Flash vacuum pyrolysis of stabilised phosphorus ylides. Part 12. Extrusion of Ph3P from sulfonyl ylides and reactivity of the resulting sulfonyl carbenes

Article abstract of DOI:10.1039/a707948f

Twelve sulfonyl stabilised phosphorus ylides have been prepared and their behaviour upon flash vacuum pyrolysis at 600°C has been examined. Examples with an arylsulfonyl substituent undergo loss of Ph₃PO to give intractable products but those with an arylmethylsulfonyl substituent separately lose Ph₃P and SO₂ to give products consistent with the intermediacy of sulfonyl carbenes. X-Ray structure determinations of one ylide from each series show a more significant P-O non-bonding interaction in the first case, providing some explanation for the different thermal reactivity.

Full text of DOI:10.1039/a707948f

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Flash vacuum pyrolysis of stabilised phosphorus ylides. Part 12.1
Extrusion of Ph3P from sulfonyl ylides and reactivity of the resulting
sulfonyl carbenes
R. Alan Aitken,*,a Martin J. Drysdale,a George Ferguson,†,b and
Alan J. Loughb
a School of Chemistry, University of St. Andrews, North Haugh, St. Andrews, Fife,
UK KY16 9ST
b Department of Chemistry and Biochemistry, University of Guelph, Guelph, Ontario, Canada,
N1G 2W1
Twelve sulfonyl stabilised phosphorus ylides have been prepared and their behaviour upon flash vacuum
pyrolysis at 600 ЊC has been examined. Examples with an arylsulfonyl substituent undergo loss of Ph3PO
to give intractable products but those with an arylmethylsulfonyl substituent separately lose Ph3P and SO2
to give products consistent with the intermediacy of sulfonyl carbenes. X-Ray structure determinations of
one ylide from each series show a more significant P᎐O non-bonding interaction in the first case, providing
some explanation for the different thermal reactivity.
In previous parts of this series we have shown that thermal
extrusion of phosphine oxide from phosphorus ylides stabilised
Ph3P
R
ArSO2F
Ph3P CHR
2
S
by an α-acyl group proceeds efficiently using flash vacuum
pyrolysis (FVP) to provide access to a variety of different
alkyne types. The corresponding reaction of phosphinimines
stabilised by an α-acyl group to give nitriles was reported at an
early date.2 Although sulfonyl stabilised phosphorus ylides are
well known,3 their pyrolysis has not previously been studied but
it is expected to give interesting results since extrusion of Ph3PO
would give sulfinyl carbenes while SO2 could be lost directly to
afford non-stabilised ylides. We report here the synthesis of a
range of sulfonyl stabilised ylides and their behaviour upon
FVP which in fact leads to loss of Ph3P and SO2 to give prod-
ucts which can be explained by the intermediacy of sulfonyl
carbenes.4
O
Ar
O
1–5
Ph3P
O
R
PhCH2SO2F
Ph3P CHR
2
S
CH2Ph
O
6–9
Ph3P
O
Me
Et–SO2F
Ph3P CHAr
2
S
CH2Ar
O
Ar
Ph3P
10–12
Results and discussion
SO2
As reported by van Leusen, α-sulfonyl ylides cannot be pre-
pared by treatment of an ylide with a sulfonyl chloride since
this results in formation of the α-chloro ylide.3 The problem can
be resolved by first converting the sulfonyl chlorides into the
corresponding sulfonyl fluorides by treatment with an excess of
aqueous potassium fluoride.5 These then react in the desired
sense3 and in this way the compounds 1–9 were obtained in
moderate to good yield as shown in Table 1. Three further
examples 10–12 were obtained by using ethanesulfonyl fluoride
in a reaction which takes a rather unexpected course involving
[2 ϩ 2] cycloaddition between methylsulfene and the ylide to
give the intermediates 13.6 The sulfonyl ylides were obtained as
high-melting point stable solids which gave the expected anal-
ytical and spectroscopic data including 31P NMR signals in the
range δP ϩ 16.9–21.7.
When the arylsulfonyl examples 1–5 were subjected to FVP
at 600 ЊC and 0.01 Torr using a conventional flow system (con-
tact time ≈ 10 ms) they gave rather disappointing results. The
products included Ph3PO together with complex mixtures of
sulfones and hydrocarbons, most of which could not be identi-
fied. In contrast to this, the arylmethylsulfonyl examples 6–12
Me
13
ArCH2
ArCH2
[1,2-H]
–SO2
–SO
:
SO2
16
14
R
R
15
ArCH2
O
R
17
underwent clean reaction at 600 ЊC to give well defined prod-
ucts. In each case a mixture of Ph3P, Ph3PO and Ph3PS was
produced together with the other products shown in Table 2.
The phosphorus products can be accounted for by the separate
extrusion of Ph3P and SO2 which then combine to some extent.
The reaction of Ph3P with SO2 to give Ph3PO and Ph3PS, which
was confirmed by a control experiment, is well known7 and in
this case most likely occurs between the hot Ph3P condensed at
the furnace exit and SO2 in the gas stream.
In all cases the alkenes 16 were formed and for 6 and 7 these
were the main products. The formation of 16 can be explained,
as shown in Scheme 1, by initial extrusion of Ph3P to give
sulfonyl carbenes 14. Intramolecular 1,3-insertion of the
† To receive any correspondence concerning the X-ray structure
determinations.
