The rearrangement of trifluoroacetylchromenes to trifluoromethylchromenols

Article abstract of DOI:10.1007/s10593-016-1931-6

[Figure not available: see fulltext.] The reaction of o-phenylenediamine with condensed 4H-pyrans containing a trifluoroacetyl group at the β-position relative to the oxygen atom led to 2-(trifluoromethyl)chroman-2-ols and 3-(trifluoromethyl)-2,3-dihydro-1H-benzo[f]chromen-3-ols via a cascade process that was initiated by a Michael reaction.

Full text of DOI:10.1007/s10593-016-1931-6

DOI 10.1007/s10593-016-1931-6
Chemistry of Heterocyclic Compounds 2016, 52(8), 559–563
The rearrangement of trifluoroacetylchromenes
to trifluoromethylchromenols
Vitaly A. Osyanin1*, Yulia V. Popova1, Darina V. Sakhnenko1,
Dmitry V. Osipov1, Yuri N. Klimochkin1
1
Samara State Technical University,
244 Molodogvardeyskaya St., Samara 443100, Russia; е-mail: VOsyanin@mail.ru
Translated from Khimiya Geterotsiklicheskikh Soedinenii,
2016, 52(8), 559–563
Submitted July 22, 2016
Accepted August 18, 2016
H2N
COCF3
H2N
R
R
OH
CF3
MeCN, , 8 h
42–78%
O
O
The reaction of o-phenylenediamine with condensed 4Н-pyrans containing a trifluoroacetyl group at the β-position relative to the oxygen
atom led to 2-(trifluoromethyl)chroman-2-ols and 3-(trifluoromethyl)-2,3-dihydro-1H-benzo[f]chromen-3-ols via a cascade process that
was initiated by a Michael reaction.
Keywords: o-phenylenediamine, 3-trifluoroacetyl-4Н-chromenes, 2-(trifluoromethyl)chroman-2-ols, Michael reaction, retro-Mannich
reaction.
The introduction of trifluoromethyl group into
molecules of organic compounds can substantially alter
their chemical, physical, and biological properties due to
the high electronegativity and lipophilicity of fluoro-
containing substituents. The presence of a trifluoromethyl
group can lead to very different biological activity profiles
of organic compounds, enhancing their therapeutic effects
or giving rise to new types of activity.1
The synthesis of trifluoromethyl-substituted benzo-
diazepines presents significant interest, because the
diazepine system is a common structural feature of many
pharmaceutical compounds.2 One of the obvious
approaches to the preparation of trifluoromethyl-substituted
benzodiazepines is the reaction between 1,3-dicarbonyl
compounds or their synthetic equivalents and o-phenylene-
diamine. According to literature data, the reaction of β-alkoxy
vinyl(trifluoromethyl) ketones with o-phenylenediamine,
depending on the conditions and the nature of substituents,
can lead to a wide range of various products: mono- and bis-
(β-enaminones),3–7 benzimidazole and 2-trifluoromethyl-
benzimidazole,7 2-(1,1,1-trifluoroacetonyl)benzimidazoles,8–10
dihydrobenzo[b][1,4]diazepinols,9,11 4-(trifluoromethyl)-1H-
benzo[b][1,4]diazepines,10,12,13 and 2-(trifluoromethyl)-3H-
benzo[b][1,4]diazepines (Scheme 1).9,14
Scheme 1
0009-3122/16/52(8)-0559©2016 Springer Science+Business Media New York
559

Chemistry of Heterocyclic Compounds 2016, 52(8), 559–563
Scheme 2
H2N
COCF3
Me
Me
Me
H2N
R
R
OH
CF3
OH
CF3
OH
CF3
MeCN, , 8 h
O
1a–f
O
2a–f
O
O
Ad
2a (78%)
2b (45%)
Br
t-Bu
Ad
F3C
N
R
OH
CF3
OH
CF3
OH
CF3
OH
O
O
O
O
N
OH
CF3
H
3
2c
(42%)
2d (58%)
2e (69%)
2f (44%)
not formed
Ad = adamantan-1-yl
We expected that the reaction of o-phenylenediamine
with 3-trifluoroacetyl-4Н-chromenes 1a,b or 2-trifluoroacetyl-
1H-benzo[f]chromenes 1c–f as structural analogs of
β-alkoxy vinyl(trifluoromethyl) ketones also can give the
respective benzodiazepines 3. However, the reaction
produced only 2-(trifluoromethyl)chroman-2-ols 2a,b and
3-(trifluoromethyl)-2,3-dihydro-1H-benzo[f]chromen-3-ols
2c–f along with benzimidazole (Scheme 2).
