A new synthesis of cyanocyclopropanes by the intramolecular alkylation of magnesium carbenoids as the key reaction

Article abstract of DOI:10.1016/j.tetlet.2010.04.090

Addition reaction of 1-chlorovinyl p-tolyl sulfoxides, derived from ketones and chloromethyl p-tolyl sulfoxide, with cyanomethyllithium gave adducts in quantitative yields. Treatment of the adducts with i-PrMgCl in THF resulted in the formation of cyanocyclopropanes via the intramolecular alkylation of the generated magnesium carbenoids. The intermediate of this reaction was proved to be a cyclopropylmagnesium chloride, and it was found to be reactive with electrophiles to give multi-substituted cyanocyclopropanes. The key reaction, intramolecular alkylation of magnesium carbenoid, is the first example for the reaction of the magnesium carbenoids with nitrile-stabilized carbanions.

Full text of DOI:10.1016/j.tetlet.2010.04.090

Tetrahedron Letters 51 (2010) 3380–3384
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Tetrahedron Letters
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A new synthesis of cyanocyclopropanes by the intramolecular alkylation of
magnesium carbenoids as the key reaction
*
Hideki Saitoh, Tsuyoshi Satoh
Graduate School of Chemical Sciences and Technology, Tokyo University of Science, Ichigaya-funagawara-machi 12, Shinjuku-ku, Tokyo 162-0826, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Addition reaction of 1-chlorovinyl p-tolyl sulfoxides, derived from ketones and chloromethyl p-tolyl
sulfoxide, with cyanomethyllithium gave adducts in quantitative yields. Treatment of the adducts with
i-PrMgCl in THF resulted in the formation of cyanocyclopropanes via the intramolecular alkylation
of the generated magnesium carbenoids. The intermediate of this reaction was proved to be a cyclopro-
pylmagnesium chloride, and it was found to be reactive with electrophiles to give multi-substituted
cyanocyclopropanes. The key reaction, intramolecular alkylation of magnesium carbenoid, is the first
example for the reaction of the magnesium carbenoids with nitrile-stabilized carbanions.
Ó 2010 Elsevier Ltd. All rights reserved.
Received 2 April 2010
Revised 20 April 2010
Accepted 22 April 2010
Available online 28 April 2010
Keywords:
Cyclopropane
Cyanocyclopropane
Multi-substituted cyclopropane
Magnesium carbenoid
Intramolecular alkylation
1. Introduction
multi-substituted cyanocyclopropanes 5 (E = electrophile). Details
of the procedure and the key reaction are reported.
Cyclopropanes are unambiguously one of the most important
and fundamental compounds in organic and synthetic organic
chemistry. Because of their highly strained nature, cyclopropanes
are quite reactive with a variety of reagents and have long been
recognized to be highly versatile and useful compounds in organic
synthesis. Innumerable studies on their chemistry, synthesis, and
synthetic uses have been performed; however, new methods for
their synthesis are still eagerly sought.1 We also have been inter-
ested in the synthesis of cyclopropanes based on our original
methods.2 In continuation of our investigation for the development
of new synthetic methods of cyclopropanes, we recently found that
the treatment of 1-chloroalkyl p-tolyl sulfoxides bearing a cyano
group at the 3-position with i-PrMgCl resulted in the formation
of cyanocyclopropanes in good yields (Scheme 1).3
2. Results and discussion
Recently, we reported a new method for the synthesis of
bicyclo[n.1.0]alkanes having a tert-butyl carboxylate or an acetam-
ide moiety 9 from 1-chlorovinyl p-tolyl sulfoxides 6.6 Thus, vinyl
sulfoxides 6 were treated with lithium enolate of tert-butyl carbox-
ylates or N,N-dimethylacetamide to afford adducts 7 in high yields.