J. Chem. Soc., Perkin Trans. 1, 1998
875

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MeX
Ph3P
O2S
MeX
•
X
– H•
1,5-insertion
– SO2
– Ph3P
X
:
X
21
O2S
+
O2S
CH2Ph
CH2Ph
23
CH2Ph
x 2
•
PhCH2CH2Ph
PhCH2
8 X = O
24
1,3-insertion
20
9 X = S
(R = 2-MeX-C6H4-)
R
R
Ph3P
R
:
– SO2
Me
1,3-insertion
– Ph3P
O2S
ArCH CHAr
ArCH CHR
O2S
O2S
CH2Ph
Ar
x 2
ArCH:
18
CH2Ph
16
22
+
RCH CHR
19
14
•
6 R = Ph
7 R = 4-MeC6H4
– SO2
1,3-insertion
(R = Me)
+
O2S
•
CHAr
MeCH:
27
Me
Ph3P
O2S
Me
H2C CH•
– Ph3P
:
1,2-H shift
gases
– SO2
+
O2S
O2S
CH2Ar
25
x 2
or
CH2Ar
CH2Ar
•
ArCH2
ArCH2CH2Ar
10 Ar = Ph
20
11 Ar = 2-MeC6H4
12 Ar = 2-MeOC6H4
Me
(Ar = 2-MeOC6H4)
CHO
26
Scheme 1
Table 1 Preparation of ylides 1–12
Table 2 FVP of ylides 6–12 at 600 ЊC
R
Ar
Yield (%)
δP/ppm
Pyrolysis products (%)
Phosphorus products (ratio)
Ph3P Ph3PO Ph3PS
1
2
Me
Et
Me
Et
Pr
Ph
4-MeC6H4
2-MeOC6H4
2-MeSC6H4
—
—
—
Ph
Ph
4-MeC6H4
4-MeC6H4
71
78
79
26
67
82
72
40
67
62
66
58
19.8
20.0
19.6
19.8
19.8
18.2
18.1
17.3
16.9
20.8
21.7
20.8
Ylide 16
18
19
20
21
3
6
7
77
47
39
5
24
7
—
6
—
—
7
9
5
—
9
—
—
(gas)
(gas)
(gas)
—
—
11
29
49
34
a
—
—
14
58
—
—
—
9
10
25
63
12
12
10
67
60
57
28
64
60
57
24
30
18
9
24
28
33
4
5
4-MeC6H4
8
6
—
—
—
—
Ph
9
7
10
11
12
8
9
6
10
11
12
2-MeOC6H4
2-MeOC6H4
a Product 26 formed (22%).
predominant loss of SO to give ketones 17 which were never
detected here.
carbene into benzylic CH would give the thiirane dioxide 22
which readily loses SO2 to give 16. For 7 and 10–12 apparent
In an attempt to verify the involvement of carbenes, ylides in
which the carbene would have an alternative reaction pathway
open to it were examined. Thus, for ylides 8 and 9 in which R is
o-methoxy- or o-methylthio-phenyl, 16 was still formed, but
a new process gave rise to bibenzyl 20 together with benzofuran
and benzothiophene, respectively. These products may be
explained by the alternative intramolecular insertion of carbene
23 into CH of the OMe or SMe group to give 24. A related
intramolecular insertion of sulfonyl carbenes into CH to give a
five-membered ring has been reported.13 Loss of SO2 from this
sulfone would then give two radicals, one of which aromatises
by loss of an H atom to 21, while the other dimerises to give
bibenzyl. Further support for this route was provided by the
GC–MS identification as minor products of 2,3-dihydro-
benzofuran from 8 and 3-benzyl-2,3-dihydrobenzothiophene
resulting from direct SO2 extrusion from 24 in the case of 9.
For the three remaining compounds 10–12, the products 16
and 18 were formed (but-2-ene 19 was presumed to be present
but was not isolated), but the major process was now the form-
ation of benzyl radical products 20. The presumed intermediate
25 can now undergo a 1,2-H shift to give the vinyl sulfone.
Loss of SO2 from this would give vinyl radical, which presum-
ably leads to gaseous products, and the benzyl radical which
dimerises to give 20 or, in the case of 2-methoxybenzyl-
8
metathesis of alkene 16 to give 18 and 19 was observed under
the pyrolysis conditions and evidence in confirmation of this
was obtained by separate pyrolysis of 16. The yield of 18
obtained, particularly from 10–12, seems rather high to be
explained wholly by this mechanism and an alternative route to
these products is provided by intramolecular hydrogen atom
abstraction in carbenes 14 and 25 to afford the diradicals 27
which may fragment as shown with loss of SO2 to produce the
carbenes which dimerise to give 18. An alternative route from 6
and 7 to 22 might involve proton transfer from the benzylic
position to the ylide carbon and intramolecular attack of the
resulting anion with expulsion of the phosphine. The latter pro-
cess has been reported in the reaction of phosphonium ylides
with sulfene to give a thiirane dioxide and Ph3P,9 and also has
some precedent in the chemistry of sulfonyl sulfonium and
sulfoxonium ylides.10 The involvement of ionic intermediates in
the gas-phase seems unlikely and, more importantly, this
mechanism is not in accord with the products obtained from
8–12. The formation of 16 could also be explained by an alter-
native mechanism involving rearrangement of 14 to the sulfene
15 in a process analogous to the Wolff rearrangement, fol-
lowed by loss of SO2 and a 1,2-H shift in the resulting carbene.
However, while there is ample precedent for the rearrangement
to 15,11 all previous pyrolyses of sulfenes12 have resulted in
substituted 2514 isomerises with loss of H to give o-tolualde-
ؒ
hyde 26.
