Synthesis and pyrolytic and kinetic behaviour of β,δ′-dioxo-stabilised phosphorus ylides: Convenient preparation of γ,δ-alkynyl ketones and 2,3-functionalised butadienes

Article abstract of DOI:10.1002/ejoc.200390127

Both ketone- and ester-stabilised phosphorus ylides undergo Michael addition to vinyl ketones to give the β,δ′-dioxo ylides 3 and 5, respectively, although in the latter case careful temperature control is required to avoid an undesired side-reaction. Under conditions of flash vacuum pyrolysis at 650 °C the ylides 3 generally undergo Ph₃PO extrusion to afford the γ,δ-alkynyl ketones 14, although these are found to partly undergo a secondary fragmentation. In contrast, the ylides 5 react under the same conditions to give the synthetically useful 1,3-dienes 20 by way of cyclobutenes. Rate constants for the reaction of selected ylides 3 and 5 are reported. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003).

Full text of DOI:10.1002/ejoc.200390127

FULL PAPER
Synthesis and Pyrolytic and Kinetic Behaviour of β,δЈ-Dioxo-Stabilised
Phosphorus Ylides: Convenient Preparation of γ,δ-Alkynyl Ketones and
2,3-Functionalised Butadienes
R. Alan Aitken,*[a] Nouria A. Al-Awadi,*[b] Mark E. Balkovich,[a] Hans Jürgen Bestmann,*[c]
Oliver Clem,[a] Scott Gibson,[a] Andreas Groß,[c] Ajith Kumar,[b] and Thomas Röder[c]
Keywords: Phosphonium salts / Ylides / Michael addition / Pyrolysis / Dienes / Kinetics
Both ketone- and ester-stabilised phosphorus ylides undergo
undergo a secondary fragmentation. In contrast, the ylides 5
Michael addition to vinyl ketones to give the β,δЈ-dioxo ylides
react under the same conditions to give the synthetically use-
3 and 5, respectively, although in the latter case careful tem- ful 1,3-dienes 20 by way of cyclobutenes. Rate constants for
perature control is required to avoid an undesired side-reac- the reaction of selected ylides 3 and 5 are reported.
tion. Under conditions of flash vacuum pyrolysis at 650 °C
the ylides 3 generally undergo Ph3PO extrusion to afford the
( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
γ,δ-alkynyl ketones 14, although these are found to partly
Germany, 2003)
Introduction
atom of R1 (Table 6, Exp. Sect.). The X-ray structure of
compound 3b has been determined and reported else-
where.[5]
In recent papers one of us has shown that thermal extru-
sion of Ph3PO from a variety of (β-oxoalkylidene)triphenyl-
phosphoranes using the technique of flash vacuum pyro-
lysis (FVP) provides a useful synthetic method for func-
tionalised alkynes and various related products.[1,2] In an
attempt to extend this chemistry, we have examined the
pyrolysis of several new types of stabilised ylides and in this
paper we describe the Michael addition of ketone- and
ester-stabilised ylides to vinyl ketones to give β,δЈ-dioxo yl-
ides[3] and their subsequent pyrolytic behaviour.[4]
Scheme 1
Table 1. Reaction of ylides 1 with vinyl ketones 2 to give ylides 3
Product
R1
R2
Yield (%)
M.p. [°C]
δP
Results and Discussion
3a
3b
3c
3d
3e
3f
Me
Me
Me
Et
Et
Ph
Ph
Me
Et
4-MeOC6H4
Me
Et
Me
Et
76
85
78
81
83
89
80
158
148
162
111
130
175
141
18.1
17.5
18.0
16.6
16.4
16.6
17.4
When ketone-stabilised ylides 1 were treated with vinyl
ketones 2 in boiling toluene for 48 h, the expected dioxo
ylides 3aϪg were formed in good yield as stable solids with
31P NMR signals in the range δ ϭ ϩ16.4 to 18.1 (Scheme 1,
Table 1). As we have previously found for other ylide
classes, the 13C NMR spectra of these compounds are
highly informative, with phosphorus coupling extending
throughout the P-phenyl groups and to the first carbon
3g
When the same conditions were applied to the ester-sta-
bilised ylides 4, the reaction took an unexpected course to
give ketone-stabilised ylides 9 together with acrylates 8. We
believe that this can be explained, as shown in Scheme 2,
by equilibration of the initial Michael adducts 6, by way of
ring closure to give phosphetanes, with the isomeric inter-
mediates 7 which can then undergo retro-Michael reaction
to afford the observed products. The greater thermodyn-
amic stability of 9 as compared to 4 evidently provides the
[a]
School of Chemistry, University of St. Andrews,
North Haugh, St. Andrews, Fife KY16 9ST, UK
Fax: (internat.) ϩ 44-1334/463808
E-mail: raa@st-and.ac.uk
[b]
Department of Chemistry, Kuwait University,
P. O. Box 5969, Safat 13060, Kuwait
[c]
Institut für Organische Chemie der Universität Erlangen-
Nürnberg,
Henkestrasse 42, 91054 Erlangen, Germany
840
 2003 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim 1434Ϫ193X/03/0305Ϫ0840 $ 20.00ϩ.50/0 Eur. J. Org. Chem. 2003, 840Ϫ847

β,δЈ-Dioxo-Stabilised Phosphorus Ylides
FULL PAPER
driving force for this process. Fortunately, this problem
could be overcome by reducing the reaction temperature,
and reaction of 4 with 2 in toluene, or more conveniently
CH2Cl2, at 40 °C gave the required products 5 in good yield
(Scheme 2, Table 2). As one of us has noted previously,[6]
ylides of this type may exhibit restricted rotation of the es-
ter group at room temperature leading to separate signals
for the (E) and (Z) isomers in the 31P and 13C NMR spectra
of 5a,b and 5d.
alkynes,[7] the β,γ,βЈ-trioxo ylides 11 undergo selective elim-
ination across the ‘‘central’’ position to give diacylalkynes
in most cases.[8] On the other hand, ylides such as 12 and
13 lose Ph3PO exclusively between the ylide function and
the more remote carbonyl group to give cyclopentenones
and cyclohexenones as shown, with no trace of the
acetylenic ketones expected from 1,2-elimination.[9]
When the ylide 3a was subjected to FVP at 10Ϫ2 Torr
reaction was found to be incomplete at 500 °C, with some
unchanged ylide being recovered. At 650 °C there was com-
plete reaction and the products included the acetylenic ke-
tone 14 expected from 1,2-elimination of Ph3PO, but this
was accompanied by methyl vinyl ketone, and propyne was
also present, although its volatility precluded an accurate
determination of the yield. It appears that the latter prod-
ucts result from a thermal retro-Michael reaction, perhaps
involving the enol form 14Ј of the initial product 14
(Scheme 3). Once this pattern had been established, most of
the other ylides 3 were found to react in the same way giv-
ing the acetylenic ketones 14 in 16Ϫ39% yield, accompan-
ied in all cases by the vinyl ketone 2 and terminal alkyne
15 (Table 3).
