Nitrogen heterocycles from trimethylbenzenes

Article abstract of DOI:10.1002/hc.20045

The reaction between 1,2,4-trimethyl-benzene 1, isobutyric aldehyde, and cyanoacetic ester afforded a mixture of three products: 3,3,5,6,8-pentamethyl-1, 2,3,4-tetraisoquinolylidene-1-acetic acid ether (2) and its 3,3,5,6,7- pentamethyl-(3)-and 3,3,6,7,8-

Full text of DOI:10.1002/hc.20045

Heteroatom Chemistry
Volume 15, Number 6, 2004
Nitrogen Heterocycles from
Trimethylbenzenes
Yu. V. Shklyaev,1 R. R. Ismagilov,2 Yu. S. Rozhkova,1 A. A. Fatykhov,2
I. B. Abdrakhmanov,1 A. G. Tolstikov,3 and V. M. Dembitsky3
1Institute of Technical Chemistry, Ural Branch, Russian Academy of Sciences, 13 Lenin Street,
614990 Perm, Russia
2Institute of Organic Chemistry, Ufa Scientific Centre, Russian Academy of Sciences,
71 October Avenue, Ufa, Russia
3N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Leninsky prospect,
47, 117913 Moscow, Russia
Received 9 July 2004
tiospecific synthesis of 3-aza-bicyclic compounds
ABSTRACT: The reaction between 1,2,4-trimethyl-
[5], cis-fused hexahydro-4aH-indeno[1,2-b]pyridine
benzene 1, isobutyric aldehyde, and cyanoacetic ester
ring system [6], and six-five-six fused-ring struc-
afforded a mixture of three products: 3,3,5,6,8-
tures [7]. Recently, we have reported that the reac-
pentamethyl-1,2,3,4-tetraisoquinolylidene-1-acetic
tion of activated arenes with nitriles and isobutyric
acid ether (2) and its 3,3,5,6,7-pentamethyl-(3)-
aldehyde in concentrated sulfuric acid gives 3,3-
and 3,3,6,7,8-pentamethyl-1,2,3,4-tetraisoquinolyli-
dimethyl-3,4-dihydroisoquioline derivatives [8,9].
dene-1-acetic acid ether isomers (3) in ratio 1:5:1.
Here we report the synthesis of nitrogen hetero-
ꢀ
C
2004 Wiley Periodicals, Inc. Heteroatom Chem
cycles derived from thimethylbenzenes in the reac-
tion with isobutyric aldehyde and cyanoacetic ester.
15:471–476, 2004; Published online in Wiley InterScience
(www.interscience.wiley.com). DOI 10.1002/hc.20045
RESULTS AND DISCUSSION
INTRODUCTION
Preparation of Isoquinolylidene Derivatives
The Ritter reaction in its original version involves
electrophilic alkylation of nitriles with carbenium
1
According to H NMR, NOESY, MS, and TLC data,
we found that the reaction between 1,2,4-trimethyl-
ions generated from olefins, or tertiary or secondary
benzene (pseudocumol 1), isobutyric aldehyde, and
alcohols in the presence of acids, and results in N-
substituted amides [1,2]. Several alternative method-
cyanoacetic ester gives a mixture of three prod-
ucts, the structures of which were those of 3,3,5,6,8-
ologies were developed for the Ritter reaction [3,4],
pentamethyl-1,2,3,4-tetraisoquinolylidene-1-acetic
and the Ritter reaction was applied to the enan-
acid ester (2) and its 3,3,5,6,7- and 3,3,6,7,8-isomers
(3 and 4) in ratio 1:5:1 (according to integral in-
tensity signals). The reaction involving preobtained
Correspondence to: V. M. Dembitsky; e-mail: dvalery@cc.huji.
carbinol 2 gave the same results (Scheme 1).
Compounds 4 and 5 were formed from 1,2,3-tri-
methylbenzene (6), isobutyric aldehyde, and cyano-
acetic ester, as well as from carbinol 7 previously
ac.il.
Present address of V. M. Dembitsky: Department of Organic
Chemistry, P.O. Box 39231, Hebrew University, Jerusalem 91391,
Israel.
c
ꢀ
2004 Wiley Periodicals, Inc.
471

472 Shklyaev et al.
SCHEME 3
i: (CH3)2CHCHO, NCCH2COOEt, H2SO4, 5–10◦C
ii: NCCH2COOEt, H2SO4, 5–10◦C, ratio 3:4:5 = 1:5:1
tions was probably exposed mainly to methyl group
migration from position 8 to 6 allowing product 4,
and to a lesser extent to methyl group migration
from position 5 to 6 allowing product 5, as shown
in Scheme 4.
