Reaction of stabilised phosphorus ylides with nitrogen dioxide

Article abstract of DOI:10.1002/(SICI)1099-0690(199901)1999:1<251::AID-EJOC251>3.0.CO;2-M

The reaction of the stabilised ylides 14-23 with an excess of NO₂ in CH₂Cl₂ at room temperature gives different results depending on the structure of the starting ylide. The monacyl ylides 14-16 give the corresponding α-oxo nitriles 4 together with Ph₃PO · HNO₃ (24) which has been fully characterised for the first time. Under the same conditions, the ylide 18 gives 2,4-dinitrobenzonitrile (26), Ph₃PO, and benzoic acid. The other ylides examined all give 24 together with a variety of other products.

Full text of DOI:10.1002/(SICI)1099-0690(199901)1999:1<251::AID-EJOC251>3.0.CO;2-M

FULL PAPER
Reaction of Stabilised Phosphorus Ylides with Nitrogen Dioxide
R. Alan Aitken*[a] and Nazira Karodia[a]
Keywords: Phosphonium ylides / Nitrogen dioxide / Oxidation / Nitriles
The reaction of the stabilised ylides 14–23 with an excess of
NO2 in CH2Cl2 at room temperature gives different results
depending on the structure of the starting ylide. The monacyl
ylides 14–16 give the corresponding α-oxo nitriles 4 together
with Ph3PO · HNO3 (24) which has been fully characterised
for the first time. Under the same conditions, the ylide 18
gives 2,4-dinitrobenzonitrile (26), Ph3PO, and benzoic acid.
The other ylides examined all give 24 together with a variety
of other products.
Reaction of β-oxoalkylidenetriphenylphosphoranes
1
with a variety of oxidising agents results in cleavage of the
PϭC bond to give Ph3PO and the 1,2-diones 2.[1] Reagents
successfully used for this transformation include ozone,[2]
peracetic acid,[3] benzoyl peroxide,[4] lead tetraacetate, iodo-
benzene diacetate and lead dioxide,[5] potassium permanga-
nate,[6] sodium periodate,[7] triphenyl phosphite ozonide,[8]
N-sulfonyloxaziridines,[9] singlet oxygen,[10] potassium per-
oxymonosulfate (Oxone ),[11] and dimethyldioxirane.[12] In
an early study Zbiral and Fenz described a different mode
of oxidation in which reaction of a range of β-oxoalkylpho-
sphonium salts 3 with ethyl nitrite gave the corresponding
α-oxonitriles 4, Ph3PO, and ethanol.[13] In this study the
ylide 5 was also found to give benzonitrile while for 6 the
oxime ether 7 was obtained. A recent detailed study by
Bestmann and coworkers described the rather complex pat-
tern of reactivity of phosphorus ylides with nitrogen diox-
ide.[14] The products obtained from 8 depended on the nat-
ure of R1 and R2 as shown. With a single non-stabilising
substituent the nitrolic acid 9 was formed while a single
stabilising substituent led to formation of the nitrile 10 to-
gether with the conjugate phosphonium salt 11. With alkyl
and ester substituents present the α-nitro-α-nitrosoester 12
was produced, while for R1 ϭ Ph nitration of the ring was
observed to give 13. In this paper we present the results of
our parallel and complementary investigation of the reactiv-
ity of stabilised ylides with NO2 which differ significantly
from those of Bestmann.
The three examples 14؊16 with a single stabilising group
were found to give the corresponding α-oxonitriles 4 to-
gether with a compound containing both phosphorus and
nitrogen. Elemental analysis showed this to have the com-
position Ph3PO ·HNO3 (24) which could be considered to
some extent as hydroxytriphenylphosphonium nitrate.
Rather surprisingly, this does not appear to have been fully
characterised before, although its structure has been investi-
gated by IR methods[15]. An authentic sample of 24 was
prepared by direct reaction of Ph3PO with nitric acid and
this was indeed identical to the product from the oxidation
reactions although the physical and spectroscopic data
seemed to vary considerably between individual samples
probably due to the presence of traces of free acid. For com-
parison the 2:1 adduct of Ph3PO with nitric acid (25) was
also prepared and characterised and it proved to have re-
markably similar spectroscopic properties to 24 so that el-
emental analysis was in fact the most reliable method to
distinguish between the two adducts.
