Synthesis, thermal reactivity and kinetics of substituted [(benzoyl)(phenylcarbamoyl)methylene]triphenylphosphoranes and their thiocarbamoyl analogues

Article abstract of DOI:10.1016/j.tet.2004.10.058

A range of 16 substituted benzoyl/arylcarbamoyl and benzoyl/ arylthiocarbamoyl stabilised ylides have been prepared. They are found under conditions of flash vacuum pyrolysis to fragment giving a benzoyl ylide and aryl isocyanate or isothiocyanate accompanied in some cases by secondary pyrolysis products. Kinetic studies show the thiocarbamoyl ylides to react consistently faster than their carbamoyl analogues and substituent effects suggest a polar cyclic transition state, which involves attack by the benzoyl oxygen on the carbamoyl/thiocarbamoyl NH. Graphical Abstract.

Full text of DOI:10.1016/j.tet.2004.10.058

Tetrahedron 61 (2005) 129–135
Synthesis, thermal reactivity and kinetics of substituted
[(benzoyl)(phenylcarbamoyl)methylene]triphenylphosphoranes
and their thiocarbamoyl analogues
b,
a
b
R. Alan Aitken,a, Nouria A. Al-Awadi, Graham Dawson, Osman M. E. El-Dusouqi,
*
*
Dorcas M. M. Farrell,a Kamini Kaulb and Ajith Kumarb
aSchool of Chemistry, University of St Andrews, North Haugh, St Andrews, Fife KY16 9ST, UK
bDepartment of Chemistry, Kuwait University, PO Box 5969, Safat 13060, Kuwait
Received 4 August 2004; revised 20 September 2004; accepted 14 October 2004
Available online 5 November 2004
Abstract—A range of 16 substituted benzoyl/arylcarbamoyl and benzoyl/arylthiocarbamoyl stabilised ylides have been prepared. They are
found under conditions of flash vacuum pyrolysis to fragment giving a benzoyl ylide and aryl isocyanate or isothiocyanate accompanied in
some cases by secondary pyrolysis products. Kinetic studies show the thiocarbamoyl ylides to react consistently faster than their carbamoyl
analogues and substituent effects suggest a polar cyclic transition state, which involves attack by the benzoyl oxygen on the
carbamoyl/thiocarbamoyl NH.
q 2004 Elsevier Ltd. All rights reserved.
1. Introduction
2. Results and discussion
In 1959 Trippett and Walker reported that stabilised
phosphorus ylides of structure 1 react with phenyl
isocyanate to form the carbamoyl stabilised ylides 2.1
There have since been several reports of the formation of
such adducts between a variety of ylides and both
isocyanates2,3 and isothiocyanates.4–7 Where R contains a
carbonyl group, these are known to exhibit intramolecular
hydrogen bonding as shown in structure 3.2–4,6 Apart from a
brief note that compounds 4 revert to their starting
components upon heating in boiling toluene,8 there has
been no systematic study of the thermal reactivity of these
compounds. In view of our long-standing interest in
synthetic applications of flash vacuum pyrolysis of stabil-
ised phosphorus ylides,9,10 we were interested to examine
these compounds where the functional groups present could
lead to several conceivable routes for thermal decompo-
sition. In this paper, we describe the synthesis of a range of
substituted benzoyl aryl(thio)carbamoyl ylides, a study of
their pyrolysis behaviour and detailed kinetic measure-
ments, almost the first for phosphorus ylides,11 which
provide evidence in support of the proposed reaction
mechanism.
A series of 16 ylides 8–23 were prepared by reacting
benzoylmethylenetriphenylphosphorane 5a or ring-substi-
tuted analogues 5b–e with aryl isocyanates 6a–e, and
isothiocyanates 7a–e (Scheme 1). The combinations were
chosen so as to examine the effects that electron-donating
and electron-withdrawing substituents in the para position
of each ring would have on the kinetics. All products were
obtained as stable crystalline solids and gave the expected
analytical and spectroscopic data, although it should be
noted that the melting points recorded for ylides 13, 15 and
17 differed markedly from the values reported in an early
paper4 for samples characterised only by elemental analysis.
In agreement with this paper, we found that the ylides 5b
and 5c with electron-withdrawing substituents failed to
react with phenyl isothiocyanate. As we have reported for
other classes of stabilised ylides, the 13C NMR spectra
formed a highly informative and regular pattern (Table 3,
Section 3) with ArNHCO giving signals in the range dC
167–169 (d, JP–CZ10 Hz), while for ArNHCS this moved
to dC 189–190 (d, JP–CZ17–18 Hz). In the light of our
previous work,12 the fact that both these coupling constants
and the value to ArCO (16–22 Hz) are R10 Hz means that
thermal extrusion of Ph3PO or Ph3PS is unlikely.
A clue to the likely pyrolysis behaviour was provided by the
mass spectra of the compounds, which in most cases showed
Keywords: Ylides; Pyrolysis; Kinetics; Substituent effects.
