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Liquid Sulfur Dioxide as a Lewis-Acidic Solvent for the Alkylation and Alkoxyalkylation of Allylsilanes.

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from 1,2 H, additions to adjoining 6-5 bonds. The formation of
this isomer is, however, unlikely because isolated X, addition to
6-5 bonds of C,, has never been observed and is calculated to be
at least 20 kcalmol-' less stable than addition to 6-6 bonds at
all levels of theory.
The coupling constants observed in the 'H NMR spectra of the
isomers A-E are all consistent with 1,2 addition to 6-6 bonds.
The assignment of product F with a resonance signal at 6 = 6.33
to 8 is tentative, but is consistent with the exceptionally low-field
resonance signal of C,,H, at 6 = 5.93. All other resonance signals observed for C,,H, products are upfield from that observed
for C,,H, . The structure of B can be unambiguously assigned
to 4, but the structures of the products A, D, and E are consistent with any of the remaining five isomers. We plan to assign
structures to these isomers through crystallographic analysis.
[7] C. C. Henderson. C. M. Rohlfing. and P. A. Cahill. Chem. Phrs. Leit. 1993,
213, 383.
[8] Equilibration of 7.8- and 1,9-C,,H2 led to excellent agreement between the
observed free energy difference (1.4k 0.2 kcal mol- I ) and calculated a b initio
HF/6-31G* total energy difference (1.3 kcalmol-I): C. C. Henderson, C. M.
Rohlfing, K. T. Gillen, P. A. Cahill. Science. in press The 1.9 isomer is both the
kinetic product of hydroborationihydrolysis and the thermodynamically most
ytable isomer.
[9] GAUSSIAN 92: M . .I.
Frisch, G. W. Trucks, M. Head-Gordon, P M. W. Gill,
M W. Wong, J. B. Foresmdn, B. G. Johnson, H. B. Schlegel, M. A. Robh, E.
S . Replogle, R . Gomberts, J. 1.Andres, K. Raghavachari, J. S. Binkley, C.
Gonzalez. R. 1.Martin. D. J. Fox, D. J. DeFrees, J. Baker, J. J. P. Stewart, and
J. A. Pople. Gaussian. Inc., Pittsburgh, PA, 1992.
[lo] Note that other C,,H, isomers, in particular, those with a 1,Caddition pattern,
may have relative energies within the span of isomer energies presented in
Table 1.
[ I l l C. J. Welch. W. H. Pirkle, J. Chromurogr. 1992, 609, 89.
1121 L. M . Jackmdn. S. Sternhell. Applicurioiis of Nuclear Mugnerir Resonance Speciroscopj, in Orgunic Chzmistrj~,2nd ed.. Pergamon, Oxford. 1969. p. 336.
Experimental Procedure
To a solution of C,,H, [I) (10 mg. 14 pmol) in toluene (15 mL) was added BH,
~
a t 0 " C under argon. Themixture wasstirred at O'C
(14pL. 1 . 0 solutioninTHF)
for 45 min. warmed to room temperature for 45 min. and quenched by addition of
water (1 .0 mL). The organic layer was separated, dried over MgSO,, and the C,,H,
fraction isolated by preparative chromatography on a Buckyclutcher I column
(10 mm x 25.0 cm) with a tolueneihexane (1 :1) mobile phase. The total yield of
C,,,H, products is 10%. less than the 20-30% yields of C,,H, that are obtained
from C,, under similar conditions (C,,H, isomers were first obtained as side products in < I "h yields in this reaction). Positive-ion FAB MS (for the mixture):
observed, 724.0309. calculated 724.03 13 (no evidence for C,,H,). From this mixture
three C,,H, isomers were separated (Table 2). The UV;VIS spectrum o f C ( = 1) in
toluene!hexane ( 1 ; l ) tails from 290 nm with a shoulder at 342 nm and a distinct
absorption at 442 nm, both of which may be diagnostic for this substitution pattern.
Positive-ion FAB MS: observed. 724.0309: calculated. 724.0313. Similar for A.
distinct maximum at 325 nm and weak absorption maxima at 410 and 430 nm. For
B, distinct maxima are absent. shoulders at 330, 380, 425, and a broad feature at
475 nm are observed. Isolation of the materials is limited to concentrated solutions
(1 m g m L - ' ) which are handled routinely in light and air. Such solutions may be
stored indefinitely at - 20 " C ,but removal of the solvent leads to solids which d o not
completely redissolve. Products A and B that were previously separated from C (1)
were eluted on a Buckyclutcher I column that contained an unusually high amount
of residual platinum from the preparation of the Buckyclutcher Iigand. Repeated
elutions resulted in conversion of A and B to C.
Received: October 28, 1993
Revised: December 27, 1993 [Z6462IE]
German version. Angckt. Cliem. 1994, 106, 803
[l] ForC,,XY.seea)C. C.Henderson.P.A.Caliil1,Scienci~1993,25Y, 1 8 8 5 ; b ) A .
