Migration of phthalimido group in the cycloheptatriene system

Full text of DOI:10.1023/A:1020930300051

Russian Journal of Organic Chemistry, Vol. 38, No. 8, 2002, pp. 1214 1215. From Zhurnal Organicheskoi Khimii, Vol. 38, No. 8, 2002,
pp. 1265 1266.
Original English Text Copyright
2002 by Dushenko, Mikhailov, Mikhailova, Minkin.
SHORT
COMMUNICATIONS
Migration of Phthalimido Group in the Cycloheptatriene
System*
G. A. Dushenko, I. E. Mikhailov, O. I. Mikhailova, and V. I. Minkin
Research Institute of Physical and Organic Chemistry at Rostov State University, Rostov-on-Don, 344090 Russia
Received April 3, 2002
Roundabout rearrangements of element-centered
cycloheptatriene derivatives up till now have been
subject only of occasional studies. Among them have
been revealed migrations of iso(thio, seleno)cyanato
[1, 2], azido [3], thio [4 6] groups and chlorine [7]
in the cycloheptatriene ring. Aiming at investigation
of new rearrangements of N-centered groups in the
cycloheptatriene system we prepared N-cycloheptatri-
enylphthalimide and studied its fluctional behavior.
where the quasiaxial position of the triphenyltin group
was proved by X-ray diffraction analysis [8]. In the
1H NMR spectra of compound III registered at 80
and 300 MHz in deuteronitrobenzene at heating the
solution to 140 C a synchronous reversible broaden-
ing was observed that at 200 C (1H NMR spectrum
at 80 MHz) resulted in the coalescence of the
indicator signals belonging to the cycloheptatrienyl
protons H7, H1, H6, H2, H5 and H3, H4. A similar
synchronous broadening in this temperature range
was also observed for the signals of 13C nuclei in the
corresponding positions of the seven-membered ring
in the course of recording dynamic 13C NMR spec-
trum of compound III solution.
Tropylium tetrafluoroborate (I) reacted with
sodium phthalimide (II) in acetonitrile to furnish
N-(cyclohepta-1,3,5-trien-7-yl)phthalimide (III)
whose composition and structure were confirmed by
1
elemental analysis and IR, H, and 13C NMR spectra.
The boat configuration of compound III with the
phthalimido group in a quasiequatorial position
follows from the values of the coupling constants
3J(H1H7) 5.10 Hz and 4J(H2H7) 1.66 Hz in the
1H NMR spectrum. These values of constants con-
siderably differ from those for C7H7SnPh3 derivative
This spectral behavior testifies to the occurrence of
roundabout rearrangements of the phthalimido group
along the perimeter of the cycloheptatriene ring that
proceed by dissociation recombination mechanism
with intermediate formation of a tight ion pair:
tropylium cation phthalimide anion (IV) (Scheme1).
(1)
*
The study was carried out under financial support of the St. Petersburg Center for Basic Research in the Field of Natural Sciences
of the Ministry of Education of Russia (grant no. 2000-5-116) and of the Russian Foundation for Basic Research (grant
no. 01-0332551).
1070-4280/02/3808-1214$27.00 2002 MAIK Nauka/Interperiodica

MIGRATION OF PHTHALIMIDO GROUP
1215
+
+
The dissociation-recombination as prevailing
mechanism operating in migration of the phthalimido
group is also confirmed by the 2D H EXSY NMR
130 (100), [C7H6N] , 91 (24.1) [C7H7] , 90 (22.5)
+
+
+
[C7H6] , 78 (28) [C6H6] , 77 (47.5) [C6H5] , 76
(88.7) [C6H4] . Found, %: C 75.88; H 4.58; N 5.98.
1
+
spectrum of compound III that reveals the presence
of exchange cross-peaks between all pairs of signals
from the seven-membered ring at 150 C. The rate of
the observed dynamic process is independent of solu-
tion concentration in the concentration range c 0.007
C15H11NO2. Calculated, %: C 75.93; H 4.67; N 5.90.
IR spectra were recorded on spectrophotometer
1
Specord 75IR from mulls in mineral oil. H NMR
spectra were registered on spectrometers Bruker AM
and Tesla BS-487C at operating frequencies 300 and
80 MHz respectively. 13C NMR spectra were obtained
on spectrometer Bruker AM at operating frequency
75.47 MHz. Internal reference TMS, concentration
1
0.2 mol l . From the analysis of peak form of the
proton and carbon signals of the heptatriene ring were
estimated the activation parameters of degenerate
migration of the phthalimide group around the perim-
eter of the cycloheptatriene ring, as follows:
1
of compounds in solution 0.2 mol l . Mass spectra
1
1
were measured on HP 5995 instrument with direct
admission of the sample into an ion source, EI,
70 eV, 60 C.
C6D5NO2, G180C 24.8 kcal mol , k180C 9.4 s .
N-(Cyclohepta-1,3,5-trien-7-yl)phthalimide (III).
To a solution of tropylium tetrafluoroborate (I)
(0.890 g, 5 mmol) in 20 ml of anhydrous acetonitrile
at 20 C was added dropwise while stirring 5 mmol
(0.845 g) of sodium phthalimide (II) in 20 ml of
anhydrous acetonitrile. The mixture was boiled at
stirring for 15 min. The separated precipitate of
NaBF4 was filtered off and washed with CH3CN
(2 10 ml). The solvent was removed in a vacuum.
The residue was twice recrystallized from aceto-
nitrile. Yield of compound III 1.08 g (91%), color-
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1
less crystals, mp 175 176 C. IR spectrum, , cm :
1760, 1710 (C=O), 1620, 1600 (C=C), 1150, 1100,
1
1070, 980. H NMR spectrum (300 MHz), , ppm:
3
4
4.48 t.t (1H, J1,7 5.10, J2,7 1.66 Hz, H7), 5.53 m
(2H, J1,2 9.01, J1,3 0.68 Hz, H1,6), 5.96 m (2H,
3J2,3 3.66 Hz, H2,5), 6.44 m (2H, H3,5), 6.93 7.47 m
(4H, H arom). 13C NMR spectrum (75.47 MHz), ,
ppm: 50.31 (C7), 123.14 (C1,6), 123.71 (C2,5),
124.08 (C3,4), 131.50 (C10,13), 132.51 (C9,14), 133.64
(C11,12). Mass spectrum, m/z (Irel, %): 237 (66.9)
[C7H7N(CO)2C6H4= M]+ , 219 (90.6) [M H2O]+ ,
208 (34.6) [M HCO]+ , 180 (21.0) [M MeNCO]+ ,
3
4
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RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 38 No. 8 2002