The conversion of 14؊16 into 4 and 24 by reaction with
two equivalents of NO2 forms a balanced equation as
shown, although the likely mechanism, as described in de-
tail by Bestmann,[14] is rather complex involving such spe-
cies as HNO2 and N2O3. The distinction between our re-
sults and the conversion of 8 into 10 is that, in that case,
more ylide was used in proportion to the NO2 so that the
nitric acid formed reacted with a second equivalent of 8 to
Results and Discussion
In the previous study[14] all reactions were performed in
THF, in which NO2 exists as a blue molecular complex, and
at temperatures of Ϫ78 to Ϫ30°C. In addition precisely two
equivalents of NO2 (one of N2O4) were generally used. For
convenience we chose instead to use dichloromethane as the
solvent at room temperature and to use 3 equiv. of NO2.
The reactivity of the ten ylides 14؊23 was examined under
these conditions.
[a]
School of Chemistry, University of St. Andrews,
North Haugh, St. Andrews, Fife, KY16 9ST, UK
Eur. J. Org. Chem. 1999, 251Ϫ254
WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1999
1434Ϫ193X/99/0101Ϫ0251 $ 17.50ϩ.50/0
251

R. A. Aitken, N. Karodia
FULL PAPER
The remaining ylides 20؊23 with more complex struc-
tures gave a variety of different products together with the
salt 24 in each case. With the trioxo ylide 20 there was oxi-
dative cleavage of the CϭP bond to give the dioxo diester
30 but also some formation of ethyl cyanoformate, with 21
both benzonitrile and a nitrated benzonitrile were pro-
duced, while 22 gave benzoyl cyanide and benzoic acid and
for 23 the other product was not identified.
In agreement with the previous study[14] we have found
that the reaction of phosphorus ylides with NO2 is rather
complex and depends on the substituents present. By using
an excess of NO2 the monoacyl ylides 14؊16 can be con-
verted entirely into the nitriles 4 rather than a 1:1 mixture
of 4 and 11 as occurs with less NO2. The reaction of 18
shows that, with suitable substituents present, the ring ni-
tration and nitrile formation processes can be combined.
Further work is clearly required to explain the reactivity of
the more complex ylide types 20؊23.
give the salt 11. In our case where an excess of NO2 is used
and this is not possible, the nitric acid instead reacts with
the Ph3PO to afford 24.
Both 17 and the dioxo ylide 19 gave rather disappointing
results in that both did give 24 but the only other product
identified was a low yield of benzoic acid in the case of 17.
The reaction of 18 with NO2 took a different course: alone
among the ylides in this study it gave almost entirely Ph3PO
as the phosphorus product with only a trace of 24. The
other products were 2,4-dinitrobenzonitrile (26) and ben-
zoic acid. In analogy to to the mechanisms proposed by
Bestmann[14] we suggest that this reaction proceeds by in-
itial electrophilic nitration of the activated ring followed by
nitrosation by N2O3 present in equilibrium from the nitrous
acid produced in the first step. Direct hydrolysis of the salt
27 then gives benzoic acid and sets up the ylide function
for Wittig-type elimination of Ph3PO to give the nitrile. It
should be noted that this sequence does not produce nitric Experimental Section
acid whereas the corresponding process applied to 14؊16
General: M. p.: Reichert hot-stage microscope, uncorrected. Ϫ IR:
1
involves the intermediacy of the salts 28 which are hydro-
lysed to give 29 and nitric acid, thus explaining the forma-
tion of 24 in our study and 11 from 8.
Perkin Elmer 1420. Ϫ NMR: Bruker AM300 (300 MHz for H, 75
MHz for 13C), Varian CFT 20 (32 MHz for 31P). All spectra,
CDCl3 as solvent. Internal TMS as reference for 1H and 13C and
252
Eur. J. Org. Chem. 1999, 251Ϫ254

Reaction of Stabilised Phosphorus Ylides with Nitrogen Dioxide
external 85% H3PO4 as reference for 31P. Ϫ GCMS: Hewlett-Pack- ethyl ether and identified as 24 (quantitative yield) Ϫ data as above,
FULL PAPER
ard 5890A/Finnigan Incos (70 eV).
and a mixture of diethyl dioxobutanedioate (30) (81 mg, 20%) and
ethyl cyanoformate (30 mg, 15%).
Preparation of Starting Materials: The required ylides 14Ϫ16 are
commercially available, while 17 and 18,[16] 19,[17] 20,[18] and
21؊23[19] were prepared using the literature methods. A stock solu-
tion of NO2 in dry CH2Cl2 was prepared by adding a weighed
amount of the liquid gas from a cylinder. This brown solution was
stored over Na2CO3 at room temp. and in the dark.