The reactions were performed by heating equimolar
amounts of o-phenylenediamine and trifluoroacetyl-
chromenes 1a–f in refluxing acetonitrile. The respective
chromenols 2a–f were obtained in 42–78% yields. These
chromenols were purified by column chromatography. The
benzimidazole formed during the synthesis also was
isolated from the reaction mixture.
The obtained chromenols 2a–f were thermally stable
compounds, which did not undergo dehydration in the
absence of strong acids.17 Their thermal stability was also
confirmed by the presence of molecular ion peak in the
mass spectrum of compound 2c (EI ionization) with the
maximum intensity, while the intensity of [М–H2O]+ peak
was less than 1%. The stability of chromenols 2a–f, which
are essentially cyclic hemiketals, can be explained by the
fact that the formation of carbocation at the carbon atom
next to the trifluoromethyl group is energetically
unfavorable.
13C NMR spectra of compounds 2a–f showed the carbon
atom of trifluoromethyl group and the adjacent carbon
1
atom as quartets at 122.7–123.7 ppm with JCF = 283.2–
2
285.1 Hz and at 93.9–94.0 ppm with JCF = 33.4 Hz,
The proposed rearrangement mechanism included the
following steps: aza-Michael reaction – addition of one of
the o-phenylenediamine amino groups to chromene, a retro-
oxa-Michael reaction – opening of dihydropyran ring,
respectively. The carbon atoms of two methylene groups
gave signals at 16.6–20.3 and 23.5–25.1 ppm, while the
corresponding hydrogen atoms were always observed in
1H NMR spectra as four signals at 1.77–3.28 ppm. The
hydroxy group proton was detected as a broadened singlet
at 2.84–3.48 ppm (in CDCl3). When changing the solvent
from CDCl3 to DMSO-d6, the proton signal of the hydroxy
group was shifted downfield (by 4.7 ppm in the spectrum
repeated aza-Michael reaction,
a
retro-Mannich
reaction15,16 accompanied by elimination of benzimidazole,
and intramolecular addition at the carbonyl group
(hemiketalization) (Scheme 3).
Scheme 3
560

Chemistry of Heterocyclic Compounds 2016, 52(8), 559–563
of compound 2b). The number of protons that were directly
JNM-ECX 400 spectrometer (400 and 100 MHz,
respectively) in DMSO-d6 (compound 2b) or in CDCl3 (the
rest of the compounds), with TMS as internal standard.
Mass spectra were recorded on a Finnigan Trace DSQ
instrument, using EI ionization (70 eV). Elemental analysis
was performed on a EuroVector EA-3000 automated
СНNS-analyzer. Melting points were determined by
capillary method on an SRS OptiMelt MPA100 apparatus.
The reaction progress was controlled by TLC on aluminum
foil-backed silica gel plates (Merck, Kiesgel 60 F254),
visualization under UV light and in iodine vapor.
linked to 13С atoms, inferred from DEPT spectra, was in
accordance with the presented structures.
The use of ethylenediamine instead of o-phenylenediamine
in the reaction with 2-trifluoroacetyl-1H-benzo[f]chromene 1с
gave less satisfactory results. A complex mixture of
products was formed, with chromenol 2c as the main
component according to 1Н NMR spectra.
Prolonged heating of chromene 1b with o-amino-
thiophenol led to a low yield (24%) of the respective
chromenol 2b, along with bis(2-aminophenyl) disulfide (4),
which was successfully isolated from the reaction mixture
as pure compound in 69% yield. Disulfide 4 was likely
formed as a result of o-aminothiophenol oxidation with air
oxygen (Scheme 4).
