A new entry to alkylidenecyclopropanes through a Ramberg-Backlund rearrangement of cyclopropylsulfones

Article abstract of DOI:10.1081/SCC-120016326

The first use of the Ramberg-Backlund rearrangement of cyclopropylsulfones in the synthesis of alkylidenecyclopropanes is reported.

Full text of DOI:10.1081/SCC-120016326

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A New Entry to Alkylidenecyclopropanes
Through a Ramberg-Backlund Rearrangement of
Cyclopropylsulfones
Angela M. Bernard a , Angelo Frongia a & Pier P. Piras a
a Dipartimento di Scienze Chimiche , Università di Cagliari , Complesso Universitario di
Monserrato , S.S. 554, Bivio per Sestu, Monserrato, Cagliari, Italy
Published online: 17 Aug 2006.
To cite this article: Angela M. Bernard , Angelo Frongia & Pier P. Piras (2003) A New Entry to Alkylidenecyclopropanes Through
a Ramberg-Backlund Rearrangement of Cyclopropylsulfones, Synthetic Communications: An International Journal for Rapid
Communication of Synthetic Organic Chemistry, 33:5, 801-817, DOI: 10.1081/SCC-120016326
To link to this article: http://dx.doi.org/10.1081/SCC-120016326
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SYNTHETIC COMMUNICATIONSÕ
Vol. 33, No. 5, pp. 801–817, 2003
A New Entry to Alkylidenecyclopropanes
Through a Ramberg-Backlund
Rearrangement of Cyclopropylsulfones
*
Angela M. Bernard,Angelo Frongia,and Pier P. Piras
Dipartimento di Scienze Chimiche, Universita di
Cagliari, Complesso Universitario di Monserrato,
S.S. 554, Bivio per Sestu, Monserrato, Cagliari, Italy
ABSTRACT
The firstuse of hte Ramberg-Backlund rearrangementof cyclo-
propylsulfones in the synthesis of alkylidenecyclopropanes is
reported.
Key Words: Cyclopropanes; Alkylidenecyclopropanes; Ramberg-
Backlund; Cyclopropylsulfones.
*Correspondence: Pier P. Piras, Dipartimento di Scienze Chimiche, Universita
di Cagliari, Complesso Universitario di Monserrato, S.S. 554, Bivio per Sestu,
I-09042 Monserrato, Cagliari, Italy; Fax: þ39 070/6754388; E-mail: pppiras@
unica.it.
801
DOI: 10.1081/SCC-120016326
Copyright & 2003 by Marcel Dekker, Inc.
0039-7911 (Print); 1532-2432 (Online)
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802
Bernard,Frongia,and Piras
INTRODUCTION
Highly strained molecules are generally not very stable and this fact
limits their use in organic synthesis. Methylene and alkylidenecyclopro-
panes are particularly interesting molecules because, despite the high level
of strain, they are very often stable and exhibit an otherwise unattainable
chemical reactivity.[1] As a matter of fact their Ni(0)- or Pd(0)-catalyzed
reaction with alkenes and alkynes constitutes an important route for the
synthesis of five membered rings[1a,2–6]; they undergo ring opening with
palladium chloride to give ꢀ-allyl palladium complexes,[7] 1,3-dipolar
cycloaddition with nitrones[8] and are suitable precursors of cyclobuta-
nones[9–12] and cyclobutanols.[13] On the other hand, an indication of their
stability is given by the aminoacids hypoglycine[14,15] and methylene-
cyclopropyl glycine,[16] two natural products exhibiting relevant biologi-
cal activity, one isolated from the unripe fruits of the ackee tree (Blighia
sapida) and the other from the kernels of the litchi fruits.
The increasing interest in these molecules has stimulated a number of
synthetic strategies that have been recently reviewed.[17] In spite of the
several methods used for their synthesis,[18–34] only one unsuccessful
attempt[35] has been published using the well known Ramberg-
Backlund reaction for the synthesis of the bicyclopropylidene. The failure
of this attempt was attributed by the authors to the established unreac-
tivity of cyclopropyl halides and sulfonate esters toward displacement
reactions due to the adverse hybridization characteristic of external
bonds attached to three-membered rings (I strain). They pointed out
that a-haloalkyl cyclopropylsulfones might be expected to afford the
corresponding methylenecyclopropanes when treated with base since
the I strain factor is not present in these cases.
RESULTS AND DISCUSSION
As a part of our continuing interest in alkylidenecyclopropanes
chemistry,[13] we herein reportour successful use of hte Ramberg-
Backlund reaction for their synthesis. Derivatives 6a–8a, and 4b pre-
pared, as shown in Sch. 1, in 60–69% and 30% yield, were submitted
to basic treatment to give the corresponding alkylidenecyclopropanes
9a–11a, 5b in yields ranging from 35% to 90%.
A preliminary study was carried out using derivative 6a, to find the
bestbase ot be used (Table 1). The use of MeLi or n-BuLi gave the
expected alkylidenecyclopropane 9a accompanied by 3a (70:30), probably
coming from a lithium–halogen exchange.