Diethyl Dioxobutanedioate: Colourless crystals. Ϫ 1H NMR: δ ϭ
4.31 (OCH2), 1.30 (CH2Me). Ϫ 13C NMR: δ ϭ 158.8 (CO), 63.2
(OCH2), 13.9 (CH2Me). Ϫ MS (GCMS); m/z (%): 202 (1) [Mϩ],
102 (2), 74 (4), 29 (100).
Ethyl cyanoformate: Ϫ IR (CH2Cl2): ν˜ ϭ 2400 cmϪ1 (CN), 1735
(CO), 1620. Ϫ 13C NMR: δ ϭ 101.4 (CN). Ϫ MS (GCMS); m/z
(%): 98 (1) [MϩϪ1], 97 (82), 81 (9), 55 (100).
Reaction of Ylides with NO2: A solution of NO2 (6.0 mmol) in
CH2Cl2 was added dropwise to a solution of the ylide (2 mmol) in
dry CH2Cl2 (25 mL). The mixture was stirred at room temp. until
all the starting material was consumed (monitored by 31P NMR)
and evaporated to give the products as follows:
From 1,4-Bis(triphenylphosphoranylidene)-1,4-diphenylbutane-2,3-
dione (21): A yellow mixture of crystals and oil which was shown
to contain 24 (quantitative yield) Ϫ data as above Ϫ and a mixture
of benzonitrile (42 mg, 10%) and an isomer of nitrobenzonitrile (88
mg, 15%). Ϫ IR (CH2Cl2): ν˜ ϭ 2250 cmϪ1 (CN). Benzonitrile: Ϫ
MS (GCMS); m/z (%): 103 (100) [Mϩ], 76 (44). Ϫ Nitrobenzoni-
trile: Ϫ MS (GCMS); m/z (%): 148 (27) [M Ϫ Hϩ], 122 (4), 102
(100), 90 (25), 75 (42).
From (Acetylmethylene)triphenylphosphorane (14): A yellow mix-
ture of crystals and oil which were separated by trituration with
dry diethyl ether and identified as Ph3PO ·HNO3 24 (quantitative
yield) m.p. 68Ϫ70°C. Ϫ 1H NMR: δ ϭ 17.72 (br s, 1 H, OH),
8.01Ϫ7.26 (m, 15 H, Ph). Ϫ 13C NMR: δ ϭ 132.9 (d, J ϭ 3, 3ϫ
C-4 of Ph), 132.1 (d, J ϭ 11, 6ϫ C-2 of Ph), 129.5 (d, J ϭ 108,
3ϫ C-1 of Ph), 128.9 (d, J ϭ 13, 6ϫ C-3 of Ph). Ϫ 31P NMR: δ ϭ
ϩ34.6. Ϫ C18H16NO4P (341.3): calcd. C 63.34, H 4.73, N 4.10;
found C 63.83, H 4.75, N 4.26. Ϫ By-product pyruvonitrile (55 mg,
40%). Ϫ IR (CH2Cl2): ν˜ ϭ 2220 cmϪ1 (CN), 1750 (CO). Ϫ 1H
NMR: δ ϭ 2.28 (s, 3 H).
From
2,5-Bis(triphenylphosphoranylidene)-1,6-diphenylhexane-
1,3,4,6-tetraone (22): A yellow mixture which contained 24 (quanti-
tative yield) Ϫ data as above Ϫ and a mixture of benzoyl cyanide
(79 mg, 15%) and benzoic acid (49 mg, 10%) Ϫ data as for products
from 15 and 18, respectively.
From (Benzoylmethylene)triphenylphosphorane (15): Pale yellow
crystals and a yellow oil which were separated by trituration with
dry diethyl ether and identified respectively as 24 (quantitative
yield) Ϫ data as above Ϫ and benzoyl cyanide (170 mg, 65%). Ϫ
From Diethyl 2,5-Bis(triphenylphosphoranylidene)hexane-3,4-dione-
1,6-dioate (23): A yellow mixture of crystals and oil which con-
tained 24 (quantitative yield) Ϫ data as aboveϪ and an unidentified
ethyl-containing material. Ϫ H NMR: δ ϭ 4.38 (q, J ϭ 7 Hz, 2
H), 1.39 (t, J ϭ 7 Hz, 3 H).
1
1
IR (CH2Cl2): ν˜ ϭ 2220 cmϪ1 (CN), 1680 (CO). Ϫ H NMR: δ ϭ
8.17Ϫ8.11 (2 H, m). Ϫ 13C NMR: δ ϭ 170.8 (CO), 136.6, 130.0,
129.2, 128.1, 112.5 (CN). Ϫ MS (GCMS); m/z (%): 131 (49) [Mϩ],
105 (100), 77 (81), 51 (60).