Scheme 2
Table 2. Reaction of ylides 4 with vinyl ketones 2 to give ylides 5
Product
R1
R2
Yield (%)
M.p. [°C]
δP
5a
5b
5c
5d
Me
Me
Et
Me
Et
Me
Et
91
92
87
86
147
104
106
117
22.0/22.6
22.8/23.3
22.5
Et
22.5/23.6
In the case of 3c the retro-Michael reaction was complete
Previous studies on the pyrolysis of ylides where there is to give only 2 and 15. A most unusual and different result
a choice of different carbonyl oxygen atoms available for was obtained for compound 3d. In this case Ph3PO was
elimination have shown that while the β,βЈ-dioxo ylides 10 again obtained together with a single major product which,
1
undergo non-selective elimination to give a mixture of on the basis of its H and 13C NMR spectroscopic data,
Table 3. Flash vacuum pyrolysis (FVP) of ylides 3
R1
R2
Temp. [°C]
Yield of 14 (%)
Yield of 2 (%)
Yield of 15 (%)
3a
Me
Me
650
500
750
650
650
650
650
650
26
10
33
39
32
14
28
49
79
ϩ
ϩ
ϩ
ϩ
ϩ
3b
3c
3d
3f
Me
Me
Et
Ph
Ph
Et
4-MeOC6H4
0
ϩ
[a]
Me
Me
Et
ϩ (?)
10
42
16
20
29
36
3g
[a]
Spectra indicate product to be 18
Eur. J. Org. Chem. 2003, 840Ϫ847
841

R. A. Aitken, N. A. Al-Awadi, H. J. Bestmann et al.
FULL PAPER
jacent ester carbonyl group is unknown. This may be attrib-
uted to the fact that such compounds prefer the configura-
tion shown in which the carbonyl group is aligned anti to
the ylide,[17] although Ϫ as noted earlier Ϫ both syn and
anti forms could be detected in solution. We have also
2
found previously that a high value of JP,CO (Ն 10 Hz) is a
reliable indicator for failure of Ph3PO elimination.[8] With
2
values of 12Ϫ20 Hz for JP,CO compounds 5aϪd therefore
appear unlikely to undergo 1,2-elimination. When the ylides
5 were subjected to FVP under the same conditions as for
3 there was again complete extrusion of Ph3PO at 650 °C
to give products which were readily identified as the substi-
tuted 1,3-dienes 20 (Table 4). A pyrolysis temperature of
700 °C gave slightly higher yields and was routinely used
for larger scale reactions.
Scheme 3
appears to be the triene 18. Because of its highly reactive
nature this product could not be isolated but we are confid-
ent the suggested structure is correct because of the excel-
lent agreement of the spectroscopic data with the analogous
dienes 20 (see later). Its formation can be explained, as
shown in Scheme 4, by postulating Ph3PO elimination be-
tween the ylide function and the δ-carbonyl group to give
a cyclobutene 16 which might undergo electrocyclic ring-
opening to the diene 17 under the conditions used, and this
could then lose two hydrogen atoms to give the doubly con-
jugated ketone triene 18. It is unclear why this ylide should
behave in such a completely different way from the other
Table 4. FVP of ylides 5 at 650 or 700 °C
R1
R2
Yield of 20 (%)
Overall yield of 23 (%)
5a
5b
5c
5d
Me
Me
Et
Me
Et
Me
Et
60
60
50
44
32
40
38
30
Et
It seems likely that these products result from elimination
of Ph3PO between the ylide function and the ketone car-
bonyl group to give the cyclobutene intermediates 19 which
undergo electrocyclic ring-opening under the conditions
used (Scheme 5). As far as we are aware this is the first
example of formation of cyclobutenes by an intramolecular
Wittig reaction apart from an isolated example reported by
Yavari and co-workers while our work was in progress.[18]
Despite their rather simple structure, compounds 20a[19]
and 20c[20] have only been mentioned briefly before, while
20b and 20d are previously unknown. Their 13C NMR spec-
tra form a regular pattern which readily confirms the struc-
tures (Table 7, Exp. Sect.).
Scheme 4
compounds 3 and this reaction merits further investigation.
The formation of the acetylenic ketone products 14 by
FVP of most of the ylides 3 is a rather useful transforma-
tion since it gets around the difficulties normally associated
with the Michael addition of a terminal alkyne to an enone.
By using the starting ylide 1 as a masked form of the alkyne
R1CϵCH we can obtain the same products in two simple
steps, although the overall yield is unfortunately low due to
the fragmentation to 15 and 2. The γ,δ-acetylenic ketones
14 have been of considerable recent interest as precursors of
substituted furans and pyrroles,[10] and previously reported
routes to them include reaction of enones with alkynylbor-
anes,[11] alkynylboranes in the presence of BF3,[12] alkynyl-
stannanes,[13] alkynylaluminium compounds with a nickel
catalyst,[14] and alkynes with a rhodium catalyst.[15] Just re-
cently the addition of a chiral binaphthyl-based alkynyl-
boronate has been used to achieve the reaction asymmetric-
ally.[16]
Attention was now turned to the ylides 5 with β-ester and
δ-ketone carbonyl groups. As far as we are aware, thermal
elimination of Ph3PO between an ylide function and an ad- Scheme 5
842
Eur. J. Org. Chem. 2003, 840Ϫ847

β,δЈ-Dioxo-Stabilised Phosphorus Ylides
FULL PAPER
75 MHz for 13C), Varian CFT 20 (32 MHz for 31P); all spectra,
While the dienes 20 are stable for an extended period in
solution, they were observed to dimerise slowly in the pure
state, a process accelerated by attempted distillation. The
resulting dimers were 1:1 mixtures of two isomers identified
as 21 and 22 resulting from reaction of only the electron-
poor double bond next to the ester group acting as dien-
ophile but reacting without any regioselectivity. This is the
expected pattern of reactivity for 2-(alkoxycarbonyl)butadi-
enes.[21]
In order to obtain crystalline derivatives for characteris-
ation and at the same time to illustrate the use of the dienes
in the DielsϪAlder reaction, pyrolyses were carried out on
a 1-g scale and the crude products from the cold trap dir-
ectly reacted with maleic anhydride to give the adducts 23
in reasonable overall yield (Table 4).
1
CDCl3 as solvent; internal TMS as reference for H and 13C and
external 85% H3PO4 as reference for 31P. GCMS: HewlettϪPackard
5890A/Finnigan Incos (70 eV). MS: AEI/Kratos MS50, EI at
70 eV, CI using isobutane.
Addition of Acyl Ylides to Vinyl Ketones: The appropriate vinyl ke-
tone (20.0 mmol) was added to a solution of the appropriate acyl
ylide (20.0 mmol) in toluene (250 mL) and the mixture was heated
under reflux for 48 h. The solvents were evaporated from the solu-
tion and the residual oil digested with diethyl ether for 4 h. The
resulting solid product was filtered off and recrystallised from ethyl
acetate to give the products as follows.
