Unexpected Rearrangement Leading to Formation of a 1,3- Bis(triphenylphosphonio)prop-1-en-3-idyl Carboxylate

Article abstract of DOI:10.1002/ejoc.201000143

Whereas biphenyl-4,4′-dicarbonyl dichloride reacts with methylenetriphenylphosphorane to give the expected bis(acylylide) 1, the same reaction of biphenyl-2,2′-dicarbonyl dichloride results in a multistep rearrangement leading to thezwitterionic 2-[1,3-bis(triphenylphosphonio)prop-1- en-3-id2-y1]biphenyl-27prime;-carboxylate 2. X-ray crystal structures of both 1 and 2 are reported.

Full text of DOI:10.1002/ejoc.201000143

SHORT COMMUNICATION
DOI: 10.1002/ejoc.201000143
Unexpected Rearrangement Leading to Formation of a
1,3-Bis(triphenylphosphonio)prop-1-en-3-idyl Carboxylate
R. Alan Aitken,*[a] Lee P. Cleghorn,[a] Rebecca M. Leitch,[a] Louis C. Morrill,[a] and
Alexandra M. Z. Slawin[a]
Keywords: Rearrangement / Phosphorus / Ylides
Whereas biphenyl-4,4Ј-dicarbonyl dichloride reacts with
methylenetriphenylphosphorane to give the expected bis-
(acylylide) 1, the same reaction of biphenyl-2,2Ј-dicarbonyl
dichloride results in a multistep rearrangement leading to the
zwitterionic 2-[1,3-bis(triphenylphosphonio)prop-1-en-3-id-
2-yl]biphenyl-2Ј-carboxylate 2. X-ray crystal structures of
both 1 and 2 are reported.
study of bis(keto ylides) involved compounds with two car-
bonyl groups between the ylide functions, thus allowing sig-
nificant interaction between them.[4] Here, in contrast, the
keto ylide functions are well separated and show the struc-
tural features characteristic of isolated keto ylides, including
substantial delocalisation equivalent to a significant contri-
bution from the (Z)-aligned coplanar P+–C=C–O– form.[4]
Introduction
Delocalisation of the negative charge associated with a
phosphonium ylide results in considerable stabilisation, and
we have previously reported the isolation of a variety of
such compounds as stable solids and their X-ray structure
determination.[1] Some time ago, we described the synthesis
of stable bis(keto ylides) by treatment of diacyl dichlorides
with simpler ylides, Ph3P=CHR.[2] In a continuation of this
study, we now report that, whereas biphenyl-4,4Ј-dicarbonyl
dichloride reacts with Ph3P=CH2 in the expected way to
give the bis(keto ylide), the corresponding reaction of the
isomeric biphenyl-2,2Ј-dicarbonyl dichloride leads by an
unprecedented rearrangement to a stable zwitterionic com-
pound containing the rare 1,3-bis(triphenylphosphonio)-
allyl anion function.
Scheme 1.
Results and Discussion
In an attempt to generate a bis(keto ylide) with the two
functions closer together, the isomeric biphenyl-2,2Ј-dicar-
bonyl dichloride was subjected to identical reaction condi-
tions. Again a yellow crystalline solid was obtained, which
had the correct molecular weight for the expected bis(keto
ylide) and gave elemental analysis results consistent with
the expected formula as a trihydrate. However, its spectro-
scopic properties revealed a radically different structure.
The 31P NMR spectrum contained two signals of equal in-
tensity at δ = +9.2 and +6.5 ppm, neither in the range ex-
pected for a keto ylide. The 13C NMR spectrum contained
signals for a carboxyl carbon atom not coupled to a phos-
phorus atom (δ = 170.8 ppm) and a series of three carbon
atoms all coupled to two phosphorus nuclei [δ = 169.3 (dd,
J = 7, 6 Hz), 61.6 (dd, J = 99, 16 Hz), 57.3 (dd, J = 123,
8 Hz)] in which both the chemical shifts and coupling con-
stants were consistent with the presence of Ph3P+–CH=C–
CH=PPh3. This was confirmed by a single-crystal X-ray
In connection with a study of the keto ylide function,
Ph3P=CH–C(=O), as a hydrogen-bond acceptor, we were
interested to prepare a series of compounds with two such
groups separated by a spacer of defined length and geome-
try. Reaction of biphenyl-4,4Ј-dicarbonyl dichloride with
4 equiv. of methylenetriphenylphosphorane in THF pro-
ceeded with transylidation[3] to give a moderate yield of the
expected bis(keto ylide) 1 (Scheme 1). This was obtained as
a high-melting solid, which gave the expected spectroscopic
data, including a single 31P NMR signal at δ = +17.8 ppm.
