Reaction of (S)-(+)-4-amino-4-aryl-5,5,5-trifluoropentan-2-ones with α-chlorobenzyl isocyanates. Synthesis of (S)-(+)-4-aryl-6-(2-arylethenyl)- 4-trifluoromethyl-3,4-dihydro-pyrimidin-2(1H)-ones

Article abstract of DOI:10.1134/S1070428010100222

(S)-(+)-4-Amino-4-aryl-5,5,5-trifluoropentan-2-ones reacted with 6h-chlorobenzyl isocyanates with formation of (S)-(+)-4-aryl-6-(2-arylethenyl)- 4-trifluoromethyl-3,4-dihydropyrimidin-2(1H)-ones.

Full text of DOI:10.1134/S1070428010100222

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2010, Vol. 46, No. 10, pp. 1571–1574. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © N.M. Golovach, V.A. Sukach, M.V. Vovk, 2010, published in Zhurnal Organicheskoi Khimii, 2010, Vol. 46, No. 10, pp. 1564–1567.
Reaction of (S)-(+)-4-Amino-4-aryl-5,5,5-trifluoropentan-2-ones
with α-Chlorobenzyl Isocyanates. Synthesis of (S)-(+)-4-Aryl-
6-(2-arylethenyl)- 4-trifluoromethyl-3,4-dihydro-
pyrimidin-2(1H)-ones
N. M. Golovach, V. A. Sukach, and M. V. Vovk
Institute of Organic Chemistry, National Academy of Sciences of Ukraine,
ul. Murmanskaya 5, Kiev, 02660 Ukraine
e-mail: mvovk@i.com.ua
Received October 5, 2009
Abstract—(S)-(+)-4-Amino-4-aryl-5,5,5-trifluoropentan-2-ones reacted with α-chlorobenzyl isocyanates with
formation of (S)-(+)-4-aryl-6-(2-arylethenyl)-4-trifluoromethyl-3,4-dihydropyrimidin-2(1H)-ones.
DOI: 10.1134/S1070428010100222
We recently [1] described (S)-(+)-4-amino-4-aryl-
5,5,5-trifluoropentan-2-ones Ia–Id which turned out to
be efficient as synthetic blocks for the preparation of
chiral 4-aryl-4-trifluoromethyl-3,4-dihydroazin-2-ones
[2]. In particular, it was shown that compounds I act as
1,4-nucleophilic–electrophilic reagents in condensa-
tions with potassium (thio)cyanate, aryl isocyanates,
and aroyl isothiocyanates. On the other hand, they
behaved as 1,5-binucleophiles in the reaction with tri-
phosgene. With a view to extend the synthetic potential
of compounds І we examined their reaction with
1,3-bielectrophilic α-chlorobenzyl isocyanates ІІa–IIc
[3]. Taking into account our previous results [2], we
expected with some probability formation of chiral
N-arylmethylideneureidoketones like ІІІ or isomeric
cyclic 1,3,5-oxadiazocines IV.
with a styryl substituent in the 6-position may involve
both intra- and intermolecular transformations. Pre-
sumably, in the first step carbamoylation of the amino
group in β-amino ketone I with α-chlorobenzyl iso-
cyanate II gives N-(α-chlorobenzyl)ureidoketone A
which loses hydrogen chloride at elevated temperature,
yielding ureidoketone III. The double C=N bond in the
latter is activated by the neighboring carbonyl group,
and it readily undergoes hydrolysis by the action of
traces of water present in the reaction mixture to pro-
duce ureidoketone B and aromatic aldehyde Ar′CHO.
As we already noted [2], intermediate B is unstable
under acidic conditions and is rapidly converted into
dihydropyrimidinone VI with elimination of water
molecule which ensures the next hydrolysis cycle. The
subsequent condensation of pyrimidinone VI with
aromatic aldehyde liberated as a result of hydrolysis
yields final product V. The proposed scheme was con-
firmed by independent synthesis of compound Va by
condensation of (S)-(–)-6-methyl-4-phenyl-4-trifluoro-
methyl-3,4-dihydropyrimidin-2(1H)-one (VIa) with
4-bromobenzaldehyde in boiling xylene in the pres-
ence of p-toluenesulfonic acid.