3-(Triphenylphosphoranylidene)heptane-2,6-dione
(3a):
From
(acetylmethylene)triphenylphosphorane and methyl vinyl ketone
(6.0 g, 76%) as colourless prisms, m.p. 158 °C. IR (KBr): ν˜ ϭ 3040
cmϪ1, 2980, 2920, 2900, 1700 (CO), 1510 (CO). 1H NMR: δ ϭ
7.6Ϫ7.4 (m, 15 H, Ph), 2.3Ϫ2.2 (m, 4 H, CH2), 2.13 (s, 3 H, 1-H3),
Since it has been established that the two types of ylide
3 and 5 both eliminate Ph3PO but in a quite different way,
it was of interest to see whether this was reflected in the 1.86 (s, 3 H, 7-H3) ppm. 13C NMR: See Table 6. 31P NMR: δ ϭ
ϩ18.1 ppm. MS: m/z ϭ 388 [Mϩ]. C25H25O2P (388.5): calcd. C
kinetics of the reactions. Kinetic studies were performed us-
ing a sealed glass tube reactor over the range 410Ϫ510 K
77.30, H 6.49; found C 76.86, H 6.25.
as detailed in the Exp. Sect. The ylides display first-order
kinetics; the resulting rates and Arrhenius parameters are methylene)triphenylphosphorane and ethyl vinyl ketone (6.8 g,
3-(Triphenylphosphoranylidene)octane-2,6-dione (3b): From (acetyl-
85%) as colourless crystals, m.p. 148 °C. IR (KBr): ν˜ ϭ 3030 cmϪ1
,
given in Table 8 (Exp. Sect.) and rate constants adjusted to
400 K are shown in Table 5.
2960, 2920, 2900, 1690 (CO), 1510 (CO), 1470, 1420, 1380, 1140,
1
1090. H NMR: δ ϭ 7.6Ϫ7.4 (m, 15 H, Ph), 2.29Ϫ2.23 (m, 4 H,
CH2CH2), 2.13 (q, J ϭ 7 Hz, CH2CH3), 2.13 (s, COMe), 0.89 (t,
J ϭ 7 Hz, CH2CH3) ppm. 13C NMR: See Table 6. 31P NMR: δ ϭ
ϩ17.5. MS: m/z ϭ 402 [Mϩ], 387, 345, 331. C26H27O2P (402.5):
calcd. C 77.59, H 6.77; found C 77.84, H 6.52.
Table 5. Kinetic data for ylides 3 and 5
Compound
R1
R2
k [sϪ1] at 400 K
3a
3b
3f
3g
5a
5b
5c
5d
Me
Me
Ph
Ph
Me
Me
Et
Me
Et
Me
Et
Me
Et
Me
Et
5.41 ϫ 10Ϫ5
2.14 ϫ 10Ϫ5
6.02 ϫ 10Ϫ8
1.66 ϫ 10Ϫ7
7.53 ϫ 10Ϫ7
5.98 ϫ 10Ϫ7
3.97 ϫ 10Ϫ6
1.49 ϫ 10Ϫ6
1-(4-Methoxyphenyl)-4-(triphenylphosphoranylidene)hexane-1,5-
dione (3c): From (acetylmethylene)triphenylphosphorane and 4-
methoxyacrylophenone (7.5 g, 78%) as yellow crystals, m.p. 162 °C.
IR (KBr): ν˜ ϭ 3060 cmϪ1, 2940, 2860, 1660 (CO), 1590, 1510 (CO),
1
1250. H NMR: δ ϭ 7.64Ϫ7.4 (m, 17 H), 6.81 (d, J ϭ 9 Hz, 2 H),
3.81 (s, 3 H, OMe), 2.81Ϫ2.77 (m, 2 H, CH2), 2.49Ϫ2.40 (m, 2 H,
CH2), 2.18 (s, 3 H, COMe) ppm. 13C NMR: See Table 6. 31P NMR:
δ ϭ ϩ18.0 ppm. MS: m/z ϭ 480 [Mϩ], 345, 331. C31H29O3P
(480.6): calcd. C 77.48, H 6.09; found C 77.38, H 5.92.
Et
For the ylides 3 there is a very marked difference of two
to three orders of magnitude between the cases where R1 ϭ
Me and R1 ϭ Ph. Since the key step in the extrusion most
likely involves interaction of OϪ with Pϩ in the resonance
form 3Ј, this effect is as expected, with the electron-releasing
methyl group accelerating the process while the relatively
electron-withdrawing phenyl group strongly retards it.
When we come to the ylides 5, the rates are considerably
lower than for 3a and 3b and do not vary greatly on chan-
ging between methyl and ethyl substituents.
5-(Triphenylphosphoranylidene)octane-2,6-dione (3d): From (pro-
pionylmethylene)triphenylphosphorane and methyl vinyl ketone
(6.5 g, 81%) as colourless crystals, m.p. 111 °C. IR (KBr): ν˜ ϭ 3040
cmϪ1, 2960, 2940, 2900, 1700 (CO), 1620, 1510 (CO), 1430, 1100.
1H NMR: δ ϭ 7.6Ϫ7.4 (m, 15 H, Ph), 2.39 (q, J ϭ 8 Hz, 2 H,
CH2CH3), 2.29Ϫ2.22 (m, 4 H, CH2CH2), 1.86 (s, 3 H, COMe),
1.14 (t, J ϭ 8 Hz, 3 H, CH2CH3) ppm. 13C NMR: See Table 6. 31P
NMR: δ ϭ ϩ16.6 ppm. MS: m/z ϭ 402 [Mϩ], 359, 345. C26H27O2P
(402.5): calcd. C 77.59, H 6.77; found C 77.74, H 6.89.
4-(Triphenylphosphoranylidene)nonane-3,7-dione (3e): From (pro-
pionylmethylene)triphenylphosphorane and ethyl vinyl ketone
(6.9 g, 83%) as bright yellow crystals, m.p. 130 °C. IR (KBr): ν˜ ϭ
3070 cmϪ1, 2970, 2930, 2890, 1710 (CO), 1600, 1510 (CO), 1480,
1430, 1100. 1H NMR: δ ϭ 7.6Ϫ7.4 (m, 15 H, Ph), 2.40 (q, J ϭ
8 Hz, 2 H, CH2COCH2CH3), 2.30Ϫ2.22 (m, 4 H, CH2CH2), 2.12
(q, J ϭ 7 Hz, 2 H, PϭCϪCOCH2CH3), 1.15 (t, J ϭ 8 Hz, 3 H,
CH2COCH2CH3), 0.88 (t, J ϭ 7 Hz, 3 H, PϭCϪCOCH2CH3)
ppm. 13C NMR: See Table 6. 31P NMR: δ ϭ ϩ16.4 ppm. MS: m/
z ϭ 416 [Mϩ], 387, 359, 345. C27H29O2P (416.5): calcd. C 77.86, H
7.02; found C 77.28, H 7.22.
Experimental Section
General: M.p.: Reichert hot-stage microscope, uncorrected values.