876
J. Chem. Soc., Perkin Trans. 1, 1998

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Table 3 Selected bond lengths (Å) and angles (Њ) for 2 and 6
2
6
S1᎐O1
S1᎐O2
1.448(2)
1.448(2)
S1᎐O1
S1᎐O2
1.440(2)
1.447(2)
S1᎐C1
S1᎐C11
1.686(2)
1.779(3)
S1᎐C1
S1᎐C2
1.695(3)
1.800(4)
P1᎐C1
P1᎐C21
1.707(2)
1.817(2)
P1᎐C1
P1᎐C21
1.724(3)
1.812(3)
P1᎐C31
P1᎐C41
1.808(3)
1.812(3)
P1᎐C31
P1᎐C41
1.817(3)
1.802(3)
P1᎐O1
2.883(2)
P1᎐O1
2.973(2)
O1᎐S1᎐O2
O1᎐S1᎐C1
O1᎐S1᎐C11
O2᎐S1᎐C1
O2᎐S1᎐C11
C1᎐S1᎐C11
C1᎐P1᎐C21
C1᎐P1᎐C31
C1᎐P1᎐C41
C21᎐P1᎐C31
C21᎐P1᎐C41
C31᎐P1᎐C41
S1᎐C1᎐P1
117.80(11)
107.64(11)
105.98(12)
110.75(12)
104.10(12)
110.33(11)
107.81(11)
116.22(12)
112.81(13)
102.93(11)
107.81(11)
108.51(13)
116.10(14)
O1᎐S1᎐O2
O1᎐S1᎐C1
O1᎐S1᎐C2
O2᎐S1᎐C1
O2᎐S1᎐C2
C1᎐S1᎐C2
C1᎐P1᎐C21
C1᎐P1᎐C31
C1᎐P1᎐C41
C21᎐P1᎐C31
C21᎐P1᎐C41
C31᎐P1᎐C41
S1᎐C1᎐P1
115.51(17)
107.79(15)
110.29(18)
114.00(17)
101.80(19)
107.01(18)
107.02(15)
116.89(16)
114.96(16)
103.29(15)
106.86(16)
106.77(15)
117.42(18)
Fig. 2 A view of molecule 6 with our numbering scheme. Anisotropic
displacement ellipsoids are drawn at the 30% level.
instrument, for 13C at 75 MHz on a Bruker AM300 instrument,
and for 31P at 32 MHz using a Varian CFT 20 instrument. All
spectra were run on solutions in CDCl3 with internal Me4Si as
1
reference for H and 13C and external 85% H3PO4 as reference
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 A.E.I. MS-902 spectrometer using
electron impact at 70 eV. GC–MS data were obtained using a
Hewlett Packard 5890A chromatograph coupled to a Finnigan
Incos mass spectrometer. Dry THF was freshly distilled from
potassium benzophenone ketyl under N2.
The required quaternary phosphonium salts were com-
mercially available or were readily prepared by reaction of the
appropriate alkyl halides with triphenylphosphine in boiling
toluene. The following two salts do not appear to have been
characterised before.
2-Methoxybenzyl(triphenyl)phosphonium bromide. A solu-
tion of 2-methoxybenzyl bromide18 (1 equiv.) and triphenyl-
phosphine (1 equiv.) in toluene was heated under reflux for 18 h.
The product was filtered off, washed with diethyl ether and
dried to give colourless crystals (68%), mp 219–220 ЊC (Found:
C, 67.3; H, 5.2. C26H24BrOP requires C, 67.4; H, 5.2%); δH 8.0–
7.7 (15 H, m), 7.6–7.25 (2 H, m), 7.0–6.7 (2 H, m), 5.19 (2 H, d,
J 14) and 3.30 (3 H, s); δC(JC᎐P) 157.0 (5), 134.9 (3 C, 2), 133.9 (6
C, 10), 132.1 (6), 130.3 (4), 130.0 (6 C, 12), 120.9 (3), 117.8 (3 C,
85), 115.2 (9), 110.4 (2), 54.8 and 25.3 (49); δP ϩ21.5.
2-Methylthiobenzyl(triphenyl)phosphonium chloride. Thio-
salicylic acid was S-methylated using Me2SO4 (92%) and the
resulting acid converted via the acid chloride (SOCl2, 89%) and
the methyl ester (MeOH, 95%) to 2-methylthiobenzyl alcohol
(LiAlH4, 89%). This was then chlorinated (SOCl2, 75%) and the
resulting 2-methylthiobenzyl chloride subjected to reaction as
above to give the product as colourless crystals (62%), mp 230–
234 ЊC (Found: C, 71.6; H, 5.3. C26H24ClPS requires C, 71.8; H,
5.6%); δH 7.8–7.5 (15 H, m), 7.4–7.0 (4 H, m), 5.48 (2 H, d, J 15)
and 2.08 (3 H, s); δC(JC᎐P) 140.0 (6), 135.0 (3 C, 2), 134.3 (6 C,
10), 131.8 (5), 130.1 (6 C, 12), 129.5 (4), 128.7 (3), 127.1 (9),
126.7 (3), 117.7 (3 C, 86), 28.7 (48) and 17.3; δP ϩ22.3.
Fig.1 A view of molecule 2 with our numbering scheme. Anisotropic
displacement ellipsoids are drawn at the 30% level.
Although the extrusion of phosphines from phosphorus
ylides to give carbenes is unusual, it has been proposed for
alkoxy-15 and acyloxy-alkylidenetriphenylphosphoranes,16 and
also more recently for a benzotriazolyl ylide.1 In order to shed
some light on the reason for the difference in behaviour between
1–5 and 6–12, the structure of one example from each group
was determined using X-ray diffraction. There have been few
previous X-ray studies of sulfonyl ylides, although the struc-
ture of p-tolylsulfonylmethylene(triphenyl)phosphorane was
reported at an early date.17 Views of molecules 2 and 6 are
shown in Figs. 1 and 2 respectively. Selected dimensions are
given in Table 3 and are entirely in accord with anticipated
values. Of interest are the P1 ؒ ؒ ؒ O1 intramolecular non-
bonded contacts in the two structures [2.883(2) Å in 2 com-
pared with 2.973(2) Å in 6]. The P ؒ ؒ ؒ O distance is ≈0.1 Å
shorter in 2 than in 6, consistent with the extrusion of Ph3PO
rather than Ph3P.