O
F3C
HN
Ar
NH
O
O
Ar
CF3
Ar
Ar
O
Me
N
H
N
Me
III
IV
We also performed cross reaction of amino ketone
Ic with α,3,4-trichlorobenzyl isocyanate (IIc) in the
presence of 4-chlorobenzaldehyde and isolated a mix-
ture of compounds Vf and Vh at a ratio of 57 :43
(Scheme 2). The assumed structure of products Vf and
However, by heating compounds Іa–Id with
α-chlorobenzyl isocyanates ІІa–IIc in boiling xylene
over a period of 8 h we obtained (S)-(+)-4-aryl-6-(2-
arylethenyl)-4-trifluoromethyl-3,4-dihydropyrimidin-
2(1H)-ones Va–Vg in 43–71% yield (Scheme 1). The
process resulting in the formation of pyrimidine ring
1
19
Vh was consistent with their H and F NMR spectra
and GC–MS data. Thus the above mechanism involv-
1571

GOLOVACH et al.
1572
Scheme 1.
O
O
O
Ar'
O
O
Ar'
Cl
CF3
NH2
CF3
CF3
Xylene, Δ
Ar
Ar
Ar
+
–HCl
Me
Me
N
H
N
Cl
Me
N
H
N
Ar'
NCO
H
IIa–IIc
Ia–Id
A
III
Ar
CF3
NH
Ar
CF3
NH
O
O
CF3
H2O
–ArCHO
Ar'CHO, HCl
Ar
–H2O
–H2O
α
Me
N
NH2
Me
N
O
N
H
O
H
H
β
Ar'
B
VI
Va–Vg
Ph
CF3
NH
CHO
Xylene, TsOH, Δ
+
Va
Br
Me
N
O
H
VIa
I, Ar = Ph (a), 4-FC6H4 (b), 4-MeC6H4 (c), 4-MeOC6H4 (d); II, Ar′ = 4-BrC6H4 (a), 4-O2NC6H4 (b), 3,4-Cl2C6H3 (c); V, Ar = Ph,
Ar′ = 4-BrC6H4 (a), 3,4-Cl2C6H4 (b); Ar = 4-FC6H4, Ar′ = 4-O2NC6H4 (c); Ar = 4-MeC6H4, Ar′ = 4-BrC6H4 (d), 4-O2NC6H4 (e),
3,4-Cl2C6H3 (f); Ar = 4-MeOC6H4, Ar′ = 3,4-Cl2C6H3 (g); VI, Ar = 4-MeC6H4.
Scheme 2.
Cl
NCO
Ar
CF3
NH
Ar
CF3
NH
CF3
NH2
4-ClC6H4CHO
xylene, TsOH, Δ
Ar
+
+
N
O
N
O
H
H
Cl
Cl
Me
O
Cl
Cl
Cl
Ic
IIc
Vf
Vh
Ar = 4-MeC6H4.
ing intermolecular formation of pyrimidine ring with
simultaneous functionalization of the 6-position with
styryl substituent seems to be highly probable. The
cyclization process does not affect the chiral carbon
atom, so that compounds Va–Vg are formed with high
enantiomeric purity (ee 73–82%).
The structure of the isolated compounds was con-
firmed by their IR, NMR, and mass spectra. In the IR
spectra of Va–Vg we observed absorption bands due to
stretching vibrations of C=O (1690–1700 cm–1), con-
jugated C=C (1635–1640 cm–1), and N–H bonds
1
(3210–3215 cm–1). Their H NMR spectra contained
singlets from 5-H (δ 5.44–5.61 ppm), N3H (δ 8.33–
8.50 ppm) and N1H protons (δ 9.03–9.21 ppm) and
doublets from the exocyclic α- and β-vinyl protons at
δ 6.82–7.05 and 7.15–7.35 ppm, respectively. Carbon
nuclei in the partially hydrogenated pyrimidine ring
resonated in the 13C NMR spectra at δC 63.12–63.60
(quartet, C4), 89.39–99.31 (singlet, C5), and 152.01–
161.91 ppm (singlet, C2). In most cases, the C6 signal
was overlapped by aromatic carbon signals.