IR: PerkinϪElmer 1420. NMR: Bruker AM300 (300 MHz for H,
1-Phenyl-2-(triphenylphosphoranylidene)hexane-1,5-dione (3f): From
(benzoylmethylene)triphenylphosphorane and methyl vinyl ketone
1
Eur. J. Org. Chem. 2003, 840Ϫ847
843

R. A. Aitken, N. A. Al-Awadi, H. J. Bestmann et al.
R1 signals R2 signals
FULL PAPER
Table 6. 13C NMR spectra [δC (JP,C)] of the ylides 3 and 5
R1 R2 PϭC
COR1
PϭCϪCH2 CH2CO COR2 P-Phenyl
C-1
C-2
C-3
C-4
3a Me Me 61.8 (106) 187.9 (6) 23.0 (14)
3b Me Et 62.0 (107) 188.1 (6) 23.3 (14)
47.9
46.7
208.2 126.9 (90) 133.0 (9) 128.3 (12) 131.2 (3) 24.3 (11)
29.2
35.4, 7.5
211.1 127.1 (89) 133.2 (9) 128.4 (12) 131.3
198.4 127.2 (90) 133.2 (9) 128.4 (12) 131.3
24.5 (11)
3c Me Ar[a] 62.4 (107) 188.3 (6) 24.55 (14) 42.8
24.59 (11) 163.0, 130.1 (2 C)
129.6, 113.4 (2 C)
55.2
3d Et Me 61.2 (107) 191.6 (5) 22.3 (14)
3e Et Et 61.3 (105) 191.7 (5) 22.4 (15)
3f Ph Me 64.5 (105) 187.0 (5) 22.7 (14)
48.4
47.1
47.9
208.5 127.3 (90) 133.1 (11) 128.3 (12) 131.2 (3) 29.0 (11), 29.3
10.7
211.0 127.4 (90) 133.1 (9) 128.4 (12) 131.2 (3) 29.1 (11), 35.4, 7.5
10.7
202.3 126.8 (90) 133.2 (9) 128.5 (12) 131.5 (3) 142.6 (12), 29.1
127.8
127.7 (2 C)
126.9 (2 C)
3g Ph Et 64.7 (104) 187.0 (5) 22.8 (14)
46.5
210.9 126.9 (92) 133.2 (9) 128.5 (12) 131.5 (3) 142.7 (14), 35.2, 7.4
127.9
127.7 (2 C)
127.0 (2 C)
5a Me Me 38.3 (128) 170.9 (18) 22.4 (14)
47.8
46.5
46.6
45.2
46.8
46.4
45.2
209.7 127.6 (89) 133.1 (9) 128.2 (12) 131.4
209.4 127.0 (91)
212.5 127.4 (90) 133.4 (9) 128.6 (12) 131.8
49.5
48.3
49.8
48.5
29.25
29.16
35.4, 7.6
37.4 (120) 170.0 (14) 21.7 (12)
5b Me Et 37.8 (121) 170.2
22.7 (14)
22.1
127.3
210.1 127.5 (90) 133.4 (9) 128.4 (12) 131.6
212.4 127.5 (87) 133.3 (11) 128.3 (12) 131.5 (3) 57.6, 15.0 35.3, 7.6
132.8 (11) 128.4 (12) 131.6
5c Et Me 37.6 (121) 170.1 (20) 22.6
5d Et Et 37.5 (120) 169.9 (12) 22.6
22.0
57.2, 13.9 29.4
127.4
57.0, 13.8
[a]
R2 ϭ 4-methoxyphenyl.
(8.0 g, 89%) as yellow crystals, m.p. 175 °C. IR (KBr): ν˜ ϭ 3060
cmϪ1, 2940, 2880, 1710 (CO), 1580, 1500 (CO), 1440, 1390, 1110,
1100. 1H NMR: δ ϭ 7.70Ϫ7.25 (m, 20 H, Ph), 2.41Ϫ2.32 (m, 2 H,
CH2), 2.15Ϫ2.12 (m, 2 H, CH2), 1.67 (s, 3 H, Me) ppm. 13C NMR:
See Table 6. 31P NMR: δ ϭ ϩ16.6 ppm. MS: m/z ϭ 450 [Mϩ], 407,
393, 381. C30H27O2P (450.5): calcd. C 79.98, H 6.04; found C 80.16,
H 6.23.
Methyl 5-Oxo-2-(triphenylphosphoranylidene)heptanoate (5b): From
(methoxycarbonylmethylene)triphenylphosphorane and ethyl vinyl
ketone (7.7 g, 92%) as colourless crystals, m.p. 104 °C. IR (KBr):
ν
˜ ϭ 3040 cmϪ1, 3020, 2980, 2940, 2910, 1700, 1620 (CO), 1440,
1
1310, 1100. H NMR (2 rotamers): δ ϭ 7.63Ϫ7.45 (m, 15 H, Ph),
3.58/3.11 (br. s, 3 H, OMe), 2.51Ϫ2.25 (m, 4 H, CH2CH2), 2.33 (q,
J ϭ 7 Hz, 2 H, CH2CH3), 0.92 (t, J ϭ 7 Hz, 3 H, CH2CH3) ppm.
13C NMR: See Table 6. 31P NMR: δ ϭ ϩ23.3/22.8 ppm. MS: m/
z ϭ 418 [Mϩ], 387, 347. C26H27O3P (418.5): calcd. C 74.62, H 6.51;
found C 74.90, H 6.51.
1-Phenyl-2-(triphenylphosphoranylidene)heptane-1,5-dione
(3g):
From (benzoylmethylene)triphenylphosphorane and ethyl vinyl ke-
tone (8.0 g, 89%) as bright yellow crystals, m.p. 141 °C. IR (KBr):
ν˜ ϭ 3040 cmϪ1, 2960, 2920, 2880, 1700 (CO), 1570, 1490 (CO),
1420, 1380, 1100. 1H NMR: δ ϭ 7.7Ϫ7.25 (m, 20 H, Ph),
Ethyl 5-Oxo-2-(triphenylphosphoranylidene)hexanoate (5c): From
2.41Ϫ2.32 (m, 2 H, CH2), 2.14Ϫ2.10 (m, 2 H, CH2), 1.95 (q, J ϭ (ethoxycarbonylmethylene)triphenylphosphorane and methyl vinyl
7 Hz, 2 H, CH2CH3), 0.77 (t, J ϭ 7 Hz, 3 H, CH2CH3) ppm. 13C
ketone (7.3 g, 87%) as colourless crystals, m.p. 106 °C. IR (KBr):
NMR: See Table 6. 31P NMR: δ ϭ ϩ17.4. MS: ϭ m/z ϭ 464 [Mϩ],
407, 393, 379. C31H29O2P (464.6): calcd. C 80.15, H 6.30; found C
79.66, H 6.40.
ν˜ ϭ 3060 cmϪ1, 3020, 2980, 2900, 1700, 1600 (CO), 1440, 1310,
1290, 1100. H NMR (2 rotamers): δ ϭ 7.64Ϫ7.44 (m, 15 H, Ph),
4.03/3.70 (br. s, 2 H, CH2CH3), 2.49 (m, 2 H, CH2), 2.28Ϫ2.20 (m,
2 H, CH2), 2.00 (s, 3 H, COMe), 1.25/0.44 (br. s, 3 H, CH2CH3)
ppm. 13C NMR: See Table 6. 31P NMR: δ ϭ ϩ22.5 ppm. MS: m/
z ϭ 418 [Mϩ], 373, 361. C26H27O3P (418.5): calcd. C 74.62, H 6.51;
found C 74.97, H 6.71.
