An efficient separation method for enol phosphate and corresponding β-ketophosphonate from their mixtures under aqueous conditions

Article abstract of DOI:10.1081/SCC-120021033

Separation of a mixture β-ketophosphonate 3 and their corresponding enol phosphate 4 is efficiently carried out in aqueous alkaline solutions. Enol phosphate 4 is first extracted with hexanes:dichloromethane (19:1). Acidification of the aqueous layer followed by extraction of the β-ketophosphonate 3 with dichloromethane completes the separation. Thus, when 1-bromo-2,4-pentadione la reacted with triethyl phosphite to give diethyl (2,4-dioxopentyl)phosphonate 3a (Arbuzov-product) and the corresponding enol phosphate 4a (Perkow-product), separation of the two compounds was carried out using this method.

Full text of DOI:10.1081/SCC-120021033

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An Efficient Separation Method for Enol Phosphate and
Corresponding β-Ketophosphonate from Their Mixtures
Under Aqueous Conditions
Cornelis M. Moorhoff a
a Department of Chemistry , The University of Tasmania , Hobart, Tasmania, Australia
Published online: 17 Aug 2006.
To cite this article: Cornelis M. Moorhoff (2003) An Efficient Separation Method for Enol Phosphate and Corresponding β-
Ketophosphonate from Their Mixtures Under Aqueous Conditions, Synthetic Communications: An International Journal for
Rapid Communication of Synthetic Organic Chemistry, 33:12, 2069-2086, DOI: 10.1081/SCC-120021033
To link to this article: http://dx.doi.org/10.1081/SCC-120021033
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SYNTHETIC COMMUNICATIONSÕ
Vol. 33, No. 12, pp. 2069–2086, 2003
An Efficient Separation Method for
Enol Phosphate and Corresponding
b-Ketophosphonate from Their Mixtures
Under Aqueous Conditions
*
Cornelis M. Moorhoff
Department of Chemistry, The University of Tasmania,
Hobart, Tasmania, Australia
ABSTRACT
Separation of a mixture b-ketophosphonate 3 and their corresponding
enol phosphate 4 is efficiently carried out in aqueous alkaline solutions.
Enol phosphate 4 is first extracted with hexanes:dichloromethane
(19:1). Acidification of the aqueous layer followed by extraction
of the b-ketophosphonate 3 with dichloromethane completes the
separation. Thus, when 1-bromo-2,4-pentadione 1a reacted with
triethyl phosphite to give diethyl (2,4-dioxopentyl)phosphonate 3a
(Arbuzov-product) and the corresponding enol phosphate 4a
(Perkow-product), separation of the two compounds was carried
out using this method.
*Correspondence: Cornelis M. Moorhoff, Department of Chemistry, The
University of Tasmania, GPO Box 252-75, Hobart, Tasmania, 7001 Australia.
2069
DOI: 10.1081/SCC-120021033
Copyright & 2003 by Marcel Dekker, Inc.
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2070
Moorhoff
INTRODUCTION
The classical Arbuzov reaction for the preparation of b-ketophos-
phonate 3 by reacting a-haloketone 1 with trialkyl phosphite 2, usually
leads to the formation of a mixture b-ketophosphonate 3 (Arbuzov-
product) and enol phosphate 4 (Perkow-product) (Sch. 1).[1] Protected
the carbonyl moiety,[2,3] and other methods[4–7] have been employed
but involves at least two or more reactions. While the reaction of
a-chloroketones with trialkyl phosphites 2 gives in mostcases overwhel-
mingly the enol phosphates 4,[1,8] a similar reaction using a-iodoketones
instead are more likely to lead to the exclusive formation of b-ketophos-
phonates 3. However, certain a-iodoketones may not be stable and
the best compromise is to use a-bromoketones in this reaction with
trialkyl phosphites. Separation of mixtures b-ketophosphonate 3 and
enol phosphate 4 may be tedious on a large scale and usually involves
chromatographic separation. In this article we give an inexpensive, easy,
and fast separation method for mixtures b-ketophosphonates 3 and enol
phosphate 4.
RESULTS
A number of differentmixutres b-ketophosphonate 3—enol phos-
phate 4 were obtained by reacting a-bromoketones with either trimethyl
phosphite or triethyl phosphite. These mixtures 3 and 4 were then
‘‘dissolved’’ in either an aqueous solution of potassium- or sodium car-
bonate, or potassium- or sodium hydroxide, depending on the stability of
the functional groups. For example, separation of substituted phenylacyl
bromide derived enol phosphate 4[9] from the corresponding compound
3,[9] was carried out in an aqueous solution of potassium hydroxide using
petroleum spirits (40–60ꢀC) and dichloromethane (19:1) for extraction.
Excellent purities of enol phosphates 4a, 4b, 4c, 4d, and 4e,[9]
Scheme 1.