Slow concentration of a dilute solution in CH2Cl2 yielded
crystals suitable for X-ray diffraction, and the resulting
structure is shown in Figure 1. The only previous structural
[a] EaStCHEM School of Chemistry, University of St Andrews,
North Haugh, St Andrews, Fife, KY16 9ST, UK
Fax: +44-1334-463808
E-mail: raa@st-and.ac.uk
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R. A. Aitken et al.
SHORT COMMUNICATION
Figure 1. X-ray structure of compound 1. Selected bond lengths [Å], angles and torsion angles [°]; P(1)–C(19) 1.718(2), C(19)–C(20)
1.399(3), C(20)–O(20) 1.266(3); P(1)–C(19)–C(20) 116.79(18), C(19)–C(20)–O(20) 121.8(2), P(1)–C(19)–C(20)–O(20) 7.0(3).
diffraction study, which showed the zwitterionic structure 2 dition of Ph3P=CH2 to alkynylphosphonium salts to give
with a carboxylate anion on one ring of the biphenyl and compounds 4[6] whose spectroscopic data also show the
the 1,3-bis(triphenylphosphonio)allyl anion group on the same patterns as observed for 2 (Table 1 and Scheme 3).
other (Figure 2).
Scheme 2.
Table 1. Selected NMR spectroscopic data for 2 and similar com-
pounds 3 and 4.
Figure 2. X-ray structure of compound 2. Selected bond lengths
Compound δ(31P) [ppm] δ(13C) [ppm] (JC,P [Hz])
C-1 C-2
[Å], angles and torsion angles [°]; P(1)–C(19) 1.725(3), C(19)–C(20)
1.391(3), C(20)–C(21) 1.394(4), C(21)–P(21) 1.720(3); P(1)–C(19)–
C(20) 126.0(2), C(19)–C(20)–C(21) 125.0(2), C(19)–C(20)–C(40)
112.9(2), C(40)–C(20)–C(21) 122.0(2), C(20)–C(21)–P(21) 133.0(2),
C(40)–C(20)–C(19)–P(1) 175.27(19), C(40)–C(20)–C(21)–P(21)
11.0(4).
C-3
2A
3
6.5, 9.2
5.5, 6.1
9.9, 11.1
11.4, 11.5
10.3, 11.4
57.3 (123, 8) 169.3 (7, 6) 61.6 (99, 16)
56.7 (119, 9) 167.6 (7, 5) 58.5 (106, 18)
59.5 (122, 6) 177.1 (8, 5) 61.0 (102, 16)
58.4 (124, 6) 167.4 (8, 6) 56.3 (108, 15)
59.4 (121, 7) 171.0 (7, 7) 60.9 (102, 17)
4a
4b
4b[a]
Whereas the bond lengths are consistent with a fully de-
localised allyl anion structure in the solid state, the spectro-
scopic data, particularly the magnitude of the P–C coupling
constants, point to a greater contribution from the more
localised structure 2A with two clearly distinct phosphorus
atoms in solution (Scheme 2). Very few compounds con-
taining this type of structure have been reported before, and
their syntheses involve several steps, but the data obtained
here are in excellent agreement with these previous exam-
ples. Schmidbaur and co-workers obtained the salt 3 and
determined its X-ray structure.[5] This showed a delocalised
allyl anion with essentially equal C(1)–C(2) and C(2)–C(3)
bond lengths, but the 13C NMR spectroscopic data were
[a] Slightly different data later reported by Schmidpeter and co-
workers.[7]
Scheme 3. Similar structures reported previously.
Further evidence for the structure of 2 was obtained by
more consistent with the localised structure (Table 1). A dissolving a sample in DCl/D2O (Scheme 4). The resulting
short time later, Bestmann and Kisielowski reported ad- solution gave a 31P NMR spectrum consisting of doublets
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Formation of a 1,3-Bis(triphenylphosphonio)prop-1-en-3-idyl Carboxylate
at δ = +11.1 and +21.0 ppm with a four-bond coupling con- Ph3P=CH2 by an acyl chloride is followed not by the nor-
stant of 7.4 Hz. This behaviour, and particularly the ap- mal deprotonation, but, at least in a small equilibrium con-
pearance of P–P coupling (absent in the non-protonated centration, by nucleophilic attack of a second ylide mole-
species), is exactly analogous to that observed for 4b, which, cule generating an alkoxide function. This is ideally placed
upon protonation with HBr, gave 31P NMR signals at δ to interact with the second acyl chloride producing a seven-
1
= +12.6 and +20.4 ppm (4JP,P = 4.6 Hz).[6] The H NMR membered ring lactone. A series of two deprotonations by
spectrum showed a broad doublet at δ = 6.30 ppm (J = the remaining molecules of Ph3P=CH2 then causes ring-
8 Hz) attributed to the newly formed CHD–P+ function, opening to give the carboxylate and formation of the di-
whereas the 13C NMR spectrum showed a signal for CO2H phosphonioallyl anion function.
at δ = 167.8 ppm and a marked lowering of the chemical
shift of the doublets due to C-1 of PPh to δ = 121.3 (J =
Conclusions
91 Hz) and 120.2 (J = 87 Hz) ppm. Slow concentration of
this solution led to deposition of small colourless crystals.