Authentic Preparation of Adducts
1:1 Adduct of Ph3PO with Nitric acid (24): Concentrated nitric acid
(0.20 cm3, 3.6 mmol) was added in one portion to a solution of
triphenylphosphane oxide (0.5 g, 1.8 mmol) in CH2Cl2 and the
mixture stirred vigorously for 10 min, then diluted with CH2Cl2
(20 cm3). The mixture was dried and the solvent evaporated to give
the title compound (0.55 g, 90%), m.p. 80Ϫ82°C. Ϫ IR (Nujol):
ν˜ ϭ 3400 cmϪ1, 1625, 1420. Ϫ 1H NMR: δ ϭ 13.25 (br s, 1 H,
OH), 7.81Ϫ7.26 (m, 15 H, Ph). Ϫ 13C NMR: δ ϭ 133.2 (d, J ϭ 3
Hz, 3ϫ C-4 of Ph), 132.2 (d, J ϭ 11 Hz, 6ϫ C-2 of Ph), 129.0 (d,
J ϭ 13 Hz, 6ϫ C-3 of Ph), 128.9 (d, J ϭ 108 Hz, 3ϫ C-1 of Ph).
From (Methoxycarbonylmethylene)triphenylphosphorane (16): A yel-
low mixture of crystals and oil which were separated by trituration
with dry diethyl ether and identified respectively as 24 (quantitative
yield) Ϫ data as above Ϫ and methyl cyanoformate (94 mg, 55%).
Ϫ IR (CH2Cl2): ν˜ ϭ 2220 cmϪ1 (CN), 1750 (CO), 1630. Ϫ 1H
NMR: δ ϭ 3.88 (s, 3 H). Ϫ 13C NMR: δ ϭ 164.3 (CO), 117.8
(CN), 54.6 (Me). Ϫ MS (GCMS); m/z (%): 86 (0.5) [M ϩ Hϩ], 84
(10), 59 (19), 54 (100), 45 (37), 41 (73), 31 (91), 29 (70), 15 (90).
From 1-Phenyl-1-triphenylphosphoranylidenepropan-2-one (17): Pale
yellow crystals and a yellow oil which was shown to contain 24 Ϫ
data as above Ϫ and benzoic acid (24 mg, 10%) and other unidenti-
fied material.
Ϫ
31P NMR: δ ϭ ϩ36.9. Ϫ C18H16NO4P (341.3): calcd. C 63.34,
H 4.73, N 4.10; found C 63.31, H 4.63, N, 4.08.
2:1 Adduct of Ph3PO with Nitric Acid (25): Reaction as above using
triphenylphosphane oxide (0.5 g, 1.8 mmol) and nitric acid (0.05
cm3, 0.90 mmol) gave [Ph3PO]2.HNO3 (0.47 g, 85%) as waxy yellow
crystals, m.p. 68Ϫ70°C. Ϫ IR (Nujol): ν˜ ϭ 1620 cmϪ1, 1440. Ϫ 1H
NMR: δ ϭ 13.34 (br s, 1 H, OH), 7.82Ϫ7.27 (m, 30 H, Ph). Ϫ 13C
NMR: δ ϭ 132.5 (d, J ϭ 3 Hz, 6ϫ C-4 of Ph), 132.1 (d, J ϭ 10
Hz, 12ϫ C-2 of Ph), 130.8 (d, J ϭ 106 Hz, 6ϫ C-1 of Ph), 128.7
(d, J ϭ 12 Hz, 12ϫ C-3 of Ph). Ϫ 31P NMR: δ ϭ ϩ32.1. Ϫ
C36H31NO5P2 (619.6): calcd. C 69.78, H 5.05, N 2.26; found C
68.36, H 4.72, N 2.43.
From 1,2-Diphenyl-2-(triphenylphosphoranylidene)ethanone (18): A
mixture containing, as major products, Ph3PO (306 mg, 55%). Ϫ
1
31P NMR: δ ϭ 29.2, benzoic acid (94 mg, 40%). Ϫ H NMR: δ ϭ
12.2 (s, 1 H), 8.15 (m, 2 H), 7.65 (m, 1 H), 7.48 (m, 2 H). Ϫ MS
(GCMS); m/z (%): 122 (7)[Mϩ], 105 (100), 77 (91), 51 (40), and
2,4-dinitrobenzonitrile (26) and, as a minor product (34 mg, 5%)
24 Ϫ data as above. Separation by chromatography (diethyl ether/
petroleum ether, 1:1) gave 2,4-dinitrobenzonitrile (26) (135 mg,
1
35%) as yellow crystals, m.p. 103.5Ϫ105°C (ref.[20] 104°C). Ϫ H
NMR: δ ϭ 9.18 (d, J ϭ 2 Hz, 1 H, 3-H), 8.70 (m, 1 H, 5-H), 8.23
(d, J ϭ 9 Hz, 1 H, 6-H). Ϫ 13C NMR: δ ϭ 150.0 (4ry), 149.3 (4ry),
137.1, 128.5, 120.9, 113.3, 113.2. Ϫ MS (GCMS); m/z (%): 193 (8)
[Mϩ], 147 (2), 100 (15), 75 (20), 50 (29), 30 (100).