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Separation of b-Ketophosphonate
2071
usually >95%, butmoslty >99% free from b-ketophosphonate 3, were
obtained. In this series two extractions were normally enough to isolate
enol phosphates 4 completely. A third extraction gave little material and
actually contained a little b-ketophosphonate 3. After acidification
to ꢁpH 2 with aqueous hydrochloric acid, the corresponding b-ketopho-
sphonates1 3a, 3b, 3c, 3d, and 3e[9] respectively, were extracted with
dichloromethane and obtained >98% free from enol phosphate 4
(Table 1). Two extractions were found to be sufficient to extract the
b-ketophosphonate 3 completely. The success of these separations is
probably due to metal enolates of the b-ketophosphonates 3.[6,10]
However, it was found that the dimethyl esters of the enol phosphate 4
and phosphonates 3 were more difficult to separate due to their higher
polarity than their diethyl ester derivatives. Another problem encoun-
tered was the formation of methylphosphonate: (MeO)2P[O]CH3.
The corresponding dipropyl- or diisopropyl phosphonyl esters were not
investigated. Ethyl g-bromoacetoacetate 1e reacted also with triethyl- and
trimethyl phosphite and gave mixtures of enol phosphate 4f and 4g,
b-ketophosphonate 3f and 3g respectively.[2,7,11–13] In this particular
case it became obvious that extraction from aqueous sodium hydroxide
was too harsh. No enol phosphate was obtained since it had totally
decomposed due to base catalyzed elimination of dialkyl phosphate
(eg. Sch. 2).[14]
On the other hand, an aqueous solution of sodium hydrogen
carbonate was not able to hold ketophosphonates 3f and 3g in the
aqueous layer. An aqueous solution of potassium carbonate was able to
successfully retain these ketophosphonates 3f and 3g without hydrolyzing
the ester group or to eliminate diethylphosphate from the enol
phosphates 4f and 4g. Bromoacetone reacted also with triethyl
phosphite.[15,16] These mixtures of enol phosphate 4h and b-ketophos-
phonate 3h were more difficult to separate, and some hydrolysis
took place since the yield of the separated compounds was 72%.
A literature search revealed that the phosphonate 3i has been
prepared in four steps.[17] Although 1-bromo-2,4-pentadione 1g has
been prepared before,[18] we adapted our bromination procedure
according to the preparation of ethyl 4-bromo-3-oxobutanoate to
1g.[19] 1-Bromo-2,4-pentadione 1g is ꢁ100% enolized (CDCl3) and is
unstable at room temperature. The bromodiketone 1g reacted with
triethylphosphite to give a mixture of phosphonate 3i and enol phosphate
4i (Sch. 3).
This mixture was added to a saturated aqueous solution of NaHCO3
and the enol phosphate 4i was extracted with 95:5 petroleum spirits
(40–60ꢀC):dichloromethane (twice). Some isomerization of the double

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Separation of b-Ketophosphonate
2073

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2074
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Separation of b-Ketophosphonate
2075
Scheme 2.
Scheme 3.
Scheme 4.
bond to 5[20] had taken place and some hydrolysis of the enol phosphate 4i
had occurred. The aqueous layer was acidified with 1M HCl solution and
extraction with dichloromethane gave the ketophosphonate 3i. NMR-
analyses revealed that the enol compound 3i was the dominant tautomer
in CDCl3 and that the keto tautomer 6 was only 13% of the mixture (Sch.
4). Condensation of 3-methyl-2-butenal 7 and the dianion of the keto-
phosphonate 3i, generated by two mole lithium diisopropylamide in THF
at room temperature,[12] gave (2Z,4E )-4-hydroxy-8-methyl-3,5,7-nona-
triene-2-one 8 in 75% yield.