* Corresponding authors. E-mail: raa@st-and.ac.uk
0040–4020/$ - see front matter q 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2004.10.058

130
R. A. Aitken et al. / Tetrahedron 61 (2005) 129–135
Scheme 3.
secondary reaction with extrusion of Ph3PO to give
phenylacetylene. Under FVP conditions a temperature of
over 650 8C is usually required for this process.13 The
substantial extent of extrusion here at 500 8C is presumed to
beduetothe formationof5ainanactivatedstatefollowing the
isocyanate elimination. For the thiocarbamoyl ylide 13 the
situation is somewhat simpler: the same type of electrocyclic
process gives PhNCS and the enol form of ylide 5a, which are
now isolated as the major products together with small
amounts of Ph3PO from decomposition of 5a, and Ph3PS
formed by an unknown route. Despite the slight complication
of secondary processes it seems clear that the primary thermal
reaction for all these compounds is dissociation into the
compounds 5 and 6 or 7 from which they were formed.
We now sought additional evidence in support of the
proposed mechanism from kinetic measurements. If, as
shown in Schemes 2 and 3, the initial step is nucleophilic
attack of the keto oxygen on the carbamoyl or thiocarba-
moyl NH, substituents on the ArCO ring should have a
marked effect on the reaction rate whereas substituents on
the ArNH ring should not affect the rate greatly. In addition,
it is of interest to compare the rates for XZO and XZS.
Kinetic studies were performed using a sealed glass tube
reactor over the range 330–440 K as detailed in Section 3.
The resulting rates and Arrhenius parameters are shown in
Table 4. Rate constants adjusted to 400 K are shown in
Tables 1 and 2. Two points are immediately apparent from
these results. In all cases, the reactions for the thiocarba-
moyl ylides are considerably faster than for the correspond-
ing carbamoyl ylides. In addition, while varying the
substituent on the ArNH ring has no significant effect on
the rates (Table 1), variation of the substituent on the ArCO
Scheme 1.
prominent loss of ArNCO or ArNCS. This was confirmed
when the reactivity of the two parent compounds 8 and
13 was examined using flash vacuum pyrolysis. Both
compounds were found to react completely at 500 8C and
10K2 Torr and the products are shown in Schemes 2 and 3
respectively. For ylide 8 the electrocyclic process shown
leads to PhNCO and the enol form of ylide 5a. The situation
is complicated by the fact that the latter can then undergo
Table 1. Rate constants and relative rates at 400 K in the gas phase (R1ZH)
R2
XZO 104k (sK1
)
XZS 102k (sK1
)
krel Z kkððXXZZOSÞÞ
H
4-NO2
4-Cl
4-Me
4-OMe
3.69
5.41
6.11
4.32
7.12
1.34
1.08
1.34
2.35
2.32
36
20
22
54
33
Table 2. Rate constants and relative rates at 400 K in the gas phase (R2ZH)
R1
XZO 104k (sK1
)
XZS 102k (sK1
)
krel Z kkððXXZZOSÞÞ
H
4-NO2
4-Cl
4-Me
4-OMe
3.69
0.90
3.42
16.42
16.18
1.34
—
—
3.10
4.53
36
—
—
19
28
Scheme 2.

R. A. Aitken et al. / Tetrahedron 61 (2005) 129–135
131
ring has the effect predicted from the mechanisms of
3. Experimental
Schemes 2 and 3, with electron-withdrawing groups
reducing the rate and electron-donating groups increasing
it (Table 2). The difference between carbamoyl and
thiocarbamoyl ylides is most likely due to the former
existing to a greater extent in the phosphonium enolate form
24 in which the C–C bond to be broken in the fragmentation
is a double bond. Due to the lower electronegativity of
sulfur, this form is likely to be less significant for the
thiocarbamoyl ylides, a fact also supported by the higher
values of JP–C, thus leading to more rapid fragmentation.
Melting points were recorded on a Reichert hot-stage
microscope and are uncorrected. Infra red spectra were
recorded as Nujol mulls on a Perkin Elmer 1420 instrument.
NMR spectra were obtained for 1H at 300 MHz and for 13
C
at 75 MHz using a Bruker AM300 instrument and for 31P at
121 MHz using a Varian Gemini 2000 instrument. All
spectra were run as solutions in CDCl3, unless otherwise
stated, with internal Me4Si as reference for 1H and 13C and
external 85% H3PO4 for 31P. Chemical shifts are reported in
ppm to high frequency of the reference and coupling
constants J are in Hz. Mass spectra were obtained on an
AEI/Kratos MS-50 spectrometer using electron impact at
70 eV.
The benzoyl ylides 5 were prepared by the reported
method,18 and the aryl isocyanates 6a–e and isothiocyanates
7a–e were commercially available.
The molecularity, order and homogeneous nature of the
reaction, as well as the Arrhenius parameters and product
analysis combine to suggest a concerted transition state for
the thermal elimination reaction of these ylides (Scheme 2).
The relative contribution to the molecular reactivity of each
of the three bonds involved in the electron flow described by
the curved arrows in Scheme 2 has been documented in
earlier studies,14,15 where it was noted that any one of these
bonds could be the prime contributor to molecular
reactivity, or that the overall reactivity could be a product
of synergism between two or all three bonds. Non-
synchronous bond breaking would explain the polarity of
the cyclic transition state, and an effective relative
contribution from a particular bond might, under favourable
structural constraints, lead to a linear Hammett corre-
lation.16,17 As shown in Figure 1, this is indeed the case and
the data show a reasonably good Hammett relationship with
values of rZK1.2 for XZO and rZK2.1 for XZS. In
Scheme 2, the protophilicity of the C]O bond depends on
the electronic effect of a substituent on the PhCO ring and an
electron-donating group will enhance the protophilicity
toward NH.
