Condensations of γ-Acetylacetonephosphonium Ylide (1-(Triphenylphosphoranylidene) pentane-2,4-dione) with Carbonyl Compounds

Article abstract of DOI:10.1007/s00706-002-0548-x

2,4-Dioxopentyltriphenylphosphonium bromide reacted with aqueous sodium hydrogen-carbonate in dichloromethane to give, in almost quantitative yield, 1-(triphenyrphosphoranylidene) pentane-2,4-dione. Dianion Wittig- and Michael Wittig condensations of the

Full text of DOI:10.1007/s00706-002-0548-x

Monatshefte f€ur Chemie 134, 429–434 (2003)
DOI 10.1007/s00706-002-0548-x
Condensations of c-Acetylacetonephosphonium
Ylide (1-(Triphenylphosphoranylidene)
pentane-2,4-dione) with Carbonyl
Compounds
ꢀ
Cornelis M. Moorhoff
Department of Chemistry, University of Tasmania, GPO Box 252-75C,
Hobart, Tasmania, Australia 7001
Received August 27, 2002; accepted September 3, 2002
Published online February 3, 2003 # Springer-Verlag 2003
Summary. 2,4-Dioxopentyltriphenylphosphonium bromide reacted with aqueous sodium hydrogen-
carbonate in dichloromethane to give, in almost quantitative yield, 1-(triphenylphosphoranylidene)
pentane-2,4-dione. Dianion Wittig- and Michael Wittig condensations of the last mentioned phospho-
nium ylide with carbonyl compounds gave unsaturated 2,4-diketones which were almost totally
enolised in deutero chloroform as 4-hydroxy-2-oxo-3,5-dienes (24–70% yields). These products
closely resembled the type of compounds derived from similar condensations with alkyl 3-oxo-4-
(triphenylphosphoranylidene)butanoate.
Keywords. ꢀ-Acetylacetonephosphonium ylide; 1-(Triphenylphosphoranylidene)pentane-2,4-dione;
Unsaturated 2,4-diketone; 4-Hydroxy-2-oxo-3,5-diene; 4-Hydroxy-2-oxo-3,5,7-triene; Michael Wittig
condensation.
Introduction
Perhaps it is not surprising that ꢀ-acetylacetonephosphonium ylide (1-(triphenyl-
phosphoranylidene)pentane-2,4-dione) (2a) is unrepresented in the large arsenal of
phosphonium ylides (Scheme 1). A literature search revealed that only the chloride
salt 1a has been prepared via a detour [1]. We prepared the bromide salt 1b [2] and
its treatment with aqueous sodium hydrogencarbonate in dichloromethane gave the
stable ꢀ-acetylacetonephosphonium ylide 2a. This new phosphonium ylide has the
potential to become a very useful compound for the transformation of carbonyl
compounds 3 into ꢀ,ꢁ-unsaturated-ꢂ-diketones (unsaturated 2,4-diketones) 4
(Scheme 1).
ꢀ
Present address: Boron Molecular Pty. Ltd., P.O. Box 756, Noble Park, Victoria, Australia 3174
E-mail: cmoorhoff@boronmolecular.com

430
C. M. Moorhoff
Scheme 1
Results and Discussion
As can be expected, this phosphonium ylide 2a showed similarities with esters of
ꢀ-acetoacetatephosphonium ylide (alkyl 3-oxo-4-(triphenylphosphoranylidene)bu-
tanoate) (2b) [3, 4]. For example, condensation of 2a with 3-methyl-2-butenal
(3a) gave a 22% yield of (3Z,5E)-4-hydroxy-2-oxo-3,5,7-triene 4a and with 2-
butenal (3b), no product could be isolated (Table 1). Last mentioned result was
not unforeseen, since the analogous phosphonium ylide 2b gave, under the so-
called mono anion condensation conditions, also low yields of condensation pro-
ducts [3, 4]. Condensation of the phosphonium ylide 2a with aliphatic aldehydes 3c
and 3d gave the wanted (3Z,5E)-4-hydroxy-2-oxo-3,5-dienes 4c and 4d in only low
yields of 11% and 15% (Table 1). Our knowledge of the formation and use of the
dianion of the phosphonium ylide 2b was applied to 2a [3, 4]. To increase the yield
of Wittig condensation product, the dianion of the phosphonium ylide 2a was
generated. The reaction of the phosphonium ylide 2a with lithium diisopropyl-
amide in THF was exothermic and resulted in an intense orange solution of the
dianion of 2a. Subsequent condensations of the dianion of 2a with ꢃ,ꢂ-unsaturated
aldehydes 3a and 3b, now gave a much higher yield of 4a and 4b (64% and 29%).