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Alkylidenecyclopropanes
803
*The chlorination was carried out by treating 3b with n-BuLi and NCS. See
experimental part.
Scheme 1.
Table 1. Reaction of derivative 6a with different bases.
Entry Substrate Base
React. cond.
Time
Productsa Yieldsb (%)
1
2
3
4
6a
6a
6a
6a
n-BuLi THF, ꢀ25ꢁC ! r.t. 10 h 9a, 3a (70:30)
MeLi THF, ꢀ80ꢁC ! r.t. 10 h 9a, 3a (68:32)
70
72
73
90
MeONa MeOH, 65ꢁC
18 h
30 min
13c
9a
LDA THF, ꢀ15ꢁC
1
aIn parentheses the ratios evaluated by H NMR (Entries 1, 2).
bIsolated products.
c[1-(Cyclopropylsulfonyl)-2-methoxyethyl]benzene was the only isolated product.
On the other hand, despite the reported[35] deprotonation of a cyclo-
propyl proton adjacent to a phenylsulfone group in a cyclopropylsulfone
by MeONa, the use of this base led to the formation of the [1-(cyclopro-
pylsulfonyl)-2-methoxyethyl]benzene 13 in 73% yield, probably through
an elimination–addition reaction involving the vinyl sulfone 12 as an
intermediate (Sch. 2). The best results were obtained using LDA at
ꢀ15ꢁC as reported in the Table 1.
Directchlorinaiton of 2a using CCl4/NaOH in DMF,[36] led to a
mixture of mono- and dichloro derivatives 14 and 15 easily separated
by column chromatography. When we forced the conditions during the

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804
Bernard,Frongia,and Piras
Scheme 2.
Scheme 3.
chlorination of 2a the trichloro sulphone 16 was obtained in 65% yield
(Sch. 3). Reaction of 14 and 15 with LDA gave the alkylidenecyclopro-
pane 17 and 18 in low yield (25% and 32%), probably as a consequence
of a very acidic proton in 14 that competes with the cyclopropylic proton

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Alkylidenecyclopropanes
805
triggering other reaction paths. In the case of 15, the low yields of 18 are,
probably due to different reaction paths on which, at the moment, we
cannotmake any hypothesis.
The trichloro derivative 16 seemed to be the ideal candidate to carry
out the transformation into the alkylidenecyclopropane 20 through an
elimination addition sequence implying the intermediacy of the cyclopro-
penylsulfone 19. As a matter of fact a similar elimination–addition
sequence has previously been reported by Paquette.[35] Reaction of 16
either with t-BuOK or p-Me–C6H4MgBr always led to the alkylidene-
cyclopropane 18 in 27% and 50% yields allowing, in this way, to overcome
the difficulties previously found by starting from the dichlorosulphone 15.
This reaction path can be justified on the basis of the high positive
character of an halogen atom in a- position to a sulphone group. In fact
(Sch. 4) the base could attack the chlorine (path b) causing the formation
of a carbanion that could trigger the Ramberg-Backlund process, instead
of attacking the cyclopropyl proton (path a) to give the intermediate
cyclopropene 19.
Our method for the synthesis of alkylidenecyclopropanes is comple-
mentary to the already published ones and can exploit the great facility of
preparing cyclopropanes carrying sulfide, sulfoxide, or a sulfone group
for example through a Michael addition to a suitably substituted alkene.
As an example we have prepared the MOM protected alkylidenecyclo-
propanemethanol 28, that is to be considered a key intermediate for the
synthesis of a hypoglycine[14,15] carrying substituents on the double bond.
The sequence, shown in Sch. 5, involves several steps with yields ranging
Scheme 4.

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Bernard,Frongia,and Piras
Scheme 5.
from 70% to 94%, except for the last step that occurs with poor
yields (30%).
The synthesis has been achieved through the preliminary synthesis of
the E-cyclopropyl ester 22 by a Michael addition in benzene of the lithium
salt of benzylmercaptane on the commercially available methyl 4-bromo
crotonate 21. The structure of 22 has been unambiguously assigned from
NOESY and differential NOE experiments and it is in accordance with
analogous products previously reported.[36,37] Reduction with LiAlH4
and protection of the alcohol with chloromethyl methyl ether led to the
compound 24 that has been first oxidized to the corresponding sulfone 25
and then alkylated with methyl iodide to give 26. The chlorination of 26
in the previously reported conditions[38] gave 27 that by treatment with
LDA at ꢀ15ꢁC in THF afforded 28 in 30% yields as a Z/E mixture
(60:40) of the two geometric isomers. The stereochemistry of 28 has
been tentatively assigned on the basis of the different chemical shift of the
methyl group in the geometric isomers. The signal at 2.23 ppm has been

