Formation of adducts of pyrilium cations with triethyl phosphite [1]

Full text of DOI:10.1007/s10593-007-0204-9

Chemistry of Heterocyclic Compounds, Vol. 43, No. 10, 2007
LETTERS TO THE EDITOR
FORMATION OF ADDUCTS
OF PYRILIUM CATIONS
WITH TRIETHYL PHOSPHITE
1
2
2
1
M. A. Kostogryz , A. A. Boumber , I. A. Profatilova , and M. S. Korobov
1
Keywords: pyrilium salts, triethyl phosphite, electron-acceptors, nucleophilic addition, UV, H and
3
1
P NMR spectroscopy.
The physicochemical properties of σ-adducts of aromatic heterocyclic cations hold interest since study
of the reversible rupture and formation of a σ-bond between a heteroelement and carbon is possible for these
compounds [1]. In turn, such behavior is extremely important for understanding the mechanism of the Arbuzov
1
+
2
rearrangement, in which (R O) P –R salts are intermediates [2].
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1
31
UV, H NMR, and P NMR spectroscopy in acetonitrile was used to study the reaction of a pyrilium or
thiapyrilium salt with triethyl phosphite (P(OEt)3).
+
R2
R2
P(OEt)3
R1
R
R3
R4
R1
R3
P(OEt)3
+
+
X
+
X
R4
R
–
–
ClO4
ClO4
1
a–5a
1
b–5b
4
1
2
3
4
1
2
3
4
1
R = R = Ph, R = R = R = H; 2 R = R = Ph, R = R = R = H; 3 R = R = Ph,
1
3
2
1
2
3
4
R = R = H, R = Me; 4 R+R = –CH=CH–CH=CH–, R = R = H, R = Ph;
1
2
3
4
5
R+R = –CH=CH–CH=CH–, R = H, R +R = –CH=CH–CH=CH–; 1,4,5 X = O, 2,3 X = S
Pyrilium salts 1a-5a are yellow-green in acetonitrile. Decoloration is noted upon the introduction of
P(OEt) to the pyrilium salt solutions studied, while the intensity of the absorption band with λ 395 nm
3
max
decreases with increasing reagent concentration.
_
3
_________________________________________________________________________________________
1
Physical and Organic Chemistry Research Institute, Southern Federal University, Rostov-on-Don
2
44090, Russia; e-mail: boom@ipos.rsu.ru and Southern Science Center, Russian Academy of
Sciences, Rostov-on-Don 344006, Russia; e-mail: ssc-ras@mmbi.krinc.ru. Translated from Khimiya
Geterotsiklicheskikh Soedinenii, No. 10, pp. 1581-1582, October, 2007. Original article submitted
August 22, 2007.
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342
0009-3122/07/4310-1342©2007 Springer Science+Business Media, Inc.

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The pyrilium-pyran transition to give a triethoxyphosphonium species was detected by H and P NMR
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spectroscopy. An sp -hybridized carbon atom appears upon the formation of the pyran adduct and there is a shift
of the protons of the pyrilium or thiapyrilium ring from low field to high field. Spin-spin coupling is noted with
the phosphorus atom, which indicates transition of the pyrilium salt to pyran with formation of a tetracoordinated
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1
phosphorus atom. The finding of an upfield shift for H-8 proton and coupling of this proton with
P
unequivocally demonstrates the existence of pyran form 5b rather than pyrilium salt form 5a.
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The H and P NMR spectra were taken on a Varian Unity-300 spectrometer at 300 and 121.5 MHz,
respectively, in deuteroacetonitrile with TMS and triphenyl phosphate as the internal standards. The spectra were
-
2
-2
obtained by adding a twofold excess of reagent (c = 2·10 M) to a solution of the starting salt (c = 10 M).
1
(
2,6-Diphenyl-4H-pyran-4-yl)triethoxyphosphonium Perchlorate (1b). H NMR spectrum, δ, ppm
(
(
J, Hz): 7.78-7.82 (4H, m, o-C H ); 7.49-7.52 (6H, m, m,p-C H ); 5.54 (2H, dd, J = 3.9, J = 4.8, H-β); 4.44
6
5
6
5
H-P
H-H
3
1
1H, dt, JH-P = 21.7, JH-H = 4.8, H-γ); 4.58 (6H, m, CH ); 1.45 (9H, m, CH ). P NMR spectrum, δ,
2
3
ppm: 33,43 (m).
1
(
2,6-Diphenyl-4H-thiapyran-4-yl)triethoxyphosphonium Perchlorate (2b). H NMR spectrum, δ,
ppm (J, Hz): 7.59-7.69 (4H, m, o-C H ); 7.42-7.52 (6H, m, m,p-C H ); 5.92 (2H, dd, J = 6.4, JH-P = 4.9, H-β);
6
5
6
5
H-H
3
1
4
3
.89 (1H, dt, JH-H = 6.4, JH-P = 27.8, H-γ); 4.60 (6H, m, CH ); 1.47 (9H, m, CH ). P NMR spectrum, δ, ppm:
2
3
2.77 ppm (m).
4-Methyl-2,6-diphenyl-4H-pyran)triethoxyphosphonium Perchlorate (3b). H NMR spectrum, δ,
ppm (J, Hz): 7.40-8.40 (10H, m, C H ); 5.45 (2H, d, J = 3.6, H-β); 2.83 (3H, s, CH ); 4.57 (6H, m, CH ), 1.43
1
(
6
5
H-P
3
2
3
1
(
9H, m, CH ). P NMR spectrum, δ, ppm: 34.34 (m).
3
1
(
4H-Flaven-4-yl)triethoxyphosphonium Perchlorate (4b). H NMR spectrum, δ, ppm (J, Hz):
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1
.20-7.90 (9H, m, Ar); 5.62 (1H, t, J = 5.6, H-β); 4.94 (1H, dd, J = 5.6, JH-P = 22.1, H-γ); 4.47 (6H, m, CH2);
H-P
3
1
.38 (9H, m, CH ). P NMR spectrum, δ, ppm: 33.63 (m).
3
Only 5b of all the systems studied could be isolated as a solid.
1
(
9H-Xanthen-9-yl)triethoxyphosphonium Perchlorate (5b). H NMR spectrum, δ, ppm (J, Hz):
3
1
7
.2-7.6 (8H, m, Ar); 5.4 (1H, d, J = 22.8, H-γ); 4.31 (6H, m, CH ); 1.27 (9H, m, CH ). P NMR spectrum, δ,
2
3
ppm: 34.07 (m).
REFERENCES
1
2
.
.
A. A. Bumber, L. I. Kisarova, E. A. Arzumanyants, V. T. Abaev, and G. A. Palui, Khim. Geterotsikl.
Soedin., 1042 (1989). [Chem. Heterocycl. Сотр., 25, 868 (1989)].
B. A. Arbuzov, Z. Chem., 14, No. 2, 41 (1974).
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