Synthesis, structure, and reactivity of iminosulfonium ylides bearing an α-carbonyl group

Article abstract of DOI:10.1016/S0040-4039(01)01186-8

Treatment of methyl(methylimino)diphenylsulfonium tetraphenylborate (3) with NaH and subsequent acylation produced a new type of iminosulfonium ylides bearing an α-carbonyl group 5. The molecular structure of iminosulfonium phenacylide 5a was determined by X-ray crystallographic analysis. The ylide 5 reacted further with methyl triflate affording the corresponding novel alkylidenesulfonium salts 6.

Full text of DOI:10.1016/S0040-4039(01)01186-8

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 42 (2001) 6151–6154
Synthesis, structure, and reactivity of iminosulfonium ylides
bearing an a-carbonyl group
Takayoshi Fujii,a,* Tetsuya Suzuki,a Takashi Sato,a Ernst Hornb and Toshiaki Yoshimuraa,*
aDepartment of Material Systems Engineering and Life Science, Faculty of Engineering, Toyama University, Gofuku,
Toyama 930-8555, Japan
bDepartment of Chemistry, Rikkyo University, 3-34-1 Nishi-Ikebukuro, Toshima-ku, Tokyo 171-8501, Japan
Received 4 June 2001; revised 27 June 2001; accepted 29 June 2001
Abstract—Treatment of methyl(methylimino)diphenylsulfonium tetraphenylborate (3) with NaH and subsequent acylation
produced a new type of iminosulfonium ylides bearing an a-carbonyl group 5. The molecular structure of iminosulfonium
phenacylide 5a was determined by X-ray crystallographic analysis. The ylide 5 reacted further with methyl triflate affording the
corresponding novel alkylidenesulfonium salts 6. © 2001 Elsevier Science Ltd. All rights reserved.
Sulfur ylides have been extensively utilized as reagents
for organic syntheses.1 The sulfur ylides such as sulfo-
nium, oxosulfonium, and (dimethylamino)oxosulfon-
ium methylides are the most generally useful in oxirane-
and cyclopropane-forming reactions.1 On the other
hand, a large number of stable sulfonium ylides bearing
electronegative groups such as cyano and carbonyl
groups on the ylidic carbon have long been known.1a,2
Iminosulfonium ylides belong to the isoelectronic com-
pounds of oxosulfonium ylides, but very little has been
reported to date on these compounds. This is mainly
due to the lack of a facile preparation of this class of
compounds, especially the difficult access to their par-
ent iminosulfonium salts. Recently, we prepared
triphenyl-l6-sulfanenitrile bearing
a sulfurꢀnitrogen
triple bond from fluorodiphenyl-l6-sulfanenitrile (1)
with phenyllithium and found it easily reacts with sev-
eral electrophiles to give the corresponding N-substi-
tuted iminosulfonium salts.3 These results prompted
us to examine the deprotonation of methyl-
(methylimino)diphenylsulfonium salts 3 and subsequent
acylation which might lead to the isolation of stable
iminosulfonium acylmethylides 5. Here we describe the
first preparation and crystal structure determination of
the iminosulfonium ylides bearing an a-carbonyl group
and their methylation, which gives the corresponding
novel alkylidenesulfonium salts 6 with a sulfurꢀcarbon
double bond.
CH3
Ph S Ph
N
CH2
CH2
CH3
Ph S Ph
N
i, ii
iii
Ph S Ph
Ph S Ph
N
N
BPh4
CH3
CH3
CH3
2
3
4
iv
Ph
Ph S Ph
+
N
COPh
CH3
Scheme 1. Reagents and conditions: (i) TfOCH3, CH2Cl2, −20°C; (ii) NaBPh4, acetone; (iii) NaH, DMSO-d6 or THF, rt; (iv)
trans-benzalacetophenone, THF, rt.
Keywords: iminosulfonium ylides; alkylidenesulfonium salts; iminosulfonium salts; methyl-l6-sulfanenitrile; methylation; X-ray crystallographic
analysis.