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Alkylidenecyclopropanes
807
attributed to the isomer with the Z configuration where the deshielding
effect of the ether group could be exerted, and consequently the other at
2.34 ppm to the E isomer.
CONCLUSIONS
A new access to alkylidenecyclopropanes through a Ramberg-
Backlund rearrangementof cyclopropylsulphones is repoertd. The
reaction is quite versatile due to the facility of synthesis of cyclopropyl-
sulphones and several new applications can be envisaged. Further studies
are in progress especially for what concerns the optimization of the
conditions of a-halogenation of the sulphone group and the results will
be published in due course.
EXPERIMENTAL
Reagent-grade commercially available reagents and solvents were
used. Analytical TLC plates and silica gel were purchased from Merck.
IR spectra were recorded on a Perkin-Elmer 1310 grating spectrophot-
1
ometer using NaCl plates. H and 13C NMR spectra were recorded on a
Varian VXR-300 spectrometer with tetramethylsilane as internal refer-
ence; ꢁ values are given in ppm and J values in Hz. Mass spectra were
obtained at 70 eV with a Hewlett-Packard 5989A mass spectrometer.
Microanalyses were carried outon a Carlo-Erba 1106 Elemenatl
Analyzer. The methyl-4-bromo crotonate 21 was commercially available.
Products 1a,[39] 2a,[39,40] 14 and 15,[40] 1b,[41] 9a and 17,[19] have been
previously reported.
Cyclopropyl Ethyl Sulfone (2b)
t-BuOK (8.1 g, 72 mmol) was added to a solution of 1b (6.2 g,
36 mmol) in t-BuOH (50 mL). After refluxing for 2 h the solution was
poured onto brine and extracted with diethyl ether. Evaporation of the
solvent and column chromatography (silica gel) with ethyl acetate–light
petroleum 4:3 gave pure 2b as a yellow oil. Yield: 75%. IR (neat, cmꢀ1):
1130, 1303. 1H NMR (CDCl3) ꢁ: 1.03–1.23 (m, 4H), 1.43 (t, 3H,
J ¼ 7.5 Hz), 2.37–2.44 (m, 1H), 3.07 (q, 2H, J ¼ 7.5 Hz). 13C NMR
(CDCl3) ꢁ: 4.41, 6.93, 28.34, 48.19. Anal. calcd. for C5H10O2S: C,
44.75; H, 7.51; S, 23.89. Found: C, 44.90; H, 7.50; S, 23.96.

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808
Bernard,Frongia,and Piras
General Method for the Synthesis of
Cyclopropylsulfones 3a,4a,5a,3b
To a stirred solution of cyclopropanes 2a or 2b (5.1 mmol) in THF
(10 mL) at ꢀ10ꢁC, a 2.08 M solution of n-butyllithium in hexane
(2.45 mL, 5.1 mmol) was added. The mixture was stirred for 1 h while
it reached room temperature, cooled to 0ꢁC, and then the alkyl halide
(5.1 mmol) was added. After 20 h at room temperature the solution was
poured onto water and ice and extracted repeatedly with diethyl ether.
The ethereal solution was dried (Na2SO4) and evaporated under vacuum.
The remaining oil was chromatographed on a silica gel column (light
petroleum/diethyl ether 1:3).
[1-(Cyclopropylsulfonyl)ethyl]benzene (3a): Pale yellow oil. Yield: 80%.
IR (neat, cmꢀ1): 1136, 1317. 1H NMR (CDCl3) ꢁ: 0.82–1.28 (m, 4H), 1.80
(d, 3H, J ¼ 7 Hz), 2.12 (m, 1H), 4.22 (q, 1H, J ¼ 7 Hz), 7.41 (s, 5H).
13C NMR (CDCl3) ꢁ: 4.60, 13.64, 27.06, 63.74, 128.61, 128.78, 129.17,
136.38. Anal. calcd. for C11H14O2S: C, 62.83; H, 6.71; S, 15.25. Found: C,
62.70; H, 6.58; S, 15.06.
[1-(Cyclopropylsulfonyl)propyl]benzene (4a): Yellow oil. Yield: 60%.
IR (neat, cmꢀ1): 1126, 1310. 1H NMR (CDCl3) ꢁ: 0.78–0.88 (m, 2H), 0.90
(t, 3H, J ¼ 7.5 Hz), 1.02–1.08 (m, 2H), 1.86–2.02 (m, 1H), 2.10–2.22 (m,
1H), 2.38–2.54 (m, 1H), 3.94 (dd , 1H, J ¼ 4.2 Hz, J ¼ 11.2 Hz), 7.37–7.46
(m, 5H). 13C NMR (CDCl3) ꢁ: 4.56, 4.62, 11.29, 20.65, 27.66, 70.82,
128.73, 128.81, 129.68, 132.80. Anal. calcd. for C12H16O2S: C, 64.25;
H, 7.19; S, 14.29. Found: C, 64.40; H, 7.28; S, 14.45.
[1-(Cyclopropylsulfonyl)-2-phenylethyl]benzene (5a): White solid,
m.p. 105ꢁC. Yield: 70%. IR (film, cmꢀ1): 1125, 1310. 1H NMR
(CDCl3) ꢁ: 0.71–0.82 (m, 2H), 1.08–1.09 (m, 2H), 1.92–2.01 (m, 1H),
3.35 (dd, 1H, J ¼ 11.4 Hz, J ¼ 13.6 Hz), 3.76 (dd, 1H, J ¼ 13.6 Hz,
J ¼ 3.6 Hz), 4.28 (dd, 1H, J ¼ 11.4 Hz, J ¼ 3.6 Hz), 6.98–7.41 (m, 10H).
13C NMR (CDCl3) ꢁ: 4.76, 27.91, 33.62, 70.60, 126.59, 128.33,
128.62, 128.83, 128.99, 129.88, 132.47, 136.79. Anal. calcd. for
C17H18O2S: C, 71.30; H, 6.34; S, 11.19. Found: C, 71.22; H, 6.28;
S, 11.30.
2-(Cyclopropylsulfonyl)propyl benzene (3b): Yellow oil. Yield: 71%.
1
IR (neat, cmꢀ1): 1132, 1310. H NMR (CDCl3) ꢁ: 1.02–1.07 (m, 2H),
1.23–1.33 (m, 2H), 1.32 (d, 3H, J ¼ 5.1 Hz), 2.31–2.37 (m, 1H), 2.69
(dd, 1H, J ¼ 10.2 Hz, J ¼ 8.1 Hz), 3.21–3.26 (m, 1H), 3.50 (dd, 1H,
J ¼ 10.2 Hz, J ¼ 2.7 Hz), 7.19–7.33 (m, 5H). 13C NMR (CDCl3) ꢁ: 4.05,
4.21, 12.23, 26.54, 34.81, 59.58, 126.48, 128.29, 128.746, 136.65.
Anal. calcd. for C12H16O2S: C, 64.25; H, 7.19; S, 14.29. Found: C,
64.38; H, 7.02; S, 14.45.