[2]
[3]
[4]
56
55
[6]
788
Hirsch, A. Soi. H. R. Karfunkel. Angrw. Cheni. 1992. fU4. 808: Angew. Chem.
fnr. Ed. Eng/. 1992. 31, 766; c) A. Hirsch. T. Grosser, A. Skiebe, A. Soi. Cfirni.
Bor. 1993, 126, 1061: d ) N. Matsurawa. D. A. Dixon, T. Fukunaga. J. Pl7y.7.
Cliem. 1992, 96,7594: e) C. C. Henderson, P. A. Cahill, Cliem. P/7y,5. Letr 1992,
IYR. 570; f) S . Ballenweg, R. Gleiter. W. Krdtschmer, 7 i c t . Left. 1993, 34,3737.
For C.,XY, see ref. [7]: H. R. Karfunkel. A. Hirsch. Anpew. Chem. 1992. 104,
1529; Angew. Cheni. Inr. Ed. Engl. 1992. 31, 1468: ref. [Ic]: C. C. Henderson,
C . M . Rohlfing, P. A. Cahill. presented to the American Chemical Society.
August 1997.
For a recent reviews of fullerene chemistry see R. Taylor. D. R. M. Walton.
Nrrturr 1993. 363, 685: A. Hirsch. Angeiv. Chem. 1993. 105. 1189; Aiigeii..
Chem. I n r . Ed. Eiipl. 1993. 32. 1138.
The numbering used is that in Fig 2 b of R. Taylor, 1 Chenf.Soc. Perkin Duns.
2 1993. 813. See diagram below.
[5] The isolation of this product was first presented to the Materials Research Society at
51
the spring meeting in San Francisco, CA.
USA. April 1991. The formation of several
58
C,,H, and C,,H, isomers by diimide reduction has also been reported: R. Taylor,
presented to the American Chemical Society. August 1993; A. G. Avent, A. D. Darwish, D. K. Heimhach, H. W. Kroto. M. F.
Meidine. J. P. Parsons, C. Remdrs, R.
9
Roers. 0. Ohashi, R. Taylor. D. R. M. Walton. J, Chrnr. SOC.Pwkiri Truns. 2. 1994. 15.
In their Table 1, isomer 1,2,57,58 should
60
read 1,2.55.60. We thank R. Taylor for a
preprint of this work.
N. Matsurawa. T. Fukunaga. D. A. Dixon, J. P h m CIimi. 1992. 96. 10747.
'i' VCH I/i,rlug.gsjiPsellscliu/l nibH, 0-69451 Weinheim, fYY4
Liquid Sulfur Dioxide as a Lewis-Acidic Solvent
for the Alkylation and Alkoxyalkylation of
Allylsilanes **
Herbert Mayr,* Gorden Gorath, and Bernhard Bauer
The use of metal halides as Lewis acids for FriedelLCrafts and
related reactions is increasingly criticized because of the nonrecyclable salts produced in the usual aqueous workup. In particular, in reactions which require stoichiometric quantities of
Lewis acid, this presents an ecological and financial problem.
Sulfur dioxide (SO,) has a high ionizing power because it can act
as an electron pair acceptor. Although this property has been
known for a long time,"] it has rarely been used to replace metal
halides in electrophilic alkylations or acylations.["
Using liquid SO, as solvent makes an aqueous workup superfluous and should enable the recondensed SO, to be recycled.
For these reasons we decided to study its use as a solvent for the
alkylation and alkoxyalkylation of allylsilanes. In this case, reactions with acetals are of particular interest because they generally require stoichiometric quantities of TiC1,i,31 but examples
with catalytic amounts of acids have been reported.[41
If acetals 1 a-1 e are treated with 1.2 equivalents of allyltrimethylsilane (2a) in liquid SO, at -60°C the homoallyl ethers
3a-3e are obtained in good yield (Table 1). The reaction of l e
with 2a shows that the reaction can also be carried out at room
temperature. Due to the low vapor pressure of SO, at 20°C
(about 3 bar at 20 oC),15a1
thick-walled glass vessels with a screwtop were employed.[5b1which were cooled for filling and emptying
and covered with a protective metal casing during the reaction.
Based on the high yields for these reactions and on earlier investigations on the electrophilicity of acetals,[61it is expected that
all ordinary acetals will react under these conditions.
Table 1 shows that alkylations with the corresponding chlorides
1 f-i were also successful. The failure of I-chloro-1 -phenylethane
and terf-butyl chloride to react under these conditions suggests
that only alkyl chlorides with high S,1 reactivities ( k , > 10-6s-'
in EtOH, 25 " C ) are reactive under these condition^.^']
["I
[**I
Prof. Dr. H. Mayr, Dipl.-Chem. G. Gordth, B. Bauer
Institut fur Orgdnische Chemie der Technische Hochschule
Petersenstrasse 22, D-64287 Ddrmstadt (FRG)
Telefax: Int. code + (6151)16-5591
This work was supported by the Fonds der Chemischen Industrie. We would
also like to thank Dr. W Siege1 and Dr. M. Eggersdorfer, BASF AG, for
stimulating this investigation.
