A new reaction of arylphospholes: Site-selective phosphorylation through reaction with phosphorus tribromide

Article abstract of DOI:10.1039/b002042g

The reaction of arylphospholes 1a-c with phosphorus tribromide followed by treatment with morpholine afforded the 2- or 3-substituted species 3a,b or 7 (which after oxidation gave 4a,b or 8) in a selective manner. The Royal Society of Chemistry 2000.

Full text of DOI:10.1039/b002042g

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A new reaction of arylphospholes: site-selective phosphorylation
through reaction with phosphorus tribromide
György Keglevich,*a Tungalag Chuluunbaatar,a András Dobób and László To´´ k e c
1
a Department of Organic Chemical Technology, Budapest University of Technology and
Economics, 1521 Budapest, Hungary. E-mail: keglevich@oct.bme.hu
b Hungarian Academy of Sciences, Chemical Research Center, 1525 Budapest, Hungary
c Research Group of the Hungarian Academy of Sciences at the Department of Organic
Chemical Technology, Budapest University of Technology and Economics, 1521 Budapest,
Hungary
Received (in Cambridge, UK) 14th March 2000, Accepted 4th April 2000
The reaction of arylphospholes 1a–c with phosphorus
tribromide followed by treatment with morpholine
afforded the 2- or 3-substituted species 3a,b or 7 (which
after oxidation gave 4a,b or 8) in a selective manner.
Phospholes are useful ligands in transient metal complexes and
have attracted considerable attention recently.1–3 Not much is
known, however, of the substitution reactions of this represen-
tative class of P-heterocycles. The modification of phospholes is
of interest, as it may lead to P-ligands with new properties. For
this reason, it was a challenge for us to study the substitution
reactions of some arylphospholes available from our previous
work.4–6
In this paper, we disclose our results on the substitution of
(trialkylphenyl)phospholes 1a–c with phosphorus tribromide.
Phosphorus halogenides are known to be useful in the phos-
phorylation of pyrroles.7,8 The reaction of (trimethylphenyl)-
phosphole 1a4 and (triisopropylphenyl)phosphole 1b5 with
phosphorus tribromide in boiling chloroform in the presence of
pyridine furnished 2-substituted products 3a and 3b, respec-
tively, after treatment with morpholine (Scheme 1). To obtain
stable derivatives, diphosphines 3a and 3b were oxidised to
compounds 4a and 4b, respectively. It is noteworthy that the
exocyclic P-moiety underwent selective oxidation, while the
phosphorus heteroatom of the phosphole remained mostly
unoxidised. According to 31P NMR, the conversion of phos-
pholes 1 to products 4 was ca. 70%. The yield of phosphole
derivatives 4a,b was ca. 45% after purification by column
chromatography. Intermediates 3, as well as products 4 were
characterised by 31P NMR; 2JPP couplings of ca. 72 and 49 Hz,
1
respectively, were detected.9–12 The H NMR spectra of com-
pounds 4a and 4b revealed that the protons of the hetero ring
were not coupled to each other.11,12 The structure of product 4b
Scheme 1
was also supported by 13C NMR.12 Bis(phosphine oxides) 5a,b
were also formed in the above mentioned oxidation reactions
in ca. 14% yields.13,14 Unlike other phosphole oxides,15 these
species resisted undergoing dimerization and could be stored at
room temperature for weeks.
A similar transformation of (tri-tert-butylphenyl)phosphole,
1c,16 resulted in the formation of product 8 via intermediates 6
and 7 (Scheme 2). Interestingly, the substitution took place at
position 3 of the phosphole moiety. The different outcome is
probably the consequence of the steric hindrance around the
phosphorus heteroatom in 1c. Species 7 and 8 were character-
ised as above. 3JPP couplings of 50.4 and 21.8 Hz were obtained
for 7 and 8, respectively.16,17 The 13C and H NMR spectral
1
parameters of compound 8 were also consistent with the substi-
tution in position 3.17
as a nucleophile to give intermediate 9 or 10 that may be stabil-
ised by the loss of a proton, by pseudorotation and finally by
the departure of a bromide anion.
In summary a new reaction of arylphospholes was explored;
their interaction with phosphorus tribromide resulted in
As can be seen, the phosphorylated phospholes are excellent
models for the study of the 2JPP and the 3JPP couplings.
In the mechanism proposed, the π-electrons of the double
bond in phosphole 1 attack the phosphorus atom of the reagent
DOI: 10.1039/b002042g
J. Chem. Soc., Perkin Trans. 1, 2000, 1495–1496
This journal is © The Royal Society of Chemistry 2000
1495