Compounds V are optically active analogs of
6-styryl-3,4-dihydropyrimidin-2(1H)-ones which are
generally synthesized by condensation of 6-methyl-
3,4-dihydropyrimidin-2(1H)-ones or -thiones with aro-
matic aldehydes [4–6] or of cross-conjugated azatri-
enes with 4-toluenesulfonyl isocyanate [7]. Obviously,
[4+2]-cyclocondensations of 6-styryl-3,4-dihydropy-
rimidin-2(1H)-ones with various dienophiles [6–9]
may be used in the synthesis of new fused and spiro-
cyclic pyrimidine derivatives possessing a trifluoro-
methyl group on chiral carbon atom.
Compound Vb displayed in the HMQC spectrum
a cross peak between the proton resonating as doublet
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 46 No. 10 2010

REACTION OF (S)-(+)-4-AMINO-4-ARYL-5,5,5-TRIFLUOROPENTAN-2-ONES
1573
at δ 6.91 ppm and carbon atom in position 5 of the
pyrimidine ring (δC 97.09 ppm); therefore, that proton
signal was assigned to the α-proton in the vinyl frag-
ment. Cross peaks in the NOESY spectrum of Vb
indicated that the 5-H proton (δ 5.48 ppm) is coupled
only with the α-vinyl proton and that the N1H proton
(δ 9.09 ppm) is coupled with the β-vinyl proton
(δ 7.18 ppm). These findings correspond to more stable
s-trans conformation of 6-styrylpyrimidinones V.
0.37 g (2 mmol) of 4-bromobenzaldehyde in boiling
benzene in the presence of a catalytic amount of p-tol-
uenesulfonic acid over a period of 8 h.
(4S)-(+)-6-[(E)-2-(3,4-Dichlorophenyl)ethenyl]-
4-phenyl-4-trifluoromethyl-3,4-dihydropyrimidin-
2(1H)-one (Vb). Yield 49%, mp >250°C, ee = 77%,
[α]D20 = +53.8° (c = 0.97, DMSO). IR spectrum, ν,
cm–1: 3225, 3220 (NH); 1690 (C=O); 1640 (C=C).
1H NMR spectrum, δ, ppm: 5.48 s (1H, 5-H), 6.91 d
(1H, α-CH, J = 16.5 Hz), 7.18 d (1H, β-CH, J =
16.5 Hz), 7.40–7.47 m (5H, Harom), 7.63–7.73 m (5H,
EXPERIMENTAL
H
arom), 8.43 s (1H, 3-H), 9.09 s (1H, 1-H). 13C NMR
The 1H, 19F, and 13C NMR spectra were recorded on
a Bruker Avance DRX-500 spectrometer at 500.13,
470.59, and 125.75 MHz, respectively, using CDCl3 as
spectrum, δC, ppm: 63.60 q (C4, J = 27.6 Hz), 97.97
(C5), 123.81 (α-CH), 126.22 (β-CH); 126.83, 127.41,
127.88, 128.44, 128.51, 130.37, 130.91, 131.62,
136.56, 136.96, 138.40 (Carom, C6); 115.25 q (CF3,
J = 291.2 Hz), 152.13 (C2). 19F NMR spectrum:
δF –77.09 ppm. Mass spectrum: m/z 414 [M]+. Found,
%: C 55.22; H 3.16; N 6.80. C19H13Cl2F3N2O. Calcu-
lated, %: C 55.23; H 3.17; N 6.78. M 413.2.
13
solvent and tetramethylsilane (1H, C), or trichloro-
fluoromethane (19F) as reference. The mass spectra
were obtained on a PE SCIEX API 150 EX instrument
equipped with UV (λ 254 nm) and ELSD detectors.
The optical rotations were measured on a Perkin–
Elmer 341 polarimeter. The optical purity was deter-
19
(4S)-(+)-4-(4-Fluorophenyl)-6-[(E)-2-(4-nitro-
phenyl)ethenyl]-4-trifluoromethyl-3,4-dihydropy-
rimidin-2(1H)-one (Vc). Yield 47%, mp > 250°C,
ee = 82%, [α]D20 = +46.8° (c = 0.64, DMSO). IR spec-
trum, ν, cm–1: 3225, 3220 (NH); 1690 (C=O); 1635
mined by F NMR spectroscopy using tris[3-(hepta-
fluoropropyl)hydroxymethylene-L-camphorato]euro-
pium(III) as lanthanide shift reagent.
