2C CH
71.51 ( CH),
79.82 (CH2C )
126.95 (Cp)
128.97 (Cm)
130.06 (Co)
134.95 (Ci)
126.45 (Cp)
128.30 (Co)
128.93 (Cm)
135.61 (Ci)
VIII
SCH C CH2
78.74 ( CH2)
85.89 (XCH )
209.35 ( C )b
125.88 (Co)
126.11 (Cp)
129.04 (Cm)
133.60 (Ci)
114.87 (Co)
121.54 (Cp)
129.45 (Cm)
157.51 (Ci)
114.25 (Co)
118.30 (Cp)
129.08 (Cm)
148.99 (Ci)
119.85 (C5),
122.00 (C3),
136.09 (C4),
149.52 (C6),
157.05 (C2)
116.77 (C5),
157.28 (C4, C6),
170 (C2)
IX
X
Ph
Ph
Ph
SC CCH3
5.19 ( CCH3),
63.86 ( CCH3),
95.25 (XC )
OCH2C CH
N(CH2C CH)CH3
SCH2C CH
75.41 ( CH),
78.61 (CH2C )
55.69
42.44
18.16
XI
XII
38.54 ( CCH3),
71.96 ( CH),
79.28 (CH2C )
2-Pyridyl
70.42 ( CH),
80.06 ( C)
XIII
XIV
2-Pyrimidyl
SCH2C CH
SCH2C CH
70.38 ( CH),
79.49 ( C)
19.15
20.66
2-Benzoxazolyl
72.38 ( CH),
77.86 ( C)
109.99 (C6),
118.67 (C5),
124.15 (C7),
124.40 (C4),
141.74 (C7a),
152.00 (C3a),
162.99 (C2)
a
The ring carbon signals were assigned according to [12].
The ring carbon signals were assigned according to [13].
b
The isomerization of phenyl 2-propynyl sulfide
The heat of formation of PhS and water is equal to
82.4 kcal/mol. The complex [H2O K]+ reacts
with 2-propynyl bromide to afford the carbocation
[H Br CH2 C CH]+ ( H = 69.1 kcal/mol).
Phenyl 2-propynyl sulfide (VII) is formed by reaction
of PhS ion with H Br CH2 C CH]+ ( H =
181.1 kcal/mol). Deprotonation of alkyne VII yields
[PhSCHC CH] ( H = 71.5 kcal/mol) (see figure,
b). In the initial state, the distance between the oxygen
into phenyl 1-propynyl sulfide under conditions of
phase-transfer catalysis was examined by the AM1
semiempirical quantum-chemical method [14, 15].
The mechanism of the process is shown in Scheme 2.
18-Crown-6 as phase-transfer catalyst ensures transfer
of K+ OH into the organic phase. According to the
results of our calculations, the first reaction stage,
deprotonation of PhSH, requires no activation energy.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 39 No. 7 2003

966
RUBINA et al.
Scheme 2.
atom of the hydroxy group and hydrogen atom on C3
is 3.5 (see figure, a). This process is energetically
phenyl 1-propynyl sulfide (IX) ( H = 253.6 kcal
1
mol ). A similar reaction heat ( 242.9 kcal/mol) is
typical of protonation of the C3 atom in the carbanion
[PhSC C CH2] , which leads to allene VIII. The
rearrangement of phenyl 2-propynyl sulfide (VII)
gave a mixture of allenyl phenyl sulfide (VIII, 60%)
and phenyl 1-propynyl sulfide (IX, 40%).
more favorable than abstraction of the terminal proton
from the acetylenic moiety ( H = 40.9 kcal/mol).
The subsequent proton transfer from the complex
[H2O K]+ to the terminal carbon atom (C1, see
figure, c; the distance bentween the C1 atom and the
corresponding proton in the complex is 2.76 ) is
characterized by a H value of 249.2 kcal/mol, and
it leads to formation of allenyl phenyl sulfide (VIII)
(see figure, d). Allene VIII then reacts with OH ,
yielding [PhSC C CH2] ( H = 74.4 kcal/mol).
Proton transfer to the terminal carbon atom C1 gives
The above rearrangement does not occur with
phenyl 2-propynyl ether (X) and N-methyl-N-(2-prop-
ynyl)aniline (XI). This may be explained in terms of
different electronegativities of the nitrogen, oxygen,
and sulfur atoms. Table 4 contains the calculated
charges on the N, O, S, and C3 atoms in compounds
VII, X, and XI.
Table 4. Calculated charges on the X and C1 C3 atoms
in 2-propynyl derivatives of benzenethiol, phenol, and
N-methylaniline (compounds VII, X, and XI)
EXPERIMENTAL
1
The H and 13C NMR spectra were recorded on
a Varian 200 Mercury spectrometer (200 and 50 MHz,
respectively) using CDCl3 as solvent and hexamethyl-
disiloxane as internal reference. The mass spectra
(70 eV) were run on an HP 6890 GC MS system.