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Separation of b-Ketophosphonate
2077

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Separation of b-Ketophosphonate
2079

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EXPERIMENTAL
All reactions were carried out in air, except the condensation of
ketophosphonate 3i and 3-methyl-2-butenal (under nitrogen).1H NMR
(ꢀ, ppm, with SiMe4 as an internal standard) and 13C NMR (ꢀ, ppm)
were recorded on a Varian Gemini 200 spectrometer at 200 MHz and
50 MHz (Table 1). High resolution electron ionization (EI) mass spectra
were obtained from a Varian MAT 311 A instrument and high
resolution chemical ionization spectra (CI) using ammonia, were
obtained from a Kratos Concept ISQ instrument. Infrared spectra
were obtained on a Hitachi 270-30 FTIR spectrophotometer (film,
NaCl plates). Bulb-to-bulb distillations were carried out on a Buchi
GKR-51 apparatus.
Note: The following additions of triethylphosphite to a-bromo-
ketones or vice versa, all produced mixtures of enol phosphate 4 and
ketophosphonate 3 during a vigorous, exothermic evolution of ethyl
bromide. CAUTION!: Enol phosphates are neurological toxins.
(a) Separation of a Mixture
1-[(Diethoxyphosphinyl)oxo]styrene 4a and
2-(Diethoxyphosphinyl)acetophenone 3a
2-Bromoacetophenone [phenacyl bromide] (2.0 g, 10.05 mmol)
was added to triethyl phosphite (1.8 g, 10.83 mmol) at 90ꢀC within
2 min and then stirred for a further 15 min at 90ꢀC with a simultaneous
release of ethyl bromide. Excess triethyl phosphite and traces of ethyl
bromide were removed under vacuum. The resulting viscous, oily
mixture of phosphonate 3a and enol phosphate 4a (82:18) was shaken
in an aqueous solution of potassium hydroxide (2.0 g KOH mmol, in
150 mL H2O) and extracted twice with a mixture petroleum spirits
(40–60ꢀC) and dichloromethane 19:1 (2 Â 100 mL) and the organic
extract dried (MgSO4). After evaporation of the solvents 1-
[(diethoxyphosphinyl )oxo]styrene 4a (0.562 g, 21.8%, 95% purity) was
isolated as
a
colorless oil. [Found: MHþ(LSIMS), 257.09517.
C12H18O4P requires M, 257.094266]; Acidification with concen-
trated hydrochloric acid to pH 4 followed by extraction with
dichloromethane (2 Â 50 mL) gave, after drying of the organic extract
(MgSO4) and evaporation of the solvent, enol phosphate free
2-(diethoxyphosphinyl )acetophenone 3a (1.489 g, 57.8%) as a colorless
oil. [ Found: MHþ(LSIMS), 257.09368. C12H18O4P requires M,
257.094266 ].