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Alkylidenecyclopropanes
809
General Method for the Synthesis of the
Chloro Cyclopropylsulfones 6a,7a,8a
To a vigorously stirred solution of powdered NaOH (88 mg,
ꢁ
2.3 mmol) in DMF (10 mL) at0 C, CCl4 (215 mg, 1.4 mmol), and the
cyclopropylsulfones (1.1 mmol) 3a or 4a, 5a were added in one portion.
After stirring for 1 h at this temperature, the solution was poured onto
brine and ice and repeatedly extracted with diethyl ether. The organic
layer was washed with saturated NaCl, dried (Na2SO4), and evaporated
under vacuum. The residual oil was chromatographed on a silica gel
column (light petroleum/diethyl ether 1:3).
[1-Chloro-1-(cyclopropylsulfonyl)ethyl]benzene (6a): Yield: 66%.
White solid m.p. 42ꢁC. H NMR (CDCl3) ꢁ: 0.81–1.22 (m, 4H), 1.82 (m,
1
1H), 2.34 (s, 3H), 7.41 (s, 5H). 13C NMR (CDCl3) ꢁ: 5.46, 24.40, 25.59,
85.74, 128.13, 128.63, 129.67, 134.78. Anal. calcd. for C11H13ClO2S:
C, 53.99; H, 5.35; S, 13.10. Found: C, 54.30; H, 5.61; S, 12.96.
[1-Chloro-1-(cyclopropylsulfonyl)propyl]benzene (7a): Yield: 69%.
White solid m.p. 38ꢁC. H NMR (CDCl3) ꢁ: 0.62–1.26 (m, 4H), 0.98 (t,
1
3H, J ¼ 7.2 Hz), 2.34–2.44 (m, 1H), 2.53–2.64 (m, 1H), 2.84–2.93 (m, 1H),
7.40–7.77 (m, 5H). 13C NMR (CDCl3) ꢁ: 5.14, 5.23, 7.72, 24.64, 28.42,
92.14, 128.16, 129.12, 129.44, 132.28. Anal. calcd. for C12H15ClO2S:
C, 55.70; H, 5.84; S, 12.39. Found: C, 55.38; H, 5.61; S, 12.76.
[1-Chloro-1-(cyclopropylsulfonyl)-2-phenylethyl]benzene (8a): Yield:
60%. Pale yellow oil. 1H NMR (CDCl3) ꢁ: 0.58–0.70 (m, 2H),
0.94–1.04 (m, 1H), 1.21–1.32 (m, 1H), 2.31–2.41 (m, 1H), 3.80, 4.16
(AB q, 2H, J ¼ 14.2 Hz), 6.96–7.87 (m, 10H). 13C NMR (CDCl3) ꢁ:
5.19, 5.35, 25.12, 40.66, 91.26, 127.30, 127.82, 128.13, 129.39, 129.61,
131.11, 132.55, 132.88. Anal. calcd. for C17H17ClO2S: C, 63.64; H,
5.34; S, 9.99. Found: C, 63.43; H, 5.61; S, 10.22.
[2-Chloro-2-(cyclopropylsulfonyl)propyl]benzene (4b): To a stirred
solution of 3b (250 mg, 1.1 mmol) in THF (8 mL) at ꢀ25ꢁC, a 2.2 M
solution ofꢁ BuLi (0.5 mL, 1.1 mmol) was added. After stirring for
30 min at0 C, N-chlorosuccinimide (146 mg, 1.1 mmol) was added and
the reaction mixture was left at room temperature for 20 h before pouring
it into brine. Extraction with diethyl ether, drying with Na2SO4 and
evaporation of the solvent gave a pale yellow oil that was chromato-
graphed on a silica gel column using diethyl ether–light petroleum 5:1
1
as eluant. Yield: 30%. H NMR (CDCl3) ꢁ: 1.13–1.39 (m, 4H), 1.76 (s,
3H), 2.74–2.80 (m, 1H), 3.42, 3.51 (AB q, 2H, J ¼ 13.8 Hz), 7.30 (m, 5H).
13C NMR (CDCl3) ꢁ: 5.29, 5.78, 23.23, 24.48, 41.77, 85.32, 127.73,
128.26, 131.34, 132.90. Anal. calcd. for C12H15ClO2S: C, 55.70; H, 5.84;
S, 12.39. Found: C, 55.49; H, 5.70; S, 12.22.

