Stereospecific cyclopropanation reactions of stannyl-substituted acetals with alkenes via γ-elimination of tin

Article abstract of DOI:10.1055/s-1998-1896

The reactions of stannyl substituted acetals with olefins resulted in the elimination of both the triorganostannyl group and the alkoxy group on the same carbon, and the production of the corresponding alkoxycyclopropanes in good yields. The stereospecifi

Full text of DOI:10.1055/s-1998-1896

October 1998
SYNLETT
1057
Stereospecific Cyclopropanation Reactions of Stannyl-Substituted Acetals with Alkenes via
γ-Elimination of Tin.
Masanobu Sugawara and Jun-ichi Yoshida*
Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Yoshida, Kyoto 606-8501, Japan
Received 27 July 1998
Abstract: The reactions of stannyl substituted acetals with olefins
resulted in the elimination of both the triorganostannyl group and the
alkoxy group on the same carbon, and the production of the
corresponding
alkoxycyclopropanes
in
good
yields.
The
stereospecificity of the present reaction suggests that γ-elimination of tin
is very fast.
The γ-elimination of tin has been recognized as a useful method for the
1
construction of cyclopropane rings. This type of reaction is normally
achieved using organostannanes having an appropriate leaving group at
1b
1c
1d
1e
γ position, such as halo, hydroxyl, carbonyl, and epoxy groups.
Recently we have developed a new acid promoted cyclopropanation of
α-oxybenzylstannanes (1) with alkenes. This reaction proceeds by the
addition of the initially generated stannyl-substituted benzyl cation to
alkenes followed by the γ-elimination of tin to produce the
2
cyclopropanes (eq. 1). Therefore, α-oxybenzylstannanes serve as
formal carbenoids.
3
In order to expand the synthetic utility of this type of cyclopropanation,
we searched for other types of organostannanes which act as formal
4
carbenoids, and envisioned that stannyl substituted acetals 2 serve as
effective reagents for cyclopropanation (eq. 2). The acid catalyzed
reaction of acetals 2 is expected to give the stannyl-substituted oxonium
ions which would add to alkenes to give the γ-stannyl-substituted
carbocations. The concept works. The acid promoted reaction of 2 with
5
alkenes gave the corresponding alkoxy-substituted cyclopropanes and
here we report preliminary results of this study.
2
The reactions of with alkenes (1.1 eq) were carried out in the presence
Scheme 1
of BF •OEt (1.1 eq) in dichloromethane at room temperature, and the
3
2
corresponding alkoxycyclopropanes were obtained in good yields as
6
2b
shown in Table 1. The dibenzyloxyacetal
gave better yields than the
2a
diethoxyacetal . Stereochemistry of the present reaction is interesting.
In most cases, the cis isomers of cyclopropanes were produced
predominantly from mono-substituted alkenes, although the reason for
with styrene afforded the cyclopropanation product in only 28% yield,
the reaction of 2-stannyl-1,3-dioxane with alkenes gave the
corresponding cyclopropanes in good yields. However, the cis/trans
7
8
this stereoselectivity has not been clarified as yet. The endo isomer was
obtained predominantly from cyclohexene. It is also worth noting that
the present reaction is stereospecific as far as the geometry of the alkene
is concerned (vide infra).
ratios of the products were much lower than those of non-cyclic stannyl
acetals, although the reason is not clear at present. It is noteworthy that
allyltrimethylsilane mainly gave the cyclopropanation product together
with a small amount of allylated product (5%), indicating that the γ-
Stannyl substituted cyclic acetals were also effective as formal tin
carbenoids (Table 2). Although the reaction of 2-stannyl-1,3-dioxolane
2
elimination of tin is more favorable than the β-elimination of silicon.