3.1. General procedure for synthesis of ylides 8–23
A solution of the ylide 5 (5 mmol) in CH2Cl2 (50 cm3) was
stirred at RT while a solution of the appropriate isocyanate 6
or isothiocyanate 7 (5 mmol) in CH2Cl2 (10 cm3) was added
dropwise. After 2 h the mixture was evaporated and the
residue recrystallised from ethyl acetate. In this way the
following compounds were prepared:
3.1.1. [(Benzoyl)(phenylcarbamoyl)methylene]triphenyl-
phosphorane 8. From 5a and 6a as colourless crystals
(89%), mp 215–217 8C (lit.,1 189 8C) (Found: C, 79.3; H,
5.4; N, 2.8. C33H26NO2P requires C, 79.3; H, 5.2; N, 2.8%);
nmax/cmK1 (KBr) 3435, 1625, 1588, 1516, 1441, 1351,
1207, 1101, 747 and 691; dH (CD3SOCD3) 11.75 (1H, br s),
7.6–7.3 (17H, m), 7.15 (2H, t) and 7.0–6.8 (6H, m); dC see
Table 3; dP 18.8; m/z 499 (MC, 3%), 407 (MCKPhNH,
100), 380 (MCKPhNCO, 30), 379 (MCKPhNHCO, 30),
303 (32), 183 (27) and 129 (63).
3.1.2. [(Benzoyl)(4-nitrophenylcarbamoyl)methylene]-
triphenylphosphorane 9. From 5a and 6b as pale yellow
crystals (80%), mp 173–175 8C (Found: C, 72.5; H, 4.8; N,
4.95. C33H25N2O4P requires C, 72.8; H, 4.6; N, 5.1%); nmax
/
cmK1 (KBr) 3435, 1638, 1598, 1505, 1489, 1439, 1328,
1233, 1199, 1174, 1107 and 690; dH 12.76 (1H, br s), 8.09
(2H, half AB pattern, JZ9 Hz), 7.75–7.30 (17H, m) and
7.02–6.80 (5H, m); dC see Table 3; dP 19.2; m/z (MC544
not apparent), 380 (MCKArNCO, 100%), 379 (MCK
ArNHCO, 92), 351 (15), 303 (98), 277 (68), 183 (50) and
105 (72).
3.1.3. [(Benzoyl)(4-chlorophenylcarbamoyl)methylene]-
triphenylphosphorane 10. From 5a and 6c as colourless
crystals (82%), mp 193–195 8C (Found: C, 74.2; H, 5.0; N,
2.6. C33H25ClNO2P requires C, 74.2; H, 4.7; N, 2.6%); nmax
/
cmK1 (KBr) 3470, 1620, 1507, 1440, 1355, 1193, 1102, 750
and 693; dH (CDCl3) 12.24 (1H, br s), 7.80–7.55 (6H, m),
7.50–7.25 (11H, m), 7.14 (2H, half AB pattern, JZ9 Hz),
7.00–6.90 (3H, m) and 6.86–6.76 (2H, m); dC see Table 3;
dP 18.9; m/z 535 (37Cl–MC, 0.1%), 533 (35Cl–MC, 0.3), 407
(MCKArNH, 15), 380 (MCKArNCO, 67), 379 (MCK
ArNHCO, 65), 303 (65), 277 (100) and 183 (45).
Figure 1. Hammett correlation for pyrolysis of ylides 18–23
The thermal reactivity and kinetics of other classes of
stabilised ylides are currently under investigation and the
results will be reported shortly.

132
R. A. Aitken et al. / Tetrahedron 61 (2005) 129–135
Table 3. 13C NMR spectra of benzoyl/carbamoyl and thiocarbamoyl ylides 8–23, dC (JP–C
)
P-Phenyl
X
R1
R2
P]C
COAr
CXNHAr
C-1
C-2
C-3
C-4
8a
9
O
O
O
O
O
S
S
S
S
S
O
O
O
O
S
H
H
H
H
H
H
H
H
H
NO2
Cl
Me
MeO
H
NO2
Cl
Me
MeO
H
H
H
75.9 (119)
76.4 (130)
76.0 (122)
76.0 (122)
75.8 (120)
88.1 (136)
89.3 (126)
88.3 (135)
87.7 (136)
87.4 (136)
77.3 (120)
76.5 (122)
75.8 (120)
75.4 (122)
87.9 (136)
87.6 (137)
191.7 (16)
193.6 (18)
193.0 (18)
192.8 (18)
192.7 (18)
192.7 (22)
192.6 (18)
192.9 (22)
192.6 (22)
192.5 (22)
189.5 (18)
191.4 (18)
193.0 (18)
192.5(18)
192.8 (22)
192.4 (21)
168.1 (10)
168.3 (10)
167.9 (10)
167.8 (10)
167.6 (10)
189.8 (17)
189.6 (13)
190.0 (17)
189.9 (17)
190.0 (17)
167.3 (10)
167.7 (10)
168.0 (10)
168.0 (10)
189.8 (18)
189.9 (17)