* Corresponding authors. Fax: +81-76-445-6850 (T.Y.); fax: +81-76-445-6853 (T.F.); e-mail: yosimura@eng.toyama-u.ac.jp; tfujii@eng.toyama-u.
ac.jp
0040-4039/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(01)01186-8

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T. Fujii et al. / Tetrahedron Letters 42 (2001) 6151–6154
The reaction of methyldiphenyl-l6-sulfanenitrile (2),4
which was prepared by the reaction of 1 with methyl-
bond length (1.538(2) A) is close to that of
,
(methylimino)triphenylsulfonium perchlorate (1.514(4)
3b
,
,
lithium,
with
methyl
triflate
(TfOMe)
in
A). The O(1)ꢀC(4) bond length (1.248(2) A) is signifi-
dichloromethane at −20°C gave the corresponding
methyl(methylimino)diphenylsulfonium triflate. This
iminosulfonium salt is very hygroscopic, and was there-
fore isolated by converting it into tetraphenylborate salt
3 upon treatment with NaBPh4.5 Treatment of 3 with
sodium hydride in DMSO-d6 at room temperature
resulted in the formation of a yellow solution of imino-
sulfonium methylide 4 (Scheme 1). The 1H and 13C
NMR signals of the methylene moiety in 4 appear at lH
1.41 and lC 13.2, respectively. Addition of 1 equiv. of
trans-benzalacetophenone to the solution of ylide 4 in
THF resulted in the production of trans-1-benzoyl-2-
phenylcyclopropane and N-methyldiphenylsulfimide in
75 and 86% yields, respectively (Scheme 1). The forma-
tion of cyclopropane presented here should proceed via
a reaction pathway similar to that suggested for oxosul-
fonium and (dimethylamino)oxosulfonium methylides.6
cantly longer than that of a typical CꢁO double bond
10
,
,
(1.21 A), and the C(1)ꢀC(4) bond length (1.408(3) A)
is significantly shorter than that of a typical CꢀC single
10
,
bond (1.51 A). These findings are indicative of a
hybrid of the canonical forms 5aA, 5aB, and 5aC
(Scheme 2).
The acyl-stabilized iminosulfonium ylides 5 conceivably
have three reaction sites, carbonyl oxygen, ylidic car-
bon, and imino nitrogen toward electrophiles. The reac-
tion of 5 with TfOMe in CDCl3 at 0°C was examined
1
(Scheme 2). For example, in the H NMR of 5a, the
peaks of 5a at l 2.95 (s, NCH3) and 5.06 (s, CH)
gradually reduced on addition of TfOMe, and the two
sets of peaks of the expected N-methylated 6a (l 3.25
(s, N(CH3)2, 5.44 (s, CH)) and O-methylated com-
pound 7a (l 3.05 (s, NCH3), 3.38 (s, OCH3), 6.32 (s,
CH)) appeared. The product ratio of 6a and 7a in the
reaction of 5a is approximately 1.2 : 1, while only N-
methylated compound 6b was obtained in 5b. The
N-methylated compound 6a is sufficiently stable in
CDCl3 at 0°C, but it completely decomposed at room
Stable iminosulfonium ylides, iminosulfonium phenac-
ylide 5a and trifluoroacetylmethylide 5b were formed by
the reaction of 4 with 0.5 equiv. of benzoyl chloride and
trifluoroacetic anhydride, respectively, and subsequent
deprotonation of parent iminosulfonium salts by 4 in
THF at 0°C (Scheme 2). The iminosulfonium ylides 5a
and 5b were purified by column chromatography on
silica gel followed by recrystallization from
dichloromethane/hexane in 89 and 54% yields, respec-
tively. NMR, IR, and mass spectroscopy and elemental
analyses were consistent with the structure of 5.7 In the
13C NMR spectra of 5a and 5b, the ylidic carbon
appears at l 58.2 and 61.4, respectively. In the IR
spectra, CꢁO and SꢁN streching bands were observed
at 1590–1608 and 1160–1164 cm−1, respectively.