SCHEME 1
It is obvious that isoquinoline 3 having a methyl
group at position 6 on the ring does not undergo
any rearrangements. Based on the concept of a tan-
dem three-component heterocyclization reaction via
spiro-intermediates, it was of interest to use mesity-
lene in the reaction. Since A- and B-type interme-
diates may be presented as uncharged C and D
structures, the reaction of these with a protonated
isobutyric aldehyde seems most likely. That interme-
diate C was not found in the reaction products was
probably due to the sterically hindered reaction ow-
ing to orthogonally positioned spirocycle [13].
Intermediate D may give E and F conform-
ers that convert to cis-(H) and trans-(G)-conjugate
tetraenes, respectively. When intermediate H is pro-
tonated, the formation of spiran 10 seems most
likely because its reaction with nitrile is also hin-
dered sterically. On the contrary, the reaction of
trans-intermediate G with nitrile is preferential, and
dispiroproduct 9 is the only reaction compound
formed (Scheme 5).
obtained from 1-bromo-2,3,4-trimethylbenzene and
isobutyric aldehyde (4:5 ratio = 5:1) in the case of
the three-component synthesis (Scheme 2).
Formation of 4 and 5 from an arene 6 and
carbinol 7 can be only due to the fact that the re-
action proceeds via spiro-intermediate A that could
be isomerized in two ways under the reaction condi-
tions (Scheme 3).
Similar reactions were previously observed for
benzoic acid phenethylamide and 2-(6ꢁ-metoxy-
naphthyl-2ꢁ)-ethylamide cyclization based on the
Bishler–Napieralski reaction [10] that is genetically
related to the Ritter reaction as they both proceed
via the same intermediate [11]. The reaction with
pseudocumol 1 should probably proceed via spiro-
intermediate B that must initially lead to isoquino-
lines 3 and 8, with the latter being predominated.
Further reaction course occurs via the Jacobs re-
action [12] typical for tetra-alkyl-substituted ben-
zenes in sulfuric acid. Since migration of alkyl substi-
tute from EWG ortho-position to para-position was
characteristic of the Jacobs reaction, isoquinoline
8 formed and protonated under the reaction condi-
Considering the fact that when mesitylene,
isobutyric aldehyde, and nitriles (cyanoacetic ester,
acetonitrile, methylrhodane) are used in equimolar
ratios, and the cascade heterocyclization product 9
i: (CH3)2CHCHO, NCCH2COOEt, H2SO4, 5–10◦C
ii: NCCH2COOEt, H2SO4, 5–10◦C, ratio 4:5 = 5:1
SCHEME 2
SCHEME 4

Nitrogen Heterocycles from Trimethylbenzenes 473
methyl groups at C3 (1.43 ppm) were observed. The
methyl groups were present at 1.86 ppm on the cyclo-
hexadiene ring and observed as two singlets. Methy-
lene proton signals at C4 were found at 2.00 ppm,
while those at C4ꢁ was found at 2.65 ppm.
According to experimental data and discussion
above, we demonstrated that the reaction of iso-
meric trimethylbenzenes with both an isobutyric
aldehyde and nitriles, and the appropriate carbinols
and nitriles, proceeds only via the formation of a
five-member spiroheterocycle, the latter being ei-
ther preserved unchanged or rearranged into 3,4-
dihydroisoquinoline derivatives.
EXPERIMENTAL
Melting points were determined using a Reichert–
Jung Thermovar apparatus and an Electrothermi-
nal IA 9000 digital melting point apparatus and are
uncorrected. IR spectra were measured in vaseline
oil using a UR-20 spectrophotometer. 1H NMR spec-
tra were monitored using a Bruker AM-300 model
(75.470 MHz) in DMSO-d6 at 303◦C K. NOESY spec-
tral mixing time was 500 ms. The HBMC experi-
ment was optimized using KCCB 8 Hz. Mass spectra
were measured using a Finnigan MAT apparatus
under standard conditions (electron impact ioniza-
tion, 70 eV). The reaction course and the purity of
the formed product were monitored using a TLC
method on Silufol UV-254 plates in chloroform–
acetone (9:1); 0.5% chloranyl solution in toluene was
used as a developer.
Scheme 5. Reagents and conditions:
c) isobutyric aldehyde, RCN, sulfuric acid, 5–10◦C
R = CHCOOEt Me SMe (9a–c)
SCHEME 5
Three-Component Synthesis of the 3 and 8
from 1,2,4-Trimethylbenzene
is solely formed, one could suppose that the proto-
nated isobutyric aldehyde attack on the intermedi-
ate D is not merely thermodynamically efficient, but
also occurs with high enantioselectivity resulting in
intermediates E, G, and I that afford ultimately the
formation of the cascade heterocyclization product
in total 65–70% yield for 10 stages [14].