Acknowledgments
From 3-Triphenylphosphoranylidenepentane-2,4-dione (19): A yellow
mixture of crystals and oil in which only 24 could be identified.
We thank Professor H. J. Bestmann (Erlangen) for helpful dis-
From Diethyl 2-Oxo-3-triphenylphosphoranylidenebutanedioate (20): cussions and for making his results available to us prior to publi-
A yellow mixture which was separated by trituration with dry di-
cation.
Eur. J. Org. Chem. 1999, 251Ϫ254
253

R. A. Aitken, N. Karodia
FULL PAPER
[1]
[11]
[12]
Review; A. W. Johnson, Ylides and Imines of Phosphorus, Wiley,
H. H. Wasserman, C. B. Vu, Tetrahedron Lett. 1990, 31,
5205Ϫ5208.
H. H. Wasserman, C. M. Baldino, S. J. Coats, J. Org. Chem.
1995, 60, 8231Ϫ8235.
Chichester, 1993, p. 133.
F. Ramirez, R. B. Mitra, N. B. Desai, J. Am. Chem. Soc. 1960,
82, 5763Ϫ5764.
D. B. Denney, L. C. Smith, J. Song, C. J. Rossi, C. D. Hall, J.
Org. Chem. 1963, 28, 778Ϫ780.
[2]
[13]
[14]
[3]
E. Zbiral, L. Fenz, Monatsh. Chem. 1965, 96, 1983Ϫ1999.
H. J. Bestmann, W. Kamberger, T. Röder, R. Zimmermann, Lie-
bigs Ann.. 1996, 845Ϫ851.
[4]
D. B. Denney, T. M. Valega, J. Org. Chem. 1964, 29, 440Ϫ442.
[15] [15a] D. Hadzi, J. Chem. Soc. 1962, 5128Ϫ5138. Ϫ [15b] D. Hadzi,
N. Kobilarov, J. Chem. Soc. ( A) 1966, 439Ϫ445.
[5a] E. Zbiral, E. Werner, Tetrahedron Lett. 1966, 2001Ϫ2004. Ϫ
[5]
[5b]
E. Zbiral, E. Werner, Monatsh. Chem. 1966, 97, 1797Ϫ
[16]
H. J. Bestmann, B. Arnason, Chem. Ber. 1962, 95, 1513Ϫ1527.
P. A. Chopard, R. J. G. Searle, F. H. Devitt, J. Org. Chem. 1965,
1820.
[17]
[6a] E. Zbiral, M. Rasberger, Tetrahedron 1968, 24, 2419Ϫ2423.
[6]
30, 1015Ϫ1019.
[6b]
Ϫ
R. A. Aitken, J. I. G. Cadogan, I. Gosney, Phosphorus,
[18]
´
R. A. Aitken, H. Herion, A. Janosi, N. Karodia, S. V. Raut, S.
Sulfur, and Silicon, 1995, 101, 281Ϫ286.
Seth, I. J. Shannon, F. C. Smith, J. Chem. Soc., Perkin Trans. 1
1994, 2467Ϫ2472.
[7]
[8]
H. J. Bestmann, R. Armsen, H. Wagner, Chem. Ber. 1969,
102, 2259Ϫ2269.
[19]
[20]
´
R. A. Aitken, H. Herion, C. E. R. Horsburgh, N. Karodia, S.
H. J. Bestmann, K. Kumar, L. Kisielowski, Chem. Ber. 1983,
116, 2378Ϫ2382.
F. A. Davis, B.-C. Chen, J. Org. Chem. 1990, 55, 360Ϫ363.
H. H. Wasserman, V. M. Rotello, D. R. Williams, J. W. Benbow,
J. Org. Chem. 1989, 54, 2785Ϫ2786.
Seth, J. Chem. Soc., Perkin Trans. 1 1996, 485Ϫ489.
P. Cohn, P. Friedländer, Ber. Dtsch. Chem. Ges. 1902, 35,
[9]
1265Ϫ1267.
[10]
Received August 7, 1998
[O98370]
254
Eur. J. Org. Chem. 1999, 251Ϫ254