Spirocyclohexadienones: VIII. 1-R-3,3-Dimethyl-2-azaspiro[5.5]undeca-1,7, 10-trien-9-ones

Article abstract of DOI:10.1134/S1070428006080045

1-R-3,3-Dimethyl-2-azaspiro[5.5]undeca-1,7,10-trien-9-ones were synthesized by condensation of 4-(p-methoxyphenyl)-2-methylbutan-2-ol with nitriles RCN in the presence of a concn. sulfuric acid. Nauka/Interperiodica 2006.

Full text of DOI:10.1134/S1070428006080045

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2006, Vol. 42, No. 8, pp. 1131 -1136. Ó Pleiades Publishing, Inc. 2006.
Original Russian Text Ó V.A. Glushkov, T.N. Vetoshkina, D.V. Kolgashev, O.A. Maiorova, S.N. Shurov, Yu.V. Shklyaev, 2006, published in Zhurnal
Organicheskoi Khimii, 2006, Vol. 42, No. 8, pp. 1153-1158.
Spirocyclohexadienones: VIII.*
1-R-3,3-Dimethyl-2-azaspiro[5.5]undeca-1,7,10-trien-9-ones
V.A. Glushkova, T.N. Vetoshkinab, D.V. Kolgashevb, O.A. Maiorovaa,
S.N. Shurovb, andYu.V. Shklyaeva
aInstitute of Technical Chemistry, Ural Division, Russian Academy of Sciences, Perm, 614600 Russia
e-mail: cheminst@mpm.ru
bPerm State University, Perm, Russia
Received April 25, 2005
Abstract—1-R-3,3-Dimethyl-2-azaspiro[5.5]undeca-1,7,10-trien-9-ones were synthesized by condensation of
4-(p-methoxyphenyl)-2-methylbutan-2-ol with nitriles RCN in the presence of a concn. sulfuric acid.
DOI: 10.1134/S1070428006080045
Heterocyclic spirocyclohexa-2,5-dien-1-ones re-
present a specific heterocyclic class attracting lately the
interest of researchers. We formerly carried out a three-
component condensation of anisole, isobutyric aldehyde,
and nitriles RCN in the presence of concn. H2SO4 to
obtain spirocyclohexadienepyrrolines (1-R-3,3-dimethyl-
2-azaspiro[4.5]-deca-1,6,9-trien-8-ones) [2, 3]. In this
study we attempted to prepare homologs of these
compounds with a piperidine ring instead of pyrroline one.
The structural unit of a spirocyclohexadienepiperidine is
encountered in some natural compounds of a high physio-
logical activity, for instance, in nitramin, an alkaloid of
plants from the genus Nitraria (2-azaspiro[5.5]undecane)
[4, 5], in histrionicotoxin, the poison of arrow-poison
South-American frogs (Dendrobatidae) (1-azaspiro-
[5.5]undecane) [6, 7], in sponge alkaloids 3-azaspiro-
[5.5]undecane [8, 9], and also in the recently described
plankton toxins, gymnodimine (2-azaspiro[5.5]undecane)
and spirolides A-D (2-azaspiro[6.5]dodecane) [10].
The synthetic approaches to this type compounds
besides the classical oxidative coupling of phenols [9, 11–
14] include an intramolecular Mannich reaction [5],
an intramolecular ene reaction [6], acyliminium ions
cyclization [15], spirofusion of tricarbonyl-1,3-cyclohexa-
diene iron [16], and also the metathesis reaction using
Grubbs catalyst [10, 17]. The synthesis of seven-
Scheme 1.
0H
ꢀ&+ ꢁ & 0H
2+
0H2
+2
+ 2
+
0H
0H
0H
0H
0H2
5&1
1
1
0H2
5
5
5
9
0H2+
0H
0H
0H
0H
0H
0H
2
2
2
1
2
0H
0H
1
1+
&22(W
0H6
60H
+
,Dꢀꢁ,E
,,,
,,
,9
R = SMe (a), SCH2Ph (b).
* For communication VII, see [1].
1131

GLUSHKOV et al.