Compounds Va–Vg (general procedure). A solu-
tion of 2.7 mmol of α-chlorobenzyl isocyanate IІa–IIc
in 5–10 ml of anhydrous xylene was added at room
temperature to a solution of 2.7 mmol of amino ketone
Іa–Id in 8–10 ml of anhydrous xylene, and the mixture
was heated for 8 h under reflux. The solvent was
distilled off, and the residue was recrystallized from
xylene–hexane (6:1).
1
(C=C). H NMR spectrum, δ, ppm: 5.61 s (1H, 5-H),
7.04 d (1H, α-CH, J = 16.5 Hz), 7.30–7.37 m (3H,
β-CH, Harom), 7.69–7.73 m (4H, Harom), 8.26 d (2H,
Harom, J = 9.0 Hz), 8.50 s (1H, 3-H), 9.21 s (1H, 1-H).
13C NMR spectrum, δC, ppm: 63.24 q (C4, J =
28.9 Hz), 98.50 (C5), 115.25 (α-CH), 115.41 (β-CH);
124.04, 127.46, 128.61, 134.54, 136.70, 142.72,
146.69, 151.88 (Carom, C6); 125.06 q (CF3, J =
292.2 Hz), 152.13 d (C2), 161.91 (C–F, J = 245.2 Hz).
19F NMR spectrum, δF, ppm: –77.30, –113.92. Mass
spectrum: m/z 408 [M]+. Found, %: C 56.01; H 3.21;
N 10.34. C19H13F4N3O3. Calculated, %: C 56.03;
H 3.22; N 10.32. M 407.3.
(4S)-(+)-6-[(E)-2-(4-Bromophenyl)ethenyl]-4-
phenyl-4-trifluoromethyl-3,4-dihydropyrimidin-
2(1H)-one (Va). Yield 60%, mp 235–236°C, ee =
78%, [α]D20 = +58.3° (c = 0.60, DMSO). IR spectrum, ν,
cm–1: 3225, 3220 (NH); 1690 (C=O); 1635 (C=C).
1H NMR spectrum, δ, ppm: 5.45 s (1H, 5-H), 6.82 d
(1H, α-CH, J = 16.5 Hz), 7.16 d (1H, β-CH, J =
(4S)-(+)-6-[(E)-2-(4-Bromophenyl)ethenyl]-4-(4-
methylphenyl)-4-trifluoromethyl-3,4-dihydropyrim-
idin-2(1H)-one (Vd). Yield 64%, mp > 250°C, ee =
73%, [α]D20 = +11.14° (c = 1.05, DMSO). IR spectrum,
ν, cm–1: 3220, 3215 (NH); 1700 (C=O); 1640 (C=C).
1H NMR spectrum, δ, ppm: 2.31 s (3H, CH3), 5.44 s
(1H, 5-H), 6.82 d (1H, α-CH, J = 16.5 Hz), 7.17 d (1H,
β-CH, J = 16.5 Hz), 7.26 d (2H, Harom, J = 8.0 Hz),
7.51 d (2H, Harom, J = 8.0 Hz), 7.42 d (2H, Harom, J =
8.5 Hz), 7.57 d (2H, Harom, J = 8.5 Hz), 8.33 s (1H,
16.5 Hz), 7.40–7.44 m (5H, Harom), 7.56 d (2H, Harom
,
J = 7.8 Hz), 7.62 d (2H, Harom, J = 7.8 Hz), 8.38 s (1H,
13
3-H), 9.05 s (1H, 1-H). C NMR spectrum, δC, ppm:
63.56 q (C4, J = 28.9 Hz), 97.09 (C5), 110.01 (α-CH),
110.94 (β-CH), 114.31 (C6); 116.17, 116.24, 116.26,
116.42, 119.03, 122.14, 123.34, 124.86 (Carom); 115.05 q
19
(CF3, J = 291.1 Hz), 152.01 (C2). F NMR spectrum:
δF –77.04 ppm. Mass spectrum: m/z 424 [M]+. Found,
%: C 53.94; H 3.35; N 6.61. C19H14BrF3N2O. Calculat-
ed, %: C 53.92; H 3.33; N 6.62. M 423.2.
