The first observation of γ-sila-pummerer rearrangement

Article abstract of DOI:10.1080/10426507.2012.744310

2-Sulfinyl-3-trimethylsilylmethylcycloalkanones unexpectedly undergo γ-sila-Pummerer rearrangement. The first examples of this new type of rearrangement are presented.

Full text of DOI:10.1080/10426507.2012.744310

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Phosphorus, Sulfur, and Silicon and the Related
Elements
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THE FIRST OBSERVATION OF γ-SILA-PUMMERER
REARRANGEMENT
Maciej Mikina a
a Centre of Molecular and Macromolecular Studies, Polish Academy of Sciences, Department
of Heteroorganic Chemistry, Sienkiewicza 112, 90-363, Łódź, Poland
Accepted author version posted online: 10 Dec 2012.
To cite this article: Maciej Mikina (2012): THE FIRST OBSERVATION OF γ-SILA-PUMMERER REARRANGEMENT, Phosphorus, Sulfur,
and Silicon and the Related Elements, DOI:10.1080/10426507.2012.744310
To link to this article: http://dx.doi.org/10.1080/10426507.2012.744310
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THE FIRST OBSERVATION OF -SILA-PUMMERER REARRANGEMENT
Maciej Mikina
Centre of Molecular and Macromolecular Studies, Polish Academy of Sciences,
Department of Heteroorganic Chemistry, Sienkiewicza 112, 90-363 Łódź, Poland
E-mail: mmikina@cbmm.lodz.pl
acylation
alkylation
O
O
base
R1
R1
O
O
P(OMe)2
P(OMe)2
R2
R2
Horner
olefination
1
Abstract: 2-Sulfinyl-3-trimethylsilylmethylcycloalkanones unexpectedly undergo - sila-
Pummerer rearrangement. The first examples of this new type of rearrangement are presented.
Key words: 2-sulfinylcycloalkenones, sila-Pummerer rearrangement, cycloalkenones, Michael
addition, elimination
Introduction
For several years our group has been involved in a program aimed at developing new
strategies for the syntheses of natural products, particularly those having five-membered ring in a
structure. The most fruitful methodology, that was devised in our laboratory for the syntheses of
cyclopentenones, is based on a selective reactivity of the trident anion derived from 3-
fosforylmethyl-cyclopentenone 1. This anion, in which the negative charge is distributed
between oxygen atom and two carbon atoms, is formed by deprotonation of 1 upon treatment
with a base (Scheme 1). It exhibits excellent selectivity in the reaction with aldehydes and gives
only trans-alkenes without other condensation products. With alkylation agents, 2-alkyl
1
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derivatives as major products are formed. Reactivity of this anion allowed us to synthesize 3-
substituted cycloalkenones, what was utilized in several syntheses of natural products. 1,2
Trying to extend our methodology and to overcome some problems observed with the
Horner olefination reaction we decided to synthesize 3-trimethylsilylmethyl-cyclopentenone 2,
expecting that a similar trident anion may be obtained from 2 after deprotonation. This anion
should exhibit a similar reactivity towards various electrophilic agents as that of the phosphoryl
analog mentioned above. In this anion, negative charge should be also distributed between
oxygen atom and two carbon atoms. Moreover, the silyl moiety in the molecule should allow to
introduce alkenyl chain at C(3) in Peterson olefination reaction (Scheme 2).
Surprisingly, 3-trimethylsilylmethylcyclopentenone has not been described in chemical
literature. Only the 6 and 7-membered ring analogs are known and their syntheses were
described by Kuwajima.3 However, they are too expensive due to the use of palladium acetate in
bulky quantities (Scheme 3).
Therefore, based on our experience in the syntheses of cyclopentenones 4 we decided to obtain
our target 2 by addition- elimination reaction sequence indicated by retrosynthetic analysis
shown in Scheme 4. This approach had, in our opinion, several advantages:
- Michael additions to 2-sulfinylcyclopentenone usually afforded products in good yields.
- elimination of sulfenic acid is well established in chemical literature and was successfully
utilized in our laboratory for the syntheses of various cycloalkenones.4
2
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- Monteiro described excellent method for the synthesis 2-sulfinylcyclopentenone 4.5
The synthesis of 4 consists of two steps. The first involves the reaction of cyclopentanone
with sulfenyl chloride leading to 2-sulfenylcyclopentenone which in the second step is oxidized
to the corresponding sulfoxide. Both reactions proceeded in high yields. Moreover, this
procedure allows to syntheses sulfoxides with 6- and 7-membered rings.6
Results and Discussion