1132
Scheme 2.
membered spirohexadienoazepines is also possible
(a system of 2-azaspiro[6.5]dodecane) [10–13].
2-ol and nitriles RCN in the presence of the concn.
sulfuric acid (Scheme 1). In the case of R = SMe,
SCH2Ph, or CH2COOEt we succeeded in preparation
of spirocycliza-tion products, the corresponding 1-R-3,3-
dimethyl-2-azaspiro[5.5]undeca-1,7,10-trien-9-ones Ia,
To synthesize 1-R-3,3-dimethyl-2-azaspiro[5.5]-
undeca-1,7,10-triene-9-ones we carried out the Ritter
reaction between 4-(p-methoxyphenyl)-2-methylbutan-
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 42 No. 8 2006

SPIROCYCLOHEXADIENONES: VIII.
1133
Enthalpy of formation DHf (kJ mol-1) of intermediates I2-I8 and activated complexes AC1, AC2 in spirocyclization reaction
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0.116 a.u. The geometry of the main carbon chain also is
not considerably affected in carbocation I2c, and the
charge on the C2 becomes equal to 0.332 a.u. Just this
electrophilic site of intermediate I2c is attacked by the
nitrogen of the methyl thiocyanate molecule. We simulated
this process by the reaction coordinate method selecting
as the coordinate the interatomic distance lC2ꢀN. On
the curve in the coordinates DHf –lC2ꢀN appeared two
minima with characteristic interatomic distances lC2ꢀN
2.943 and 1.451 A, and a maximum (lC2ꢀN 1.998 A).
The first minimum corresponds to ion-dipole complex I3c
which governs the character of the reagents approach,
and the second minimum is nitrilium cation I4c.
Ib, and II, whereas at R = Me, Ph no spirocompounds
formed under the same conditions. We formerly
mentioned the favorable effect of alkylsulfanyl groups
on the stability of spirocompounds I and II [18, 19].
In the 1H NMR spectra of compounds Ia and Ib the
protons at C8H and C10H give rise to doublets in the region
6.25–6.30 ppm (J 9.6 Hz). The signals of protons C7H
and C11H appear as doublets in the region 6.8 ppm
(7.2 ppm for compound II) with the same coupling
constant. Compound II exists in an enamine form as
proved by the olefin proton singlet at 4.20 ppm and the
singlet of the NH group at 8.75 ppm. In the 13C NMR
spectra of compounds Ia, Ib, and II a signal from the
spiro atom C6 is observed in the region d 93–94 ppm.
We estimated the opportunity and limits of the
spirocyclization under study by simulation of the formation
of compound Ia and its four-membered (III, n = 0) and
seven-membered (IV, n = 3) analogs. The probable path
of 4-(p-methoxyphenyl)-2-methyl-2-butanol (V) trans-
formation into 1-substituted 3,3-dimethyl-2-azaspiro[5.5]-
undeca-1,7,10-trien-9-ones is presented in Scheme 2 by
an example of compound Ia. The probability of the
realization of the suggested scheme was evaluated by
simulating separate stages of the process with the use of
semiempirical method SCF MO LCAO in the AM1
approximation [20], and also by calculation of the enthalpy
of formation (DHf) for the possible intermediates and the
preceding activated complexes. The calculated DHf
values are given in the table.
°
°
The maximum on the potential curve corresponds to
activated complex AC1c that is the transition state of
the reaction. The activation energy of nitrilium ion
formation Ea was estimated from the difference
DHf (AC1c) – DHf (I1c) at 46.0 kJ mol-1.
The geometry of the main carbon chain is retained in
going from intermediate I3c to intermediate I4c, the
aromatic substituent in the latter is turned with respect to
virtually planar main carbon chain through 70.1°, the
spatial position of the nitrogen atom can be described
with a dihedral angle QNC2C3C4 59.9°. The interatomic
distance between the future reaction centers, the
sp-hybridized carbon of the methyl thiocyanate fragment
°
and C1' atom of the benzene ring, amounts to 5.070 A.