126.2 (92)
125.0 (93)
125.6 (93)
126.0 (93)
126.0 (93)
126.8 (96)
126.4 (93)
126.5 (95)
126.9 (95)
126.9 (95)
125.3 (93)
125.8 (94)
126.0 (93)
126.1 (93)
126.9 (95)
127.2 (95)
134.0 (10)
133.3 (10)
133.3 (10)
133.4 (10)
133.3 (10)
133.5 (9)
134.2 (9)
133.5 (9)
133.5 (9)
133.5 (9)
133.2 (10)
133.3 (9)
133.4 (9)
133.3 (10)
133.5 (9)
133.6 (8)
129.6 (12)
128.8 (13)
128.7 (13)
128.6 (13)
128.6 (13)
128.3 (12)
129.6 (12)
128.4 (13)
128.3 (12)
128.3 (12)
128.7 (13)
128.7 (13)
128.5 (13)
128.6 (12)
128.2 (12)
128.7 (12)
132.8 (3)
132.0 (2)
131.8 (3)
131.6 (2)
131.6 (2)
131.3 (2)
132.7 (!2)
131.4 (2)
131.3 (2)
131.3 (2)
132.0 (3)
131.8 (2)
131.9 (2)
131.6 (2)
131.3 (2)
131.5 (3)
10
11
12
13
14a
15
16
17
18
19
20
21
22
23
H
H
NO2
Cl
Me
OMe
Me
OMe
H
H
H
S
Ar signals
8a
9
144.4, 140.7, 129.5, 129.2, 128.3, 127.6, 122.9, 119.7 (11)
146.1, 143.7, 141.9 (4ry), 128.8 (CH), 127.9 (2CH), 127.0 (2CH), 125.0 (2CH), 118.9 (2CH)
144.0, 138.5, 129.4 (4ry), 128.9 (CH), 128.5 (2CH), 127.8 (2CH), 127.0 (2CH), 121.0 (2CH)
144.3, 137.3, 131.6 (all 4ry), 129.1 (2CH), 128.5 (CH), 127.8 (2CH), 127.1 (2CH), 119.8 (2CH), 20.8
154.9, 144.2, 128.5 (4ry), 128.3 (CH), 127.8 (2CH), 127.1 (2CH), 121.2 (2CH), 113.8 (2CH), 55.5
144.3, 140.4 (4ry), 129.0 (CH), 128.3 (2CH), 127.9 (2CH), 127.3 (2CH), 124.6 (CH), 123.8 (2CH)
147.6, 143.5 (4), 143.2, 129.9 (CH), 128.5 (2CH), 127.8 (2CH), 125.1 (2CH), 122.1 (2CH)
144.1, 139.0, 129.5 (4ry), 129.1 (CH), 128.3 (2CH), 127.9 (2CH), 127.3 (2CH), 124.9 (2CH)
144.3, 137.8, 134.4 (all 4ry), 128.95 (CH), 128.87 (2CH), 127.9 (2CH), 127.4 (2CH), 124.0 (2CH), 21.0
156.7, 144.3, 128.9 (CH), 128.6 (4ry), 127.8 (2CH), 127.3 (2CH), 125.6 (2CH), 113.5 (2CH), 55.4
149.4 (4ry), 146.9 (4ry), 139.3 (4ry), 128.5 (2CH), 127.5 (2CH), 122.8 (2CH), 122.5 (CH), 119.8 (2CH)
142.5 (4ry), 139.7 (4ry), 134.4 (4ry), 128.6 (2CH), 128.4 (2CH), 127.9 (2CH), 122.3 (CH), 119.8 (2CH)
141.4 (4ry), 139.9 (4ry), 138.4 (4ry), 128.6 (2CH), 128.3 (2CH), 127.2 (2CH), 122.5 (CH), 119.8 (2CH), 21.2
160.0 (4ry), 139.9 (4ry), 137.1 (4ry), 128.9 (2CH), 128.6 (2CH), 122.1 (CH), 119.8 (2CH), 113.1 (2CH), 55.2
141.6 (4ry), 140.4 (4ry), 139.1 (4ry), 128.4 (2CH), 128.3 (2CH), 127.4 (2CH), 124.6 (CH), 123.8 (2CH)
160.7 (4ry), 140.6 (4ry), 137.4 (4ry), 129.4 (2CH), 128.4 (2CH), 124.7 (CH), 123.9 (2CH), 113.3 (2CH), 55.3
10
11
12
13
14a
15
16
17
18
19
20
21
22
23
a In CD3SOCD3.
3.1.4. [(Benzoyl)(4-methylphenylcarbamoyl)methylene]-
triphenylphosphorane 11. From 5a and 6d as colourless
needles (76%), mp 206–209 8C (Found: C, 79.4; H, 5.6; N,
(1H, br s), 7.80–7.70 (8H, m), 7.45–7.25 (11H, m), 7.15–
6.95 (4H, m) and 6.87–6.77 (2H, m); dC see Table 3; dP 13.3;
m/z 515 (MC, 1%), 380 (MCKPhNCS, 100), 379 (MCK
PhNHCS, 96), 351 (20), 303 (98), 277 (80), 202 (35), 183
(75) and 77 (56).
2.7. C34H28NO2P requires C, 79.5; H, 5.5; N, 2.7%); nmax
/
cmK1 3432, 1732, 1602, 1518, 1288, 1123, 1073, 740 and
722; dH 12.02 (1H, br s), 7.7–7.5 (6H, m), 7.5–7.2 (11H, m),
7.0 –6.7 (7H, m) and 2.24 (3H, s); dC see Table 3; dP 18.8;
m/z 513 (MC, 0.5%), 407 (40), 380 (45), 379 (44), 337 (30),
303 (45) and 277 (100).