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Separation of b-Ketophosphonate
(b) Separation of a Mixture
1-[(Dimethoxyphosphinyl)oxo]styrene
2081
4b and 2-(Dimethoxyphosphinyl)acetophenone 3b
2-Bromoacetophenone (1.0 g, 5.025 mmol) was added to excess
trimethyl phosphite (0.8 g, 6.45 mmol) under the same conditions as in
(a). The resulting viscous oily mixture of phosphonate 3b and enol
phosphate 4b (72:28) was treated in the same way as described under
(a) to give phosphonate free 2-[(dimethoxyphosphinyl )oxo ]styrene 4b
(0.31 g, 27.0%), as a colorless oil. [Found: MHþ(LSIMS), 229.06764.
C10H14O4P requires M, 229.062967]. IR: ꢁmax 3020, w; 2956, m; 2855,
w; 1676, s; 1596, m; 1581, w; 1535, w; 1448, s; 1351, w; 1258, vs; 1187,
m; 1029, vs; 879, m; 808, s; 732, m. Enol phosphate free 2-(dimethox-
yphosphinyl )acetophenone 3b (0.81 g, 70.6%) as a colorless oil. [Found:
MHþ(LSIMS), 229.06235. C10H14O4P requires M, 229.062967]. IR
(cmÀ1): ꢁmax 3070, w; 2960, s; 2858, m; 1760, m; 1725, s; 1684, m;
1635, s; 1577, m; 1492, s; 1447, s; 1269, vs; 1186, s; 1011, vs; 844, s;
773, s; 705, s.
(c) Separation of a Mixture 2-[(Diethoxyphosphinyl)oxo]-
2-[4-bromophenyl]ethane 4c and 2-(Diethoxyphosphinyl)-
40-bromoacetophenone 3c
Triethyl phosphite (1.8 g, 10.83 mmol) was added to 40-bromo-a-
bromoacetophenone [2,40-dibromoacetophenone or 40-bromophenacyl
bromide] (2.0 g, 7.196 mmol) at90 ꢀC within 2 min and then
stirred for a further 15 min at 90ꢀC. The workup of the resulting
viscous oily mixture of phosphonate 3c and enol phosphate 4c
(64:36) proceeded in the same way as described under (a) but with
the use of potassium carbonate (2.0 g, K2CO3 mmol, in 200 mL H2O).
2-[(Diethoxyphosphinyl)oxo]-2-[4-bromophenyl ]ethane 4c (0.633 g, 26.3%,
91% pure) [Found: MHþ(LSIMS), 335.00537. C12H17BrO4P
requires M, 335.004777]; IR (cmÀ1): ꢁmax 3070, w; 2983, s; 2932, m;
2920, m; 1681, s; 1585, w; 1484, w; 1444, w; 1396, m; 1254, s; 1163, m;
1026, s; 972, s; 806, s. Enol phosphate free 2-(diethoxyphosphinyl)-40-
bromoacetophenone. 3c (1.72 g, 71.5%) as a colorless oil. [Found:
MHþ(LSIMS), 335.00382. C12H17BrO4P requires M, 335.004777].
IR (cmÀ1): ꢁmax 2985, s; 2950, m; 2910, m; 1712, s; 1680, s; 1586, s;
1485, m; 1444, m; 1395, s; 1370, w; 1238, s; 1160, s; 1029, vs; 817, s;
759, m.