The direct approach of the reaction centers looks
impossible for the trans-orientation of the bonds C1–C2
and C3–C4 with respect to the C2–C3 bond is also
conserved in intermediate I4c. Therefore we suggested
that cation I4c could take a form more convenient for
the electrophilic attack of the C1' atom by a rotation of
fragments around the C2–C3 bond. Actually, on the
potential curve in the DHf–QC1C2C3C4 coordinates a
minimum was found at the dihedral angle value QC1C2C3C4
–68.6° corresponding to one more stable conformer of
nitrilium cation I4'c. The transformation of nitrilium cation
I4c into I4'c requires going over a low activation barrier
(2.7 kJ mol-1). The reaction centers in cation I4'c are at
The reaction apparently starts by the protonation of
the oxygen atom in alcohol V followed by water elimination
from oxonium cation I1c. In the most stable conformation
of alcohol V the carbon atoms of the main chain are
located actually in the same plane, and the bonds C1–C2
and C3–C4 are directed trans with respect to the C2–C3
bond.
The proton addition to the oxygen virtually does not
affect the geometry of the main carbon–carbon chain,
but the charge on the C2 atom grows from 0.076 to
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 42 No. 8 2006

GLUSHKOV et al.
1134
°
a distance 3.533 A. Their further approach results in the
formation of a carbon-carbon bond in a cation of
arenonium type I5c.According to calculations performed
analogously the activation energy of the process equals
111.6 kJ mol-1. The activation energy of the reverse
process is 59.6 kJ mol-1.
7-one (III), and water elimination from oxonium cation
I1a should lead to the formation of a benzyl type cation
I1a, which is more efficiently stabilized by the presence
of the electron-donor p-methoxyphenyl group. It is
evidenced partly by a smaller positive charge on the C2
atom (0.225 a.u.) and shorter bond MeO–C4' compared
with cations I1b and I1c.Apparently due to this stabiliza-
tion the reactivity of cation I1a with respect to methyl
thiocyanate is reduced, and the calculated activation
energy of formation for nitrilium cation I2a rises to
73.4 kJ mol-1. The spatial arrangement of the reaction
Arenonium cation I5c is likely attacked further by
water, but we failed to detect oxonium cation I6c on the
reaction coordinate. No minimum was found on the
potential curve describing this process, and at the
optimization of its geometry occurred “water ejection”.
The attack of C4' atom of the aromatic ring probably
involves either a proton transfer to the oxygen of the
methoxy group and methanol elimination leading to the
formation of intermediate I7c, or a proton elimination
giving rise to neutral intermediate I8c. The deprotonation
of intermediate I7c or methanol ejection from inter-
mediate I8c results in 2-azaspiro[5.5]-undeca-1,6,9-trien-
8-one (I).
°
centers in this species (interatomic distance 2.635 A)
should not in principle hamper the ipso-attack, but the
higher calculated activation energy of formation of cation
I5a equal to 223.0 kJ mol-1 suggests that this process is
considerably less probable than those already discussed.
Arenonium type cation I5a is characterized by a high
positive value of the enthalpy of formation and a too long
°
C3–C4 bond (1.681A) evidencing its possible instability.
The activation barrier to the reverse process I5a g AC2a
equal 31.6 kJ mol-1, considerably lower than for the similar
reactions at n = 1, 2. Therefore intermediate I5a should
form with greater difficulty but easier transforms into
the initial nitrilium cation. Intermediate I7a apparently
does not exist: the attempts at optimization of its geometry
resulted in the cleavage of the C3–C4 bond and to forma-
tion of methylsulfanyl-p-methoxyphenyl(2-propylidene)-
aminomethyl cation. Thus the synthesis of 1-methylthio-
2-azaspiro[3.5]nona-1,5,8-trien-7-one (III) by the above
described procedure is most unlikely.
We believe that the scheme of compound I formation
(I5c g I7c g I) is more reasonable since the water
dissociation in the course of arenonium ion attack seems,
firstly, unprobable (the reaction occurs in acid medium)
and, secondly, the neutral intermediate is sufficiently stable
as shows its DHf value.