In these cases 5:1 and 4:1 mixtures of (3Z,5E)- and (3Z,5Z) and (3Z,5E,7E)- and
(3Z,5Z,7E) isomers of 4a and 4b were obtained. With 2-butenal (3b), no Michael
Wittig condensation product was detected. The dianion of 2a condensed also with
aliphatic aldehydes 3c and 3d in a much higher yield of 4c (55%) and 4d (70%),
but in mixtures of 3:2 and 2:1 (3Z,5E)- and (3Z,5Z) isomers (Table 1). The dianion
of 2a condensed with the aldehyde 3e to give a 1:1 (E)- and (Z)-isomeric mixture

Condensations of ꢀ-Acetylacetonephosphonium Ylide
431
Table 1. Yield of Wittig- and dianion Wittig condensations of carbonyl compounds 3 and the phosphonium ylide 2a
Carbonyl compound 3 Product 4
Yield of product 4
Wittig (3Z,5E):(3Z,5Z) Dianion Wittig (3Z,5E):(3Z,5Z)
22%
1:0
–
64%
29%
5:1
4:1
ꢂ 0%
11%
1:0
55%
3:2
15%
–
1:0
–
70%
49%
2:1
1:1
of 4e. We have not yet explored Michael Wittig condensations of 2a in great detail,
however, preliminary results seem to suggest that the phosphonium ylide 2a is less
able to condense in a Michael Wittig fashion than the corresponding phosphonium
ylide 2b [3, 5, 6]. In an analogous manner as for the condensation of the phos-
phonium ylide 2b and 2H-pyran-5-carboxylates [7], the Michael Wittig condensa-
tion of the 2H-pyran ester 5 and 2a gave the cyclohexenonecarboxylate 6 (70%
enolised in CDCl3) in a modest yield of 24%.
Experimental
All reactions were carried out under N2. 1H NMR (with SiMe4 as an internal standard) and 13C NMR
spectra (ꢁ, ppm) were recorded in CDCl3 on a Varian Gemini 200 spectrometer at 200 MHz and
50.3MHz. Infrared spectra were obtained on a Hitachi 270-30 FTIR spectrophotometer (film, NaCl
plates). Ultraviolet absorbance was measured as solutions in 96% EtOH on a Shimadzu UV-150
spectrophotometer. Column chromatography was performed using Merck Si-60 (40–63mm) silica
gel. Petroleum spirits is the fraction distilled between 40–60ꢁC.
1-(Triphenylphosphoranylidene)pentane-2,4-dione (2a,C23H21O2P): (2,4-Dioxopentyl)triphenyl-
phosphonium bromide (1) [1, 2] (0.58 g, 1.314 mmol) in 30cm3 of CH2Cl2 was treated with an
aqueous solution of 0.16 g of NaHCO3 (1.90 mmol) in 30 cm3 of H2O and stirred vigorously for
30min at room temperature. The CH2Cl2 layer was separated and dried (Na2SO4). Evaporation of
the solvent gave 0.47g of crude 2a (99.4%). This residue was recrystallised from benzene [8] to give
pure 2a.

432
C. M. Moorhoff
1H NMR (CDCl3): ꢁ ¼ 2.263 (s, 3H), 3.425 (s, 2H), 3.5–4.0 (broad, 1H), 7.44–7.65 (m, 15H)
(Note: 2a is 10% enolised) ppm; 13C NMR (CDCl3): ꢁ ¼ 29.92, 53.65 (d, JCP ¼ 106.9Hz), 58.20 (d,
JCP ¼ 15.2Hz), 126.17 (d, JCP ¼ 90.4 Hz), 128.78 (d, JCP ¼ 12.3Hz), 132.30 (d, JCP ¼ 2.6 Hz), 132.89
(d, JCP ¼ 10.3Hz), 184.09 (d, JCP ¼ 3.2 Hz), 206.29 ppm.