The sulfonyl fluorides were prepared by treatment of the cor-
responding sulfonyl chlorides with boiling aqueous potassium
fluoride and were obtained as follows: benzenesulfonyl fluoride
(53%), bp 62–63 ЊC/6 Torr (lit.,5 207 ЊC/760 Torr); toluene-p-
sulfonyl fluoride (90%), bp 92–93 ЊC/9 Torr, mp 41–42 ЊC (lit.,5
41–42 ЊC); phenylmethanesulfonyl fluoride (54%), mp 89–90 ЊC
(lit.,19 90–91 ЊC); ethanesulfonyl fluoride (60%), bp 133–134 ЊC
(lit.,19 134–135 ЊC).
Experimental
Melting points were recorded on a Kofler hot-stage microscope
and are uncorrected. Infrared spectra were recorded for sol-
utions in chloroform in matched sodium chloride cells of
path length 0.1 mm, on a Perkin-Elmer 1420 instrument. NMR
spectra were obtained for 1H at 80 MHz using a Bruker WP80
Preparation of the sulfonyl ylides 1–12
A suspension of the appropriate phosphonium salt (25 mmol)
J. Chem. Soc., Perkin Trans. 1, 1998
877

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in dry THF (150 cm3) was stirred at RT under nitrogen while
butyllithium in hexane (26 mmol) was added by syringe. After
the addition the mixture was stirred for 30 min and then a
solution of the sulfonyl fluoride (12.5 mmol) in dry THF (10
cm3) was added slowly. After 2–3 h the mixture was filtered and
the filtrate was evaporated. The residue was dissolved in CH2Cl2
(250 cm3) and washed with water (3 × 100 cm3), dried and
evaporated. The residue was triturated with diethyl ether to give
the product as a yellow solid which was recrystallised from ethyl
acetate–hexane.
[(4-Methylphenyl)(phenylmethylsulfonyl)methylene]triphenyl-
phosphorane 7. From 4-methylbenzyl(triphenyl)phosphonium
bromide and phenylmethanesulfonyl fluoride as pale yellow
crystals (72%), mp 188–189 ЊC (Found: C, 75.8; H, 5.8.
C33H29O2PS requires C, 76.1; H, 5.6%); νmax/cmϪ1 1625, 1502,
1483, 1435, 1264, 1244, 1144, 1106, 1094, 1043, 1028, 935, 864,
788, 754, 714 and 694; δH 7.55–6.95 (22 H, m), 6.84 (2 H, half
AB pattern, J 6), 3.97 (2 H, s) and 2.21 (3 H, s); δP ϩ18.1; m/z
520 (Mϩ, 15%), 429 (36), 414 (10), 381 (32), 366 (100), 352 (14),
277 (60) and 119 (55).
(1-Phenylsulfonylethylidene)triphenylphosphorane 1. From
ethyl(triphenyl)phosphonium bromide and benzenesulfonyl
fluoride as yellow crystals (71%), mp 138–140 ЊC (Found: C,
72.6; H, 5.4. C26H23O2PS requires C, 72.5; H, 5.4%); νmax(film)/
cmϪ1 1582, 1480, 1435, 1300, 1270, 1220, 1180, 1110, 1068, 992,
780, 747, 720 and 690; δH 7.8–7.25 (20 H, m) and 1.72 (3 H, d,
J 13); δP ϩ19.8; m/z 430 (Mϩ, 57%), 415 (2), 365 (4), 294 (9),
289 (100), 277 (36), 262 (25) and 183 (85).
[(2-Methoxyphenyl)(phenylmethylsulfonyl)methylene]tri-
phenylphosphorane 8. From 2-methoxybenzyl(triphenyl)phos-
phonium bromide and phenylmethanesulfonyl fluoride as col-
ourless crystals (40%), mp 210–213 ЊC (Found: C, 73.6; H, 5.4.
C33H29O3PS requires C, 73.9; H, 5.4%); νmax/cmϪ1 1590, 1486,
1440, 1312, 1265, 1192, 1122, 1103, 1044, 1028, 1000, 965, 756,
723 and 698; δH 7.95–6.8 (23 H, m), 6.50 (1 H, m), 4.03 (2 H, s)
and 3.35 (3 H, s); δP ϩ17.3; m/z 536 (Mϩ, 90%), 445 (100), 415
(78), 397 (22), 381 (32), 367 (30), 351 (48), 277 (40) and 262 (90).
[(2-Methylthiophenyl)(phenylmethylsulfonyl)methylene]tri-
phenylphosphorane 9. From 2-methylthiobenzyl(triphenyl)-
phosphonium chloride and phenylmethanesulfonyl fluoride as
colourless crystals (67%), mp 248–251 ЊC (Found: C, 71.3; H,
5.0. C33H29O2PS2 requires C, 71.7; H, 5.3%); νmax/cmϪ1 1439,
1265, 1105, 1080, 1040, 1028, 950, 938, 772, 754, 735, 720 and
703; δH 8.0–7.1 (23 H, m), 6.91 (1 H, m), 4.26 (2 H, s) and 2.15
(3 H, s); δP ϩ16.9; m/z 552 (Mϩ, 36%), 461 (40), 397 (16), 350
(18), 277 (90), 262 (100), 219 (24) and 137 (50).
(1-Phenylsulfonylprop-1-ylidene)triphenylphosphorane
2.