A mixture of pseudocumol (1.2 g, 10 mmol), isobu-
tyric aldehyde (0.72 g, 10 mmol), and cyanoacetic
ester (1.13 g, 10 mmol) was added, dropwise with
stirring, to sulfuric acid (15 mL, 95%) at 5–10◦C
for 1 min. After 3–5 min. stirring the reaction mix-
ture was poured on to 100 g of crushed ice and
extracted with benzene (25 mL). The organic layer
was separated, and the water layer was basified with
ammonium carbonate up to pH 8–9. The resulting
layer was extracted with chloroform (2 × 50 mL),
dried over MgSO4. After distilling off the solvent
on a rotary evaporator, 2.3 g of the product mix-
ture was obtained. Using column chromatography
(triethanolamine-deactivated silica gel, 30/50 mesh;
benzene–ester, 35:1), compound 3 (85% yield) was
isolated with isoquinoline 4 (15%) as admixture,
whereas compound 5 (80% yield) was obtained with
isoquinoline 4 (20%) as admixture (according to 1H
NMR).
1H NMR spectrum of 9b reveals duplications
of all aliphatic proton signals. Thus, there are two
triplets (ꢀ = 1.12 and 1.17 ppm) of methyl groups and
two quadruplets (3.85 and 4.01 ppm) of a methylene
ring of two ethoxy groups which are difficult to as-
sign. Two vinyl proton singlets at 3.83 and 4.78 ppm
were assigned to spiropyrrolidine and pyrrolidene
fragments, respectively. Vinyl proton signals of a cy-
clohexadiene ring are observed at 6.18 ppm (C7-H)
and 6.73 ppm (C9-H). We failed to assign NH-proton
signals, which were observed at 8.23 and 8.41 ppm, to
an appropriate ring. Furthermore, two methyl group
signals at C5ꢁ (1.24 and 1.25 ppm) and a singlet of two

474 Shklyaev et al.
3,3,5,6,8-Pentamethyl-1,2,3,4-tetrahydroisoqui-
nolylidene-1-acetic Acid Ether (3). 1H NMR ꢀ: 1.22
(s, 6H, gem-Me); 1.30 (t, 3H, OCH2 CH3, J = 7.2 Hz);
2.19 (s, 3H, 5ꢁ-CH3); 2.32 (s, 3H, 6ꢁ-CH3); 2.51 (s, 3H,
8ꢁ-CH3); 2.78 (s, 2H, 4-CH2); 4.20 (q, 2H, OCH2CH3,
J = 7.2 Hz); 4.81 (s, 1H, Hvinyl); 6.97 (s, H, 7-Haryl);
9.11 (w.s., 1H, NH).
6H, gem-di-Me); 1.29 (t, 3H, OCH2CH3; J = 7.2 Hz);
2.21 (s, 3H, 6ꢁ-Me); 2.30 (s, 3H, 7ꢁ-Me); 2.48 (s, 3H,
8ꢁ-Me); 4.15 (q, 2H, OCH2CH3, J = 7.2 Hz); 4.77 (s,
1H, 4-CH2); 6.81 (s, 1H, 5-H); 9.12 (w.s., 1H, NH).
Preparation of 2,3,4-Trimethylbromobenzene
Water (100 mL) was added to 1,2,3-trimethylbenzene
(60 g, 0.5 mol) in CCl4(400 mL) then bromine (80 g,
0.5 mol) was added, dropwise with stirring, to
achieve slight staining of the solution. The reaction
mixture was stirred for 30 min; the water layer was
separated, and the organic layer was washed with
water (2 × 200 mL), next with a saturated sodium
bicarbonate solution (200 mL) and finally with wa-
ter to achieve pH 7. After removing the solvent on a
rotary evaporator, alcohol (200 mL) and solid KOH
(20 g) were added to the residue. The resultant layer
was stirred for 20 min, heated for 30 min with the
boiling solvent and poured into water (700 mL).
This was further extracted with methyl-tert-butyl es-
ter (2–300 mL) and dried over MgSO4. The solvent
was removed on the water bath, and the residue
was distilled in vacuum and collected in a fraction
which was boiling away at 110–115◦C at 15 mm.