The starting compounds 1а–f were obtained according
to a published procedure.20
Preparation of 2-(trifluoromethyl)chroman-2-ols
2a,b and 3-(trifluoromethyl)-2,3-dihydro-1H-benzo[f]-
chromen-3-ols 2c–f (General method). A mixture of
trifluoroacetylchromene 1а–f (3 mmol), o-phenylene-
diamine (0.32 g, 3 mmol), and MeCN (10 ml) was refluxed
for 8 h. The solvent was removed by evaporation at
reduced pressure, the residue was purified by silica gel
column chromatography (eluent CHCl3), followed by
recrystallization from hexane or cyclohexane. Further
elution with 5:1 CHCl3–EtOH mixture led to the isolation
of benzimidazole, with spectral characteristics that matched
the literature data.21
Scheme 4
Dehydration of trifluoromethylchromenols by the action
of concd. H2SO4 in CH2Cl2 at room temperature has been
described in the literature.17 However, the conversion
degree of chromenol 2c in our experiments was only about
10% after 12 h. It is also known that dehydration of related
systems can be achieved with SOCl2 in the presence of
pyridine.18,19 When the reaction was performed at room
temperature under these conditions, the starting chromenol 2c
was not observed already after 2 h, while the reaction
mixture contained not only chromene 5, but also about 25%
of the product due to hydroxy group substitution with
chlorine atom, 3-chloro-3-(trifluoromethyl)-2,3-dihydro-1H-
benzo[f]chromene (6), from which the target product was
difficult to separate. At the same time, refluxing the
chromenol 2c for 4 h with excess of thionyl chloride in the
absence of pyridine allowed to obtain chromene 5 in 86%
yield (Scheme 5). The content of by-product 6 in the
reaction mixture was less than 3% in this case, according to
the chromato–mass spectrometry data.
8-(Adamantan-1-yl)-6-methyl-2-(trifluoromethyl)-
chroman-2-ol (2a). Yield 78%, colorless crystals, mp 137–
138°С (hexane). IR spectrum, ν, cm–1: 3518, 3406 (OH),
2967, 2905, 2851 (CHAd), 1463, 1450, 1342, 1323, 1258,
1215, 1180, 1157, 1099, 1084, 1030, 984, 856, 721.
1H NMR spectrum, δ, ppm (J, Hz): 1.76 (6H, br. s, 3CH2
Ad); 1.95 (1H, td, J = 13.5, J = 6.0) and 2.20 (1H, ddd,
J = 13.0, J = 6.0, J = 1.6, 3-CH2); 2.07 (9H, br. s, 3CH2 Ad,
3CH Ad); 2.27 (3H, s, CH3); 2.74 (1H, dd, J = 16.3,
J = 4.6) and 3.01–3.10 (1H, m, 4-CH2); 2.88 (1H, br. s,
OH); 6.79 (1H, d, J = 1.8, H Ar); 6.93 (1H, d, J = 1.8,
H Ar). 13C NMR spectrum, δ, ppm (J, Hz): 20.3 (CH2);
20.9 (CH3); 23.5 (CH2); 29.1 (3CH Ad); 36.9 (C Ad); 37.1
2
(3CH2 Ad); 40.7 (3CH2 Ad); 93.9 (q, JCF = 33.4, CCF3);
1
121.1 (C); 122.9 (q, JCF = 284.1, CF3); 126.1 (CH); 127.5
(CH); 130.8 (C); 138.0 (C); 147.0 (C–O). Found, %: C 68.90;
H 6.81. C21H25F3O2. Calculated, %: C 68.84; H 6.88.
6,7-Dimethyl-2-(trifluoromethyl)chroman-2-ol (2b).
Yield 45%, colorless crystals, mp 84–85°С (hexane).