X-ray diffraction studies of these failed to give data of suit-
able quality for publication, but key features of the prelimi-
nary structure obtained were in agreement with those ex-
pected for 5. Thus, whereas the central carbon atom,
PCCCP, was still planar (angle sum 359.9°), bond lengths
The unexpected rearrangement reported here makes
available a compound containing the unusual bis(triphenyl-
phosphonio)allyl anion function in two simple steps from
commercially available starting materials, and should facili-
tate further studies on the structure and reactivity of such
systems.
and angles clearly indicated one singly bonded C–
+
CH2PPh3
[C–C 1.58(2), C–P 1.746(15) Å, C–C–P
+
117.6(9)°] and one doubly bonded C=CHPPh3 [C–C
1.386(18), C–P 1.790(13) Å, C–C–P 123.2(10)°].
Experimental Section
General: M.p.: Reichert hot-stage microscope, uncorrected values.
NMR: Bruker AM300 (300 MHz for 1H, 75 MHz for 13C,
121 MHz for 31P); internal TMS as reference for H and 13C and
1
external 85% H3PO4 as reference for 31P. MS: Micromass LCT by
using electrospray ionization.
Biphenyl-4,4Ј-bis(2-triphenylphosphoranylideneethanone) (1): A sus-
pension of methyltriphenylphosphonium bromide (17.9 g,
50 mmol) in dry THF (100 cm3) was stirred under nitrogen, while
butyllithum in hexane (2.5 , 20 cm3, 50 mmol) was added slowly.
After 30 min, a solution of biphenyl-4,4Ј-dicarbonyl dichloride[8]
(3.49 g, 12.5 mmol) in dry THF (50 cm3) was added dropwise, and
the mixture was stirred for 18 h. The mixture was added to water
and extracted with ethyl acetate. The ethyl acetate extracts were
washed thoroughly with water to remove Ph3PMe+Cl–, dried and
concentrated to give the product 1 (5.1 g, 54%) as pale yellow crys-
Scheme 4.
We propose that the formation of compound 2 most
likely proceeds according to the mechanism shown in
Scheme 5. In this, the acylation of one molecule of ylide
1
tals, m.p. 256–262 °C. H NMR (CDCl3): δ = 8.00 (d, J = 6 Hz, 4
H), 7.75–7.40 (m, 34 H), 4.45 (br. s, 2 H, CH=P) ppm. 13C NMR
(CDCl3): δ = 184.3 (CO), 141.8 (C-1, C-1Ј), 140.0 (d, J = 15 Hz,
C-4, C-4Ј), 133.1 (d, J = 9 Hz, C-2 of PPh), 132.0 (C-4 of PPh),
128.8 (d, J = 13 Hz, C-3 of PPh), 127.3 (4 CH), 126.4 (4 CH), 127.0
(d, J = 91 Hz, C-1 of PPh), 51.0 (d, J = 111 Hz, C=P) ppm. 31P
NMR (CDCl3): δ = +17.8 ppm. MS (ES+): m/z = 781 [M + Na+],
759 [M + H+]. C52H40O2P2 (758.8): calcd. C 82.31, H 5.31; found
C 82.44, H 5.70.
2Ј-[1-(Triphenylphosphonio)-3-(triphenylphosphoranylidene)prop-1-
en-2-yl]biphenyl-2-carboxylate Trihydrate (2): The same procedure
as above, but using biphenyl-2,2Ј-dicarbonyl dichloride[9] gave the
product 2 (1.89 g, 20%) as yellow prisms, m.p. 214–218 °C. 1H
NMR (CD3SOCD3): δ = 7.77–7.72 (m, 3 H), 7.65–7.54 (m, 17 H),
7.43 (td, J = 8, 3 Hz, 6 H), 7.37–7.32 (m, 1 H), 7.17–7.09 (m, 2 H),
6.95 (dd, J = 12, 7 Hz, 6 H), 6.89 (d, J = 8 Hz, 1 H), 6.78–6.76 (m,
2 H), 5.56 (d, J = 8 Hz, 1 H, CH-P), 3.14 (d, J = 14 Hz, 1 H,
CH=P) ppm. 13C NMR (CD3SOCD3): δ = 170.8 (CO), 169.3 (dd,
J = 7, 6 Hz, PCCCP), 142.0 (C), 140.3 (d, J = 5 Hz, 1 C), 140.1
(d, J = 5 Hz, 1 C), 138.1 (C), 133.3 (d, J = 3 Hz, C-4 of PPh),
133.2 (d, J = 10 Hz, C-2 of PPh), 133.0 (d, J = 3 Hz, C-4 of PPh),
132.8 (d, J = 10 Hz, C-2 of PPh), 130.6 (CH), 129.8 (d, J = 12 Hz,
C-3 of PPh), 129.4 (d, J = 12 Hz, C-3 of PPh), 127.7 (CH), 127.6
(CH), 127.5 (CH), 127.0 (CH), 126.2 (d, J = 90 Hz, C-1 of PPh),
Scheme 5.