Adducts 7 were then treated with i-PrMgCl to result in the forma-
tion of magnesium carbenoids 8. 1,3-CH insertion of the generated
magnesium carbenoids 8 took place between the carbenoid and
MgCl
Thus, 1-chlorovinyl p-tolyl sulfoxides 1, prepared from ketones
and chloromethyl p-tolyl sulfoxide,4 were treated with cya-
nomethyllithium to give adducts, 1-chloroalkyl p-tolyl sulfoxides
bearing a cyano group at 3-position 2, in high yields.5 Treatment
of 2 with i-PrMgCl resulted in the formation of cyanocyclopropanes
5 (E = H) in good to high yields. This reaction was proved to pro-
ceed via the intramolecular alkylation of the generated magnesium
carbenoid 3 and the intermediate of this alkylation was found to be
cyclopropylmagnesium chloride 4. The cyclopropylmagnesium
intermediates 4 could be trapped with some electrophiles to give
LiCH2CN
i-PrMgCl
R
R
Cl
R
R
CH2CN
S(O)Tol
R
R
CHCN
MgCl
S(O)Tol
Cl
1
Cl
2
3
H
H
C
CN
CN
E
Electrophile
R
R
R
C
R
MgCl
H
H
5
4
* Corresponding author. Tel.: +81 3 5228 8272; fax: +81 3 5261 4631.
E-mail address: tsatoh@rs.kagu.tus.ac.jp (T. Satoh).
Scheme 1.
0040-4039/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2010.04.090

H. Saitoh, T. Satoh / Tetrahedron Letters 51 (2010) 3380–3384
3381
Cl
LiCH2X
CH2X
S(O)Tol
CH2X
MgCl
i-PrMgCl
CH2X
1,3-CH insertion
S(O)Tol
( )n
( )n
( )n
( )n
Cl
Cl
6
9
8
7
X = COOBu-t, CONMe2
Cl
CN
O
O
O
LiCH2CN (2 eq)
99%
i-PrMgCl (5 eq)
O
S(O)Tol
S(O)Tol
Toluene, -78 ~ 0 °C, 2 h
Cl
10
11
CN
CN
CN
O
O
O
O
+
+
O
O
CH2Cl
12
13
14
Yield / %
11
12
14
13
11-L
11-P
11
4
23
0
46
94
Scheme 2.
methylene carbon of the ring to give bicyclo[n.1.0]alkanes 9 in high
yields (Scheme 2).
14 selectively in high yield and no 13 was observed (see the table
in Scheme 2).
As we were highly interested in this reaction, the scope and
limitation of the aforementioned procedure were investigated with
nitriles. Thus, as shown in Scheme 2, treatment of 1-chlorovinyl
p-tolyl sulfoxide 10, which was derived from 1,4-cyclohexanedione
mono ethylene ketal and chloromethyl p-tolyl sulfoxide,4 with cya-
nomethyllithium gave adduct 11 in quantitative yield as a mixture
of two diastereomers (we express the diastereomers as 11-L (less
polar product) and 11-P (more polar product), 11-L:11-P = 4:1).
The diastereomers were easily separated by silica gel column chro-
matography. At first, main product 11-L was treated with 5 equiv
of i-PrMgCl in toluene at À78 °C and the temperature of the reac-
tion mixture was slowly allowed to warm to 0 °C for 2 h. Three
products were obtained from this reaction. One product was chlo-
roalkane 12 (11%) and the other was the expected bicy-
clo[4.1.0]heptane 13 (23%). Somewhat surprisingly, the main
product was proved to be 1-cyanospiro[2.5]octane derivative 14
(46%). Interestingly, the same reaction of diastereomer 11-P gave
At first, we presumed that the products 13 and 14 were pro-
duced by the 1,3-CH insertion reaction of the generated magne-
sium carbenoid intermediate 15 (Scheme 3).6 Namely, when the
1,3-CH insertion reaction takes place between the magnesium
carbenoid and the carbon bearing Ha, 13 must be produced. On
the other hand, when the reaction takes place between the magne-
sium carbenoid and the carbon bearing Hb, 14 should be produced.
However, based on our experiences, it was expected that the 1,3-
CH insertion reaction between the carbenoid and the carbon bear-
ing an electron-withdrawing group was thought to take place with
difficulty.6,7 In order to obtain some information about the mecha-
nism of this reaction, we quenched this reaction with CH3OD and,
somewhat surprisingly, we found that the cyclopropane ring of
spiro-cyclic cyanocyclopropane 14 was perfectly deuterated at 2-
position.