IR spectrum, ν, cm–1: 3553 (OH), 2943, 1628, 1582, 1508,
1458, 1412, 1389, 1342, 1300, 1238, 1207, 1188, 1173,
1111, 1092, 1007, 968, 899, 872. 1H NMR spectrum, δ, ppm
(J, Hz): 1.77 (1H, tdd, J = 13.0, J = 5.8, J = 1.5) and 2.02
(1H, ddd, J = 13.2, J = 5.8, J = 2.5, 3-СН2); 2.08 (3H, s,
CH3); 2.10 (3H, s, CH3); 2.61 (1H, ddd, J = 16.2, J = 5.8,
J = 2.0) and 2.74–2.83 (1H, m, 4-СН2); 6.61 (1H, s, H Ar);
6.85 (1H, s, H Ar); 7.74 (1H, d, J = 1.7, OH). 13C NMR
spectrum, δ, ppm (J, Hz): 18.9 (CH3); 19.5 (CH2); 19.6
(CH3); 25.1 (CH2); 94.0 (q, 2JCF = 33.4, CCF3); 117.8 (CH);
Scheme 5
Thus, we have demonstrated that reactions of
trifluoroacetylchromenes with o-phenylenediamine result in
recyclization to trifluoromethylchromenols.
1
118.8 (C); 123.7 (q, JCF = 285.1, CF3); 129.4 (C); 130.3
Experimental
(CH); 136.0 (C); 149.1 (C–O). Found, %: C 58.47; H 5.27.
C12H13F3O2. Calculated, %: C 58.54; H 5.32.
IR spectra were recorded on a Shimadzu IRAffinity-1
spectrometer in KBr pellets. 1Н and 13C NMR spectra
(including DEPT experiments) were acquired on a JEOL
Compound 2b was also obtained by the following
procedure: a solution of chromene 1b (0.30 g, 1.2 mmol)
561

Chemistry of Heterocyclic Compounds 2016, 52(8), 559–563
and o-aminothiophenol (0.15 g, 1.2 mmol) in MeCN (5 ml)
1219, 1180, 1111, 1084, 1022, 976, 891, 868, 806.
1H NMR spectrum, δ, ppm (J, Hz): 2.04–2.12 (1H, m) and
2.41 (1H, dd, J = 13.5, J = 5.5, 2-CH2); 3.06–3.20 (2H, m,
1-CH2); 3.48 (1H, br. s, OH); 7.09 (1H, d, J = 9.0, H-5);
7.54 (1H, d, J = 8.7) and 7.56 (1H, d, J = 8.7, H-9,10); 7.69
(1H, d, J = 9.0, H-6); 7.90 (1H, s, H-7). 13C NMR
spectrum, δ, ppm (J, Hz): 16.6 (CH2); 23.5 (CH2); 94.0 (q,
2JCF = 33.4, CCF3); 114.0 (C); 118.0 (C); 119.6 (CH);
was refluxed for 48 h, the solvent was removed by
evaporation under reduced pressure, the residue was
separated by silica gel column chromatography (eluent
CH2Cl2), first eluting the starting chromene 1b (0.19 g),
then chromenol 2b (0.07 g, 24%), and finally the disulfide
4 (0.10 g, 69%).
Bis(2-aminophenyl) disulfide (4). Mp 89–91°С
(cyclohexane) (mp 90–92°С22). IR spectrum, ν, cm–1: 3379,
3298 (NH2), 1612, 1582, 1474, 1447, 1300, 1246, 752, 698,
1
122.7 (q, JCF = 283.2, CF3); 124.0 (CH); 127.4 (CH);
130.0 (CH); 130.5 (CH); 130.9 (2C); 148.2 (C–O). Found,
%: C 48.37; H 2.84. C14H10BrF3O2. Calculated, %:
C 48.44; H 2.90.
1
671. H NMR spectrum, δ, ppm (J, Hz): 4.15 (4H, br. s,
2NH2); 6.58 (2H, tt, J = 7.6, J = 1.2, H Ar); 6.70 (2H, d,
J = 8.5, H Ar); 7.13–7.18 (4H, m, H Ar). 13C NMR
spectrum, δ, ppm: 115.3 (2CH); 118.3 (2CH); 118.9 (2C);
131.7 (2CH); 136.9 (2CH); 148.7 (2C).