Wittig Condensations of 2a with Carbonyl Compounds
(3Z,5E)-4-Hydroxy-8-methylnona-3,5,7-triene-2-one (4a, C10H14O2): 0.19 g 2,4-Dioxo-1-(triphenyl-
phosphoranylidene)pentane (2a) (0.527 mmol) in 1 cm3 of benzene [8] was treated with 60mg of 3-
methyl-2-butenal (3a) (0.74 mmol) and heated for 5 h at 75ꢁC. The reaction mixture was diluted
with 10 cm3 of light petroleum and filtered over silica gel. The filtrate was concentrated and chroma-
tographed over silica gel and eluted with ethyl acetate:light petroleum (1:9) to give 19mg of 4a
(21.7%).
UV (EtOH): ꢄmax ¼ 240.5 (263.8enol) nm; 1H NMR (CDCl3): ꢁ ¼ 1.89 (sm, 3H), 1.9 (s, 3H), 2.1
(s, 3H), 5.52 (s, 1H), 5.8 (d, J ¼ 15.1 Hz, 1H), 6.0 (dm, J ¼ 11.7Hz, 1H), 7.49 (dd, J ¼ 15.1,
11.7Hz, 1H), ꢂ 12 (s, OH) ppm; IR: ꢅꢀ ¼ 2980 (s), 2933 (s), 2880 (m), 1712 (s), 1600 (m), 1369 (s),
913 (s), 738 (s) cmꢃ 1
.
The procedure for other aldehyde-Wittig condensations is exactly the same as for the example
described above.
(3Z,5E)-4-Hydroxyundeca-3, 5-diene-2-one (4c, C11H18O2): UV (EtOH): ꢄmax ¼ 242, (ꢂ270 enol)
nm; 1H NMR (CDCl3): ꢁ ¼ 0.85 (sm, 3H), 1.3–1.5 (m, 6H), 2.08 (s, 3H), 2.1–2.25 (m, 2H), 5.463 (s,
1H), 5.799 (d, J ¼ 15.4Hz, 1H), 6.823 (dt, J ¼ 15.4, 7.2 Hz, 1H), ꢂ12 (s, OH) ppm; IR: ꢅꢀ ¼ 2936 (s),
2880 (s), 1709 (s), 1615 (m), 1466 (m), 1376 (s), 1240 (s), 1165 (s), 732 (m) cmꢃ 1
.
(3Z,5E)-7-Ethyl-4-hydroxynona-3,5-diene-2-one (4d, C11H18O2): UV (EtOH): ꢄmax ¼ 223.5
1
(ꢂ305 enol) nm; H NMR (CDCl3): ꢁ ¼ 0.858 (t, J ¼ 7.3Hz, 6H), 1.2–1.6 (m, 2 pentets, 4H), 1.9–
2.1 (m, 1H), 2.127 (s, 3H), 5.518 (s, 1H), 5.810 (d, J ¼ 15.4 Hz, 1H), 6.617 (dt, J ¼ 15.4, 9.2 Hz, 1H),
ꢂ12 (s, OH) ppm; IR: ꢅꢀ ¼ 2962 (s), 2930 (s), 2880 (m), 1710 (s), 1659 (m), 1430 (m), 1379 (m), 1120
(s), 722 (m) cmꢃ 1
.
Dianion Condensations of 2a with Carbonyl Compounds
(3Z,5E)- and (3Z,5Z)-4-Hydroxy-8-methylnona-3,5,7-triene-2-one (4a): A yellow suspension of 1.00g
of 2a (2.78 mmol) in THF (20 cm3) was added within 1 min to a freshly prepared solution of lithium
diisopropylamide (3mmol) in THF (10 cm3) at room temperature. The resulting warm (ꢂ35ꢁC),
orange solution of the dianion was treated with is 0.35 g of 3-methyl-2-butenal (3a) (4.2mmol) in
THF (0.5cm3) within 2 minutes. The condensation mixture was stirred for another 20 min at room
temperature and monitored by thin layer chromatography. The reaction mixture was quenched with
brine (50 cm3) and cautiously acidified with aqueous 2 M H2SO4 to pH 3. 50cm3 of petroleum
spirits:ether (1:1) was added to the acidified aqueous mixture and the condensation products were
extracted. The extraction process was repeated. The combined extract was dried and the solution
filtered over silica gel to remove Ph3P¼O. The evaporated residue was separated on silica gel and
eluted with petroleum spirits:ethyl acetate (9:1) to give a 5:1 mixture of (3Z,5E)-4a and (3Z,5Z)-4a
(0.305 g, 63.9%).