Eur. J. Org. Chem. 2010, 3211–3214
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R. A. Aitken et al.
SHORT COMMUNICATION
126.1 (CH), 125.3 (CH), 124.8 (CH), 123.5 (d, J = 87 Hz, C-1 of
PPh), 61.6 (dd, J = 99, 16 Hz, P-C), 57.3 (dd, J = 123, 8 Hz, P=C)
ppm. 31P NMR (CD3SOCD3): δ = +9.2, +6.5 ppm. MS (ES+): m/z
= 781 [M + Na], 759 [M + H]. C52H40O2P2·3H2O (812.9): calcd.
C 76.83, H 5.70; found C 76.83, H 5.75.
CCDC-760279 (1) and -760280 (2) contain the supplementary crys-
tallographic data for this paper. These data can be obtained free
of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
Crystal Data for 1: C52H40O2P2·4CH2Cl2, M = 1098.48, colourless
prism, crystal dimensions 0.10ϫ0.10ϫ0.10 mm, triclinic, space
group P1, a = 9.0123(16), b = 11.924(2), c = 14.115(2) Å, α =
[1] a) R. A. Aitken, E. N. Kozminykh, V. O. Kozminykh, P. Light-
foot, Phosphorus Sulfur Silicon Relat. Elem. 1998, 134/135,
487–492; b) R. A. Aitken, P. Lightfoot, N. J. Wilson, Eur. J.
Org. Chem. 2001, 35–37; c) R. A. Aitken, S. J. Costello,
A. M. Z. Slawin, N. J. Wilson, Eur. J. Org. Chem. 2003, 623–
625.
[2] R. A. Aitken, M. J. Drysdale, L. Hill, K. W. Lumbard, J. R.
MacCallum, S. Seth, Tetrahedron 1999, 55, 11039–11050.
[3] H. J. Bestmann, B. Arnason, Chem. Ber. 1962, 95, 1513–1527.
[4] R. A. Aitken, N. Karodia, P. Lightfoot, J. Chem. Soc. Perkin
Trans. 2 2000, 333–340.
¯
112.396(11), β = 99.650(12), γ = 103.341(12)°, V = 1308.4(4) Å3, Z
= 1, Dc = 1.394 Mgm–3, T = 93(2) K, 13040 reflections, 4746 of
which unique (Rint = 0.055), R1 = 0.0543, wR2 = 0.1392 for 4160
reflections with IϾ2σ(I) and 307 variables. Data were recorded
by using a Rigaku MM007, Mo-Kα radiation (confocal optic, λ =
0.71073 Å) and Saturn detector. The structure was solved by direct
methods and refined by using full-matrix least-squares methods.
Crystal Data for 2: C52H40O2P2·3H2O, M = 812.83, yellow prism,
[5] H. Schmidbaur, C. Paschalidis, O. Steigelmann, G. Müller, An-
gew. Chem. 1989, 101, 1739–1740; Angew. Chem. Int. Ed. Engl.
1989, 28, 1700–1701.
¯
crystal dimensions 0.15ϫ0.15ϫ0.10 mm, triclinic, space group P1,
a = 11.616(3), b = 12.001(3), c = 16.208(5) Å, α = 103.506(8), β =
[6] H. J. Bestmann, L. Kisielowski, Tetrahedron Lett. 1990, 31,
107.254(5), γ = 90.610(8)°, V = 2090.3(11) Å3, Z = 2, Dc
=
3301–3304.
1.291 Mgm–3, T = 93(2) K, 13388 reflections, 7398 of which unique
(Rint = 0.056), R1 = 0.0579, wR2 = 0.1457 for 5632 reflections with
IϾ2σ(I) and 551 variables. Data were recorded by using a Rigaku
MM007, Mo-Kα radiation (confocal optic, λ = 0.71073 Å) and
Mercury detector. The structure was solved by direct methods and
refined by using full-matrix least-squares methods.
[7] G. Jochem, A. Schmidpeter, H. Nöth, Chem. Eur. J. 1996, 2,
221–227.
[8] T. S. Work, J. Chem. Soc. 1940, 1315–1320.
[9] F. Bell, P. H. Robinson, J. Chem. Soc. 1927, 1695–1699.
Received: February 2, 2010
Published Online: May 4, 2010
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Eur. J. Org. Chem. 2010, 3211–3214