3.1.7. [(Benzoyl)(4-nitrophenylthiocarbamoyl)methyl-
ene]triphenylphosphorane 14. From 5a and 7b as orange
needles (82%), mp 186–187 8C (Found: C, 70.4; H, 4.4; N,
5.2; S, 5.3. C33H25N2O3PS requires C, 70.7; H, 4.5; N, 5.0;
S, 5.7%); nmax/cmK1 (KBr) 3436, 1512, 1439, 1341, 1243,
1179, 1103, 745 and 690; dH 14.40 (1H, br s), 8.16 and 8.10
(4H, AB pattern, JZ9 Hz), 7.80–7.65 (6H, m), 7.50–7.30
(9H, m), 7.10–7.00 (3H, m) and 6.90–6.80 (2H, m); dC see
Table 3; dP 14.1; m/z (MC 560 not apparent) 380 (MCK
ArNCS, 97%), 379 (95), 351 (16), 303 (100), 277 (50) and
183 (65).
3.1.5. [(Benzoyl)(4-methoxyphenylcarbamoyl)methyl-
ene]triphenylphosphorane 12. From 5a and 6e as pale
yellow crystals (88%), mp 180–182 8C (Found: C, 77.4; H,
5.5; N, 2.5. C34H28NO3P requires C, 77.1; H, 5.3; N, 2.6%);
nmax/cmK1 (KBr) 3435, 1620, 1510, 1440, 1351, 1246,
1202, 1100, 760, 749, 738 and 693; dH 12.00 (1H, br s),
7.70–7.60 (6H, m), 7.50–7.25 (9H, m), 7.46 and 6.77 (4H,
AB pattern, JZ9 Hz), 7.00–6.90 (3H, m), 6.84–6.74 (2H,
m) and 3.74 (3H, s); dC see Table 3; dP 18.7; m/z 529 (MC,
2%), 407 (MCKArNH, 75), 380 (100), 379 (90), 303 (90),
277 (77) and 183 (50).
3.1.8. [(Benzoyl)(4-chlorophenylthiocarbamoyl)methyl-
ene]triphenylphosphorane 15. From 5a and 7c as yellow
needles (88%), mp 189–190 8C (lit.,4 151 8C) (Found: C,
71.8; H, 4.6; N, 2.5; S, 5.3. C33H25ClNOPS requires C, 72.1;
H, 4.6; N, 2.5; S, 5.8%); nmax/cmK1 (KBr) 3436, 1584,
1546, 1497, 1439, 1338, 1283, 1173, 1105, 749 and 690; dH
13.92 (1H, br s), 7.80–7.65 (8H, m), 7.50–7.25 (9H, m), 7.24
(2H, half AB pattern, JZ9 Hz), 7.08–6.98 (3H, m) and
6.87–6.78 (2H, m); dC see Table 3; dP 13.6; m/z (MC 551/
549 not apparent), 380 (MCKArNCS, 86), 379 (80), 351
3.1.6. [(Benzoyl)(phenylthiocarbamoyl)methylene]tri-
phenylphosphorane 13. From 5a and 7a as yellow needles
(90%), mp 186–187 8C (lit.,4 167–167.5 8C) (Found: C,
76.9; H, 4.95; N, 2.9; S, 5.8. C33H26NOPS requires C, 76.9;
H, 5.1; N, 2.7; S, 6.2%); nmax/cmK1 (KBr) 3436, 1596,
1550, 1504, 1440, 1340, 1176, 1106, 752 and 690; dH 13.80

R. A. Aitken et al. / Tetrahedron 61 (2005) 129–135
133
(15), 303 (72), 294 (40), 277 (70), 171 (37Cl–ArNCS, 38)
and 169 (35Cl–ArNCS, 100).
3.1.14. [(4-Methoxybenzoyl)(phenylcarbamoyl)methyl-
ene]triphenylphosphorane 21. From 5e and 6a as colour-
less crystals (80%), mp 197–199 8C (Found: C, 76.6; H,
5.15; N, 2.3. C34H28NO3P requires C, 77.1; H, 5.3; N,
2.6%); nmax/cmK1 3420, 1627, 1606, 1505, 1440, 1355,
1254, 1209, 1180, 1104, 1029, 850, 754 and 691; dH 12.10
(1H, br s), 7.75–7.60 (6H, m), 7.60–7.50 (2H, m), 7.50–7.30
(9H, m), 7.30–7.15 (2H, m), 7.00–6.90 (1H, m), 6.92 and
6.33 (4H, AB pattern, JZ9 Hz) and 3.68 (3H, s); dC see
Table 3; dP 18.9; m/z 529 (MC, 0.4%), 437 (MCKPhNH,
12), 410 (MCKPhNCO, 35), 409 (MCKPhNHCO, 32),
303 (25), 277 (40) and 91 (100).