2,3,4-trimethylbrombenzene was obtained in 65%
3,3,5,7,8-Pentamethyl-1,2,3,4-tetrahydroisoqui-
nolylidene-1-acetic Acid Ether (8). mp 71–72◦C
(hexane). IR (ꢁ/cM−1): 3250; 2960; 2850; 1640; 1600;
1
1370. H NMR (ꢀ): 1.22 (s, 6H, gem- CH3); 1.29 (t,
3H, OCH2CH3, J = 7.2 Hz); 2.22 (s, 3H, 5ꢁ-CH3);
2.26 (s, 3H, 7ꢁ-CH3); 2.44 (s, 3H, 8ꢁ-CH3); 2.67 (s, 2H,
4-CH2); 4.15 (q, 2H, OCH2CH3, J = 7.2 Hz); 4.76 (s,
1H, Hvinyl); 7.01 (s, 1H, Harom); 9.12 (w.s., 1H, NH). It
was found (%) C 75.19; H 8.72; N 4.93. C18H25NO2.
It was calculated (%) C 75.26; H 8.71; N 4.88.
Synthesis of 4 and 5 from
1,2,4-Trimethylbenzene
A
mixture of 1,2,3-trimethylbenzene (1.2 g,
10 mmol), isobutyric aldehyde (0.72 g, 10 mmol),
and cyanoacetic ester (1.13 g, 10 mmol) was added,
dropwise with stirring, to sulfuric acid (15 mL, 95%)
at 5–10◦C for 3 min. After stirring for 15 min, the
mixture was poured on to 100 g of crushed ice. The
organic layer was extracted with 25 mL of benzene,
and the water layer was basified with ammonium
carbonate up to pH 8–9. The resulting layer was
extracted with chloroform (2 × 50 mL), dried over
MgSO4. After removing the solvent, 2.3 g of the
product mixture was obtained. Column chromatog-
raphy (triethanolamine-deactivated silica gel, 30/50;
benzene–ester, 35:1) afforded compound 4 in 52%
yield (15 g, mp 83–84◦C, hexane) and a mixture of
5 (80%) and 4 (20%) that were not separated into
pure products (according to 1H-NMR).
1
yield (65 g). H-NMR spectrum was similar to that
described previously [6].
Preparation of 2-Methyl-1-
(2ꢁ,3ꢁ,4ꢁ-trimethylphenyl)-propanol-1 (7)
Fresh-distilled isobutyric aldehyde (15 g, 0.21 mol)
in 50 mL of dry THF was added, dropwise upon
cooling with water and ice, to 0.2 mol of 2,3,4,-
trimethylphenylmagnesium bromide solution (pre-
pared from 40 g (0.2 mol) of 2,3,4-trimethylbromo
benzene and 5 g (0.21 mol) of magnesium in 15 g
of dry THF). The reaction mixture was stirred with
heating for 30 min, cooled, and dissolved with sat-
urated NH4Cl solution. The organic layer was sepa-
rated, and the water layer was extracted with methyl-
tert-butyl ether (2 × 150 mL). Combined organic lay-
ers were washed with water, dried over MgSO4; the
solvent was removed on a water bath, and the residue
was distilled at 5 mm and collected in a fraction
which boiled away at 140–145◦C. Product 7 was
formed in 77% yield (∼30 g) and used without be-
ing further purified. It was found (%) 81.33; H 10.61.
C13H20O. It was calculated (%) C 81.20; H 10.48.
3,3,5,6,7-Pentamethyl-1,2,3,4-tetrahydroisoqui-
nolylidene-1-acetic Acid Ether (4). IR (ꢁ/cM−1):
3260, 2960, 2850, 1630, 1600, 1380. 1H NMR ꢀ:
1.28 (s, 6H, gem-di-Me); 1.30 (t, 3H, OCH2CH3, J =
7.1 Hz); 2.20 (s, 3H, 5ꢁ-Me); 2.23 (s, 3H, 6ꢁ-Me);
2.34 (s, 3H, 7ꢁ-Me); 2.76 (s, 2H, 4-CH2); 4.16 (q, 2H,
OCH2CH3, J = 7.1 Hz); 5.12 (s, 1H, Hvinyl); 7.40 (s,1H,
8-H); 9.00 (w.s., 1H, NH). 13C-NMR ꢀ: 14.8(CH2CH3);
15.4(5ꢁ-CH3); 16.3 (6ꢁ-CH3); 20.9 (7ꢁ-CH3); 28.9
(gem-CH3); 39.1 (4-CH2); 49.0 (3-C); 58.4(CH2CH3);
77.0 (Cvinyl); 124.2 (8-C); 125.7 (8a-C); 131.2 (4a-
C); 134.2 (5-C); 134.3 (6-C); 138.3(7-C); 156.5(1-C);
171.3(C O). It was found (%) C 75.13; H 8.62; N 4.95.