13
3-H), 9.04 s (1H, 1-H). C NMR spectrum, δC, ppm:
Compound Va was also synthesized in 74% yield
by heating 0.5 g (2 mmol) of pyrimidinone VIa and
23.08 (CH3), 63.45 q (C4, J = 28.9 Hz), 89.39 (C5),
109.99 (α-CH), 110.98 (β-CH), 114.24 (C6); 121.18,
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 46 No. 10 2010

GOLOVACH et al.
1574
122.31, 126.05, 128.40, 128.55, 131.61, 136.56,
137.75 (Carom); 125.05 q (CF3, J = 291.1 Hz), 152.02
(C2). 19F NMR spectrum: δF –77.24 ppm. Mass spec-
trum: m/z 438 [M]+. Found, %: C 54.92; H 3.67;
N 6.42. C20H16BrF3N2O. Calculated, %: C 54.94;
H 3.69; N 6.41. M 437.2.
CH3O), 5.46 s (1H, 5-H), 6.91 d (1H, α-CH, J =
16.5 Hz), 7.01 d (2H, Harom, J = 8.5 Hz), 7.15 d (1H,
β-CH, J = 16.5 Hz), 7.43 d (2H, Harom, J = 8.0 Hz),
7.53 d (2H, Harom, J = 8.5 Hz), 7.63 d (1H, Harom, J =
13
8.0 Hz), 8.35 s (1H, 3-H), 9.04 s (1H, 1-H). C NMR
spectrum, δC, ppm: 55.19 (CH3O), 63.12 q (C4, J =
28.9 Hz), 98.15 (C5), 113.82 (α-CH), 123.90 (β-CH);
126.30, 127.26, 127.63, 127.86, 128.15, 130.33,
130.95, 131.61, 136.38, 137.01, 152.08 (Carom, C6);
(4S)-(+)-4-(4-Methylphenyl)-6-[(E)-2-(4-nitro-
phenyl)ethenyl]-4-trifluoromethyl-3,4-dihydropy-
rimidin-2(1H)-one (Ve). Yield 58%, mp 225–227°C,
ee = 73%, [α]D20 = +16.70° (c = 1.20, DMSO). IR spec-
trum, ν, cm–1: 3220, 3210 (NH); 1680 (C=O); 1640
19
125.01 q (CF3, J = 290.9 Hz), 159.16 (C2). F NMR
spectrum: δF –77.47 ppm. Mass spectrum: m/z 444
[M]+. Found, %: C 54. 22; H 3. 43; N 6. 33.
C20H15Cl2F3N2O2. Calculated, %: C 54.19; H 3.41;
N 6.32. M 443.2.
1
(C=C). H NMR spectrum, δ, ppm: 2.30 s (3H, CH3),
5.56 s (1H, 5-H), 7.05 d (1H, α-CH, J = 16.8 Hz),
7.26 d (2H, Harom, J = 7.8 Hz), 7.31 d (1H, β-CH, J =
16.8 Hz), 7.50 d (2H, Harom, J = 7.8 Hz), 7.71 d (2H,
Reaction of (S)-(+)-4-amino-5,5,5-trifluoro-4-(4-
methylphenyl)pentan-2-one (Ic) with α,3,4-tri-
chlorobenzyl isocyanate (IIc) and 4-chlorobenzal-
dehyde. A solution of 0.64 g (2.7 mmol) of isocyanate
IIc in 10 ml of anhydrous xylene was added at room
temperature to a solution of 0.66 g (2.7 mmol) of
amino ketone Іc and 0.4 g (2.7 mmol) of 4-chloro-
benzaldehyde in 10 ml of anhydrous xylene, and the
mixture was heated for 8 h under reflux. The solvent
was distilled off, and the residue was recrystallized
H
arom, J = 8.5 Hz), 8.22 d (2H, Harom, J = 8.5 Hz),
8.40 s (1H, 3-H), 9.15 s (1H, 1-H). 13C NMR spec-
trum, δC, ppm: 20.50 (CH3), 63.42 q (C4, J = 28.9 Hz),
99.31 (C5), 125.97 (α-CH), 127.76 (β-CH); 124.12,
126.19, 127.50, 129.06, 135.38, 136.47, 137.94,
142.83, 146.66 (Carom, C6); 124.95 q (CF3, J =
291.2 Hz), 152.06 (C2). 19F NMR spectrum:
δF –77.16 ppm. Mass spectrum: m/z 404 [M]+. Found,
%: C 59.58; H 4.03; N 10.40. C20H16F3N3O3. Calculat-
ed, %: C 59.55; H 4.00; N 10.42. M 403.3.