The calculations show, that the stage of the arenonium
cation formation has the largest activation energy and
thus controls the rate of the total process.
We performed further the simulation of formation of
four-membered (III, n = 0) and seven-membered (IV,
n = 3) compound I analogs. We performed by analogous
procedure a parallel calculation of the formation path for
3,3-dimethyl-1-methylsulfanyl-2-azaspiro[4.5]-deca-
1,6,9-trien-8-one (VI), which we had synthesized before
[2, 3, 21].
To obtain 3,3-dimethyl-1-methylsulfanyl-2-azaspiro-
[6.5]dodeca-1,8,10-trien-9-one (IV) 2-methyl-5-(p-meth-
oxyphenyl)-2-pentanol (VIII) can be used as a source
of a carbocation of I1d type. The calculations suggest
that the carbon atoms of the main carbon chain in this
molecule are also located practically in one plane. The
bonds C1–C2, C3–C4, and C1'–C5 are trans-oriented rela-
tive to C2–C3 and C4–C5 respectively. The geometry of
the main chain is retained in going to carbocation I2d
and nitrilium cation I4'd. The distance between the reac-
The calculation shows that the activation parameters
of formation of nitrilium cation I4'b are virtually similar
to those for the above discussed reaction: the calculated
activation energy Ea is 46.7 kJ mol-1. However the position
of the reaction centers in the cation (interatomic distance
°
tion centers in the latter is 5.081A. The calculated activa-
°
3.568 A) made possible its direct transformation into
tion energy of formation of nitrilium cation I4d from carb-
ocation I3d and methyl isocyanate equals 44.4 kJ mol-1.
Cation I4d can transform into I4'd by the rotation of
fragments around C3–C4 and C4–C5 bonds; the distance
between the reaction centers in the latter is smaller
arenonium cation I5b. The calculated value of Ea was
109.7 kJ mol-1 also close to the corresponding value for
cation I5c. The activation energy of the reverse process
turned out to be 43.4 kJ mol1.
°
(3.098 A). Unlike the previously considered cases cation
The protonation of 2-methyl-2-(p-methoxyphenyl)-2-
propanol (VII), a presumable initial compound for the
synthesis of hypothetical 2-azaspiro[3.5]nona-1,5,8-trien-
I4'd proved to be less stable than cation I4d (the dif-
ference in the enthalpy of formation was 11.1 kJ mol-1).
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 42 No. 8 2006

SPIROCYCLOHEXADIENONES: VIII.
1135
Consequently the activation barrier to the conversion of
these cataions cannot be less than this value which is
obviously larger than the activation barrier to the transition
I4c g I4'c. The calculated value of the activation energy
for reaction I4'd g I5d amounts to 115.3 kJ mol-1, also
exceeding the Ea values for the really occurring reactions.
Thus the conversion of compound VIII into 3,3-di-
methyl-1-methylsulfanyl-2-azaspiro[6.5]dodeca-1,8,10-
trien-9-one (IV), is apparently less probable due to the
high activation barrier to the transformation of a nitrilium
cation into arenonium type cation. However the nitrilium
cation whose energy cosumption at the formation is
comparable with those of cations I2b, I2c can
participate in the other processes, for instance, in the
classical Ritter reaction.
stirring to 4 ml of concn. sulfuric acid (at cooling with
a water bath). The reaction mixture was stirred for
30 min and poured into 200 ml of cold water. The organic
layer was separated, the water layer was extracted with
dichloromethane (50 ml). The combined organic solutions
were washed with a saturated NaCl solution and dried
with MgSO4. On evaporating the solvent the residue was
recrystallized from ethanol. Yield 0.79 g (26%), colorless
–1
crystals, mp 84–85°C. IR spectrum, cm : 1665 (C=O),
1630 (C=N), 1610 (C=C), 1260, 1235, 1220. 1H NMR
spectrum (300 MHz, CDCl3), d, ppm: 1.20 s (6H, 2Me),
1.67 m (2H, C4H2), 1.84 m (2H, C5H2), 2.13 C (3H,
SMe), 6.31 d (2H, H8, H10, J 9.9 Hz), 6.78 d (2H, H7,
H11, J 9.9 Hz). 13C NMR spectrum (DMSO-d6), d, ppm:
182.5 (C=O), 155.4 (C=N), 149.1 (C7, C11), 127.1 (C8,,
C10), 93.5 (C6), 54.3 (C5), 45.5 (C3), 28.3* (C4), 28.2*
(CH3), 27.3* (CH3), 9.8 (SCH3). Mass spectrum, m/z
(Irel, %): [M]+ 235 (4), 162 (43), 147 (52), 120 (19), 107
(100), 91 (20). Found, %: C 66.23; H 7.36; N 5.76.