From propyl(triphenyl)phosphonium bromide and benzenesul-
fonyl fluoride as yellow crystals (78%), mp 136–139 ЊC (Found:
C, 72.9; H, 5.6. C27H25O2PS requires C, 73.0; H, 5.7%); νmax
/
cmϪ1 1592, 1442, 1365, 1322, 1260, 1177, 1145, 1120, 1106,
1073, 963, 940, 758, 720, 699 and 648; δH 7.85–7.25 (20 H, m),
2.12 (2 H, d of q, J 19, 7) and 0.83 (3 H, t, J 7); δC 134.8 (2 C),
134.0 (d, J 10, C-2 of P-Ph), 131.7 (d, J 2, C-4 of P-Ph), 129.7,
127.9 (2 C), 128.4 (d, J 12, C-3 of P-Ph), 128.0, 126.3 (d, J 94,
C-1 of P-Ph), 41.3 (d, J 123, P᎐C), 21.5 (d, J 10, CH ) and 18.2
᎐
2
(CH3); δP ϩ20.0; m/z 444 (Mϩ, 12%), 430 (29), 429 (100), 414
(1), 303 (10), 287 (43), 279 (2), 262 (5) and 183 (19).
(1-Phenylmethylsulfonylethylidene)triphenylphosphorane 10.
From benzyl(triphenyl)phosphonium chloride and ethane-
sulfonyl fluoride as yellow crystals (62%), mp 170–172 ЊC (lit.,6
171.5–172.5 ЊC); δH 7.7–7.4 (15 H, m), 7.27 (5 H, s), 3.97 (2 H, s)
and 1.58 (3 H, d, J 14); δP ϩ20.8.
[1-(4-Methylphenylsulfonyl)ethylidene]triphenylphosphorane
3. From ethyl(triphenyl)phosphonium bromide and toluene-p-
sulfonyl fluoride as yellow crystals (79%), mp 150–153 ЊC
(Found: C, 73.0; H, 5.7. C27H25O2PS requires C, 73.0; H, 5.7%);
νmax/cmϪ1 1595, 1440, 1315, 1260, 1186, 1142, 1105, 1070, 1002,
905, 865, 825, 756, 721, 699 and 670; δH 7.8–7.2 (17 H, m), 7.05
(2 H, half AB pattern, J 9), 2.35 (3 H, s) and 1.69 (3 H, d, J 13);
δP ϩ19.6; m/z 444 (Mϩ, 33%), 379 (7), 294 (16), 289 (100), 282
(22), 277 (56), 262 (22) and 183 (82).
[1-(4-Methylphenylsulfonyl)prop-1-ylidene]triphenylphos-
phorane 4. From propyl(triphenyl)phosphonium bromide and
toluene-p-sulfonyl fluoride as yellow crystals (26%), mp 161–
163 ЊC (Found: C, 73.0; H, 6.15. C28H27O2PS requires C, 73.3;
H, 5.9%); νmax/cmϪ1 1586, 1435, 1310, 1280, 1254, 1165, 1133,
1104, 1062, 968, 950, 927, 810, 752, 740, 712, 690 and 660; δH
7.85–7.3 (15 H, m), 7.27 and 7.03 (4 H, AB pattern, J 9), 2.33
(3 H, s), 2.3–1.8 (2 H, m) and 0.82 (3 H, t, J 7); δP ϩ19.8; m/z
458 (Mϩ, 56%), 443 (100), 423 (8), 409 (20), 391 (3), 377 (2), 363
(3), 328 (3), 310 (49), 294 (100), 284 (17) and 269 (26).
[1-(2-Methylphenylmethylsulfonyl)ethylidene]triphenylphos-
phorane 11. From 2-methylbenzyl(triphenyl)phosphonium
chloride and ethanesulfonyl fluoride as colourless crystals
(66%), mp 150–153 ЊC (Found: Mϩ, 458.1461. C28H27O2PS
requires Mϩ, 458.1469); νmax/cmϪ1 1588, 1440, 1318, 1298, 1264,
1150, 1139, 1112, 1056, 998, 842, 765, 752, 725 and 693; δH 7.9–
7.4 (15 H, m), 7.3–7.1 (4 H, m), 4.34 (2 H, br s), 2.26 (3 H, s)
and 1.74 (3 H, d, J 15); δP ϩ21.7; m/z 458 (Mϩ, 18%), 354 (22),
353 (100), 305 (16), 291 (52), 289 (77), 263 (47) and 183 (48).
[1-(2-Methoxyphenylmethylsulfonyl)ethylidene]triphenylphos-
phorane 12. From 2-methoxybenzyl(triphenyl)phosphonium
chloride and ethanesulfonyl fluoride as colourless crystals
(58%), mp 193–194 ЊC (Found: C, 70.75; H, 5.9. C28H27O3PS
requires C, 70.9; H, 5.7%); νmax/cmϪ1 1580, 1493, 1436, 1264,
1250, 1235, 1188, 1130, 1100, 1072, 1022, 892, 872, 787, 756,
712 and 694; δH 7.8–7.35 (15 H, m), 7.25 (2 H, m), 7.0–6.75 (2
H, m), 4.30 (2 H, s), 3.78 (3 H, s) and 1.62 (3 H, d, J 16);
δP ϩ20.8; m/z 474 (Mϩ, 12%), 353 (100), 305 (4), 289 (12), 277
(8), 262 (56), 205 (24) and 121 (18).