1058
LETTERS
SYNLETT
1988
The cyclopropanes thus obtained would be able to be transformed into
the corresponding cyclopropanol by oxidation of the side chain
according to the literature procedure.
E. J. Org. Chem.
J. Org. Chem.
, 53, 1894. (e) Plamondon, L.; Wuest, J. D.
1991
, 56, 2066.
9
1997
, 119, 11986.
(2) Sugawara, M.; Yoshida, J. J. Am. Chem. Soc.
1960
, 82, 1888.
(3) (a) Clark, H. C.; Willis, C. J. J. Am. Chem. Soc.
(b) Seyferth, D.; Dertouzos, H.; Suzuki, R.; Mui, J. Y. P. J. Org.
1967
Chem.
B.; Cross, R. J. J. Organometal. Chem.
D.; Armbrecht, F. M. J. Am. Chem. Soc.
Seyferth, D.; Lambert, R. L. J. Organometal. Chem.
2a
, 32, 2980. (c) Seyferth, D.; Armbrecht, F. M.; Prokai,
1966
, 6, 573. (d) Seyferth,
1969
, 91, 2616. (e)
1975
, 91, 31.
was prepared according to the
literature procedure: (a) Shiner, C. S.; Tsunoda, T.; Goodman, B.
1989
(4) Stannyl substituted acetal
A.; Ingham, S.; Lee, S-h.; Vorndam, P. E. J. Am. Chem. Soc.
111, 1381. The other method: (b) Quintard, J. P.; Elissondo, B.;
1983
,
Mpegna, D. M. J. Ornanomet. Chem.
, 251, 175.
1989
(5) Wong, H. N. C.; Hon, M.; Tse, C.; Yip, Y. Chem. Rev.
, 89,
165.
2b 3a
,
3b
(6) Acetals
, and
were prepared by TsOH catalyzed
2a
transacetalization of
alcohols.
in the excess amount of the corresponding
1986
(7) Doyle, M. P. Acc. Chem. Res.
, 19, 348.
(8) Recently, it was reported that the reactions of α-stannyl cyclic
acetals with allyl stannanes and enol silyl ethers afforded the
corresponding products. Cintrat, J. C.; Blart, E.; Parrain, J. L.;
Quintard, J. P. Tetrahedron 1997, 53, 7615.
Scheme 2
1988
(9) Sugimura, T.; Futagawa, T.; Tai. A. Tetrahedron Lett.
, 29,
The stereospecificity of the present reaction seems to be important for
the elucidation of the reaction mechanism (Scheme 1). The reaction of
2a with trans-stilbene gave rise to the formation of the
5775
4a
4b
(10) The stereochemistry of
The stereochemistry of
NOE experiments.
was determined by NOE experiment.
4c
and that of were also determined by
10,11
ethoxycyclopropane 4a in 78% yield as a single isomer (Scheme 2).
In 4a two phenyl groups are trans to each other. On the other hand, the
reaction with cis-stilbene afforded the cyclopropane 4b preferentially
together with a small amount of the epimer 4c. In 4b and 4c two phenyl
groups are cis to each other. The formation of 4a was not detected.
Therefore, the stereochemistry of the starting alkene was retained. The
observed stereospecificity indicates that the γ-elimination of tin is too
fast to allow the rotation about the carbon-carbon bond of the original
alkene. The stereospecificity can also be explained in terms of
synchronous formation of two carbon-carbon bonds of the
cyclopropane. Anyway the present stereospecificity suggests that γ-
elimination of tin is a very fast process. Although more data should be
accumulated before elucidation of the detailed mechanism, its complete
stereospecificity opens possibilities of various synthetic applications of
this reaction.
(11) Typical experimental procedure for the cyclopropanation.
Synthesis of 4a. To a solution of (diethoxy)(tributylstannyl)-
methane 2a (74.8 mg, 0.190 mmol) and trans-stilbene (36.3 mg,
0.201 mmol) in toluene (0.50 mL) was added BF •OEt (25.0 µl,
3
2
0.197 mmol) at room temperature. The reaction mixture was
stirred at the same temperature for 1 h. After 2a was consumed,
sat aq NaHCO (1.0 mL) was added to the reaction mixture, and
3
the organic phase was separated. The aqueous phase was extracted
with ether (x3), and the combined organic phase was washed with
sat. aq NaCl, and dried over MgSO . After removal of the solvent,
4
the residue was purified via flash chromatography to obtain 35.2
mg (78%) of the 2,3-diphenylethoxycyclopropane.
1
4a: TLC Rf 0.29 (hexane:AcOEt = 20:1); H NMR (300 MHz,
CDCl ) δ 1.12 (t, J = 7.2 Hz, 3 H), 2.38 (t, J = 6.9 Hz, 1 H), 2.59
3
(dd, J = 6.6, 3.6 Hz, 1 H), 3.35 (dq, J = 9.3, 7.2 Hz, 1 H), 3.53 (dq,
Acknowledgment.
This research was partly supported by a Grant-in-
J = 9.3, 7.2 Hz, 1 H), 3.78 (dd, J = 6.9, 3.6 Hz, 1 H), 7.1-7.4 (m,
13
Aid for Scientific Research on Priority Area (No. 283, ”Innovative
Synthetic Reactions“) from Monbusho.
10 H); C NMR (75 MHz, CDCl ) δ 14.72, 31.79, 33.55, 65.98,
3
66.19, 125.87, 126.07, 126.30, 127.95, 128.04, 128.50, 137.53,
+
140.70; MS (EI) m/e (%) 238 (M , 100), 209 (32), 178 (48), 105
(88); HRMS calcd for C
4b: TLC Rf 0.31 (hexane:AcOEt = 20:1); H NMR (300 MHz,
H
O 238.1358, found 238.1365.
17 18
References and Notes:
1
(1) (a) Pereyre, M.; Quintard, J-B.; Rahm, A. Tin in Organic
CDCl ) δ 1.05 (t, J = 7.2 Hz, 3 H), 2.43 (d, J = 6.6 Hz, 2 H), 3.31
3
Synthesis; Butterworth
references cited therein. Selected examples (b) Peterson, D. J.;
1974
&
Co.: London, 1987;
p
235 and
(q, J = 7.2 Hz, 2 H), 3.89 (t, J = 6.6 Hz, 1 H), 7.0-7.2 (m, 10 H);
13
C NMR (75 MHz, CDCl ) δ 14.62, 26.49, 60.85, 66.30, 125.49,
3
+
Robbins, M. D.; Hansen, J. R. J. Organometal. Chem.
, 73,
, 24, 4591.
(d) Sato, T.; Watanabe, M.; Watanabe, T.; Onoda, Y.; Murayama,
127.45, 130.62, 135.48; MS (EI) m/e (%) 238 (M , 100), 209
1983
237. (c) Fleming, I.; Urch, C. Tetrahedron Lett.
(25), 178 (41), 105 (80); HRMS calcd for C
found 238.1367.
H O 238.1358,
17 18