From this result, it became apparent that the mechanism of this
reaction is as follows (Scheme 3). Thus, treatment of adduct 11
Hb
CN
i-PrMgCl
CN
CN
O
O
O
O
CN
1,3-CH insertion
+
S(O)Tol
MgCl
Cl
Ha Cl
15
11
14
13
CH3OH or
CH3OD
MgCl
CN
CN
CN
O
O
O
O
O
O
MgCl
MgCl
H (D)
Cl
17
14
D content 99%
16
Scheme 3. Mechanism for the generation of cyanocyclopropane 14 by the treatment of 11 with i-PrMgCl.

3382
H. Saitoh, T. Satoh / Tetrahedron Letters 51 (2010) 3380–3384
with i-PrMgCl results in the formation of magnesium carbenoid 15
by the sulfoxide–magnesium exchange reaction. The acidic hydro-
gen (Hb) was eliminated with the excess i-PrMgCl to produce cya-
no-stabilized carbanion 16. Intramolecular alkylation of the
magnesium carbenoid with the cyano-stabilized carbanion occurs
to give cyclopropylmagnesium chloride intermediate bearing a cy-
ano group 17. Quenching of 17 with deuterio methanol gives a
cyanocyclopropane bearing deuterium at 2-position 14 with high
deuterium incorporation. Intermolecular- or intramolecular-pro-
ton abstruction of magnesium carbenoid 15 afforded chloroalkane
12.
i-PrMgCl
(in Et2
PhCOCl (8 eq)
CuI (20 mol%)
CN
O, 5 eq)
CN
O
O
THF, 0 °C,
30 min
S(O)Tol
0 °C, 1 h
65%
MgCl
Cl
17
11-L
H
H
CN
CN
O
O
O
+
O
COPh
H
COPh
H
Since this is an unprecedented and interesting reaction for the
synthesis of cyanocyclopropanes, we investigated to find the con-
ditions of choice for obtaining 14 from 11-L and the results are
summarized in Table 1. When this reaction was conducted in ethe-
real solvent, generation of bicyclic compound 13 was eliminated.
Solvation of the magnesium carbenoid intermediate with Lewis ba-
sic ethereal solvent was thought to be the reason for this result. As
shown in entries 1–5, this reaction can be carried out at 0 °C or at
room temperature to afford the desired 14 in up to 78% yield. Espe-
cially, when this reaction was carried out with 5 equiv of i-PrMgCl
in THF at 0 °C and the reaction was quenched with CH3OD, spiro-
cyanocyclopropane 14 was obtained in 78% yield with 99% deute-
rium content. In these conditions the yield of 12 could be reduced
to 10% (entry 4).
Methylmagnesium chloride, ethylmagnesium chloride, and
cyclopentylmagnesium chloride worked; however, no better result
was obtained (entries 6–8). Isopropylmagnesium bromide worked
well to give 14 in somewhat better yield; however, quite low deu-
terium incorporation was observed (entries 9 and 10). Reducing
the amount of i-PrMgCl resulted in increasing the protonated prod-
uct 12 (entries 11–13). We selected the conditions shown in entry
4 as the conditions of choice for this study.
18
19
18:19 = 2:1
Scheme 4. Generation of cyclopropylmagnesium chloride intermediate 17 from
11-L and trapping with benzoyl chloride.
investigated the feasibility of this plan as shown in Scheme 4. Thus,
adduct 11-L was treated with 5 equiv of i-PrMgCl in THF at 0 °C.
After 30 min, Cu(I) iodide (20 mol %) followed by benzoyl chloride
(8 equiv) were added to the reaction mixture and the whole reac-
tion mixture was stirred at 0 °C for 1 h. This procedure gave the de-
sired benzoylated products 18 and 19 (18:19 = 2:1) in 65% yield.
The stereochemistry of the products was easily determined from
the coupling constant of their 1H NMR (JH–H of 18, 5.2 Hz; JH–H of
19, 7.8 Hz).8 When this reaction was conducted without Cu(I)
iodide, only a complex mixture was obtained.