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The bisphosphine (3a, 3b or 7) (~1.17 mmol) was dissolved in
CHCl3 (50 cm3) and oxidised by the addition of 30% hydrogen
peroxide (0.68 cm3, ~6.0 mmol) at 0 ЊC. After stirring at room
temperature for 1 h, the mixture was extracted with water
(2 × 20 cm3). The organic phase was dried (Na2SO4), the solvent
evaporated and the residue so obtained purified by repeated
column chromatography (silica gel, 3% MeOH in CHCl3) to
furnish product 4a, 4b or 8, respectively.
Acknowledgements
Thanks are due to OTKA for financial support (Grant No.:
T 029039). T. C. is grateful for the support from the Ministry of
Education.
Notes and references
1 K. B. Dillon, F. Mathey and J. F. Nixon, in Phosphorus: the Carbon
Copy, from Organophosphorus to Phospha-Organic Chemistry,
Wiley, Chichester, 1998, ch. 8, p. 203.
2 L. D. Quin, ‘Phospholes’, in Comprehensive Heterocyclic Chemistry
II, vol. 2, eds. A. R. Katritzky, C. W. Rees and E. F. V. Scriven,
vol. ed. C. W. Bird, Pergamon, Oxford, 1996.
3 Zs. Csók, Gy. Keglevich, Gy. Peto´´ cz and L. Kollár, Inorg. Chem.,
1999, 38, 831.
4 L. Nyulászi, L. Soós and Gy. Keglevich, J. Organomet. Chem., 1998,
566, 29.
5 Gy. Keglevich, L. D. Quin, Zs. Böcskei, Gy. M. Keseru´´ ,
R. Kalgutkar and P. M. Lahti, J. Organomet. Chem., 1997, 532, 109.
6 Gy. Keglevich, Zs. Böcskei, Gy. M. Keseru´´ , K. Újszászy and
L. D. Quin, J. Am. Chem. Soc., 1997, 119, 5095.
7 S. P. Ivonin, T. E. Terikovska, A. A. Chaikovskaya, A. P.
Marchenko, G. N. Koydan, A. M. Pinchuk and A. A. Tolmachev,
Heteroat. Chem., 1999, 10, 213.
8 A. A. Tolmachev, S. P. Ivonin, A. A. Chaikovskaya, T. E. Teriko-
vska, T. N. Kudrya and A. M. Pinchuk, Heteroat. Chem., 1999, 10,
223.
Scheme 2
2
9 Selected data for 3a: δP (CDCl3) 5.5 (P1), 93.3 (C2–P), JPP = 72.6;
Mϩfound = 418.1920, C22H32N2O2P2 requires 418.1939.
2
10 Selected data for 3b: δP (CDCl3) 0.2 (P1), 94.1 (C2–P), JPP = 70.6;
Mϩfound = 502.2870, C28H44N2O2P2 requires 502.2878.
11 Selected data for 4a: δP (CDCl3) 5.3 (P1), 23.4 (C2–P), 2JPP = 48.3; δH
6.90 (dm, JPH = 38.0, C5–H), 7.49 (ddd, JPH = JPЈH ≈ 13, JHH = 1.4,
C3–H); Mϩfound = 434.1887, C22H32N2O3P2 requires 434.1888.
12 Selected data for 4b: δP (CDCl3) 0.9 (P1), 24.1 (C2–P), JPP = 49.4;
2
δC (CDCl3) 18.4 (JPC = 3.6, C4–CH3), 23.1 (p-CH(CH3)2), 24.2
(o-CH(CH3)2), 32.1 (JPC = 15.9, o-CHMe2), 34.4 (p-CHMe2), 44.5