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Bernard,Frongia,and Piras
General Procedure for the Synthesis of the
Alkylidene Cyclopropanes 9a,[19] 10a,11a,5b
To a solution of lithium diisopropylamide (LDA) (2.4 mmol) in THF
(2.5 mL) at ꢀ15ꢁC, 2 mmol of a-chloro cyclopropylsulfones 6a–8a, 4b
in THF (2.5 mL) were added. After stirring for 30 min at room
temperature the reaction mixture was diluted with water and ice, and
extracted with diethyl ether. The ethereal solution was washed with
10% HCl, dried (Na2SO4), and the solvent removed in vacuo. The
residual oil was chromatographed on a silica gel column with diethyl
ether/light petroleum 1:1.
(3-Cyclopropylidene-3-propyl)benzene (10a): Yield: 66%. Yellow oil.
1H NMR (CDCl3) ꢁ: 0.88–1.35 (m, 4H), 1.52 (t, 3H, J ¼ 7.5 Hz), 2.66 (q,
2H, J ¼ 7.5 Hz), 7.21–7.57 (m, 5H). 13C NMR (CDCl3) ꢁ: 1.07, 4.25,
13.29, 26.99, 119.70, 125.86, 126.33, 128.12, 128.56, 140.14. Anal.
calcd. for C12H14: C, 91.08; H, 8.92. Found: C, 91.10; H, 8.88. MS m/z
(relative intensity): 158 (Mþ (4)), 143 (9), 129 (100), 115 (16), 91 (7).
(2-Cyclopropylidene-2-phenylethyl)benzene (11a): Yield: 35%. Yellow
1
oil. H NMR (CDCl3) ꢁ: 0.82–1.58 (m, 4H), 4.03 (s, 2H), 7.12–7.57 (m,
10H). 13C NMR (CDCl3) ꢁ: 1.24, 5.50, 40.01, 123.47, 125.79, 126.06,
126.49, 128.09, 128.22, 128.40, 131.57, 139.67, 140.48. Anal. calcd. for
C17H16: C, 92.68; H, 7.32. Found: C, 92.50, 7.15. MS m/z (relative
intensity): 220 (Mþ (7)), 205 (25), 129 (100), 91 (53).
(2-Cyclopropylidenepropyl)benzene (5b): Yield: 45%. Yellow oil.
1H NMR (CDCl3) ꢁ: 0.84–1.27 (m, 4H), 1.75 (s, 3H), 3.46 (s, 2H),
7.14–7.26 (m, 5H). 13C NMR (CDCl3) ꢁ: 2.29, 2.86, 20.14, 43.31, 117.42,
123.54, 125.79, 128.14, 128.84, 140.60. Anal. calcd. for C12H14: C, 91.08;
H, 8.92. Found: C, 90.95; H, 8.87. MS m/z (relative intensity): 158
(Mþ (10)), 143 (100), 129 (70), 115 (35), 104 (30), 91 (49), 77 (15).
[1-(Cyclopropylsulfonyl)-2-methoxyethyl]benzene (13): A solution of
6a (700 mg, 2.8 mmol) and sodium methoxide (16.8 mmol) in 10 mL of
CH3OH was heated at reflux for 18 h, cooled and then quenched with
water (5 mL). The aqueous layer was extracted with CH2Cl2. The organic
layer washed with 10% HCl and saturated NaCl, dried (Na2SO4), evapo-
rated to give an oil which was chromatographed on a silica gel column
(ethyl acetate–light petroleum 4:1). Yield: 73%. 1H NMR (CDCl3) ꢁ:
0.85–1.10 (m, 4H), 2.24–2.36 (m, 1H), 3.38 (s, 3H), 4.02 (dd, 1H,
J ¼ 6.6 Hz, J ¼ 10.2 Hz), 4.25, 4.37 (AB q, 1H, J ¼ 6.3 Hz), 4.28, 4.35
(AB q, 1H, J ¼ 6.3 Hz), 7.36–7.48 (m, 5H). 13C NMR (CDCl3) ꢁ: 4.64,
4.70, 29.26, 58.91, 68.48, 70.34, 128.65, 128.91, 129.61, 131.29. Anal.
calcd. for C12H16O3S: C, 59.98; H, 6.71; S, 13.34. Found: C, 59.73;
H, 6.65; S, 13.12.