In order to investigate the generality of this procedure, various
1-chloroalkyl p-tolyl sulfoxides bearing a cyano group 2, derived
from symmetrical ketones, were treated with i-PrMgCl under the
aforementioned conditions followed by electrophiles and the re-
sults are summarized in Table 2. As shown in entries 1–3, the reac-
tion of 2, derived from acetone, gave benzoylated and benzylated
cyanocyclopropanes in up to 70% yield. The reaction with benzal-
dehyde proceeded in the presence of EtAlCl2 as a Lewis acid to give
adducts as a mixture of four diastereomers.
As mentioned above, the intermediate of this reaction was
proved to be cyclopropylmagnesium chloride bearing a cyano
group 17. If this intermediate can be trapped with electrophiles
other than proton, the whole procedure becomes a new method
for the synthesis of multi-substituted cyanocyclopropanes. We
The reaction of 2 derived from benzophenone gave 5 in 42%
with significant amount of rearranged product 20 as a by-product
Table 1
Investigation for the best conditions for obtaining cyanocyclopropane 14 by the treatment of 11-L with Grignard reagent
1) Grignard reagent (equiv)
CN
CN
O
O
CN
O
O
O
O
Conditions
+
S(O)Tol
CH2Cl
H (D)
2) CH3OH or CH3OD
Cl
12
14
11-L
Entry
Grignard reagent (equiv)
Solvent
Temp (°C)
Time (h)
Yield/% (D content/%)
12
14
1
2
3
4
5
6
7
8
9
10
11
12
13
i-PrMgCla (5)
i-PrMgCla (5)
i-PrMgCla (5)
i-PrMgCla (5)
i-PrMgCla (5)
MeMgCl (5)
Et2O
THF
THF
THF
THF
THF
THF
THF
THF
THF
THF
THF
THF
À78 to 0
À78 to 0
À40
2
2
12
8
64
69
67
78 (99)
75
49
53
77
74 (18)
86 (12)
77 (33)
61 (20)
0
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
15
10
13
43
32
14
16
13
18
28
47
0
Room temperature
0
0
0
EtMgCl (5)
c-PentMgCl (5)
i-PrMgBrb (5)
i-PrMgBrb (5)
i-PrMgCla (3.5)
i-PrMgCla (3)
i-PrMgCla (2)
0
Room temperature
0
0
0
a
Isopropylmagnesium chloride in diethyl ether was used.
Isopropylmagnesium bromide in THF was used.
b

H. Saitoh, T. Satoh / Tetrahedron Letters 51 (2010) 3380–3384
3383
Table 2
Synthesis of multi-substituted cyanocyclopropanes 5 from 1-chloroalkyl p-tolyl sulfoxides bearing a cyano group at the 3-position 2 with i-PrMgCl followed by electrophiles
H
C
H
C
CN
E
CN
i-PrMgCl
Electrophile
R
R
CH2CN
S(O)Tol
R
R
R
R
MgCl
H
H
Cl
5
4
2
Entry
2
Electrophilea
Additive
5
R
Yield/% (diastereomeric ratio)
1
2
3
4
5
CH3
CH3
CH3
Ph
PhCOCl
PhCH2Br
PhCHO
CH3OD
CH3OD
CuIb
70 (3:2)
44 (1:0)
50 (Four diastereomers)
42d (Deuterium content; 95%)
79 (Deuterium content; 91%)
CuIb
c
EtAlCl2
PhCH2CH2
-H2CH2C
O
CH2CH2-
O
6
7
8
9
CH3OD
78 (Deuterium content; 99%)
-H2CH2C
O
CH2CH2-
O
PhCOCl
CuIb
CuIb
CuIb
65 (2:1)
58 (3:1)
14 (1:0)
-H2CH2C
O
CH2CH2-
O
PhCH2CH2COCl
PhCH2Br
-H2CH2C
O
CH2CH2-
O
10
11
12
13
–(CH2)11
–(CH2)11
–(CH2)14
–(CH2)14
–
–
–
–
CH3OD
PhCOCl
CH3OD
PhCOCl
78 (Deuterium content; 99%)
64 (3:1)
73 (Deuterium content; 99%)
61 (3:1)
CuIb
CuIb
a
b
c
Eight equivalents of electrophile were used.