8-tert-Butyl-3-(trifluoromethyl)-2,3-dihydro-1H-benzo-
[f]chromen-3-ol (2f). Yield 44%, colorless crystals, mp 120–
122°С (hexane). IR spectrum, ν, cm–1: 3348 (OH), 2967,
2870, 1605, 1508, 1470, 1435, 1393, 1369, 1273, 1238,
1211, 1184, 1150, 1119, 1084, 1030, 999, 980, 891,
3-(Trifluoromethyl)-2,3-dihydro-1H-benzo[f]chromen-
3-ol (2c). Yield 42%, colorless crystals, mp 140–142°С
(cyclohexane). IR spectrum, ν, cm–1: 3345 (OH), 1628,
1601, 1514, 1468, 1435, 1335, 1258, 1223, 1204, 1184,
1
826, 810. H NMR spectrum, δ, ppm (J, Hz): 1.42 (9H,
s, С(СН3)3); 2.09 (1H, td, J = 13.0, J = 6.4) and 2.42 (1H,
dd, J = 13.3, J = 6.0, 2-CH2); 2.90–3.28 (3H, m, 1-CH2,
OH); 7.08 (1H, d, J = 9.0, H Ar); 7.62–7.67 (2H, m,
H Ar); 7.73 (1H, s, H-7); 7.82 (1H, d, J = 8.7, H Ar).
13C NMR spectrum, δ, ppm (J, Hz): 16.6 (CH2); 23.7
(CH2); 31.3 (C(CH3)3); 34.7 (C(CH3)3); 93.9 (q,
2JCF = 33.4, CCF3); 113.4 (C); 118.3 (CH); 122.0 (CH);
1
1159, 1123, 1082, 1032, 1020, 1001, 972, 810. H NMR
spectrum, δ, ppm (J, Hz): 2.06–2.16 (1H, m) and 2.42 (1H,
ddd, J = 13.3, J = 6.0, J = 1.8, 2-CH2); 2.84 (1H, br. s,
OH); 3.11–3.20 (1H, m) and 3.26 (1H, dd, J = 16.5, J = 5.5,
1-CH2); 7.11 (1H, d, J = 9.0, H Ar); 7.41 (1H, ddd, J = 8.0,
J = 7.1, J = 1.2, H Ar); 7.54 (1H, ddd, J = 8.5, J = 7.1,
J = 1.4, H Ar); 7.68 (1H, d, J = 9.0, H Ar); 7.79 (1H, d,
J = 8.2, H Ar); 7.87 (1H, d, J = 8.5, H Ar). 13C NMR
spectrum, δ, ppm (J, Hz): 16.6 (CH2); 23.6 (CH2); 94.0 (q,
2JCF = 33.4, CCF3); 113.7 (C); 118.5 (CH); 122.3 (CH);
122.8 (q, 1JCF = 283.2, CF3); 124.3 (CH); 126.9 (CH); 128.4
(CH); 128.6 (CH); 129.8 (C); 132.3 (C); 147.9 (C–O). Mass
spectrum, m/z (Irel, %): 268 [M]+ (100), 199 [M–CF3]+ (5),
157 [C11H9O]+ (82), 144 (28), 128 [C10H8]+ (57), 69 [CF3]+
(16). Found, %: C 62.60; H 4.07. C14H11F3O2. Calculated,
%: C 62.69; H 4.13.
1
122.8 (q, JCF = 284.1, CF3); 123.7 (CH); 125.6 (CH);
128.4 (CH); 129.7 (C); 130.4 (C); 147.0 (C); 147.5 (C).
Found, %: C 66.73; H 5.84. C18H19F3O2. Calculated, %:
C 66.66; H 5.90.
3-(Trifluoromethyl)-1H-benzo[f]chromene (5).
A
solution of chromenol 2с (0.15 g, 0.56 mmol) in SOCl2
(4 ml) was refluxed for 4 h. The excess of thionyl chloride
was removed by distillation at reduced pressure. The
product was purified by recrystallization from МеОН.