The crystal structure of the novel iminosulfonium ylide
5a was determined by X-ray crystallographic analysis
(Fig. 1).8 The X-ray analysis clearly reveals that the
configuration around the sulfur atom in 5a is a slightly
distorted tetrahedral structure with one SN bond and
three SC bonds. The bond length of the sulfurꢀylidic
Figure 1. The molecular structure of 5a. Selected bond dis-
,
tances (A) and bond angles (°): S(1)ꢀN(1), 1.538(2);
S(1)ꢀC(1), 1.672(2); S(1)ꢀC(2), 1.783(2); S(1)ꢀC(3), 1.803(2);
O(1)ꢀC(4), 1.248(2); N(1)ꢀC(5), 1.460(3); C(1)ꢀC(4), 1.408(3);
N(1)ꢀS(1)ꢀC(1), 122.0(1); N(1)ꢀS(1)ꢀC(2), 103.39(9); N(1)ꢀ
S(1)ꢀC(3), 113.20(9); C(1)ꢀS(1)ꢀC(2), 111.24(10); C(1)ꢀS(1)ꢀ
C(3); 101.44(9); C(2)ꢀS(1)ꢀC(3), 104.54(9); S(1)ꢀN(1)ꢀC(5),
116.7(2); S(1)ꢀC(1)ꢀC(4), 118.4(2); O(1)ꢀC(4)ꢀC(1), 122.8(2).
,
carbon (S(1)ꢀC(1)) is 1.672(2) A, which is shorter than
9
,
the sum of the covalent radii of S and C (1.81 A), and
those of sulfonium ylides, 2-dimethylsulfuranylidene-
2
,
malononitrile (1.719(8) A) and 2-dimethylsulfuranyli-
2
,
dene-1,3-indanedione (1.707(3) A). The S(1)ꢀN(1)
Ph
O
Ph
O
Ph
OCH3
i, ii
iii
+
3
Ph S CH CR
Ph S CH CR
N
Ph S CH CR
N
N
CH3
CH3
CH3
CH3
OTf
OTf
a: R = Ph
b: R = CF3
5
6
7
Ph
O
Ph
O
Ph
O
Ph S CH CPh
Ph S CH CPh
Ph S CH CPh
N
N
N
CH3
CH3
CH3
5aA
5aC
5aB
Scheme 2. Reagents and conditions: (i) NaH, THF, 0°C; (ii) PhCOCl or (CF3CO)2O, 0°C-rt; (iii) TfOCH3, CDCl3, 0°C.

T. Fujii et al. / Tetrahedron Letters 42 (2001) 6151–6154
6153
Chem. 1997, 62, 3802–3803; (b) Yoshimura, T.; Fujii, T.;
Hamata, K.; Imado, M.; Morita, H.; Ono, S.; Horn, E.
Chem. Lett. 1998, 1013–1014.
1
4. For 2: hygroscopic compound; mp 177°C (decomp.); H
NMR (400 MHz, CDCl3): l 3.52 (s, 3H), 7.50–7.55 (m,
6H), 7.83–7.86 (m, 4H); 13C NMR (100 MHz, CDCl3): l
48.2, 125.5, 129.2, 131.8, 147.5; IR (KBr) 1250 cm−1 (SN);
HRMS, calcd. for C13H13NS: 215.0769. Found: 215.0736.
1
5. For 3: mp 158–159°C; H NMR (400 MHz, CD3CN): l
2.84 (s, 3H), 3.99 (s, 3H), 6.84 (t, J=7.4 Hz, 4H), 6.99 (t,
J=7.4 Hz, 8H), 7.25–7.29 (m, 8H), 7.77–7.81 (m, 4H),
7.89–7.95 (m, 6H); 13C NMR (100 MHz, CD3CN): l
31.9, 39.1, 122.8, 126.6 (q, JCB=2.5 Hz), 128.9, 131.5,
131.9, 136.7, 137.3, 164.8 (q, JCB=49.3 Hz); IR (KBr)
1209 cm−1 (SN); FAB (m/z) 230 (M+−BPh4). Elemental
analysis calcd for C38H36BNS: C, 83.05; H, 6.60; N, 2.55.
Found: C, 83.43; H, 6.73; N, 2.55.
Figure 2. The molecular structure of 6b%. For clarity, the
6. Johnson, C. R.; Schroeck, C. W.; Shanklin, J. R. J. Am.
Chem. Soc. 1973, 95, 7424–7431.