1
Addition of Alkoxycarbonyl Ylides to Vinyl Ketones: The appropri-
ate vinyl ketone (20.0 mmol) was added to a solution of the appro-
priate alkoxycarbonyl ylide (20.0 mmol) in dichloromethane
(250 mL) and the mixture was heated under reflux for 36 h. The
solvents were evaporated from the solution and the residue recrys-
tallised from ethyl acetate to give the products as follows:
Ethyl 5-Oxo-2-(triphenylphosphoranylidene)heptanoate (5d): From
(ethoxycarbonylmethylene)triphenylphosphorane and ethyl vinyl
ketone (7.4 g, 86%) as colourless crystals, m.p. 117 °C. IR (KBr):
ν˜ ϭ 3060 cmϪ1, 3020, 2980, 2920, 1700, 1610 (CO), 1440, 1310,
1290, 1100, 1090. 1H NMR (2 rotamers): δ ϭ 7.64Ϫ7.46 (m, 15 H,
Ph), 4.05/3.70 (br. s, 2 H, OCH2CH3), 2.50Ϫ2.22 (m, 6 H,
CH2CH2, COCH2CH3), 0.93 (t, J ϭ 7 Hz, 3 H, COCH2CH3), 1.20/
0.44 (br. s, 3 H, OCH2CH3) ppm. 13C NMR: See Table 6. 31P
NMR: δ ϭ ϩ23.6/22.5 ppm. MS: m/z ϭ 432 [Mϩ], 387, 361.
C27H29O3P (432.5): calcd. C 74.98, H 6.76; found C 75.11, H 6.52.
Methyl 5-Oxo-2-(triphenylphosphoranylidene)hexanoate (5a): From
(methoxycarbonylmethylene)triphenylphosphorane and methyl vi-
nyl ketone (7.4 g, 91%) as colourless crystals, m.p. 147 °C. IR
(KBr): ν˜ ϭ 3040 cmϪ1, 2920, 2890, 1700, 1630 (CO), 1470, 1430,
1
1120, 1090. H NMR (2 rotamers): δ ϭ 7.64Ϫ7.45 (m, 15 H, Ph),
3.58/3.11 (s, 3 H, OMe), 2.52Ϫ2.25 (m, 4 H, CH2CH2), 2.00/1.93
(s, 3 H, COMe) ppm. 13C NMR: See Table 6. 31P NMR: δ ϭ
ϩ22.6/22.0 ppm. MS: m/z ϭ 404 [Mϩ]. C25H25O3P (404.5): calcd.
C 74.24, H 6.23; found C 74.58, H 6.34.
844
Eur. J. Org. Chem. 2003, 840Ϫ847

β,δЈ-Dioxo-Stabilised Phosphorus Ylides
FULL PAPER
137.5 (2 C), 129.1, 122.8, 117.0, 20.8 ppm. Methyl Vinyl Ketone:
1H and 13C NMR as in FVP of 3a. But-1-yne (15d): Possibly.
Flash Vacuum Pyrolysis of Ylides 3 and 5: The apparatus used was
as described previously.[22] All pyrolyses were conducted at pres-
sures in the range 10Ϫ2 to 10Ϫ1 Torr and were complete within 2 h.
Under these conditions the contact time in the hot zone was estim-
ated to be about 10 ms. In all cases Ph3PO collected at the furnace
exit and the more volatile products were recovered from the cold
trap. Yields were determined either by isolation or, for small-scale
FVP of 1-Phenyl-2-(triphenylphosphoranylidene)hexane-1,5-dione
(3f): FVP of the ylide 3f (56 mg) at 650 °C gave a solid at the
furnace exit which was shown to be Ph3PO by 31P NMR spectro-
scopy. The liquid in the cold trap consisted of three products. 6-
Phenylhex-5-yn-2-one (14f): 16%. IR: ν˜ ϭ 1721 cmϪ1 1H NMR:
.
1
experiments, by calibration of the H NMR spectra by adding an
δ ϭ 7.55Ϫ7.25 (m, 5 H), 2.80Ϫ2.65 (m, 4 H), 2.21 (s, 3 H). 13C
NMR: δ ϭ 191.5 (CO), 131.6 (Ph C-2, C-6), 128.3 (Ph C-3, C-
5), 128.2 (Ph C-4), 84.0 (ϵCϪ), 77.2 (ϵCϪ), 42.5 (COCH2), 30.0
(COMe), 14.0 (ϵCϪCH2) [signal for Ph C-1 not apparent] ppm.
Methyl Vinyl Ketone: 29%. 1H and 13C NMR as in FVP of 3a.
Ethynylbenzene (15f): 10%. 1H NMR: δ ϭ 7.55Ϫ7.31 (m, 5 H), 3.09
(s, 1 H) ppm. 13C NMR: δ ϭ 132.1 (C-2, C-6), 128.8 (C-4), 128.3
(C-3, C-5), 122.3 (C-1), 83.6 (ϵCϪ), 77.1 (ϵCH) ppm.
accurately weighed quantity of a solvent such as CH2Cl2 and com-
paring integrals, a procedure estimated to be accurate to within
Ϯ10%.
FVP of 3-(Triphenylphosphoranylidene)heptane-2,6-dione (3a): FVP
of the title ylide 3a (5.0 g) at 650 °C gave a solid at the furnace exit
which was shown to be Ph3PO by 31P NMR spectroscopy. The
liquid in the cold trap consisted of three compounds. Methyl Vinyl
1
Ketone (2a): 32%. H NMR: δ ϭ 6.32 (half AB pattern of d, J ϭ
FVP of 1-Phenyl-2-(triphenylphosphoranylidene)heptane-1,5-dione
(3g): FVP of the title ylide 3g (16.2 mg) at 650 °C gave a solid
at the furnace exit which was shown to be Ph3PO by 31P NMR
spectroscopy. The liquid in the cold trap contained three products.
Ethyl Vinyl Ketone: 36%. 1H and 13C NMR as in FVP of 3b. Ethyn-
18, 10 Hz, 1 H), 6.21 (half AB pattern of d, J ϭ 18, 2 Hz, 1 H),
5.92 (dd J ϭ 10, 2 Hz, 1 H), 2.29 (s, 3 H). 13C NMR: δ ϭ 199.1,
137.4, 129.1, 26.4 ppm. Propyne (15a): 1H NMR: δ ϭ 1.82 (s, 4 H)
ppm. 13C NMR: δ ϭ 80.0 (ϵCϪ), 67.4 (ϵCH), 3.2 ppm. Hept-5-
yn-2-one (14a): Kugelrohr distillation gave 14a (0.37 g, 26%) as a
colourless oil. IR: ν˜ ϭ 1718 cmϪ1. 1H NMR: δ ϭ 2.63 (t, J ϭ 7 Hz,
2 H), 2.38 (t of q, J ϭ 7, 2 Hz, 2 H), 2.17 (s, 3 H), 1.75 (t, J ϭ
2 Hz, 3 H) ppm. 13C NMR: δ ϭ 207.4 (CO), 77.7 (ϵCϪ), 76.2
(ϵCϪ), 42.9 (COCH2), 29.9 (COMe), 13.4 (ϵCϪCH2), 3.4
(ϵCϪMe) ppm. MS (CI): m/z ϭ (%) ϭ 111 (100) [M ϩ Hϩ], 97
(10), 85 (6). C7H11O [M ϩ Hϩ]: calcd. 111.0810; found 111.0814
(MS). The pyrolysis was repeated as above but at 500 °C (99.5 mg)
and gave 14a (10%), 2a (14%) and 15a while at 750 °C (43.1 mg)
the products were 14a (33%), 2a (28%) and 15a.