1
from xylene–hexane (6:1). The H NMR spectrum of
the product mixture contained (apart from other
signals) singlets at δ 5.44 and 5.46 ppm typical of 5-H
in the pyrimidine ring. Analysis of the mixture by GC–
MS showed the presence of two peaks with m/z values
for molecular ions of 428 (Irel 57%; Vf) and 393
(Irel 43%; Vh).
(4S)-(+)-6-[(E)-2-(3,4-Dichlorophenyl)ethenyl]-4-
(4-methylphenyl)-4-trifluoromethyl-3,4-dihydropy-
rimidin-2(1H)-one (Vf). Yield 71%, mp 243–245°C,
ee = 74%, [α]D20 = +21.3° (c = 0.93, DMSO). IR spec-
trum, ν, cm–1: 3225, 3215 (NH); 1670 (C=O); 1635
1
(C=C). H NMR spectrum, δ, ppm: 2.31 s (3H, CH3),
5.44 s (1H, 5-H), 6.91 d (1H, α-CH, J = 17.0 Hz),
7.13 d (1H, β-CH, J = 17.0 Hz), 7.26 d (2H, Harom, J =
7.8 Hz), 7.42 d (1H, Harom, J = 8.4 Hz), 7.49 d (2H,
REFERENCES
1. Sukach, V.A., Golovach, N.M., Pirozhenko, V.V., Rusa-
nov, E.B., and Vovk, M.V., Tetrahedron: Asymmetry,
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H
arom, J = 7.8 Hz), 7.62 d (1H, Harom, J = 8.4 Hz),
7.71 s (1H, Harom), 8.34 s (1H, 3-H), 9.03 s (1H, 1-H).
13C NMR spectrum, δC, ppm: 20.47 (CH3), 63.38 q
(C4, J = 28.9 Hz), 98.10 (C5), 123.87 (α-CH), 126.15
(β-CH); 126.84, 127.30, 127.86, 129.02, 130.33,
130.92, 131.60, 135.47, 136.45, 136.99, 137.86 (Carom
,
C6); 125.01 q (CF3, J = 290.4 Hz), 152.10 (C2).
19F NMR spectrum: δF –77.20 ppm. Mass spectrum:
m/z 428 [M]+. Found, %: C 56.25; H 3.57; N 6.54.
C20H15Cl2F3N2O. Calculated, %: C 56.22; H 3.54;
N 6.56. M 427.2.
6. Zigenner, G., Brunetti, H., Ziegler, H., and Bayer, M.,
Monatsh. Chem., 1970, vol. 101, p. 1767.
(4S)-(+)-6-[(E)-2-(3,4-Dichlorophenyl)ethenyl]-
4-(4-methoxyphenyl)-4-trifluoromethyl-3,4-dihy-
dropyrimidin-2(1H)-one (Vg). Yield 43%, mp 215–
217°C, ee = 76%, [α]D20 = +93.5° (c = 1.39, DMSO). IR
spectrum, ν, cm–1: 3220, 3215 (NH); 1660 (C=O);
7. Saito, T., Kimura, H., Chonan, T., Soda, T., and Kara-
kosa, T., Chem. Commun., 1997, no. 11, p. 1013.
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Monatsh. Chem., 1970, vol. 101, p. 1794.
1
1640 (C=C). H NMR spectrum, δ, ppm: 3.77 s (3H,
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 46 No. 10 2010