,
tetraphenylborate is ommited. Selected bond distances (A)
and bond angles (°): S(1)ꢀN(1), 1.647(4); S(1)ꢀC(1), 1.660(5);
S(1)ꢀC(2), 1.772(4); S(1)ꢀC(3), 1.768(4); O(1)ꢀC(4), 1.201(6);
N(1)ꢀC(5), 1.490(6); N(1)ꢀC(6), 1.474(6); C(1)ꢀC(4), 1.414(7);
N(1)ꢀS(1)ꢀC(1), 122.0(2); N(1)ꢀS(1)ꢀC(2), 103.7(2); N(1)ꢀ
S(1)ꢀC(3), 103.5(2); C(1)ꢀS(1)ꢀC(2), 111.6(2); C(1)ꢀS(1)ꢀC(3);
108.6(2); C(2)ꢀS(1)ꢀC(3), 106.1(2); S(1)ꢀN(1)ꢀC(5), 112.7(3);
S(1)ꢀN(1)ꢀC(6), 117.3(3); S(1)ꢀC(1)ꢀC(4), 118.2(4); O(1)ꢀ
C(4)ꢀC(1), 127.0(4).
1
7. For 5a: mp 140°C; H NMR (400 MHz, CDCl3): l 2.95
(s, 3H), 5.06 (s, 1H), 7.36–7.43 (m, 3H), 7.50–7.57 (m,
6H), 7.91–7.93 (m, 2H), 8.03–8.06 (m, 4H); 13C NMR
(100 MHz, CDCl3): l 30.9, 58.2, 126.9, 127.0, 128.0,
129.6, 130.4, 132.5, 138.5, 139.7, 182.9; IR (KBr) 1590
cm−1 (CO), 1164 cm−1 (SN); MS (m/z) 333 (M+). Elemen-
tal analysis calcd for C21H19NOS: C, 75.64; H, 5.74; N,
4.20. Found: C, 75.85; H, 5.83; N, 4.10. For 5b: mp
1
120°C; H NMR (400 MHz, CDCl3): l 2.93 (s, 3H), 4.96
temperature. The N-methylated 6b and O-methylated
compound 7a could be isolated by converting them into
the corresponding tetraphenylborates 6b% and 7a%,
respectively.11 Furthermore, the molecular structure of
a novel alkylidenesulfonium tetraphenylborate 6b% was
determined by X-ray crystallographic analysis (Fig.
2).12 Further investigation of the chemistry of iminosul-
fonium ylides and alkylidenesulfonium salts is now in
progress.
(s, 1H), 7.54–7.64 (m, 6H), 7.95–7.98 (m, 4H); 13C NMR
(100 MHz, CDCl3): l 30.9, 61.4, 117.7 (q, JCF=289.6
Hz), 126.9, 129.9, 133.4, 136.6, 171.4 (q, JCF=32.9 Hz);
19F NMR (376 MHz, CDCl3): l −76.6; IR (KBr) 1608
cm−1 (CO), 1160 cm−1 (SN); MS (m/z) 325 (M+). Elemen-
tal analysis calcd for C16H14F3NOS: C, 59.07; H, 4.34; N,
4.31. Found: C, 59.37; H, 4.23; N, 4.39.
8. Crystal data of 5a: C21H19NOS, M=333.45, monoclinic,
,
a=9.974(1), b=8.670(1), c=20.516(2) A, i=91.620(9)°,
3
,
U=1773.6(3) A , T=242 K, space group P21/c (no. 14),
Z=4, v(Mo Ka)=1.89 cm−1, 5467 reflections measured,
5153 unique (Rint=0.020); R (I>3s(I))=0.041, Rw=0.050
for 3249 reflections and 293 parameters. Crystallographic
data for the structural analysis have been deposited with
the Cambridge Crystallographic Data Centre, CCDC No.
163270 for compound 5a.
Acknowledgements
This work was supported in part by a Grants-in-Aid for
Research (No. 09239218, 10133218, and 11120219)
from the Ministry of Education, Science, Sports and
Culture and by the Asahi Glass Foundation.