GLC analysis was performed on a Chrom-5 chromato-
graph equipped with a flame-ionization detector (glass
column, 1.2 m 3 mm, packed with 5% of OV-101
on Chromosorb W-HP, 80 100 mesh; carrier gas
nitrogen, flow rate 60 ml/min; oven temperature was
varied from 180 to 250 C, depending on the composi-
tion of the reaction mixture). Thiols, phenol, and
18-crown-6 were commercial reagents (from Acros)
and were used without additional purification.
Charge, a.u.
Comp.
X
no.
X
C1
C2
C3
VII
X
S
O
0.237
0.204
0.234
0.182
0.172
0.198
0.182
0.210
0.207
0.184
0.087
0.048
XI
NCH3
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 39 No. 7 2003

PROTOTROPIC REARRANGEMENT OF 2-PROPYNYL(METHYL)AMINO. . .
(b) (c)
967
(a)
(d)
AM1 simulation of the rearrangement of phenyl 2-propynyl sulfide into allenyl phenyl sulfide; the distances are given in
;
for better clearness, the potassium oxygen distance in the structures of KOH and [H2O K]+ is elongated relative to the
calculated value.
2-Propynyl bromide and N-methylaniline were dis-
tilled prior to use.
3. Wojtkowiak, B. and Romanet, R., Bull. Soc. Chim.
Fr., 1962, p. 805.
Reaction of thiols, phenol, and N-methylaniline
with 2-propynyl bromide. 2-Propynyl bromide,
1.33 ml (15 mmol), was added to a suspension of
10 mmol of substrate I VI, 0.264 g (1 mmol) of
18-crown-6, and 20 mmol of powdered K2CO3 or
KOH in 20 ml of toluene. The mixture was stirred
for 0.25 24 h at room temperature, filtered through
a layer of silica gel, and evaporated to isolate com-
pounds VII IX and XI. Product X was purified by
vacuum distillation, bp 84 86 C (10 mm). Com-
pounds XII XIV were purified by column chromatog-
raphy using toluene hexane mixtures (at various
ratios) as eluent. The reaction conditions and spectral
parameters of alkynes VII XIV are collected in
Tables 1 3.
Quantum-chemical calculations. Semiempirical
quantum-chemical calculations were performed with
the use of MOPAC 6 software (AM1 Hamiltonian)
[11, 12]. The equilibrium geometric parameters were
determined by full optimization using PRECISE
keyword. Insofar as MOPAC 6 lacks parametrization
for potassium atom, a sparkle pseudospecies was
used instead. Supporting information (Cartesian coor-
dinates of all initial and optimized structures) is
available from the author (Dr. chem. M. Fleisher
<misha@osi.lv>).
4. De Medeiros, E.F., Herbert, J.M., and Taylor, R.J.K.,
Tetrahedron Lett., 1990, vol. 31, p. 5843.
5. Filippova, A.Kh., Frolov, Yu.L., Lyashenko, G.S.,
Modonov, V.B., Ivanova, N.A., Kalikhman, I.D.,
Voronkov, M.G., and Vyazankin, N.S., Izv. Akad.
Nauk SSSR, Ser. Khim., 1986, p. 1847.
6. Magee, T.V., Stork G., and Fludzinski, P., Tetra-
hedron Lett., 1995, vol. 36, p. 7607.
7. Klein, J. and Becker, J.Y., Tetrahedron, 1972,
vol. 28, p. 5385.
8. Ogawa, A., Sakagami, K., Shima, A., Suzuki, H.,
Komiya, S., Katano, Y., and Mitsunobu, O., Tetra-
hedron Lett., 2002, vol. 43, p. 6387.
9. Florio, S., Granito, C., Ingrosso, G., and Troisi, L.,
Eur. J. Org. Chem., 2002, vol. 20, p. 3465.
10. Kobychev, V.B., Vitkovskaya, N.M., Klyba, N.S.,
and Trofimov, B.A., Izv. Ross. Akad. Nauk, Ser.
Khim., 2002, p. 713.
11. Ficini, J. and Barbara, C., Bull. Soc. Chim. Fr.,
1965, p. 2787.
12. Ewing, D.F., Org. Magn. Reson., 1979, vol. 12,
p. 499.
13. Kalinowski, H.-O., Berger, S., and Braun, S.,
13C-NMR Spektroskopie, Stuttgart: Georg Thieme,
1984, p. 133.
14. Stewart, J.J.P., MOPAC, version 6.0. Quantum
Chemical Program Exchange (QCPE), Program
Number 455, Bloomington, IN, 1984.
REFERENCES
1. Jacobs, T.L., Org. React., 1949, vol. 5, p. 13.
2. Jacobs, T.L., Akawie, R., and Cooper, R.G., J. Am.
Chem. Soc., 1951, vol. 73, p. 1273.
15. Stewart, J.J.P., MOPAC, version 6.0. Manual.
Program Number 455, Bloomington, IN, 1984.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 39 No. 7 2003