C13H17NOS. Calculated, %: C 66.35; H 7.38; N 5.95.
EXPERIMENTAL
IR spectra were recorded on a spectrophotometer
UR-20 from mulls in mineral oil. 1H NMR spectra were
registered at 30°C on a spectrometer Bruker DRX-500
(500 MHz) in DMSO-d6, internal reference HMDS.
13C NMR spectra were registered on a spectrometer
Varian Mercury Plus at 75 MHz. Mass spectrum of
compound I (electron impact, 70 eV) was measured on
Finnigan MAT instrument. The reaction progress was
monitored and the purity of compounds obtained was
checked by TLC on Silufol plates in the system chloro-
form–acetone, 9:1, development with 1% chloranil solution
in toluene. 3-(p-Methoxyphenyl)propionic acid was
a commercial product. Its methyl ester was prepared by
a standard procedure by treating the acid with methanol
in the presence of sulfuric acid, mp 36–38°C (from
hexane) (publ.: mp 38°C [22]). 4-(p-Methoxyphenyl)-2-
methylbutan-2-ol (V) was obtained by reaction of methyl
3-(p-methoxyphenyl)propionate with excess methyl-
magnesium iodide in ether, yield 82%, mp 35–36°C (from
a mixture ethanol–water), {publ.: bp. 133°C (2 mm Hg)
[23]}. Quantum-chemical calculations were performed
with the use of MOPAC 7.0 software[24] on PC Pentium
IV. The transition states were localized using algorithm
NLLSQ. The validity of localization of each transition
state was proved by a single negative eigenvalue of the
Hesse matrix.
1-Benzylsulfanyl-3,3-dimethyl-2-azaspiro-[5.5]-
undeca-1,7,10-trien-9-one (Ib). A solution of 3.74 g
(19.3 mmol) of carbinol V and 2.88 g (15.6 mmol) of
benzyl thiocyanate in 40 ml of toluene was added
dropwise at vigorous stirring to 6 ml of concn. sulfuric
acid (at cooling with a water bath). The reaction mixture
was stirred for 30 min and poured on a mixture of 100 ml
of ice, 25 ml of 25% NH4OH, and 25 ml of saturated
NaCl solution. The water layer was separated and
extracted with toluene (50 ml). The combined organic
solutions were washed with a saturated NaCl solution
and dried with MgSO4. On evaporating the solvent the
residue was twice re-crystallized from hexane. Yield 2.65
g (71%), colorless crystals, mp 122–124°C. IR spectrum,
–1
cm : 1660 (C=O), 1625 (C=C), 1600 (C=C), 1260, 1240,
1220, 1185, 1135, 1095, 1070, 1045 w, 1030, 990, 970 s,
1
930, 895, 860 s, 810. H NMR spectrum (300 MHz,
CDCl3), d, ppm: 1.23 s (6H, 2Me), 1.65 m (2H, C4H2),
1.82 m (2H, C5H2), 4.00 s (3H, SCH3), 6.28 d (2H, H8,
H10), 6.75 d (2H, H7, H11), 7.16 m (5H, Ph). 13C NMR
spectrum (CDCl3), d, ppm: 182.4 (C=O), 154.6 (C=N),
148.8 (C7, C11), 136.2 (C1'), 127.3 (C2', C6'), 126.9 (C3',
C5'), 126.1 (C8, C10), 124.7 (C4'), 93.5 (C6), 54.6 (C5),
45.4 (C3), 30.3 (C4), 28.2* (SCH2), 28.1* (CH3), 27.3*
(CH3). Found, %: C 73.19; H 6.85; N 4.37. C19H21NOS.