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2082
Moorhoff
(d) Separation of a Mixture 2-[(Diethoxyphosphinyl)oxo]-
2-[4-nitrophenyl]ethane 4d and 2-(Diethoxyphosphinyl)-
40-nitroacetophenone 3d
Triethyl phosphite (1.70 g, 10.23 mmol) was added to 2-bromo-40-
nitroacetophenone (2.0 g, 8.20 mmol) as described under (c). The
resulting light-brown viscous oily mixture of phosphonate 3d and enol
phosphate 4d (35:65) was treated for separation as described in (a) (Note:
the aqueous solution became dark yellow to yellow-brown). 2-[(Diethoxy-
phosphinyl )oxo]-2-[4-nitrophenyl ]ethane 4d (1.40 g, 56.7%) as a light
yellow viscous oil was obtained phosphonate free [Found:
MHþ(LSIMS), 302.07913. C12H17NO6P requires M, 302.079345]. IR
(cmÀ1): ꢁmax3120, w; 3080, w; 2991, s; 2940, m; 2920, m; 1694, w; 1632,
s; 1599, s; 1522, vs; 1444, m; 1394, m; 1350, s; 1272, vs; 1164, s; 1103, s;
1034, vs; 860, s; 830, s; 760, s; 709, m. Enol phosphate free 2-(diethoxy-
phosphinyl )-40-nitroacetophenone 3d (0.57 g, 23.1%) as a yellow oil.
[Found: MHþ(LSIMS), 302.07809. C12H17NO6P requires M,
302.079345]. IR (cmÀ1): ꢁmax 3111, w; 2990, s; 2940, m; 2920, m; 1720,
s; 1688, s; 1603, s; 1527, s; 1405, s; 1348, s; 1265, vs; 1103, s; 1022, vs; 970,
s; 857, s; 835, s; 785, m; 716, m.
(e) Separation of a Mixture 2-[(Diethoxyphosphinyl)oxo]-
2-[3-nitrophenyl]ethane 4e and 2-(Diethoxyphosphinyl)-
30-nitroacetophenone 3e
Triethyl phosphite (1.7 g, 10.23 mmol) and 2-bromo-30-nitroaceto-
phenone (2 g, 8.20 mmol) was reacted and worked up in a similar
manner as in the previous example. The resulting light-yellow viscous
oily mixture of phosphonate 3e and enol phosphate 4e (34:66) was
worked up as described under (a) butusing sodium hydroxide (2.0 g.
NaOH mmol, in 150 mL H2O). 2-[(Diethoxyphosphinyl )oxo]-2-[3-nitro-
ꢀ
phenyl ]ethane 4e (1.584 g, 64.2%) as a lightyellow viscous oil, b.p. 112 C/
0.5 mm Hg. [Found: MHþ(LSIMS), 302.07955. C12H17NO6P requires M,
302.079345]. IR (cmÀ1): ꢁmax 3097, w; 2991, s; 2940, m; 2920, m; 1637, s;
1531, vs; 1481, m; 1446, w; 1351, vs; 1263, vs; 1166, m; 1132, s; 1031, vs;
901, m; 831, s; 743, m. 2-(Diethoxyphosphinyl )-1-oxo-30-nitroacetophe-
none 3e (0.864 g, 35.0%) as a dark yellow solid. m.p. 126ꢀC. [Found:
MHþ(LSIMS), 302.0. C12H17NO6P requires M, 302.079345]. IR
(cmÀ1): ꢁmax 3106, w; 2993, s; 2929, s; 2880, m; 1720, s; 1686, s; 1613,
s; 1577, s; 1528, s; 1479, s; 1442, s; 1395, s; 1347, vs; 1265, vs; 1030, vs;
965, s; 884, s; 805, s; 732, s.

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Separation of b-Ketophosphonate
(f ) Separation of a Mixture Ethyl
2083
3-[(Diethoxyphosphinyl)oxo]-3-butenoate 4f and Ethyl
4-(Diethoxyphosphinyl)-3-oxobutanoate 3f
Ethyl 4-bromo-3-oxobutanoate (7.0 g, 33.49 mmol) was added to
triethyl phosphite (7.0 g, 42.13 mmol) and treated the same way as
described under (a). The resulting viscous oily mixture of phosphonate
3f and enol phosphate 4f (43:57) was shaken in an aqueous solution of
potassium carbonate (7.0 g. K2CO3 mmol, in 200 mL H2O) (pH ꢁ10) and
then extracted three times with a mixture petroleum spirits (40–60ꢀC) and
dichloromethane 19:1 (3 Â 100 mL) and the organic phase of the first two
extractions were combined and dried (MgSO4). After evaporation of the
solvents phosphonate free ethyl 3-[(diethoxyphosphinyl )oxo]-3-butenoate
4f (2.9 g, 32.5%), b.p. 112ꢀC/0.5 mm Hg. [Found: Mþꢂ(EI), 266.0916.
C10H19O6P requires M, 266.09193]; m/z ¼ 221 (MHþꢂ -(CH3)2CH,
45%); 179 (Mþꢂ-CH2CO2CH(CH3)2, 28%), 155 (100%); 127 (MHþꢂ
-
(EtO)2P[O}OH, 72%), 99 (MHþꢂ-69%). (Found: C, 44.81; H, 7.02; P,
11.47. C10H19O6P requires C, 45.11; H, 7.19; P, 11.63%). IR (cmÀ1):
ꢁ
max 2988, s; 2940, s; 2920, s; 1738, s; 1662, s; 1546, w; 1447, m; 1395, m;
1371, m; 1272, s; 1160, s; 1040, s; 867, w; 802, m. The third intermediate
extract was kept separate and dried to give after evaporation a mixture of
57% enol phosphate 4f and 43% phosphonate 3f (0.83 g, 9.3%).
Acidification of the aqueous layer with aqueous hydrochloric acid fol-
lowed by extraction with dichloromethane gave ethyl 4-(diethoxyphosphi-
nyl )-3-oxobutanoate 3f (2.51 g, 28.2%, 97% pure) as a pale yellow oil b.p.
126ꢀC/0.5 mm Hg. [Found: Mþ(EI), 266.0924. C10H19O6P requires M,
266.09193];
m/z ¼ 221
(MHþꢂ-(CH3)2CH,
45%);
179
(Mþꢂ-
CH2CO2CH(CH3)2, 28%), 155 (100%); 127 (MHþꢂ-(EtO)2P[O}OH,
72%), 99 (MHþꢂ-69%). (Found: C, 44.18; H, 7.16; P, 11.70. C10H19O6P
requires C, 45.11; H, 7.19; P, 11.63%). IR (cmÀ1): ꢁmax 2986, s; 2940, s;
2920, s; 1750, s; 1716, s; 1446, w; 1393, m; 1369, m; 1257, s; 1029, vs; 973, s;
805, m.
(g) Separation of a Mixture Ethyl
3-[(Dimethoxyphosphinyl)oxo]-3-butenoate 4g and Ethyl
4-(Dimethoxyphosphinyl)-3-oxobutanoate 3g
Ethyl 4-bromo-3-oxobutanoate (1.4 g, 6.697 mmol) was added to
excess trimethyl phosphite (0.9 g, 7.253 mmol) in a similar manner as in
the previous example. The resulting viscous oily mixture of phosphonate
3g and enol phosphate 4g (21:79) and (dimethoxyphosphinyl)methane