1
ylbenzene: 42%. H and 13C NMR as in FVP of 3f. 7-Phenylhept-
6-yn-3-one (14g): 20%. 1H NMR: δ ϭ 7.60Ϫ7.25 (m, 5 H),
2.75Ϫ2.45 (m, 6 H), 1.09 (t, J ϭ 7 Hz, 3 H) ppm.
FVP of Methyl 5-Oxo-2-(triphenylphosphoranylidene)hexanoate
(5a): FVP of the title ylide 5a (56.4 mg) at 650 °C gave a solid
at the furnace exit which was shown to be Ph3PO by 31P NMR
spectroscopy. The liquid in the cold trap contained one product.
Methyl 3-Methyl-2-methylenebut-3-enoate (20a): 47% as a yellow
liquid. 1H NMR: δ ϭ 5.93, 5.64, 5.27, 5.12 (4 ϫ s, 4 ϫ 1 H, ϭ
CH2), 3.80 (s, 3 H, OMe), 1.95 (s, 3 H, CϪMe) ppm. 13C NMR:
See Table 7. C7H10O2: calcd. 126.0681; found 126.0684 (MS). Reac-
tion of 5a on a larger scale (1.07 g) at 700 °C gave 20a (0.20 g,
60%) as a yellow liquid. Attempted kugelrohr distillation of 20a
from a repeat preparation caused dimerisation to yield a 1:1 mix-
ture: Dimethyl 4-Methyl-1-isopropenylcyclohex-3-ene-1,3-dicarb-
oxylate (21a) and Dimethyl 3-Methyl-1-isopropenylcyclohex-3-ene-
1,4-dicarboxylate (22a): 14% as a colourless liquid, b.p. 160Ϫ170
°C/20 Torr. IR: ν˜ ϭ 1690 cmϪ1, 1630, 1060, 890. 1H NMR: δ ϭ
4.98 (s, 1 H), 4.85 (s, 1 H), 3.72 (s, 3 H), 3.69 (s, 3 H), 2.8Ϫ2.2 (m,
6 H), 2.10 (s, 3 H), 1.75 (s, 3 H) ppm. 13C NMR: δ ϭ 175.0, 169.6,
145.1, 144.8, 122.8, 112.1 (ϭCH2), 52.2, 51.2, 50.6, 47.0, 40.8, 34.6,
27.9, 26.1, 24.7, 24.1, 21.7, 19.7 ppm. MS: m/z (%) ϭ 252 (11)
[Mϩ], 220 (65), 193 (50), 161 (100), 133 (86), 121 (82), 93 (80).
C14H20O4: calcd. 252.1362; found 252.1370 (MS).
FVP of 3-(Triphenylphosphoranylidene)octane-2,6-dione (3b): FVP
of the title ylide 3b (36.9 mg) at 650 °C gave a solid at the furnace
exit which was shown to be Ph3PO by 31P NMR spectroscopy. The
liquid in the cold trap consisted of three products. Oct-6-yn-3-one
(14b): 39%. 1H NMR: δ ϭ 2.47 (q, J ϭ 7 Hz, 2 H, CH2CH3),
2.6Ϫ2.35 (m, 4 H, CH2CH2), 1.74 (t, J ϭ 2 Hz, 3 H, COMe), 1.07
(t, J ϭ 7 Hz, 3 H, CH2CH3) ppm. 13C NMR: δ ϭ 209.9 (CO), 77.8
(ϵCϪ), 76.0 (ϵCϪ), 41.5 (COCH2CH2), 36.0 COCH2CH3), 13.4
(ϵCϪCH2), 7.7 (CH2Me), 3.4 (ϵCϪMe) ppm. Ethyl Vinyl Ketone
(4b): 49%. 1H NMR: δ ϭ 6.44 (half AB pattern of d, J ϭ 18, 10 Hz,
1 H), 6.23 (half AB pattern of d, J ϭ 18, 2 Hz, 1 H), 5.85 (dd, J ϭ
10, 2 Hz, 1 H), 2.63 (q, J ϭ 7 Hz, 2 H), 1.13 (t, J ϭ 7 Hz, 3 H)
ppm. 13C NMR: δ ϭ 202.0, 136.4, 127.8, 32.8, 7.9 ppm. Propyne:
1H and 13C NMR as in FVP of 3a.
FVP of 1-(4-Methoxyphenyl)-4-(triphenylphosphoranylidene)hexane-
1,5-dione (3c): FVP of the title ylide 3c (77 mg) at 650 °C gave a
solid at the furnace exit which was shown to be Ph3PO by 31P
NMR spectroscopy. The liquid in the cold trap contained two prod-
ucts. 4-Methoxyacrylophenone (2c): 79%. 1H NMR: δ ϭ 7.97 (d,
J ϭ 5 Hz, 2 H), 7.19 (dd, J ϭ 18, 10 Hz, 1 H), 6.97 (d J ϭ 5 Hz,
2 H), 6.44 (dd, J ϭ 18, 2 Hz, 1 H), 5.85 (dd, J ϭ 10, 2 Hz, 1 H),
3.87 (s, 3 H) ppm. 13C NMR: δ ϭ 189.3 (CO), 163.6 (Ar-C-4),
132.2 (ϭCH2), 131.1 (2 C, Ar-C-2, C-6), 129.3 (COCHϭ), 126.5
Table 7. 13C NMR spectra of dienes 20
Com- CO
pound
ϭCϽ
ϭCH2
R1 signals R2 signals
20a
20b
20c
20d
167.8 142.6, 139.8 122.8, 117.0 52.0
167.6 146.9, 142.5 124.0, 114.3 52.0
167.3 142.9, 139.8 122.4, 116.9 60.9, 14.2 21.4
21.4
27.5, 12.5
1
(Ar-C-1), 113.9 (2 C, Ar-C-3, C-5), 55.5 (OMe) ppm. Propyne: H
167.2 147.0, 142.9 123.5, 114.2 60.9, 14.2 27.4, 12.6
and 13C NMR as in FVP of 3a.
FVP of 4-(Triphenylphosphoranylidene)octane-3,7-dione (3d): FVP
of the title ylide 3d (15.2 mg) at 650 °C gave a solid at the furnace
exit which was shown to be Ph3PO by 31P NMR spectroscopy. The
liquid in the cold trap appeared to consist of three products. 5-
FVP of Methyl 5-Oxo-2-(triphenylphosphoranylidene)heptanoate
(5b): FVP of the title ylide 5b (800 mg) at 650 °C gave a solid
at the furnace exit which was shown to be Ph3PO by 31P NMR
spectroscopy. The liquid in the cold trap proved to be: Methyl 2,3-
Methyl-4-methylenehexa-1,5-dien-3-one (18): 1H NMR:
δ ϭ
6.95Ϫ6.80 (m, 2 H), 6.65Ϫ6.55 (m, 1 H), 5.94, 5.65, 5.28, 5.14 (4 Dimethylenepentanoate (20b): 160 mg, 60% as a colourless liquid.