Calculated, %: C 73.27; H 6.80; N 4.50.
3,3-Dimethyl-1-methylsulfanyl-2-azaspiro-[5.5]-
undeca-1,7,10-trien-9-one (Ia). A solution of 3.02 g
(15.6 mmol) of 4-(p-methoxyphenyl)-2-methylbutan-2-ol
(V) and 1.1 ml (15.6 mmol) of methyl thiocyanate in
40 ml of dichloromethane was added dropwise at vigorous
3,3-Dimethyl-1-ethoxycarbonylmethylene-2-aza-
spiro[5.5]undeca-7,10-dien-9-one (II) was prepared
* The precise assignment of these signals was not performed.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 42 No. 8 2006

GLUSHKOV et al.
1136
similarly to compound Ib from 3.74 g (19.3 mmol) of
carbinol V, 2.1 ml (2.23 g, 19.5 mol) of ethyl cyanoacetate,
and 60 ml of dichloromethane in the presence of 5 ml of
concn. sulfuric acid. Yield 0.6 g (16%), colorless crystals,
7. Tanner, D., Hagberg, L., and Pousen,A., Tetrahedron, 1999,
vol. 55, p. 1427.
8. Copp, B.R., Fulton, K.F., Perry, N.B., Blunt, J.W., and Mun-
ro, M.H.G., J. Org. Chem., 1994, vol. 59, p. 8233.
9. Tohma,H.,Harayama,Y.,Hashizume,M.,Iwata,M.,Egi,M.,
and Kita, Y., Angew. Chem. Int. Ed., 2002, vol. 41, p. 348.
10. Trzoss, M. and Brimble, M.A., Synlett., 2003, p. 2042.
11. Kita, Y., Arisawa, M., Gyoten, M., Nakajima, M., Hama-
da, R., Tohma, H., and Takada, T., J. Org. Chem., 1998,
vol. 63, p. 6625.
12. Ley, V.S., Schucht, O., Thomas, A.W., and Murray, P.J.,
J. Chem. Soc., Perkin Trans. 1, 1999, p. 1251.
13. Tohma, H., Morioka, H., Takisawa, S., Arisawa, M., and
Kita, Y., Tetrahedron, 2001, vol. 57, p. 345.
–1
mp 113–115°C. IR spectrum, cm : 3250 br (NH), 1640
br (O–C=O and C=O), 1605 (C=C), 1280, 1215. 1H NMR
spectrum, d, ppm: 1.12 t (3H, CH3), 1.31 s (6H, 2Me),
1.85 m (2H, C4H2), 1.91 m (2H, C5H2), 3.95 q (2H,
OCH2), 4.13 s (1H, CH=), 6.20 d (2H, H8, H10), 7.19 d
(2H, H7, H11), 8.74 C (1H, NH). 13C NMR spectrum
(CDCl3), d, ppm: 183.2 (C=O), 168.6 (O–C=O), 156.3
(C1), 149.1 (C7, C11), 126.3 (C8, C10), 94.2 (C6), 80.7
(–HC=), 56.8 (OCH2), 49.2 (C3), 41.7 (C5), 30.4 (C4),
28.9 (CH3), 27.6 (CH3), 12.5 (CH2CH3). Found, %:
C 70.03; H 7.55; N 5.18. C16H21NO3. Calculated, %:
C 69.79; H 7.69; N 5.09.
14 .Martin-Lopez, M.J. and Bermejo, F., Tetrahedron, 1998,
vol. 54, p. 12379.
The study was carried out under a financial support
by the Russian Foundation for Basic Research (grant
Ural 04-03-96045), and by a grant of the Presidium of
the RussianAcademy of Sciences “Purposeful synthesis
of substances with desired properties, and creation of
functional materials thereof”.
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RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 42 No. 8 2006