Yield 0.12 g (86%), yellow crystals, mp 67–69°С. IR
spectrum, ν, cm–1: 2893, 2839, 1713 (C=Cpyran), 1686,
1626, 1605, 1518, 1470, 1402, 1393, 1352, 1319, 1281,
8-(Adamantan-1-yl)-3-(trifluoromethyl)-2,3-dihydro-
1H-benzo[f]chromen-3-ol (2d). Yield 58%, colorless
crystals, mp 243–244°С (decomp., hexane). IR spectrum, ν,
cm–1: 3600–3300 (OH), 3070, 2909, 2847 (CH Ad), 1605,
1508, 1474, 1450, 1393, 1342, 1319, 1215, 1188, 1088,
1
1229, 196, 1125, 1092, 1011, 804, 764, 741. H NMR
spectrum, δ, ppm (J, Hz): 3.77–3.80 (2H, m, 1-CH2); 5.83
(1H, t, J = 3.7, 2-СН); 7.17 (1H, d, J = 9.0, H Ar); 7.47
(1H, ddd, J = 8.0, J = 7.1, J = 1.2, H Ar); 7.57 (1H, ddd,
J = 8.5, J = 6.9, J = 1.4, H Ar); 7.69 (1H, d, J = 8.5, H Ar);
7.72 (1H, d, J = 9.0, H Ar); 7.83 (1H, d, J = 8.0, H Ar).
13C NMR spectrum, δ, ppm (J, Hz): 21.1 (CH2); 102.6 (q,
3JCF = 3.8, 2-CH); 110.2 (C); 117.6 (CH); 119.6 (q,
1JCF = 269.8, CF3); 122.5 (CH); 124.9 (CH); 127.1 (CH);
128.5 (CH); 128.8 (CH); 130.9 (C); 131.7 (C); 140.1 (q,
2JCF = 36.2, CCF3); 147.8 (C–O). Mass spectrum, m/z
(Irel, %): 250 [M]+ (66), 249 [M–H]+ (75), 201 (16), 181
[M–CF3]+ (90), 152 [C12H8]+ (100), 151 (48), 126 (12), 69
[CF3]+ (42). Found, %: C 67.15; H 3.57. C14H9F3O.
Calculated, %: C 67.20; H 3.63.
1
1026, 999, 972, 883, 810, 721. H NMR spectrum, δ, ppm
(J, Hz): 1.81 (6H, br. s, 3CH2 Ad); 2.01 (6H, br. s, 3CH2 Ad);
2.04–2.14 (1H, m) and 2.41 (1H, ddd, J = 13.3, J = 6.0,
J = 1.8, 2-CH2); 2.15 (3H, br. s, 3CH Ad); 2.91 (1H, br. s,
OH); 3.09–3.18 (1H, m) and 3.24 (1H, dd, J = 16.5,
J = 5.5, 1-CH2); 7.07 (1H, d, J = 9.0, H-5); 7.63 (1H, dd,
J = 8.7, J = 2.1, H-9); 7.65 (1H, d, J = 8.7, H-10); 7.68
(1H, d, J = 2.1, H-7); 7.82 (1H, d, J = 9.0, H-6). 13C NMR
spectrum, δ, ppm (J, Hz): 16.6 (CH2); 23.6 (CH2); 29.0
(3CH Ad); 36.2 (C Ad); 36.9 (3CH2 Ad); 43.2 (3CH2 Ad);
2
93.9 (q, JCF = 33.4, CCF3); 113.4 (C); 118.3 (CH); 122.0
1
(CH); 122.8 (q, JCF = 283.2, CF3); 123.7 (CH); 125.0
(CH); 128.4 (CH); 129.8 (C); 130.4 (C); 147.2 (C); 147.5
(C). Found, %: C 71.58; H 6.20. C24H25F3O2. Calculated,
%: C 71.63; H 6.26.
8-Bromo-3-(trifluoromethyl)-2,3-dihydro-1H-benzo[f]-
chromen-3-ol (2e). Yield 69%, colorless crystals, mp 150–
152°С (hexane). IR spectrum, ν, cm–1: 3480 (OH), 1620,
1589, 1501, 1458, 1443, 1393, 1358, 1323, 1254, 1231,
The work was performed with financial support from the
Ministry of Education and Science of the Russian Federation
within the framework of the Project part of the State
assignment for scientific activity (4.1597.2014/К) and the
Grant Council of the President of the Russian Federation for
support of young Russian scientists (grant MD-5833.2016.3).
562

Chemistry of Heterocyclic Compounds 2016, 52(8), 559–563
10. Chandra Sheker Reddy, A.; Shanthan Rao, P.;
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