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2084
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was worked up in a similar manner as the previous example to give ethyl
3-[(dimethoxyphosphinyl )oxo]-3-butenoate 4g (0.73, 45.7%, 97% pure)
[Found: MHþꢂ(LSIMS), 239.06769. C8H16O6P requires M, 239.068447].
IR (cmÀ1): ꢁmax 2980, s; 2962, s; 2860, w; 1741, s; 1660, s; 1449, m; 1372,
m; 1276, s; 1190, s; 1039, s; 954, m; 855, s. Ethyl-4-(dimethoxyphosphinyl )-
3-oxobutanoate 3g (0.40 g, 25.1%, 89% pure) as a pale yellow oil. [Found:
MHþ(LSIMS), 239.06836. C8H16O6P requires M, 239.068447]. IR
(cmÀ1): ꢁmax 2961, m; 2860, w; 1740, s; 1720, s; 1449, w; 1405, w; 1369,
w; 1266, s; 1030, vs; 813, m. (14% of keto-enol mixture). Note: this
compound still had significant impurities of (dimethoxyphosphinyl)-
methane.
(h) Separation of a Mixture 2-[(Diethoxyphosphinyl)oxo]-
1-propene 4h and 1-(Diethoxyphosphinyl)-2-oxopropene 3h
Bromo-2-oxopropane (1.4 g, 10.22 mmol) was added to excess triethyl
phosphite (2.0 g, 12.04 mmol) in the same manner as described under (f ).
The resulting viscous oily mixture (1.76 g, ꢁ100%) of phosphonate 3h and
enol phosphate 4h (64:36) was shaken in an aqueous solution of lithium
carbonate (0.5 g mmol, in 60 mL H2O) and the extraction and separation
procedure followed through as described under (f). After evaporation
solvents of the the first two extracts phosphonate free 2-[(diethoxyphosphi-
nyl )oxo]-1-propene 4h (0.23 g, 13.5%, 88% pure) was obtained [Found:
MHþ(LSIMS), 167.04806. C5H12O4P requires M, 167.04732]. The third
fraction (0.31 g, 18.3%) was a mixture of enol phosphate:phosphonate
(4:1). Acidification with aqueous hydrochloric acid to pH 2.5 followed
by extraction with dichloromethane gave 1-(diethoxyphosphinyl )-2-oxo-
propane 3h (0.67 g, 39.5%) as a pale yellow oil, containing 4% enol
phosphate as an impurity. [Found: MHþ(LSIMS), 167.04657. C5H12O4P
requires M, 167.04732].
(i) Separation of a Mixture 2-[(Diethoxyphosphinyl)oxo]-
1-penten-4-one 4i and 5-(Diethoxyphosphinyl)-
2,4-dioxopentane(diethyl-2,4-dioxopentylphosphonate) 3i
Triethyl phosphite (6.0 g, 36.11 mmol) was added to 1-bromo-2,4-
dioxopentane (5.0 g, 27.93 mmol) at 60ꢀC within one minute and then
stirred for a further 10 min at 90ꢀC. The separation procedure for the
viscous oily mixture of phosphonate 3i and enol phosphate 4i (73:27) was