20 mol % of copper(I) iodide, based on 2 was used.
Eight equivalents of EtAlCl2 were added.
d
Significant amount (25%) of rearranged product 20 was obtained.
CH2CN
Ph
Ph
20
(entry 4). The reaction of 2 derived from 1,5-diphenyl-3-pentanone
gave 5 in 79% yield (entry 5). The results in entries 6 and 7 were
mentioned before (Table 1 and Scheme 4). Alkylation of the cyclo-
propylmagnesium intermediate with benzyl bromide again gave
the desired product in low yield (entry 9). The reaction of 2 derived
from cyclododecanone and cyclopentadecanone gave moderate to
good yield of the desired products (entries 10–13).
In conclusion, a method for the synthesis of multi-substituted
cyanocyclopropanes was established starting from 1-chlorovinyl
p-tolyl sulfoxides with acetonitrile and electrophiles. The key
reaction of this procedure is the intramolecular alkylation of mag-
nesium carbenoid with cyano-stabilized carbanion followed by
trapping the cyclopropylmagnesium chloride intermediate with
electrophiles. We believe that the results described in this Letter
References and notes
1. Some recent reviews concerning chemistry, synthesis, and synthetic uses of
cyclopropanes: (a) Wong, H. N. C.; Hon, M.-Y.; Tse, C.-W.; Yip, Y.-C.; Tanko, J.;
Hudlick, T. Chem. Rev. 1989, 89, 165; (b) Salaun, J. Chem. Rev. 1989, 89, 1247; (c)
Sonawane, H. R.; Bellur, N. S.; Kulkarni, D.; Ahuja, J. R. Synlett 1993, 875; (d)
Doyle, M. P.; Protopopova, M. N. Tetrahedron 1998, 54, 7919; (e) Donaldson, W.
A. Tetrahedron 2001, 57, 8589; (f) Lebel, H.; Marcoux, J.-F.; Molinaro, C.;
Charette, A. B. Chem. Rev. 2003, 103, 977; (g) Pietruszka, J. Chem. Rev. 2003, 103,
1051; (h) Reissig, H.-U.; Zimmer, R. Chem. Rev. 2003, 103, 1151; (i) Kulinkovich,
O. G. Chem. Rev. 2003, 103, 2597; (j) Halton, B.; Harvey, J. Synlett 2006, 1975; (k)
Pellissier, H. Tetrahedron 2008, 64, 7041.
2. Some recent papers concerning synthesis of cyclopropanes by our original
methods: (a) Satoh, T.; Musashi, J.; Kondo, A. Tetrahedron Lett. 2005, 46, 599; (b)
Satoh, T.; Miura, M.; Sakai, K.; Yokoyama, Y. Tetrahedron 2006, 62, 4253; (c)
Fukushima, I.; Gouda, Y.; Satoh, T. Tetrahedron Lett. 2007, 48, 1855; (d) Ogata, S.;
Masaoka, S.; Sakai, K.; Satoh, T. Tetrahedron Lett. 2007, 48, 5017; (e) Yamada, Y.;
Miura, M.; Satoh, T. Tetrahedron Lett. 2008, 49, 169; (f) Miyagawa, T.; Tatenuma,
T.; Tadokoro, M.; Satoh, T. Tetrahedron 2008, 64, 5279; (g) Satoh, T.; Nagamoto,
S.; Yajima, M.; Yamada, Y.; Ohata, Y.; Tadokoro, M. Tetrahedron Lett. 2008, 49,
5431; (h) Yajima, M.; Nonaka, R.; Yamashita, H.; Satoh, T. Tetrahedron Lett. 2009,
50, 4754; (i) Yamada, Y.; Mizuno, M.; Nagamoto, S.; Satoh, T. Tetrahedron 2009,
65, 10025.
will contribute to
clopropanes.
a synthesis of multi-substituted cyanocy-
Acknowledgements
3. Some recent papers for the synthesis of cyanocyclopropanes: (a) D’hooghe, M.;
Mangelinckx, S.; Persyn, E.; Van Brabandt, W.; De Kimpe, N. J. Org. Chem. 2006,
71, 4232; (b) Barbasiewicz, M.; Marciniak, K.; Fedorynski, M. Tetrahedron Lett.