1
(3Z,5E)-(4a): H NMR (CDCl3): ꢁ ¼ 1.766 (sm, 6H), 1.986 (s, 3H), 5.405 (s, 1H), 5.682 (d,
J ¼ 15.0Hz, 1H), 5.874 (dm, J ¼ 11.7Hz, 1H), 7.365 (dd, J ¼ 15.0, 11.7Hz, 1H), ꢂ12 (s, OH)
ppm; 13C NMR (CDCl3): ꢁ ¼ 18.57, 26.23, 26.38 (3 CH3), 100.18 (¼CH), 123.25, 124.31, 135.21
(3 ¼CH), 145.21 (¼C–), 177.86 (¼C(OH)), 196.62 (C¼O) ppm.
(3Z,5Z)-(4a): 1H NMR (CDCl3): ꢁ ¼ 1.766 (sm, 6H), 1.971 (s, 3H), 5.394 (s, 1H), 5.38 (d,
J ¼ ꢂ12.0Hz, 1H), 6.601 (dd, J ¼ ꢂ12.0, 11.5Hz, 1H), 7.105 (dm, J ¼ 11.5, 1.1 Hz, 1H), ꢂ12 (s,
OH) ppm; 13C NMR (CDCl3): ꢁ ¼ 17.70, 25.66, 26.62 (3 CH3), 101.73 (¼CH), 119.32, 123.05, 137.39
(3 ¼CH), 145.73 (¼C–), 180.68 (¼C(OH)), 195.56 (C¼O) ppm.

Condensations of ꢀ-Acetylacetonephosphonium Ylide
433
Some 3,6,6-trimethylcyclohexa-1,3-diene-1-carbaldehyde as a self-condensation product of 3-
methyl-2-butenal (3a) was also isolated [3].
The procedure for other aldehyde-dianion Wittig condensations is exactly the same as for the
example described above.
(3Z,5E,7E)- and (3Z,5Z,7E)-4-Hydroxynona-3,5,7-triene-2-one (4b): For the 4:1 mixture of
(3Z,5E,7E)-4b and (3Z,5Z,7E)-4b.
1
(3Z,5E,7E)-4b: H NMR (CDCl3): ꢁ ¼ 1.781 (d, J ¼ 5.5, 3H), 2.031 (s, 3H), 5.455 (s, 1H), 5.735
(d, J ¼ 15.3Hz, 1H), 5.9–6.2 (m, 2H), 7.107 (dd, J ¼ 15.3, 9.7 Hz, 1H), ꢂ12 (s, OH) ppm; 13C NMR
(CDCl3): 18.48, 26.62, (2 CH3), 100.37 (¼CH), 123.63, 130.34, 138.25, 140.24 (4 ¼CH), 177.47
(¼C(OH)), 197.13 (C¼O) ppm.
1
(3Z,5Z,7E)-4b: H NMR (CDCl3, 200 MHz): ꢁ ¼ 1.801 (d, J ¼ 5.5, 3H), 2.041 (s, 3H), 5.430 (s,
1H), ꢂ5.4 (m, 1H), 5.9–6.2 (m, 2H), 6.350 (t, J ¼ ꢂ11Hz, 1H), ꢂ12 (s, OH) ppm; 13C NMR (CDCl3):
ꢁ ¼ 17.50, 26.31 (2 CH3), 101.76 (¼CH), 119.83, 129.45, 139.55, 142.03 (4 ¼CH), 179.93 (¼C(OH)),
192.67 (C¼O) ppm.
(3Z,5E)- and (3Z,5Z)-4-Hydroxyundeca-3,5-diene-2-one (4c): For the 3:2 mixture (3Z,5E)-4c and
(3Z,5Z)-4c.