[1-(4-Methylphenylsulfonyl)but-1-ylidene]triphenylphos-
phorane 5. From butyl(triphenyl)phosphonium bromide and
toluene-p-sulfonyl fluoride as yellow crystals (67%), mp 184–
186 ЊC (Found: C, 73.5; H, 6.2. C29H29O2PS requires C, 73.7;
H, 6.2%); νmax/cmϪ1 1586, 1440, 1256, 1218, 1186, 1140, 1110,
1065, 1030, 1010, 962, 832, 812, 750, 718 and 687; δH 7.95–7.25
(15 H, m), 7.37 and 7.10 (4 H, AB pattern, J 9), 2.37 (3 H, s),
2.0–1.1 (4 H, m) and 0.55 (3 H, t, J 7); δP ϩ19.8; m/z 472 (Mϩ,
11%), 443 (100), 423 (25), 317 (6), 287 (81) and 262 (13).
[(Phenylmethylsulfonyl)(phenyl)methylene]triphenylphosphor-
ane 6. From benzyl(triphenyl)phosphonium chloride and
phenylmethanesulfonyl fluoride as pale yellow crystals (82%),
mp 210–211 ЊC (lit.,6 210–211 ЊC) (Found: C, 75.9; H, 5.1.
C32H27O2PS requires C, 75.9; H, 5.4%); δH 7.55–6.95 (25 H, m)
Flash vacuum pyrolysis of ylides
The apparatus used was as described previously.20 All pyrolyses
were conducted at pressures in the range 10Ϫ3 to 10Ϫ1 Torr and
were complete within 1 h. Under these conditions the contact
time in the hot zone was estimated to be ≈10 ms.
In some cases the phosphorus containing products collected
at the furnace exit and the more volatile products were
recovered from the cold trap. Where necessary in the case of less
volatile products the entire pyrolysate was washed out together
and separated by chromatography. Yields were determined by
1
and 3.98 (2 H, s); δ 135.5 (2 C, d, J 3, C-2 of P᎐C᎐Ph), 134.8
calibration of the H NMR spectra by adding an accurately
᎐
C
(d, J 9, C-1 of P᎐C᎐Ph), 133.8 (d, J 10, C-2 of P-Ph), 131.5 (d,
weighed quantity of a solvent such as CH2Cl2 and comparing
integrals, a procedure estimated to be accurate to 10%.
FVP of the ylide 3 (200 mg) at 600 ЊC gave an oil at the
furnace exit which was shown by 31P NMR spectroscopy and
GC–MS to consist mainly of Ph3PO together with some un-
reacted starting material. In the cold trap was a mixture of
᎐
J <2, C-4 of P-Ph), 131.4, 131.2 (2 C), 128.3 (d, J 12, C-3 of
P-Ph), 128.1 (2 C), 127.7 (2 C), 127.5, 126.2 (d, J 119, C-1 of
P-Ph), 61.4 (CH ) and 47.0 (d, J 130, P᎐C) (one 4ry carbon not
᎐
2
apparent); δP ϩ18.2; m/z 506 (Mϩ, 18%), 415 (55), 367 (32), 351
(58), 273 (8), 271 (7), 241 (14), 183 (28), 165 (67) and 105 (100).
878
J. Chem. Soc., Perkin Trans. 1, 1998

View Article Online
Table 4 Summary of crystal data, data collection, structure solution and refinement details
(a) Crystal data
Molecular formula
Molar mass
C27H25O2PS
444.50
C32H27O2PS
506.57
Colour, habit
Crystal size, mm
Crystal system
a/Å
b/Å
c/Å
α(Њ)
Colourless, plate
0.37 × 0.25 × 0.13
Monoclinic
9.1270(10)
21.934(3)
11.692(2)
90
Colourless, block
0.33 × 0.25 × 0.25
Monoclinic
9.0145(15)
9.8195(15)
15.018(3)
90
β(Њ)
93.940(10)
90
2335.1(6)
P21/n
103.320(15)
90
1293.6(4)
P21
γ(Њ)
V/Å3
Space group
Z
4
2
F(000)
dcalc
936
1.264
0.228
532
1.300
0.215
µ/mmϪ1
(b) Data aquisitiona
Temp./K
294(1)
25 (10.0, 16.8)
26.89
Ϫ11 11; 0 27; 0 14
294(1)
25 (10.1, 18.2)
26.95
0 11; 0 12; Ϫ19 19
Unit cell reflections (θ rangeЊ)
Max. θ (Њ) for reflections
hkl range of reflections
Variation in 3 standard reflections
Reflcns measured
Unique reflections
Rint
1.0
1.0
5371
5069
0.017
2449
3175
2998
0.006
2191
Reflections with I > 2σ(I)
(c) Structure solution and refinement
H-atom treatment
Riding
280
Riding
325
No. of variables in L.S.
Weights
k in w = 1/(σ2Fo2 ϩ k)
[P = (Fo2 ϩ 2Fc2)/3] R, Rw, gof
Flack parameter
(0.0640P)2
0.043, 0.124, 0.92
—
Ϫ0.212, 0.228
0.000
(0.0613P)2
0.036, 0.099, 1.02
Ϫ0.01(10)
Ϫ0.228, 0.207
0.000
Density range in final ∆ map/e ÅϪ3
Final shift/error ratio
a Data collection on an Enraf Nonius CAD4 diffractometer with graphite monochromated Mo-Kα radiation (λ 0.7107 Å).
products whose main constituents were identified by NMR
spectroscopy, GC–MS and comparison with authentic samples
as 4-methylphenyl vinyl sulfone; m/z 182 (Mϩ, 12%), 139 (70),
107 (17) and 91 (100), ethyl 4-methylphenyl sulfone; δH 7.63 and
7.18 (4 H, AB pattern, J 8), 2.98 (2 H, q, J 7), 2.36 (3 H, s) and
1.18 (3 H, t, J 7); m/z 184 (Mϩ, 9%), 155 (12), 139 (6), 108 (12),
107 (12) and 91 (100); and di(4-methylphenyl) disulfide; m/z 246
(Mϩ, 35%), 137 (37), 123 (100) and 119 (38).