(C2Љ), 66.9 (JPC = 6.9, C3Љ), 119.8 (C1Ј), 122.2 (JPC = 11.1, C3Ј), 133.7
(JPC = 19.9, JPЈC = 151.4, C2), 137.7 (JPC = JPЈC = 5.4, C5), 142.4
(JPC = 18.4, JPЈC = 14.6, C4), 147.5 (JPC = 17.3, JPЈC = 6.1, C3), 152.8
(C4Ј), 156.9 (JPC = 14.7, C2Ј); δH (CDCl3) 7.04 (dm, JPH = 38.2, C5–
H), 7.42 (ddd, JPH = JPЈH ≈ 13, JHH = 1.2, C3–H); Mϩfound = 518.2832,
C28H44N2O3P2 requires 518.2827.
2-substitution, or, in the case of the starting material with a
bulky P-aryl group, the reaction led to 3-substitution.
Future work will be directed towards the utilisation of the
above reaction in the preparation of a variety of phosphoric
amides and esters and a study of their properties.
13 Selected data for 5a: δP (CDCl3) 19.1 (P1), 51.3 (C2–P), JPP = 34.7;
2
Experimental
Mϩfound = 450.
14 Selected data for 5b: δP (CDCl3) 19.5 (P1), 52.2 (C2–P), JPP = 36.1;
2
General procedure for the phosphorylation of phospholes 1a–c
Mfound = 534.
Phosphorus tribromide (0.12 cm3, 1.26 mmol) and pyridine
(0.10 cm3, 1.24 mmol) were added to phosphole 1a, 1b or 1c
(1.17 mmol) in dry CHCl3 (50 cm3), and the solution was stirred
at boiling point for 48 h under a nitrogen atmosphere. The
volatile components were removed in vacuo to give 2a, 2b or 6,
respectively.
The intermediate (2a, 2b or 6) (~1.17 mmol) was taken up in
dry benzene (50 cm3) and treated with morpholine (0.41 cm3,
4.70 mmol) at 0 ЊC. After stirring at room temperature for 1 h,
the mixture was filtered and the solvent of the filtrate evapor-
ated to afford 3a, 3b or 7, respectively.
15 L. D. Quin, Rev. Heteroat. Chem., 1990, 3, 39.
16 Selected data for 7: δP (CDCl3) 3.4 (P1), 90.7 (C3–P), JPP = 33.6;
3
Mϩfound = 544.3323, C31H50N2O2P2 requires 544.3348.
17 Selected data for 8: δP (CDCl3) 7.1 (P1), 23.4 (C3–P), JPP = 21.8;
3
δC (CDCl3) 19.2 (JPC = 6.2, C4–CH3), 31.3 (p-C(CH3)3), 33.3
(JPC = 3.5, o-C(CH3)3), 35.4 (p-CMe3), 38.9 (JPC = 3.5, o-CMe3), 44.9
(C2Љ), 67.5 (JPC = 5.8, C3Љ), 118.6 (JPC = 4.6, C1Ј), 123.1 (JPC = 10.5,
C3Ј), 126.8 (JPC = 13.2, JPЈC = 21.0, C5), 128.2 (JPC = 21.4,
JPЈC = 154.5, C3), 139.7 (JPC = 15.8, C4), 139.9 (JPC = 14.6, JPЈC = 8.6,
C2), 153.3 (JPC = 2.4, C4Ј), 158.8 (JPC = 11.7, C2Ј); δH (CDCl3) 6.66
(dm, JPH = 35.5, C5–H), 7.37 (ddd, JPH = 28.1, JPЈH = 12.1, JHH = 2.5,
C2–H); Mϩfound = 560.3292, C31H50N2O3P2 requires 560.3297.
1496
J. Chem. Soc., Perkin Trans. 1, 2000, 1495–1496