(3Z,5E)-4c: 1H NMR (CDCl3): ꢁ ¼ 0.84 (sm, 3H), 1.2–1.5 (m, 6H), 2.02 (s, 3H), 2.2 (m, 2H), 5.44
(s, 1H), 5.77 (d, J ¼ 15.5 Hz, 1H), 6.78 (dt, J ¼ 15.5, 7.6Hz, 1H), ꢂ12 (s, OH) ppm; 13C NMR
(CDCl3): ꢁ ¼ 13.40 (CH3), 22.06 (CH2), 25.71 (CH3), 27.65, 31.00, 32.23 (3 CH2), 99.17 (¼CH),
125.32, 144.11 (2 ¼CH), 177.63 (¼C(OH)), 196.46 (C¼O) ppm.
(3Z,5Z)-4c: 1H NMR (CDCl3) ꢁ ¼ 0.84 (sm, 3H), 1.2–1.5 (m, 6H), 2.2 (m, 2H), 2.02 (s, 3H), 5.43
(s, 1H), 5.65 (d, J ¼ 12.2 Hz, 1H), 5.99 (dt, J ¼ 12.2, 7.8Hz, 1H), ꢂ12 (s, OH) ppm; 13C NMR
(CDCl3): ꢁ ¼ 13.40 (CH3), 22.06 (CH2), 25.99 (CH3), 28.70, 29.31, 31.13 (3 CH2), 101.21, 123.60,
146.96 (3 ¼CH), 180.46 (¼C(OH)), 195.71 (C¼O) ppm.
(3Z,5E)- and (3Z,5Z)-7-Ethyl-4-hydroxynona-3,5-diene-2-one (4d): For the 2:1 mixture of (3Z,5E)-
4d and (3Z,5Z)-4d.
(3Z,5E)-4d: 1H NMR (CDCl3): ꢁ ¼ 0.779 (t, J ¼ 7.3 Hz, 6H), 1.2–1.6 (m, 4H), 1.9 (m, 1H), 2.026
(s, 3H), 5.437 (s, 1H), 5.731 (d, J ¼ 15.5Hz, 1H), 6.533 (dd, J ¼ 15.5, 9.3 Hz, 1H), ꢂ12 (s, OH) ppm;
13C NMR (CDCl3): ꢁ ¼ 11.25 (2 CH3), 26.13 (CH3), 26.62 (2 CH2), 46.05 (CH), 99.27, 125.45, 148.20
(3 ¼CH), 177.64 (¼C(OH)), 196.44 (C¼O) ppm.
(3Z,5Z)-4d: 1H NMR (CDCl3): ꢁ ¼ 0.771 (t, J ¼ 7.3 Hz, 6H), 1.2–1.6 (m, 4H), 1.9 (m, 1H), 2.012
(s, 3H), 5.408 (s, 1H), 5.60–5.74 (m, 2H), ꢂ12 (s, OH) ppm; 13C NMR (CDCl3): ꢁ ¼ 11.25 (2 CH3),
26.00 (CH3), 27.58 (2 CH2), 41.40 (CH), 101.36, 123.89, 151.58 (3 ¼CH), 180.25 (¼C(OH)), 196.10
(C¼O) ppm.
(3Z,5E)- and (3Z,5Z)-4-Hydroxy-7-phenylhepta-3,5-diene-2-one (4e): For the 1:1 mixture (3Z,5E)-
4e and (3Z,5Z)-4e.
1
(3Z,5E)-4e: H NMR (CDCl3): ꢁ ¼ 2.097 (s, 3H, CH3), 3.525 (d, J ¼ 6.5 Hz, 2H, CH2), 5.545 (s,
1H, ¼CH), 5.838 (dt, J ¼ 15.4, 1.1 Hz, 1H, ¼CH), 7.012 (dt, J ¼ 15.4, 6.5Hz, 1H, ¼CH), 7.4ꢃ 7.1 (m,
5H, Ar), 12.0 (s, OH) ppm; 13C NMR (CDCl3): ꢁ ¼ 26.08 (CH3), 38.49 (CH2), 101.81, 125.96, 144.48
(3 ¼CH), 180.08, (¼C(OH)), 196.38 (C¼O), and 126.28, 128.28 (2C), 128.35 (2C), 139.50 (Ar) ppm.