FVP of the ylide 4 (200 mg) at 750 ЊC gave an oil at the
furnace exit which was shown by 31P NMR spectroscopy and
GC–MS to consist almost entirely of Ph3PO. In the cold trap
was a mixture of products whose main constituents were iden-
tified by NMR spectroscopy, GC–MS and comparison with
authentic samples as toluene and 4-methylphenyl prop-1-enyl
sulfone; δH 7.7–7.3 (4 H, m), 6.91 (1 H, d of q, J 15, 7), 6.30
(1 H, d of q, J 15, 1) and 1.87 (3 H, dd, J 7, 1); m/z 196 (Mϩ,
16%), 139 (100), 117 (10), 108 (25) and 91 (76).
FVP of the ylide 6 (1.0 g) at 750 ЊC gave an oil at the furnace
exit which was shown by 31P NMR spectroscopy and GC–MS
to consist of (E)-stilbene (56%), (Z)-stilbene (11%) and Ph3P,
Ph3PO and Ph3PS in a ratio of 9:67:24. Chromatography on
silica using CH2Cl2 gave pure (E)-stilbene, identical with an
authentic sample.
FVP of the ylide 7 (2.0 g) at 600 ЊC gave an oil at the furnace
exit which was shown by 31P NMR spectroscopy and GC–MS
to consist of stilbene (6%, E:Z 5:1), 4-methylstilbene (47%,
E:Z 3:1), 4,4Ј-dimethylstilbene (9%, E:Z 2:1), bibenzyl (4%),
4-methylbibenzyl (8%), 4,4Ј-dimethylbibenzyl (3%) and Ph3P,
Ph3PO and Ph3PS in a ratio of 10:60:30. Chromatography on
silica using CH2Cl2 gave pure (E)-4-methylstilbene, identical
with an authentic sample.
FVP of the ylide 8 (200 mg) at 600 ЊC gave an oil at the
furnace exit which was shown by 31P NMR spectroscopy and
GC–MS to consist of Ph3P, Ph3PO and Ph3PS in a ratio of
25:57:18. In the cold trap was a mixture of products whose
main constituents were identified by NMR spectroscopy, GC–
MS and comparison with authentic samples as benzofuran
(14%); m/z 118 (Mϩ, 100%) 90 (65), 89 (70) and 63 (38), 2,3-
dihydrobenzofuran (7%); m/z 120 (Mϩ, 91%), 119 (67), 92 (55),
91 (100) and 65 (37), 2-methoxystilbene (39%, E:Z 5:1); δH
7.7–6.8 (11 H, m), 3.90 (3 H, s, E) and 3.82 (3 H, s, Z); m/z 210
(Mϩ, 65%), 179 (18), 167 (48), 165 (26), 152 (52), 119 (64), 104
(62) and 91 (100) and bibenzyl (11%); δH 7.7–7.3 (10 H, m) and
2.95 (4 H, s); m/z 182 (Mϩ, 14%), 165 (3), 104 (3) and 91 (100).
FVP of the ylide 9 (200 mg) at 600 ЊC gave an oil at the
furnace exit which was shown by 31P NMR spectroscopy and
GC–MS to consist of Ph3P, Ph3PO and Ph3PS in a ratio of
63:28:9. In the cold trap was a mixture of products whose
main constituents were identified by NMR spectroscopy, GC–
MS and comparison with authentic samples as benzothiophene
(58%); δH 8.1–7.9 (2 H, m) and 7.6–7.3 (4 H, m); m/z 134 (Mϩ,
100%) 108 (6), 90 (10) and 89 (8), (E)-2-methylthiostilbene
(5%); δH 7.7–7.0 (11 H, m), 2.48 (3 H, s); m/z 226 (Mϩ, 67%),
211 (100), 178 (43), 165 (18), 151 (12) and 77 (21), 3-benzyl-
2,3-dihydrobenzothiophene (5%); m/z 226 (Mϩ, 8%), 135 (100),
134 (35) and 91 (40), and bibenzyl (29%); δH 7.7–7.3 (10 H, m)
and 2.96 (4 H, s); m/z 182 (Mϩ, 8%), 165 (2), 104 (3) and 91
(100).
J. Chem. Soc., Perkin Trans. 1, 1998
879

View Article Online
FVP of the ylide 10 (200 mg) at 600 ЊC gave an oil at the
furnace exit which was shown by 31P NMR spectroscopy and
GC–MS to consist of Ph3P, Ph3PO and Ph3PS in a ratio of
12:64:24. In the cold trap was a mixture of hydrocarbons iden-
tified by NMR spectroscopy, GC–MS and comparison with
authentic samples as prop-1-enylbenzene (24%, E:Z 3:1), (E)-
stilbene (7%) and bibenzyl (49%).
FVP of the ylide 11 (200 mg) at 600 ЊC gave an oil at the
furnace exit which was shown by 31P NMR spectroscopy and
GC–MS to consist of Ph3P, Ph3PO and Ph3PS in a ratio of
12:60:28. In the cold trap was a mixture of products whose
main constituents were identified by NMR spectroscopy, GC–
MS and comparison with authentic samples as 2-methylprop-1-
enylbenzene (7%, E:Z 1:1), 2,2Ј-dimethylstilbene (9%, E:Z
1:1) and 2,2Ј-dimethylbibenzyl (34%).
details of the deposition scheme, see ‘Instructions for Authors’,
J. Chem. Soc., Perkin Trans 1, available via the RSC Web page
(http://www.rsc.org/authors). Any request to the CCDC for
this material should quote the full literature citation and the
reference number 207/180.