2006, 47, 3871; (c) Elinson, M. N.; Feducovich, S. K.; Vereshchagin, A. N.;
Gorbunov, S. V.; Belyakov, P. A.; Nikishin, G. I. Tetrahedron Lett. 2006, 47, 9129;
(d) D’hooghe, M.; Vervisch, K.; De Kimpe, N. J. Org. Chem. 2007, 72, 7329; (e) Liu,
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This work was supported by a Grant-in-Aid for Scientific Re-
search No. 19590018 from the Ministry of Education, Culture,
Sports, Science and Technology, Japan, which is gratefully
acknowledged.

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H. Saitoh, T. Satoh / Tetrahedron Letters 51 (2010) 3380–3384
Lett. 2007, 17, 3784; (f) Cao, W.; Zhang, H.; Chen, J.; Deng, H.; Shao, M.; Lei, L.;
added to the reaction mixture. After the reaction mixture was stirred for 5 min,
benzoyl chloride (1.6 mmol; 8 equiv) was added and the whole reaction mixture
was stirred for 1 h. The reaction was quenched with satd aq NH4Cl and the
whole reaction mixture was extracted with CHCl3. The products were purified
by silica gel column chromatography to afford 38.7 mg (65%) of a 2:1 mixture of
cyanocyclopropanes 18 and 19. Compound 18: colorless crystals; mp 175–
176 °C (hexane–AcOEt); IR (KBr) 3015, 2939, 2234 (CN), 1680 (CO), 1595, 1451,
Qian, J.; Zhu, Y. Tetrahedron 2008, 64, 6670; (g) Chen, S.; Ma, J.; Wang, J.
Tetrahedron Lett. 2008, 49, 6781; (h) Denton, J. R.; Cheng, K.; Davies, H. M. L.
Chem. Commun. 2008, 1238; (i) Mangelinckx, S.; D’hooghe, M.; Peeters, S.; De
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Tetrahedron 2003, 59, 9599.
1265, 1240, 1213, 1030, 903 cmÀ1 1H NMR d 1.40–1.51 (1H, m), 1.57–1.66 (3H,
;
5. (a) Satoh, T.; Ota, H. Tetrahedron Lett. 1999, 40, 2977; (b) Satoh, T.; Ota, H.
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8. To a flame-dried flask was added dry THF (3 mL) followed by i-PrMgCl (1 mmol;
5 equiv, in ether) at 0 °C. A solution of adduct 11-L (73.6 mg; 0.2 mmol) in THF
(1 mL) was added to the solution of i-PrMgCl dropwise with stirring. After the
reaction mixture was stirred at 0 °C for 30 min, CuI (0.04 mmol; 0.2 equiv) was
m), 1.80–2.16 (4H, m), 2.46 (1H, d, J = 5.2 Hz), 3.09 (1H, d, J = 5.2 Hz), 3.88–3.99
(4H, m), 7.47–7.55 (2H, m), 7.59–7.66 (1H, m), 7.93–7.99 (2H, m). MS m/z (%)
297 (M+, 9), 192 (66), 105 (100), 99 (30), 86 (31), 77 (33). Calcd for C18H19NO3:
M, 297.1365. Found: m/z 297.1363. Compound 19: colorless crystals; mp 141–
142 °C (hexane–AcOEt); IR (KBr) 2925, 2949, 2864, 2238 (CN), 1668 (CO), 1594,
1557, 1448, 1412, 1220, 1129, 1098, 1040, 715 cmÀ1 1H NMR d 1.48–1.59 (1H,
;
m), 1.64–1.85 (4H, m), 1.86–1.99 (3H, m), 1.92 (1H, d, J = 7.7 Hz), 2.89 (1H, d,
J = 7.7 Hz), 3.88–4.01 (4H, m), 7.46–7.54 (2H, m), 7.57–7.65 (1H, m), 7.92–7.99
(2H, m). MS m/z (%) 297 (M+, 10), 192 (46), 105 (100), 99 (19), 86 (30), 77 (34).
Calcd for C18H19NO3: M, 297.1365. Found: m/z 297.1366.