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Alkylidenecyclopropanes
Chlorination of Benzyl Cyclopropyl Sulfone (2a)
811
To a vigorously solution of powdered NaOH (1.12 g, 28 mmol) in
DMF (30 mL), at0 ꢁC the cyclopropylsulfone 2a (5 g, 25 mmol) and
CCl4 (4.9 mL, 50 mmol) were added. After stirring for 1 h at the same
temperature, the reaction mixture was poured onto water and ice,
extracted with diethyl ether, dried (Na2SO4), and evaporated under
vacuum. The residue was chromatographed on a silica gel column
with a diethyl ether–light petroleum 3:1 to give 1.5 g of the chloro-
(phenyl)methyl cyclopropyl sulfone 14 as a yellow liquid and 3.1 g of
the cyclopropyl dichloro(phenyl)methyl sulfone 15 as white crystals,
m.p. 78ꢁC.
1
14: H NMR (CDCl3) ꢁ: 0.92–1.35 (m, 4H), 2.26–2.74 (m, 1H); 5.70
(s, 1H), 7.30–7.72 (m, 5H). 13C NMR (CDCl3) ꢁ: 5.25, 5.57, 26.63, 74.01,
128.57, 129.50, 130.35, 130.44. Anal. calcd. for C10H11ClO2S: C, 52.05;
H, 4.80; S, 13.88. Found: C, 52.20; H, 4.70; S, 13.97.
15: 1H NMR (CDCl3) ꢁ: 0.90–1.20 (m, 4H), 2.40–2.82 (m, 1H);
7.22–7.88 (m, 5H). 13C NMR (CDCl3) ꢁ: 6.45, 24.56, 99.23, 128.10,
129.53, 131.07, 132.82. Anal. calcd. for C10H10Cl2O2S: C, 45.29;
H, 3.80; S, 12.07. Found: C, 45.40; H, 3.65; S, 11.97.
Dichloro[(1-chlorocyclopropyl)sulfonyl]-methyl
Benzene (16)
To a vigorously stirred solution of powdered KOH (5 g, 89 mmol) in
t-butanol (30 mL), the cyclopropylsulfone 2a (0.5g , 2.5 mmol) and CCl4
(7.5 mL) were added. After stirring 2 h at reflux, the reaction mixture was
poured onto water, extracted with dichloromethane, dried (Na2SO4), and
evaporated under vacuum.
The residue was chromatographed on a silica gel column with a
diethyl ether–light petroleum 3:1 to give 0.48 g of white crystals, m.p.
74ꢁC. Yield: 65%. 1H NMR (CDCl3) ꢁ: 1.34 (m, 2H), 1.69 (m, 2H);
7.45–8.01 (m, 5H). 13C NMR (CDCl3) ꢁ: 18.84, 50.18, 125.21, 128.28,
128.64, 131.46, 133.57. Anal. calcd. for C10H9Cl3O2S: C, 40.08; H,
3.02; S, 10.68. Found: C, 40.20; H, 3.14; S, 10.87.
Following the method used for the synthesis of 9a the compounds
17[19] and 18 have been prepared in low yields (25% and 32%) starting
from 14[38]and 15.[38] On the other hand, 18 was also prepared from 16 by
treatment with p-tolyl-magnesium bromide (Method a) or t-butoxide in
t-butanol (Method b).

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812
Bernard,Frongia,and Piras
[Chloro(Cyclopropylidene)methyl]benzene (18)
Method a: To a solution of 16 (0.3 g, 1 mmol) in THF (10 mL), at
ꢀ70ꢁC was added 2 mL (2 mmol) of p-tolyl-magnesium bromide (1.0 M
solution in diethyl ether). After stirring 20 h at room temperature, the
mixture was treated with brine and extracted with diethyl ether. The
organic solution was dried and evaporated to give, after chromatography
(silica gel, diethyl ether–light petroleum 3:1) a yellow oil. Yield: 50%.
1H NMR (CDCl3) ꢁ: 0.82–1.78 (m, 4H), 7.25–7.83 (m, 5H). 13C NMR
(CDCl3) ꢁ: 4.28, 9.68, 121.21, 126.19, 128.13, 129.36, 132.37, 136.80.
Anal. calcd. for C10H9Cl: C, 72.96; H, 5.51. Found: C, 72.81; H, 5.42.
MS m/z (relative intensity): 166 (Mþ þ 2 (5)), 164 (Mþ (15)), 129 (100).
Method b: To a solution of 16 (0.5 g, 1.7 mmol) in THF (20 mL)
ꢁ
at0 C, t-BuOK (0.57 g, 5.1 mmol) was added in small portions. After
stirring 20 h at room temperature the mixture was treated with brine and
extracted with diethyl ether. The organic solution was dried and
evaporated to give, after chromatography (silica gel, diethyl ether–light
petroleum 3:1) 18 as a yellow oil. Yield: 27%.
(E )-Methyl [2-(benzylsulfanyl)cyclopropyl]carboxylate (22)
To a solution of benzylmercaptane (10 g, 81 mmol) in benzene
(50 mL), 1.4 M solution of BuLi in hexane (57.5 mL, 81 mmol) was
added dropwise at ꢀ20ꢁC under an argon atmosphere. After 20 min
the solution of the so formed lithium thiolate was added dropwise at
0ꢁC to a solution of methyl 4-bromo crotonate 21 (14.5 g, 81 mmol) in
benzene (70 mL). The reaction mixture was kept for 20 h at room
temperature under stirring and then diluted with diethyl ether, washed
first with 10% NaOH and then with brine. After drying and evaporation
of the solvent, the oil obtained (18 g) was chromatographed on a silica gel
column with (light petroleum–diethyl ether) (10:1). Eleven point five
grams of 22 as a pale yellow oil were obtained (yield: 70%) together
with 5 g of methyl 3-(benzylsulfanyl)-2-propenoate coming from direct
1
substitution of the bromine of the methyl 4-bromo crotonate. H NMR
(CDCl3) ꢁ: 1.06 (ddd, 1H, J ¼ 4.8 Hz, J ¼ 5.7 Hz, J ¼ 8.7 Hz), 1.41 (ddd,
1H, J ¼ 4.8 Hz, J ¼ 5.2 Hz, J ¼ 8.4 Hz), 1.66 (ddd, 1H, J ¼ 3.6 Hz,
J ¼ 5.2 Hz, J ¼ 8.7 Hz), 2.28 (ddd, 1H, J ¼ 3.6 Hz, J ¼ 5.7 Hz,
J ¼ 8.4 Hz), 3.63 (s, 3H), 3.76 (s, 2H), 7.27 (m, 5H). 13C NMR (CDCl3)
ꢁ: 16.78, 22.54, 23.59, 37.71, 51.64, 126.89, 128.33, 128.65, 172.69. IR
(neat, cmꢀ1): 1731. Anal. calcd. for C12H14O2S: C, 64.84; H, 6.35; S,
14.42. Found: C, 64.68; H, 6.16; S, 14.22.