3.1.9. [(Benzoyl)(4-methylphenylthiocarbamoyl)methyl-
ene]triphenylphosphorane 16. From 5a and 7d as colour-
less crystals (36%), mp 192 8C (Found: C, 77.0; H, 5.35; N,
2.7. C34H28NOPS requires C, 77.1; H, 5.3; N, 2.6%); nmax
/
cmK1 3432, 1732, 1584, 1287, 1120, 1072, 748 and 686; dH
13.70 (1H, br s), 7.85–7.7 (6H, m), 7.60 and 7.12 (4H, AB
pattern, JZ9 Hz), 7.5–7.3 (9H, m), 7.1–7.0 (3H, m), 6.9–6.8
(2H, m) and 2.33 (3H, s); dC see Table 3; dP 13.1; m/z
(MC529 not apparent) 380 (MCKArNCS, 55%), 351 (10),
343 (10), 303 (50) and 277 (100).
3.1.15. [(4-Methylbenzoyl)(phenylthiocarbamoyl)methyl-
ene]triphenylphosphorane 22. From 5d and 7a as pale
yellow crystals (36%), mp 160–162 8C (Found: C, 76.65; H,
5.5; N, 2.5. C34H28NOPS requires C, 77.1; H, 5.3; N, 2.6%);
nmax/cmK1 3420, 1587, 1545, 1503, 1339, 1184, 1102, 828,
752 and 694; dH 13.85 (1H, br s), 7.80–7.70 (8H, m), 7.50–
7.25 (11H, m), 7.10 (1H, t, JZ7 Hz), 6.92 (2H, d, JZ7 Hz),
6.62 (2H, d, JZ7 Hz) and 2.18 (3H, s); dC see Table 3; dP
13.3; m/z (MC529 not apparent) 394 (MCKPhNCS,
100%), 393 (MCKPhNHCS, 92), 365 (25), 303 (85), 277
(44), 202 (36), 183 (62), 135 (98) and 77 (82).
3.1.10. [(Benzoyl)(4-methoxyphenylthiocarbamoyl)-
methylene]triphenylphosphorane 17. From 5a and 7e as
yellow crystals (85%), mp 181–182 8C (lit.,4 149 8C)
(Found: C, 74.85; H, 5.4; N, 2.5; S, 5.1. C34H28NO2PS
requires C, 74.8; H, 5.2; N, 2.6; S, 5.9%); nmax/cmK1 (KBr)
3436, 1512, 1439, 1341, 1243, 1179, 1103, 745 and 690; dH
13.56 (1H, br s), 7.80–7.67 (6H, m), 7.57 and 6.85 (4H, AB
pattern, JZ9 Hz), 7.50–7.25 (9H, m), 7.08–6.98 (3H, m),
6.86–6.78 (2H, m) and 3.78 (3H, s); dC see Table 3; dP 13.2;
m/z (MC545 not apparent), 467 (MCKPh, 3%), 423 (MCK
ArNH, 1), 380 (MCKArNCS, 64), 379 (65), 375 (100), 303
(100), 277 (48) and 183 (70).
3.1.16. [(4-Methoxybenzoyl)(phenylthiocarbamoyl)-
methylene]triphenylphosphorane 23. From 5e and 7a as
pale yellow crystals (58%), mp 169–171 8C (Found: C,
75.0; H, 5.3; N, 2.5. C34H28NO2PS requires C, 74.8; H, 5.2;
N, 2.6%); nmax/cmK1 3418, 1603, 1500, 1348, 1245, 1172,
1106, 840, 748 and 691; dH 13.68 (1H, br s), 7.80–7.70 (8H,
m), 7.45–7.25 (11H, m), 7.15–7.00 (1H, m), 7.03 and 6.36
(4H, AB pattern, JZ9 Hz) and 3.68 (3H, s); dC see Table 3;
dP 13.2; m/z (MC545 not apparent), 410 (MCKPhNCS,
100%), 409 (MCKPhNHCS, 82), 381 (20), 303 (56), 277
(35), 209 (35) and 183 (42).
3.1.11. [(4-Nitrobenzoyl)(phenylcarbamoyl)methylene]-
triphenylphosphorane 18. From 5b and 6a as yellow
crystals (50%), mp 215–217 8C (Found: C, 72.6; H, 4.6; N,
4.8. C33H25N2O4P requires C, 72.8; H, 4.6; N, 5.1%); nmax
/
cmK1 1628, 1589, 1510, 1494, 1440, 1342, 1206, 1103, 857,
763, 746 and 692; dH 12.10 (1H, br s), 7.70–7.58 (9H, m),
7.55 and 7.47 (4H, AB pattern, JZ9 Hz), 7.42–7.30 (6H,
m), 7.24 (2H, t, JZ7 Hz), 7.05 (2H, d, JZ7 Hz) and 6.97
(1H, t, JZ7 Hz); dC see Table 3; dP 18.2; m/z 544 (MC,
2%), 452 (MCKPhNH, 96), 425 (60), 424 (58), 303 (80),
277 (100), 183 (86) and 174 (60).
3.2. Flash vacuum pyrolysis
The sample was volatilised from a tube in a Bu¨chi
Kugelrohr oven through a 30!2.5 cm horizontal fused
quartz tube. This was heated externally by a Carbolite
Eurotherm tube furnace MTF-12/38A at a temperature of
500 8C, the temperature being monitored by a Pt/Pt-13%Rh
thermocouple situated at the centre of the furnace. The
products were collected in a U-shaped trap cooled in liquid
nitrogen. The whole system was maintained at a pressure of
10K2 Torr by an Edwards Model E2M5 high capacity rotary
oil pump, the pressure being measured by a Pirani gauge
situated between the cold trap and the pump. Under these
conditions the contact time in the hot zone was estimated to
be z10 ms.