To synthesize 2, the adduct 3 was prepared in the reaction between Grignard reagent and
racemic sulfoxide 4. It is worthy to mention, that this adduct 3 was formed in almost quantitative
yield. However, is was unstable and found to undergo slow decomposition at room temperature
and fast in a boiling benzene or chloroform. After being refluxed for 5 hours it was completely
decomposed. However, instead of the expected silane 2 3-methylcyclopentenone was
surprisingly obtained (Scheme 5). Hexamethyldisiloxane and phenyl benzenethiosulfinate were
also isolated as other products of this decomposition. It is reasonably to expect that they were
formed from trimethylsilyl benzenesulphenate as the initially formed reaction product. The latter
is known from the literature to be unstable and rearrange to a mixture of siloxane and
benzenethiosulfinate after very quick decomposition.7 There is no doubt that trimethylsilyl
benzenesulphenate is formed due to the interaction between the sulfinyl oxygen and silicon
atoms.
3
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Analysis of the reaction products and consideration of a possible way of their formation
led us to the conclusion that a new type of a sila-Pummerer rearrangement is observed.
According to the well established mechanism of sila-Pummerer rearrangement, -silylsulfoxides
initially undergo isomerization to sulfur ylide due to the shift of silicon from carbon atom to the
sulfinyl oxygen atom via a four center transition state. In our case, we propose similar migration
of silicon from carbon atom to the sulfinyl oxygen atom in which six-membered transition state
is involved (Scheme 6). Interestingly, when -silyl sulfoxides are subjected to similar
transformations, the attack on -hydrogen atom preferentially occurs.8,9 The attack of the sulfinyl
oxygen atom on the -silicon atom is possible (the reaction proceeds through five-membered
transition state) only when hydrogen atom is absent in a  position.
Unexpected course of this reaction enabled us to examine the scope and limitation of the
rearrangement presented here. We found that the use of sulfoxides with six- and seven-
membered rings also led to the corresponding products of the -sila-Pummerer rearrangement
(Scheme 7).
There was another question: is the reaction specific for sulfoxides only? To answer this
question, three adducts of similar structures were prepared from sulfide, sulfoxide and sulfone. It
4
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was found that the adducts having sulfenyl and sulfonyl groups are relatively stable in boiling
chloroform and only the sulfoxide adduct gave the desired cyclopentenone.
In summary, a new kind of -sila-Pummerer rearrangement of 2-sulfinyl-3-
trimethylsilylmethylcycloalkanones 3 is described. The utility of this reaction is demonstrated by
the synthesis of various C(3)-substituted cycloalkenones 5.
References:
[1] Mikina, M., Mikołajczyk, M. Phosphorus, Sulfur, and Silicon 1993, 75, 39-42
[2] Mikołajczyk, M., Mikina, M. J. Org. Chem. 1994, 59, 6760-6765
[3] Hatanaka, Y., Kuwajima, I. J. Org. Chem. 1986, 51, 1932-1934
[4] a) Mikołajczyk, M., Perlikowska, W. Synthesis 2007, 8, 1225-1229
b) M. Mikołajczyk, M. Mikina, A. Jankowiak, M.J. Mphahlele, Synthesis, 2000, 1075-
1077.
c) M. Mikołajczyk, M. Mikina, A. Jankowiak, J. Org. Chem. 2000, 65, 5127-5130.
[5] Monteiro, H. J. J. Org. Chem. 1977, 42, 2324- 2326
[6] Yechezkel, T., E Ghera, E., Ostercamp, D., Hassner, A. J. Org. Chem. 1995, 60,
5135-5142
[7] Davis, A.F., Rizvi, S.Q.A., Ardecky, R., Gosciniak, D.J., Friedman, A.J.,
Yocklovich,
S.G. J. Org. Chem. 1980, 45, 1650-1653
[8] Fleming, I., Perry, D.A. Tetrahedron Lett. 1981, 22, 5095-5096
[9] Nakamura, S., Takemoto, H., Ueno, Y., Toru, T., Kakumoto, T., Hagiwara, T. J. Org.
Chem. 2000, 65, 469-474
5
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acylation
alkylation
O
O
base
R1
R1
O
O
P(OMe)2
P(OMe)2
R2
R2
Horner
olefination
1
Scheme 1
O
alkylation
O
base
SiMe3
SiMe3
Peterson
olefination
2
Scheme 2
O
OSiMe3
O
a
b
SiMe3
SiMe3
a) Me3SiCH2MgCl, Me3SiCl, catalytic Cu – SMe2, THF, -78oC
b) 0.25 eq Pd(OAc)2, (CH2=CHCH2O)2C=O, CH3CN
Scheme 3
O
O
O
O
O
SPh
SPh
-
Me3SiCH2 Li+
+
SiMe3
SiMe3
2
4
3
Scheme 4
6
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O
SiMe3
O
O
O
O
2
SPh
SPh
+
Me3SiCH2MgCl
SiMe3
O
Me3SiOSiMe3
4
3
+
PhS(O)SPh
Scheme 5
SiMe3
O
S
OSiMe3
Ph
OSiMe3
SPh
CH2
S
Ph
Ph
O
O
S
O
+
PhS-O-SiMe3
SiMe3
H
3
Scheme 6
O
O
O
SPh
Me3Si
X
+
X
n
4
5
n=1
n=2
n=3
X = H
X = P(O)(OMe)2
X = P(O)(OMe)2
Yield [%] 66
35
58
X = P(O)(OMe)2
59
Scheme 7
7
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