ϫ s, 4 ϫ 1 H), 1.93 (m, 3 H) ppm. 13C NMR: δ ϭ 196.4, 142.6, 1H NMR: δ ϭ 6.02, 5.65, 5.16, 5.09 (4 ϫ s, 4 ϫ 1 H, ϭCH2), 3.79
Eur. J. Org. Chem. 2003, 840Ϫ847
845

R. A. Aitken, N. A. Al-Awadi, H. J. Bestmann et al.
FULL PAPER
(s, 3 H), 2.30 (q, J ϭ 8 Hz, 2 H), 1.05 (t, J ϭ 8 Hz, 3 H) ppm. 13C 134Ϫ137 °C. 1H NMR (CD3COCD3): δ ϭ 3.70 (s, 3 H), 3.15Ϫ3.02
NMR: See Table 7. C8H12O2: calcd. 140.0837; found 140.0840 (m, 2 H), 2.90Ϫ2.50 (m, 4 H), 2.45Ϫ2.30 (q, J ϭ 7 Hz, 2 H), 1.05
(MS). Attempted kugelrohr distillation of 20b caused dimerisation (t, J ϭ 7 Hz, 3 H) ppm. 13C NMR: (CD3COCD3): δ ϭ 174.5, 174.4
to yield a 1:1 mixture: Dimethyl 1-(But-1-en-2-yl)-3-ethylcyclohex-
3-ene-1,4-dicarboxylate (21b) and Dimethyl 1-(But-1-en-2-yl)-4-
ethylcyclohex-3-ene-1,3-dicarboxylate (22b): 12% as a colourless li-
(2 ϫ anhydride CϭO), 167.0 (ester CO), 150.7 (CϭC), 122.8 (Cϭ
C), 51.4 (OMe), 39.8 (2 C), 32.3, 28.6, 28.0 (CH2Me), 13.1
(CH2Me) ppm. MS: m/z (%) ϭ 238 (2) [Mϩ], 225 (26), 224 (100),
quid, b.p. 100 °C/0.1 Torr. MS: m/z ϭ (%) ϭ 280 (14) [Mϩ], 248 206 (84), 179 (35), 133 (35), 107 (50), 105 (50). C12H14O5 (238.3):
(82), 221 (40), 192 (65), 189 (85), 135 (100). C16H24O4 calcd. calcd. C 60.50, H 5.93; found C 60.76, H 5.91.
280.1675; found 280.1678 (MS).
cis-1-Ethoxycarbonyl-2-methylcyclohexene-4,5-dicarboxylic Anhyd-
FVP of Ethyl 5-Oxo-2-(triphenylphosphoranylidene)hexanoate (5c):
ride 23c from Ylide 5c: 216 mg, 38% as colourless crystals, m.p.
FVP of the title ylide 5c (29.6 mg) at 650 °C gave a solid at the 133Ϫ135 °C. 1H NMR (CD3COCD3): δ ϭ 4.20Ϫ4.10 (q, J ϭ 7 Hz,
furnace exit which was shown to be Ph3PO by 31P NMR spectro-
scopy. The liquid in the cold trap was: Ethyl 3-Methyl-2-methyl-
2 H), 3.15Ϫ3.05 (m, 2 H), 2.90Ϫ2.50 (m, 4 H), 2.07 (s, 3 H), 1.28
(t, J ϭ 7 Hz, 3 H) ppm. 13C NMR: (CD3COCD3): δ ϭ 174.6, 174.4
enebut-3-enoate (20c): 40%. 1H NMR: δ ϭ 5.93, 5.62, 5.30, 5.12 (4 (2 ϫ anhydride CϭO), 167.0 (ester CO), 145.2 (CϭC), 123.5 (Cϭ
ϫ s, 4 ϫ 1 H, ϭCH2), 4.25 (q, J ϭ 8 Hz, 2 H), 1.95 (s, 3 H), 1.32 C), 60.5 (OCH2Me), 39.9, 39.8, 34.8, 28.1, 21.7 (ϭCMe), 14.6
(t, J ϭ 8 Hz, 3 H). 13C NMR: see Table 7. C8H12O2: calcd. (OCH2Me) ppm. MS: m/z (%) ϭ 238 (57) [Mϩ], 165 (94), 99 (55),
140.0837; found 140.0843 (MS). Reaction of 5c on a larger scale
(1.39 g) at 500 °C gave 20c (0.11 g, 24%) as a colourless liquid while
using 5c (1.60 g) at 700 °C gave 20c (0.27 g, 50%). Attempted kugel-
rohr distillation of 20c caused dimerisation to yield a 1:1 mixture:
Diethyl 3-Methyl-1-(propen-2-yl)cyclohex-3-ene-1,4-dicarboxylate
(21c) and Diethyl 4-Methyl-1-(propen-2-yl)cyclohex-3-ene-1,3-di-
carboxylate (22c): MS: m/z (%) ϭ 280 (11) [Mϩ], 234 (60), 207 (42),
161 (100), 133 (60), 121 (56), 93 (65). C16H24O4: calcd. 280.1675;
found 280.1668 (MS).
93 (100). C12H14O5: calcd. 238.0841; found 238.0850 (MS).
cis-1-Ethoxycarbonyl-2-ethylcyclohexene-4,5-dicarboxylic Anhydride
23d from Ylide 5d: 175 mg, 30% as colourless crystals, m.p.
148Ϫ150 °C. 1H NMR (CD3COCD3): δ ϭ 4.15 (q, J ϭ 7 Hz, 2
H), 3.05 (m, 2 H), 2.8Ϫ2.3 (m, 6 H), 1.26 (t, J ϭ 7 Hz, 3 H), 1.00
(t, J ϭ 7 Hz, 3 H) ppm. 13C NMR (CD3COCD3): δ ϭ 174.7, 174.5
(2 ϫ anhydride CO), 166.7 (ester CO), 150.1 (CϭC), 123.1 (CϭC),
60.6 (OCH2), 39.9 (2 C), 32.4, 28.7, 28.0 (CH2Me), 14.7
(OCH2Me), 13.3 (CH2Me) ppm. MS: m/z (%) ϭ 252 (2) [Mϩ], 206
(100), 179 (20), 151 (22), 133 (35), 105 (42). C13H16O5 (252.3):
calcd. C 61.89, H 6.40; found C 61.65, H 6.36.