3.1.12. [(4-Chlorobenzoyl)(phenylcarbamoyl)methyl-
ene]triphenylphosphorane 19. From 5c and 6a as colour-
less crystals (65%), mp 220 8C (Found: C, 74.4; H, 4.7; N,
2.7. C33H25ClNO2P requires C, 74.2; H, 4.7; N, 2.6%); nmax
/
cmK1 3432, 1732, 1627, 1586, 1289, 1280, 1073, 842, 745,
723 and 693; dH 12.14 (1H, br s), 7.75–7.35 (15H, m), 7.3–
7.2 (3H, m), 7.03–6.9 (2H, m) and 6.90 and 6.80 (4H, AB
pattern, JZ9 Hz); dC see Table 3; dP 18.7; m/z 535 (37Cl–
MC, 0.2%), 533 (35Cl–MC, 0.6), 443 (37Cl–MCKPhNH,
6), 441 (35Cl–MCKPhNH, 17), 414 (14), 343 (26), 303
(16), 277 (20) and 91 (100).
3.1.13. [(4-Methylbenzoyl)(phenylcarbamoyl)methyl-
ene]triphenylphosphorane 20. From 5d and 6a as colour-
less prisms (31%), mp 201–203 8C (Found: C, 79.8; H, 5.7;
N, 2.7. C34H28NO2P requires C, 79.5; H, 5.4; N, 2.7%);
nmax/cmK1 3436, 1632, 1514, 1441, 1342, 1208, 1101, 840,
766, 751 and 692; dH 12.18 (1H, br s), 7.75–7.15 (19H, m),
6.94 (1H, t, JZ7 Hz), 6.85 (2H, d, JZ7 Hz), 6.60 (2H, d,
JZ7 Hz) and 2.15 (3H, s); dC see Table 3; dP 18.9; m/z 513
(MC, 1%), 421 (MCKPhNH, 40), 394 (MCKPhNCO, 50),
393 (MCKPhNHCO, 45), 351 (15), 303 (45), 277 (100),
121 (82) and 91 (87).
Pyrolysis of 8 (100 mg) at 500 8C gave two fractions. In the
cold trap there was a liquid, which proved to be a mixture of
phenyl isocyanate 6a (60%); dC 124.8 (2 C), 125.7, 129.5
(CO), 129.6 (2 C) and 133.6 (quaternary) and phenyl-
acetylene (75%); dH 3.10. At the furnace exit there was a
solid, which was a mixture of Ph3PO (75%); dP 29.5 and the
ylide 5a (5%); dP 17.0.
Pyrolysis of 13 (60 mg) at 500 8C gave two fractions. In the
cold trap there was a liquid which proved to be phenyl

Table 4. Kinetic data for the gas-phase elimination reaction of 8–23
X
O
R1
H
R2
H
104k (sK1) at T (K)
log10A (sK1
8.95G0.30
)
Ea (kJ molK1
94.73G2.35
)
8
1.02
382.25
1.08
380.25
2.16
386.25
1.64
388.35
1.46
378.95
1.61
341.45
1.70
346.25
4.28
356.25
3.35
346.30
3.77
347.15
2.34
411.85
4.54
403.15
0.43
362.35
3.17
373.65
0.98
333.35
0.52
332.20
2.12
391.65
3.05
391.85
5.41
398.05
3.28
395.05
2.95
389.05
4.92
352.35
3.72
355.05
10.69
369.95
6.11
352.35
7.20
355.25
5.30
421.85
6.75
409.15
0.91
371.05
5.66
381.95
1.36
342.45
1.70
341.85
3.87
400.25
7.11
10.84
415.85
12.71
17.78
422.25
32.17
424.55
37.79
424.85
10.68
413.55
28.75
419.95
53.98
383.95
26.06
380.95
63.49
388.75
34.94
35.13
433.75
9
O
O
O
O
S
H
NO2
Cl
9.93G0.35
9.86G0.45
9.38G0.47
9.60G0.44
10.10G0.57
10.05G0.57
10.40G0.35
10.28G0.51
10.19G0.19
10.66G0.34
10.12G0.34
12.78G0.41
7.12G0.16
12.09G0.69
12.93G0.42
101.01G2.65
100.15G3.48
97.64G3.66
97.52G3.40
90.68G2.89
92.02G3.90
93.85G2.48
91.18G3.54
90.58G1.31
112.62G2.78
104.02G2.67
119.24G2.96
75.92G1.22
104.18G4.63
109.33G2.83
402.55
8.62
412.65
17.58
10
11
12
13
14
15
16
17
18
19
20
21
22
23
H
405.95
4.89
415.05
7.12
H
Me
OMe
H
20.54
422.25
401.05
8.32
407.35
15.94
H
400.15
20.84
369.25
6.76
410.95
38.34
378.59
15.05
H
S
H
NO2
Cl
51.53
387.85
364.45
17.78
373.45
11.22
360.40
13.29
362.25
9.81
373.85
34.87
381.05
15.88
365.15
28.41
371.35
17.87
S
H
S
H
Me
OMe
H
373.15
48.24
377.85
S
H
O
O
O
O
S
NO2
Cl
429.85
10.14
415.05
2.51
439.10
18.11
422.35
5.96
H
31.21
430.15
35.58
408.25
19.13
403.20
32.62
372.45
35.29
371.80
Me
OMe
Me
OMe
H
380.05
7.96
389.40
12.55
H
388.00
4.44
395.45
11.98
H
352.80
5.44
351.40
362.25
14.84
362.35
S
H

R. A. Aitken et al. / Tetrahedron 61 (2005) 129–135
135
isothiocyanate (56%); nmax/cmK1 2080, 1592, 1490, 752
Acknowledgements
and 685; dH 7.38–7.20 (5H, m, pattern identical to authentic
sample). At the furnace exit there was a solid which was a
mixture of Ph3PS (ca. 5%); dP 43.7, Ph3PO (ca. 5%); dP
29.5 and the ylide 5a (72%); dP 17.0; dH 8.0–7.94 (2H, m),
7.8–7.6 (6H, m), 7.6–7.4 (9H, m), 7.4–7.3 (3H, m) and 4.40
(1H, br s).