1
(3Z,5Z)-4e: H NMR (CDCl3): ꢁ ¼ 2.118 (s, 3H, CH3), 4.071 (d, J ¼ 7.7 Hz, 2H, CH2), 5.489 (s,
1H, ¼CH), 5.806 (dt, J ¼ 11.5, 1.6 Hz, 1H, ¼CH); 6.203 (dt, J ¼ 11.5, 7.7 Hz, 1H, ¼CH), 7.4–7.1 (m,
5H, Ar), 12.0 (s, OH) ppm; 13C NMR (CDCl3): ꢁ ¼ 26.43 (CH3), 35.59 (CH2), 99.82, 123.90, 142.18
(3 ¼CH), 177.02, (¼C(OH)), 197.28 (C¼O), and 126.28, 128.28 (2C), 128.47 (2C), 137.77 (Ar) ppm.
Michael Wittig Condensation of 2a with 2H-Pyranester 5
Ethyl 5-acetyl-2-methyl-6-(2-methyl-1-propenyl)-4-oxo-2-cyclohexene carboxylate (6): 0.19g of 2a
(0.527 mmol) in 1 cm3 of benzene [8] was treated with 50mg of ethyl 2,2,6-trimethyl-2H-pyran-5-
carboxylate (5) [7] (0.223 mmol) and heated for 5 h at 75ꢁC. The reaction mixture was
diluted with 10 cm3 of light petroleum and filtered over silica gel. The filtrate was concentrated and

434
C. M. Moorhoff: Condensations of ꢀ-Acetylacetonephosphonium Ylide
chromatographed over silica gel and eluted with ethyl acetate:light petroleum (1:9) to give 16 mg of 6
(23.5%) (ꢂ70% enol tautomer).
1H NMR (CDCl3, enol tautomer): ꢁ ¼ 1.200 (t, J ¼ 7.1 Hz, 3H, CH3), 1.640 (sm, J ¼ 1.3 Hz, 3H,
CH3), 1.917 (sm, J ¼ 1.1 Hz, 3H, CH3), 1.994 (d, J ¼ 1.5 Hz, 3H, CH3), 2.014 (s, CH3), 2.896 (d,
J ¼ 1.5 Hz, 1H, ring-CH), 3.909 (dd, J ¼ 9.9, 1.5 Hz, 1H, ring-CH), 4.15 (q, J ¼ 7.1 Hz, 2H, CH2),
5.072 (dm, J ¼ 9.9, 1.6 Hz, 1H, ¼CH), 5.977 (q, J ¼ 1.5 Hz, 1H, ¼CH), 12.0 (s, OH) ppm; 13C NMR
(CDCl3, enol tautomer): ꢁ ¼ 13.93, 17.64, 21.84, 25.46, 27.55 (5 CH3), 35.62, 51.91 (2 ring CH), 61.12
(CH2), ꢂ105.4 (¼C), 124.37, 125.54 (2 ¼CH), 139.54, 149.96 (2 ¼C), 170.49 (C¼O), 180.15
(¼C(OH)), 188.77 (C¼O) ppm; IR: ¼ ꢅꢀ ¼ ꢂ3400 (w), 2984 (s), 2865 (m), 1735 (s), 1715 (s),
1610 (m), 1445 (m), 1369 (m) cmꢃ 1
.
Acknowledgements
Financial assistance from the Australian Research Council is gratefully acknowledged.
References
€
[1] Ohler E, Zbiral E (1980) Chem Ber 111: 2852
[2] Moorhoff CM, Manuscript in preparation
[3] Moorhoff CM, Schneider DF (1987) Tetrahedron Lett 28: 4721
[4] Moorhoff CM, Schneider DF, Winkler D (1998) J Chem Res (M) 3461; (1998) J Chem Res (S)
763
[5] Moorhoff CM (1997) Tetrahedron 53: 2241
[6] Moorhoff CM (2002) J Chin Chem Soc. Accepted for publication
[7] Moorhoff CM (1997) Synthesis, 685
[8] Due to its carcinogenicity, the author recommends that toluene should be used instead