9. Emsley, J. The Elements, 3rd ed.; Oxford Univerity Press:
Oxford, 1998.
10. Smith, M. B.; March, J. March’s Advanced Organic
Chemistry, 5th ed.; Wiley: New York, 2001; Table 1.5,
pp. 21.
References
11. For 6b%: mp 127°C (decomp.); 1H NMR (400 MHz,
CD3CN): l 3.09 (s, 6H), 5.45 (s, 1H), 6.83 (t, J=7.2 Hz,
4H), 6.98 (t, J=7.2 Hz, 8H), 7.25–7.29 (m, 8H), 7.79–
7.83 (m, 4H), 7.95–7.99 (m, 2H), 8.03–8.06 (m, 4H); 13C
NMR (100 MHz, CD3CN): l 41.3, 51.2, 122.8, 125.1,
126.6 (q, JCB=2.5 Hz), 130.0, 133.0, 136.7, 138.8, 164.8
(q, JCB=49.4 Hz), 175.9 (q, JCF=36.2 Hz); IR (KBr)
1646 cm−1 (CO); FAB (m/z) 340 (M+-BPh4). Elemental
analysis calcd for C41H37BF3NOS: C, 74.66; H, 5.65; N,
2.12. Found: C, 74.78; H, 5.74; N, 2.31. For 7a%: mp
149–150°C; 1H NMR (400 MHz, CD3CN): l 3.01 (s,
3H), 3.41 (s, 3H), 6.35 (s, 1H), 6.83 (t, J=7.2 Hz, 4H),
6.98 (t, J=7.2 Hz, 8H), 7.24–7.29 (m, 8H), 7.56–7.60 (m,
2H), 7.65–7.76 (m, 7H), 7.81–7.85 (m, 2H), 8.05–8.08 (m,
1. For reviews, see: (a) Trost, B. M.; Melvin, Jr., L. S.
Sulfur Ylides; Academic Press: New York, 1975; (b)
Block, E. In The Chemistry of the Sulfonium Group;
Stirling, C. J. M.; Patai, S., Eds.; Wiley: New York, 1981;
Chapter 16, pp. 673–702; (c) Aggarwal, V. K. Synlett
1998, 329–336 and references cited therein.
2. Perozzi, E. F.; Paul, I. C. In The Chemistry of the
Sulfonium Group; Stirling, C. J. M.; Patai, S., Eds.;
Wiley: New York, 1981; Chapter 2, pp. 15–77 and refer-
ences cited therein.
3. (a) Yoshimura, T.; Hamada, K.; Imado, M.; Hamata, K.;
Tomoda, K.; Fujii, T.; Morita, H.; Shimasaki, C.; Ono,
S.; Tsukurimichi, E.; Furukawa, N.; Kimura, T. J. Org.

6154
T. Fujii et al. / Tetrahedron Letters 42 (2001) 6151–6154
4H); 13C NMR (100 MHz, CD3CN): l 32.0, 61.2, 94.2,
122.7, 126.6 (q, JCB=2.5 Hz), 128.2, 130.0, 130.1, 130.7,
131.7, 133.9, 134.6, 136.3, 136.7, 164.7 (q, JCB=49.4 Hz);
IR (KBr) 1265, 1084 cm−1 (COC), 1194 cm−1 (SN); FAB
(m/z) 348 (M+−BPh4). Elemental analysis calcd for
C46H42BNOS: C, 82.74; H, 6.34; N, 2.10. Found: C,
82.71; H, 6.38; N, 2.11.
clinic, a=9.541(2), b=16.739(2), c=10.902(2) A, i=
,
3
,
95.23(1)°, U=1733.8(4) A , T=296 K, space group P21
(no. 4), Z=2, v(Mo Ka)=1.43 cm−1, 5501 reflections
measured, 5428 unique (Rint=0.013); R (I>3s(I))=0.042,
Rw=0.056 for 2952 reflections and 436 parameters. Crys-
tallographic data for the structural analysis have been
deposited with the Cambridge Crystallographic Data
Centre, CCDC No. 163271 for compound 6b%.
12. Crystal data of 6b%: C41H37BF3NOS, M=659.61, mono-
.