We thank Kuwait University for support (Research Grant
SC 03/99) and provision of facilities through ANALAB and
SAF.
3.3. Kinetic studies
References and notes
Reaction set-up. Preliminary kinetic results were obtained
on a system featuring a Eurotherm 093 pyrolysis unit
coupled to a Perkin Elmer Sigma 115 Gas Chromatograph.
The kinetic data reported are from a reactor set-up 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, 4.6 mm (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.
1. Trippett, S.; Walker, D. M. J. Chem. Soc. 1959, 3874–3876.
2. Blanchard, M.-L.; Strzelecka, H.; Martin, G. J.; Simalty, M.;
Fugnitto, R. Bull. Soc. Chim. Fr. 1967, 2677–2679.
3. Strzelecka, H. Ann. Chim. (Paris) 1966, 201–220.
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Obshch. Khim. 1969, 39, 1282–1287.
5. Bestmann, H. J.; Pfohl, S. Angew. Chem., Int. Ed. Engl. 1969,
8, 762–763.
6. Tolochko, A. F.; Megera, I. V.; Zykova, L. V.; Shevchuk, M. I.
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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 10–20%
pyrolysis was deemed to occur. The contents of the tube
were analyzed using HPLC.
8. Bestmann, H. J.; Schade, G.; Schmid, G. Angew. Chem., Int.
Ed. Engl. 1980, 19, 822–824.
9. Aitken, R. A.; Karodia, N.; Massil, T.; Young, R. J. J. Chem.
Soc., Perkin Trans. 1 2002, 533–541 and preceding parts in
this series.
10. Reviews: Aitken, R. A.; Thomas, A. W. In Chemistry of the
Functional Groups, Supplement A3; Patai, S., Ed.; Wiley:
Chichester, 1997; pp 503–507. Symery, F.; Iorga, B.;
Savignac, P. Synthesis 2000, 185–213.
11. Kinetic data for a series of 8 b,d0-dioxo ylides have been
reported: Aitken, R. A.; Al-Awadi, N. A.; Balkovich, M. E.;
Bestmann, H. J.; Clem, O.; Gibson, S.; Gross, A.; Kumar, A.;
At least three kinetic runs were carried out for each 5–10 8C
rise in temperature of the pyrolyzer and for the same time
interval until 90–95% pyrolysis was achieved. The reactions
were ascertained to be homogeneous, unimolecular, and
free of reactor surface effects. The homogeneous nature of
the reactions was tested by comparing rates using a normal
reactor with those obtained when the reactor vessel is
packed with helices. Absence of free radical pathways in the
elimination reactions was confirmed using established
procedures.
¨
Roder, Th. Eur. J. Org. Chem. 2003, 840–847.
´
12. Aitken, R. A.; Herion, H.; Janosi, A.; Karodia, N.; Raut, S. V.;
Seth, S.; Shannon, I. J.; Smith, F. C. J. Chem. Soc., Perkin
Trans. 1 1994, 2467–2472.
13. Aitken, R. A.; Atherton, J. I. J. Chem. Soc., Perkin Trans. 1
1994, 1281–1284.
14. Al-Awadi, N. A.; Al-Bashir, R. F.; El-Dusouqui, O. M.
J. Chem. Soc., Perkin Trans. 2 1989, 579–581.
15. Al-Awadi, N. A.; El-Dusouqui, O. M. Int. J. Chem. Kinet.
1997, 29, 295–298.
The rates were followed over a temperature range of 30–
40 K, and the rate coefficients were calculated using the
expression for a first-order reaction: ktZln(ao/a) (Table 4).
Each rate coefficient represents the mean of three kinetic
runs in agreement to within G2%. The Arrhenius
parameters were obtained from a plot of log k against 1/T
(K). The Arrhenius plots were linear up to z95% reaction.
Rate constants adjusted to 400 K are given in Tables 1
and 2.
16. Al-Awadi, N. A.; El-Dusouqui, O. M.; Mathew, T. Int.
J. Chem. Kinet. 1997, 29, 289–293.
17. Al-Awadi, N. A.; Al-Bashir, R. F.; El-Dusouqui, O. M.
Tetrahedron Lett. 1989, 30, 1699–1702.
18. Dombrovskii, A. V.; Shevchuk, M. I. Zh. Obshch. Khim. 1963,
33, 1263–1269.