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Separation of b-Ketophosphonate
2085
then followed through as described under (f), but an aqueous solution of
sodium hydrogencarbonate (3.0 g. NaHCO3 35.7 mmol, in 100 mL H2O)
(pH ꢁ8) was used. 2-[(diethoxyphosphinyl )oxo]-1-penten-4-one 4i (0.95 g,
14.4%, 97% pure). IR (cmÀ1): ꢁmax 2988, s; 2928, s, 2850, m; 1657, s;
1444, m; 1395, m; 1368, m; 1272, vs; 1165, s; 1030, vs; 950, s; 809, m.
5-(Diethoxyphosphinyl )-2,4-dioxopentane 3i (3.9 g, 59.1%, 93% pure) as a
pale yellow oil (87% enolised in CDCl3). IR (cmÀ1): ꢁmax 2991, m; 2930,
m; 2910, m; 1730, m; 1704, m; 1619, s; 1445, m; 1392, m; 1255, vs; 1150,
1
m; 1030, vs; 970, s; 825, w; 786, w. Significant H NMR signals of the
1
keto isomer 6 (13% of keto-enol mixture). H NMR (CDCl3, 200 MHz):
ꢀ ¼ 2.134 (s, 3H), 3.128 (d, JP ¼ 22.7 Hz, 2H), 3.712 (s, 2H). Distillation
(Bulb-to-bulb: 120ꢀC at 0.1 mm Hg) of the ketophosphonate 3i improved
the purity to 98%. [Found: MHþ(LSIMS), 237.08966. C9H18O5P
requires M, 237.08919].
Condensation of the Dianion of the Phosphonate 3i
and 3-Methyl-2-butenal
Phosphonate 3i (2.0 g, 8.46 mmol) in dry THF (10 mL) was added
to a freshly prepared solution of lithium diisopropylamide (19.8 mmol)
in THF (22 mL) at room temperature. 3-Methyl-2-butenal (1.0 g,
11.9 mmol) in THF (2 mL) was added within 2 min at room temperature
and stirred for 30 min. The solution became warm. A solution of brine
(50 mL) was added then acidified to ꢁpH 3 and extracted with ether. The
extract was dried, then filtered over silica gel and the solvent evaporated.
The residue chromatographed with petroleum:diethyl ether (9:1) to give
4-hydroxy-8-methyl-3,5,7-nonatriene-2-one (1.05 g, 75%). 13C NMR
(CDCl3, 20 MHz): ꢀ (3Z,5E-isomer) ¼ 196.59, 177.85, 145.18, 136.20,
1
124.31, 123.25, 100.17, 26.24, 25.67, 18.58. H NMR (CDCl3, 80 MHz):
ꢀ ¼ 1.886 (sm, 3H), 1.904 (s, 3H), 2.121 (s, 3H), 5.515 (s, 1H), 5.799
(d, J ¼ 15.1 Hz, 1H), 5.997 (dm, J ¼ 11.7 Hz, 1H), 7.490 (dd, J ¼ 15.1,
11.7 Hz, 1H), ꢁ15 (s, OH) and dimer aldehyde.[12]
ACKNOWLEDGMENTS
The expertise of Mr. Marshall Hughes and Dr. Noel Davies
(University of Tasmania) for mass spectral analyses is gratefully
acknowledged. A preliminary investigation into the separation of the

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2086
Moorhoff
vinylenolphosphate 4f and b-ketophosphonate 3f was carried outatht e
University of Stellenbosch.
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Received in the USA October 1, 2002