Acknowledgements
We thank Mrs Caroline Horsburgh for experimental assistance,
British Petroleum Research International Ltd for a Research
Studentship (M. J. D.) and the Royal Society for a Warren
Research Fellowship (R. A. A.).
References
1 Part 11, R. A. Aitken, I. M. Fairhurst, A. Ford, P. E. Y. Milne,
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2 H. Staudinger and E. Hauser, Helv. Chim. Acta, 1921, 4, 861.
3 A. M. van Leusen, B. A. Reith, A. J. W. Iedema and J. Strating, Recl.
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4 Preliminary communication, R. A. Aitken and M. J. Drysdale,
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5 W. Davies and J. H. Dick, J. Chem. Soc., 1931, 2104.
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7 B. C. Smith and G. H. Smith, J. Chem. Soc., 1965, 5516; E. Fluck
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8 R. A. Aitken, I. Gosney and J. I. G. Cadogan, Prog. Heterocycl.
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9 Y. Ito, M. Okano and R. Oda, Tetrahedron, 1967, 23, 2137.
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1967, 3057.
12 B. E. Sarver, M. Jones and A. M. van Leusen, J. Am. Chem. Soc.,
1975, 97, 4771, and references therein.
13 M. Hrytsuk, N. Etkin and T. Durst, Tetrahedron Lett., 1986, 27,
5679.
FVP of the ylide 12 (200 mg) at 600 ЊC gave an oil at the
furnace exit which was shown by 31P NMR spectroscopy and
GC–MS to consist of Ph3P, Ph3PO and Ph3PS in a ratio of
10:57:33. In the cold trap was a mixture of products whose
main constituents were identified by NMR spectroscopy, GC–
MS and comparison with authentic samples as 2-methoxyprop-
1-enylbenzene (6%, E:Z 1:1), 2,2Ј-dimethoxystilbene (5%,
E:Z 1:1) and 2-methylbenzaldehyde (22%).
Authentic samples of 4,4Ј-dimethylstilbene, 2,2Ј-dimethyl-
stilbene, 2-methoxyprop-1-enylbenzene, 2,2Ј-dimethoxystil-
bene, 2-methylprop-1-enylbenzene and prop-1-enylbenzene
were prepared as mixtures of E and Z isomers by Wittig reac-
tion under standard conditions followed by distillation or
column chromatography.
FVP of 4-methylstilbene (500 mg, E:Z 4:1) at 750 ЊC gave
a mixture of products which was largely unchanged starting
material but was shown by 1H NMR spectroscopy and GC–MS
to also contain (E)-stilbene and 4,4Ј-dimethylstilbene (~5% of
each).
FVP of prop-1-enylbenzene (500 mg) at 750 ЊC gave a liquid
in the cold trap which was mainly the unchanged starting
material and a solid at the furnace exit which was shown by
GC–MS to contain (E)-stilbene, bibenzyl and biphenyl, all in
low yield.
14 J. I. G. Cadogan, J. B. Husband and H. McNab, J. Chem. Soc.,
Perkin Trans. 2, 1983, 697.
15 G. Wittig and W. Böll, Chem. Ber., 1962, 95, 2526.
16 E. Anders, T. Clark and T. Gassner, Chem. Ber., 1986, 119, 1350.
17 A. J. Speziale and K. W. Ratts, J. Am. Chem. Soc., 1965, 87, 5603;
P. J. Wheatley, J. Chem. Soc., 1965, 5785.
FVP of triphenylphosphine (100 mg) at 750 ЊC under a
stream of SO2 gas gave a solid at the furnace exit which was
shown by 31P NMR spectroscopy and GC–MS to contain
mainly Ph3P together with Ph3PO and Ph3PS in an approximate
ratio of 5:2:1.
18 E. Späth, Monatsh. Chem., 1913, 34, 1965.
19 W. Davies and J. H. Dick, J. Chem. Soc., 1932, 483.
20 R. A. Aitken and J. I. Atherton, J. Chem. Soc., Perkin Trans. 1, 1994,
1281.
21 E. J. Gabe, Y. Le Page, J.-P. Charland, F. L. Lee and P. S. White,
J. Appl. Crystallogr., 1989, 22, 384.
X-Ray structure determinations
22 G. M. Sheldrick, SHELXS97, Program for the solution of crystal
structures, 1997, University of Göttingen, Germany.
23 G. M. Sheldrick, SHELXL97, Program for the refinement of crystal
structures, 1997, University of Göttingen, Germany.
24 C. K. Johnson, ORTEP—A Fortran Thermal Ellipsoid Plot
Program, Technical Report ORNL-5138, 1976, Oak Ridge National
Laboratory, USA.
Details of crystal data, data collection, structure solution and
refinement for 2 and 6 are summarised in Table 4. Molecule 6
crystallises in a chiral space group and the refinement allows the
direction of the chiral axis to be determined. Structure solution
was via the NRCVAX21 and SHELXS9722 programs; refine-
ment employed all F2 data and SHELXL97.23 In the final
refinement cycles, all non-H atoms were allowed anisotropic
displacement parameters. The ORTEP24 plots (Figs. 1 and 2)
were prepared with the aid of PLATON.25
25 A. L. Spek, PLATON Molecular Geometry and Graphics Program,
September 1997 version, University of Utrecht, Netherlands.
Atomic coordinates, molecular dimensions and anisotropic
displacement parameters have been deposited in CIF format at
the Cambridge Crystallographic Data Centre (CCDC). For
Paper 7/07948F
Received 4th November 1997
Accepted 4th December 1997
880
J. Chem. Soc., Perkin Trans. 1, 1998