C18H25NO2. It was calculated (%): C 75.26; H 8.71; N
Reaction between Compound 7 and Cyanoacetic
Ester
A mixture of 7 (1.92 g, 0.01 mol) and cyanoacetic
ester (1.13 g, 0.01 mol) was added dropwise to
1
4.88. Compound 5: differential H-NMR ꢀ: 1.22 (s,

Nitrogen Heterocycles from Trimethylbenzenes 475
1H NMR ꢀ, ppm.
IR spectrum 3-(Me)2, 4-(CH)2, 6,10-(Me)2, C7H, C9H 4ꢁ-CH2, 2H, 5ꢁ-(Me)2,
(v/cm−1
)
6H, s
2H, s
6H, d
two s.
(AB-system)
two s.
Others
9a 3355 (w.s.);
3335
1.43
2.00
1.86
6.18; 6.73
2.65
1.24
1.25
1.12 (3H, t, Me-ester.); 1.17
(3H, t, Me-ester.); 3.85
(2H, q, OCH2); 4.01 (2H, q,
OCH2); 3.83 (1H, s,
(w.s.);
1735;
1723;
C1-CꢂH); 4.78 (1H, s,
ꢁ
1650;
C2 -CꢂH); 8.24 (1H, s, NH);
1600;
8.41 (1H, s, NH)
1580; 1500
9b 1650; 1598;
1510
9c 1650; 1600;
1580
1.31
1.34
1.87
2.00
1.74
1.78
6.16; 6.81
6.15; 7.09
2.55
2.68
1.15
1.16
1.19
1.20
1.58 (3H, s, 1-Me); 2.27 (3H,
s, 2ꢁ-Me)
2.31 (3H, s, 1-SMe);
2.42 (3H, s, 2ꢁ-SMe)
Mass-spectrometry data:
9a: (EI, 70 eV), m/z (Irel.(%)): 454 [M]+ (100); 439 [M CH3]+ (25); 409 [M OEt]+ (24); 393 [M OOEt]+ (23);
381 [M COOEt]+ (30); 341 [M NCCH2COOEt]+ (98); 326 [M NCCH2COOEt Me]+ (97); 300 (90).
9b: (EI, 70 eV), m/z (Irel.(%)): 310 [M]+ (5); 269 [M CH3CN]+ (100); 254 [M CH3CN CH3]+ (96);
231 [M CH3CN CH3 CH3CN]+ (25).
9c: (EI, 70 eV), m/z (Irel.(%)): 374 [M]+ (5); 301 [M CH3SCN]+ (100); 286 [M CH3CN CH3]+ (47);
213 [M CH3SCN CH3 CH3SCN]+ (15).
FIGURE 1 Spectral characteristics of compounds 9 a–c.
concentrated sulfuric acid (15 mL). The reaction
mixture was treated following the procedure de-
scribed for a three-component synthesis. The total
yield and the 4:5 ratio was consistent with those ob-
tained in the three-component synthesis.
tallized from the appropriate solvent. Compound 9a
was obtained in 67% yield (mp 143–144◦C, hexane)
(see Fig. 1). It was found (%) C 67.50; H 8.10; N 7.60;
S 9.41. C21H30N2S. It was calculated (%): C 67.38; H
8.02; N 7.49; S 9.36. Compound 9b was obtained in
65% yield (mp 107–108◦C, hexane) in a similar way.
It was found (%) C 81.12; H 9.70; N 9.18. C21H30N2.
It was calculated (%): C 81.29; H 9.68; N 9.03. Com-
pound 9c was obtained in 71% yield (mp 190–191oC,
alcohol). It was found (%): C 71.46; H 8.33; N 6.23.
C27H38N2O4. It was calculated (%): C 71.37; H 8.37;
N 6.23.
Preparation of 8-[2ꢁ-R-5ꢁ,5ꢁ-Dimethylpyrrolyl-3ꢁ-
idene]-1-R-3,3,6,10-tetramethyl-2-azaspiro[4,5]-
deca-1,6,9-trienes(9a–c)
A mixture of mesitylene (0.1 mol), isobutyric alde-
hyde (0.2 mol), and appropriate nitrile was added,
dropwise upon cooling with water and ice, to concen-
trated sulfuric acid (50 mL). The mixture was stirred
for 15 min and poured into water with ice (300 mL).
The water layer was separated; the organic layer was
treated with methyl-tert-butyl ether and 10% NaOH,
washed with water and dried, then the solvent was re-
moved on a rotary evaporator. The residue was crys-
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