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Alkylidenecyclopropanes
[2-(Benzylsulfanyl)cyclopropyl]methanol (23)
813
ꢁ
A solution of 1 M LiAlH4 (20 mL, 20 mmol) was added at0 C t o a
solution in THF (60 mL) of 22 (4 g, 18 mmol) under an argon atmosphere.
After 20 h at room temperature, the reaction mixture was treated with
wetNa 2SO4, filtered on a buchner, and the salt washed with diethyl ether.
The organic layer, after drying and evaporation of the solvent gave a pale
yellow oil that was chromatographed (ethyl acetate–light petroleum 4:3)
1
on a silica gel column to give 2.7 g of pure 23. Yield: 77%. H NMR
(CDCl3) ꢁ: 0.68–0.73 (m, 2H), 1.15–1.21 (m, 1H), 1.59–1.65 (m, 1H), 2.87
(br s, 1H), 3.24–3.39 (AB q, 1H, J ¼ 11.4 Hz), 3.26–3.37 (AB q, 1H,
J ¼ 11.4 Hz), 3.71 (s, 3H), 7.12–7.32 (m, 4H). 13C NMR (CDCl3) ꢁ:
12.62, 17.24, 24.32, 37.66, 64.53, 126.52, 128.08, 128.52, 138.4. IR
(neat, cmꢀ1): 3347. Anal. calcd. for C11H14OS: C, 68.00; H, 7.26; S,
16.50. Found: C, 68.24; H, 7.06; S, 16.22.
[({2-[(Methoxymethoxy)methyl]cyclopropyl}sulfanyl)-
methyl]benzene (24)
A solution of 23 (1.8 g, 9.3 mmol) in THF (30 mL) was treated with
NaH (0.22 g, 18.6 mmol) previously washed with light petroleum. After
5 min chloromethyl methylether (1.4 mL, 18.6 mmol) was slowly added
and the reaction mixture was stirred for 20 h at room temperature.
Methanol was slowly added before treatment with brine and extraction
with diethyl ether. Drying (Na2SO4) and evaporation of the solvent gave
an oil that, after chromatography with ethyl acetate–light petroleum (4:3),
left2 g of pure 24 as a yellow oil. Yield: 93%. 1H NMR (CDCl3)
ꢁ: 0.69–0.78 (m, 2H), 1.20–1.26 (m, 1H), 1.64–1.68 (m, 1H), 3.25–3.40
(m, 2H), 3.30 (s, 3H), 3.73 (s, 2H), 4.56 (s, 2H), 7.19–7.33 (m, 5H).
13C NMR (CDCl3) ꢁ: 12.99, 17.74, 22.12, 37.89, 54.99, 69.86, 95.93,
126.65, 128.24, 128.73, 138.73. Anal. calcd. for C13H18O2S: C, 65.51;
H, 7.61; S, 13.45. Found: C, 65.49; H, 7.70; S, 13.22.
[({2-[(Methoxymethoxy)methyl]cyclopropyl}sulfonyl)methyl]-
benzene (25)
To a solution of 24 (1.7 g, 7.1 mmol) in MeOH (32 mL), in the
presence of a catalytic amount of ammonium molybdate, 35% hydrogen