FVP of Ethyl 5-Oxo-2-(triphenylphosphoranylidene)heptanoate (5d):
FVP of the title ylide 5d (14.1 mg) at 650 °C gave a solid at the
furnace exit which was shown to be Ph3PO by 31P NMR spectro-
scopy. The liquid in the cold trap was: Ethyl 2,3-Dimethylenepen-
Kinetic Studies
1
tanoate (20d): 41%. H NMR: δ ϭ 6.00, 5.63, 5.16, 5.08 (4 ϫ s, 4
Reaction Setup: Preliminary kinetic results were obtained with a
system featuring a Eurotherm 093 pyrolysis unit coupled to a
PerkinϪElmer Sigma 115 Gas Chromatograph. The kinetic data
reported are from a reactor setup including an HPLC (BioRad
Model 2700) fitted with a UV/Vis detector (BioRad Model 1740)
adjusted to 254 nm; HPLC column LC-8, 25 cm, 4.6µm (Supelco);
and CDS custom-made pyrolysis unit for the thermolysis reactions.
The pyrolysis tube is jacketed by an insulating aluminum block
fitted with a platinum resistance thermometer and a thermocouple
connected to a Comark microprocessor thermometer.
ϫ 1 H, ϭCH2), 4.25 (q, J ϭ 8 Hz, 2 H, OCH2CH3), 2.30 (q, J ϭ
8 Hz, 2 H, C-CH2CH3), 1.31 (t, J ϭ 8 Hz, 3 H, OCH2CH3), 1.06
(t, J ϭ 8 Hz, 3 H, C-CH2CH3) ppm. 13C NMR: see Table 7.
C9H14O2: calcd. 154.0994; found 154.0989 (MS). Reaction of 5d on
a larger scale (1.03 g) at 500 °C gave 20d (0.062 g, 17%) as a colour-
less liquid while using 5d (1.19 g) at 700 °C gave 20d (0.19 g, 44%).
Attempted kugelrohr distillation of 20d caused dimerisation to
yield a 1:1 mixture: Diethyl 1-(But-1-en-2-yl)-3-ethylcyclohex-3-ene-
1,4-dicarboxylate (21d) and Diethyl 1-(But-1-en-2-yl)-4-ethylcyclo-
hex-3-ene-1,3-dicarboxylate (22d): MS: m/z (%) ϭ 308 (10) [Mϩ],
262 (65), 235 (28), 192 (60), 189 (80), 154 (48), 135 (100). C18H28O4:
calcd. 308.1988; found 308.1994 (MS).
Kinetic Runs and Data Analysis: Aliquots (0.2 mL) of very dilute
solutions (ppm) of neat substrates in acetonitrile as solvent and
chlorobenzene as internal standard were pipetted into the reaction
tube, which was then sealed under vacuum (0.2 Torr). The tube was
then placed inside the pyrolyzer for 600 s at a temperature at which
10Ϫ20% pyrolysis is deemed to occur. The contents of the tube
were analyzed using HPLC. At least three kinetic runs were carried
out for each 5Ϫ10 °C rise in temperature of the pyrolyzer and for
the same time interval until 90Ϫ95% pyrolysis was achieved. The
reactions were ascertained to be homogeneous, unimolecular, and
free of reactor surface effects. The homogeneous nature of the reac-
tions was tested by comparing rates using a normal reactor with
those obtained when the reactor vessel was packed with helices.
The absence of free radical pathways in the elimination reactions
was confirmed using established procedures. The rates were mon-
itored over a temperature range of 20 to 40 K, and the rate coeffi-
cients were calculated using the expression for a first-order reac-
tion, kt ϭ ln(ao/a) (Table 8). Each rate coefficient represents the
mean of three kinetic runs in agreement to within Ϯ2%. The
Arrhenius parameters were obtained from a plot of log k against
1/T [K]. The Arrhenius plots are linear up to about 95% reaction.
Diels؊Alder Reaction of Dienes 20 with Maleic Anhydride: FVP of
the appropriate ylide 5 (1.0 g, ca. 2.4 mmol) was completed as usual
at 650 °C. The liquid in the cold trap was quickly dissolved in dry
toluene (2 mL) and a solution of maleic anhydride (0.24 g,
2.4 mmol) in toluene (8 mL) was added. The solution was heated
under reflux for 2 h and then concentrated to yield a pale brown
liquid, which crystallised. Recrystallisation from ethyl acetate and
a small amount of diethyl ether gave the products as follows.
cis-1-Methoxycarbonyl-2-methylcyclohexene-4,5-dicarboxylic An-
hydride 23a from Ylide 5a: 177 mg, 32% as colourless crystals, m.p.
1
129Ϫ132 °C. H NMR (CD3COCD3): δ ϭ 3.70 (s, 3 H), 3.08 (m,
2 H), 2.95Ϫ2.50 (m, 4 H), 2.05 (s, 3 H). 13C NMR: (CD3COCD3):
δ ϭ 174.3 (2 ϫ anhydride CO), 166.9 (ester CO), 145.6 (CϭC),
123.1 (CϭC), 51.4 (OMe), 39.81, 39.78, 34.8, 28.1, 21.7 (Me). MS:
m/z (%) ϭ 224 (6) [Mϩ], 210 (100), 192 (85), 165 (50), 151 (46), 119
(30), 93 (75), 91 (60). C11H12O5: calcd. 224.0685; found 224.0679
(MS).
cis-2-Ethyl-1-methoxycarbonylcyclohexene-4,5-dicarboxylic Anhyd-
ride 23b from Ylide 5b: 228 mg, 40% as colourless crystals, m.p. Rate constants adjusted to 400 K are given in Table 5.
846 Eur. J. Org. Chem. 2003, 840Ϫ847

β,δЈ-Dioxo-Stabilised Phosphorus Ylides
FULL PAPER
Table 8. Kinetic data for the gas-phase elimination reaction of selected ylides 3 and 5
R1
R2
104k [sϪ1
T [K]
]
log10A [sϪ1
]
Ea [kJ·molϪ1
]
3a
3b
3f
Me
Me
Ph
Ph
Me
Me
Et
Me
Et
1.04
409.05
3.94
442.25
2.16
481.10
1.21
470.35
1.69
458.05
1.36
461.95
3.35
456.75
1.76
3.04
419.65
6.04
450.05
5.51
492.95
2.07
479.95
3.70
467.05
4.12
472.35
4.75
461.90
2.57
5.38
428.15
9.24
457.25
12.27
504.90
6.30
490.50
8.91
476.80
8.13
482.20
8.14
470.15
4.51
472.35
10.78
438.35
14.90
464.85
36.74
516.90
11.90
501.05
14.84
484.85
14.20
491.75
11.95
476.10
12.52
30.21
453.15
10.79 Ϯ 0.51
8.46 Ϯ 0.39
13.79 Ϯ 0.88
12.30 Ϯ 0.94
12.63 Ϯ 0.68
11.86 Ϯ 1.04
10.10 Ϯ 0.02
10.96 Ϯ 1.06
115.34 Ϯ 4.21
100.59 Ϯ 3.35
160.94 Ϯ 8.39
146.19 Ϯ 8.79
143.64 Ϯ 6.22
138.52 Ϯ 9.66
118.74 Ϯ 1.66
128.59 Ϯ 9.66
Me
Et
3g
5a
5b
5c
5d
20.90
510.75
24.54
493.40
24.59
501.40
21.52
485.65
26.56
494.95
Me
Et
Me
Et
Et
454.20
462.90
483.75
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