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814
Bernard,Frongia,and Piras
peroxide (1.2 g, 34.7 mmol) was added dropwise. After refluxing for 24 h,
the reaction mixture was poured onto water and extracted with dichloro-
methane. Drying and evaporation of the solvent led to an oil that after
chromatography (ethyl acetate–light petroleum 4:3) gave 1.8 g of pure 25
1
as an yellow oil. Yield: 94%. H NMR (CDCl3) ꢁ: 0.91–1.01 (m, 1H),
1.17–1.30 (m, 1H), 1.70–1.76 (m, 1H), 2.15–2.19 (m, 1H), 3.26 (s, 3H),
3.29–3.48 (m, 2H), 7.36–7.40 (m, 5H). 13C NMR (CDCl3) ꢁ: 8.80, 18.36,
32.39, 55.27, 60.17, 66.56, 96.17, 128.78, 128.83, 130.75, 134.80.
IR (neat, cmꢀ1): 1120, 1310. Anal. calcd. for C13H18O4S: C, 57.76;
H, 6.71; S, 11.86. Found: C, 57.49; H, 6.70; S, 12.02.
[1-({2-[(Methoxymethoxy)methyl]-
cyclopropyl}sulfonyl)ethyl]benzene (26)
To a stirred mixture of finely grounded NaOH (0.13 g, 3.3 mmol)
with DMF (20 mL), the cyclopropane 25 (0.9 g, 3.3 mmol) was added
under stirring at room temperature. Methyl iodide (0.22 mL, 3.4 mmol)
was then added in one portion and the reaction mixture was left at room
temperature for 20 h. The solution was poured onto water and extracted
with diethyl ether. The organic phase, dried and then evaporated under
vacuum, left an oil that was chromatographed with ethyl acetate–light
petroleum (4:3) to give 0.8 g of pure 26 as a yellow oil. Yield: 85%.
1H NMR (CDCl3) ꢁ: 0.86–0.97 (m, 1H), 1.20–1.32 (m, 1H), 1.62–1.86
(m, 1H), 1.77 (d, 3H, J ¼ 6.9 Hz), 1.79 (d, 3H, J ¼ 6.9 Hz), 2.01–2.11
(m, 1H), 3.27 (s, 3H), 3.29 (s, 3H), 3.35 (dd, 1H, J ¼ 10.9 Hz, J ¼ 6 Hz),
3.48 (dd, 1H, J ¼ 5.1 Hz, J ¼ 10.9 Hz), 4.19–4.26 (m, 1H), 4.49 (s, 2H),
4.55 (s, 2H), 7.31–7.40 (m, 5H). 13C NMR (CDCl3) ꢁ: 8.46, 8.60, 13.66,
13.76, 18.04, 18.51, 31.07, 31.41, 55.11, 55.17, 60.05, 63.74, 63.91, 66.28,
66.63, 96.00, 96.06, 128.52, 128.61, 128.67, 128.72, 129.12, 129.22, 130.66,
134.28. Anal. calcd. for C14H20O4S: C, 59.13; H, 7.09; S, 11.27. Found: C,
59.33; H, 7.20; S, 11.42.
[1-Chloro({2-[(methoxymethoxy)methyl]-
cyclopropyl}sulfonyl)ethyl]benzene (27)
In a two necked flask finely grounded NaOH (0.084 g, 2.1 mmol) and
DMF (15 mL) were mixed under magnetic stirring keeping the tempera-
ture at 0ꢁC. CCl4 (0.23 g, 1.5 mmol) and the cyclopropylsulfone 26 (0.4 g,

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Alkylidenecyclopropanes
815
1.4 mmol) were then added in sequence. The reaction was left at room
temperature for 20 h and then poured into brine and extracted several
times with diethyl ether. Drying and evaporation of the solvent gave
0.43 g of almostpure 27 as a yellow oil that was chromatographed on
a silica gel column using light petroleum–ethyl acetate (1:2). Yield: 90%.
1H NMR (CDCl3) ꢁ: 0.92–1.56 (m, 2H), 1.78–1.89 (m, 1H), 2.38 (s, 3H),
2.39 (s, 3H), 2.40–2.47 (m, 1H), 3.31 (s, 3H), 3.33 (s, 3H), 3.34–3.40 (m,
1H), 3.47–3.58 (m, 1H), 4.52 (s, 2H), 4.58 (s, 2H), 7.41–7.82 (m, 5H).
13C NMR (CDCl3) ꢁ: 9.26, 9.36, 19.03, 25.53, 25.80, 28.41, 28.52, 55.24,
55.27, 65.74, 65.09, 85.75, 96.09, 96.11, 128.11, 128.16, 128.70, 128.74,
129.67, 134.64, 134.73. Anal. calcd. for C14H19ClO4S: C, 52.74; H, 6.01;
S, 10.06. Found: C, 52.49; H, 5.90; S, 10.22.
(1E- and 1Z-)-1-{2-[((Methoxymethoxy)methyl]-
cyclopropylidene}ethyl)benzene (28)
To a magnetically stirred solution of 27 (0.2 g, 0.63 mmol) in THF
(15 mL), LDA (0.8 mmol), prepared in a separate flask from 0.6 mL of a
1.2 M solution of n-BuLi (0.8 mmol) and 0.1 mL of diisopropylamine
(0.8 mmol), was added very slowly at ꢀ25ꢁC under an argon atmosphere.
The reaction mixture was kept at room temperature for 20 h and then
poured onto ice-water. After acidification with diluted HCl the mixture
was extracted several times with diethyl ether. The organic solvent was
dried and then evaporated to give an oil that, after chromatography on a
silica gel column using light petroleum–ethyl acetate (1:2), gave a 60: 40
Z/E mixture of unseparated 28. Yield: 30%. 1H NMR of the Z/E mixture
(CDCl3) ꢁ: 1.02–1.40 (m, 3H), 2.23 (s, 3H), 2.34 (s, 3H), 3.20–3.35 (m,
2H), 3.33 (s, 3H), 3.36–3.42 (m, 2H), 3.39 (s,3H), 4.63 (s, 2H), 4.69 (s,
2H), 7.22–7.81 (m, 10H). MS m/z (major isomer): 203 (Mþ ꢀ15 (8)), 173
(21), 156 (62), 143 (100), 129 (83); MS m/z (minor isomer): 203 (Mþ ꢀ15
(4)), 173 (30), 156 (56), 143 (100), 129 (79).
ACKNOWLEDGMENTS
Financial support from the Ministero dell’Universita e della Ricerca
Scientifica e Tecnologica, Rome, and by the University of Cagliari
(National Project ‘‘Stereoselezione in Sintesi Organica. Metodologie ed
Applicazioni’’) and from C.N.R. (Italy) is gratefully acknowledged.

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816
Bernard,Frongia,and Piras
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Alkylidenecyclopropanes
817
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Received in the USA February 19, 2002

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