0570-0833i9410707-07RH $ 1U.OO-t .25;0
Angpir.. Chem. Inr. Ed. Engl. 1994. 33, No. 7
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OCH,
R-CH
/
\
OCH,
so
+m S i M e , A R - C H ~
- Me,SiX
OCH,
2a
la-le
If-1 i
3a-3e
2a
3f-3i
Table 1. Reactions of acetals l a - e and alkyl chlorides I f - i with allyltrimethylsilane in liquid SO,.
R
Reactant/Product
T["C]
t[hILa1
Yield [%]
1 a/3 a
lb/3b
1 c/3c
ld/3d
le/3e
Ifi3f
w 3 g
1 h/3 h
lii3i
- 60
- 60
- 60
18
72
22
72
46
330
48
20
96
98
83
93
86 [bl
80
85
76
93
- 60
20
20
- 60
- 60
20
185
[a] Reaction times have not been optimized. [b] With a trace of I, present.
As shown in Table 2, other allylsilanes also react with benzaldehyde dimethyl acetal in SO,. However, it is unclear why
prenyltrimethylsilane 2c reacts significantly more slowly than
would be expected from its high nucleophilicity observed in
other reactions.[*] Formation of allylsilane/SO, copolymers[91
was occassionally observed for which a radical chain process or
Table 2. Reactions of benzaldehyde dimethyl acetal (1 a) with allylsilanes in liquid
so,.
Reactant
T[T]
Product
2b
&si~e,
t [ h ][a]
Yield
4b
-60
24
85
4d
-60
23
41
Ph
OMe
o
s
N
e
3
2d
Ph
U
[a] Reaction times have not been optimized
Angiw (7iem. hi.Ed. Engl. 1994. 33. N o . 7
$-:
[Oh]
an ionic mechanism could be envisaged. In the reaction of 1 e
with 2a the formation of copolymers could be suppressed by the
addition of a tiny crystal of I,, indicating the operation of a
radical mechanism for copolymerization.
Preliminary experiments of the alkylation and alkoxyalkylation
of silylenol ethers and/or electron-rich arenes were also successful.
It can therefore be assumed that the solvent SO, could replace
metal halides as Lewis acids in numerous reactions. Addition of
catalytic quantities of 2,6-di-tert-butyl-4-methylpyridine
inhibits
product formation, suggesting that the ionization is catalyzed by
traces of acid (possibly H,SO,).
Experimental Procedure
Dry SO, (10mL) was condensed in a Schlenk tube at - 4 0 ° C under a nitrogen
atmosphere. Benzaldehyde dimethyl acetal (1.31 g, 8.61 mmol) and allyltrimethylsilane ( I .1 8 g, 10.3 mmol) were then dissolved with stirring and the reaction mixture
allowed to stand at -60 C. After 18h the SO, was allowed to evaporate at room
temperature and the residue was distilled; yield: 3.34 g (96%) ruc-4-methoxy-4phenyl- 1 -butene (3 a).
Received: October 26. 1993 I26451 IE]
German version: Angew. Chem. 1994, 106. 7Y3
[l] N. N. Lichtin in Carhonium Ions, General Aspects und Methods of Inw?tigution,
Vol. I (Eds.: G. A. Olah, P. von R. Schleyer), Wiley. New York. 1968, pp. 1351 5 1 ; D. F. Burow ("Liquid Sulfur Dioxide") in Chemistry of'Nonuqueous Solvents, Vol. 3 (Ed.: J. J. Lagowski), Academic Press, New York. 1970.
[2] N. Tokura, S.ynthesis 1971, 639-645.
[3] a) H. Sakurai, Pure Appl. Chem. 1985, 57. 3759-1770; b) T. Mukaiyama, M.
Murakami, Synthesis 1987, 1043-1054; c) E. W. Colvin. Silicon m Orgunic STnthesis. Butterworths, London, 1981; d) W. P. Weber. Silicon R i ~ u g r n/or
~ . ~OrgunIC Synlhesis, Springer, Berlin, 1983; e) I . Fleming in Cornprehmmv Orgunic
Chemistry. Vol. 3(Eds.: D. H. R. Barton. W D. Ollis), Pergamon, Oxford. 1979,
pp. 541; f) H. Sakurai, Pure Appl. Chem. 1982,54, 1-22; g) D. Schinzer. S w
thesis 1988,263-273; i) 1. Fleming, J. Dunogues. R. Smithers. Org. Reurt. N . Y
1989,37, 57; j) R. Eaborn, W. Bott in Orgunometullic Compuunds of the Group
IV Elements, Vol. f, (Ed.: A . G. Mac-Diarmid), Marcel Dekker, New York,
1968, Part 1; k) 1. Fleming in Comprehensive Orgunii Sjnthc,.si.\, Yo/. 2 (Eds.:
B. M. Trost, 1. Fleming. C. H. Heathcock). Pergamon. Oxford. 1991. pp. 563593.
[4] a) T. Tsnnoda, M. Suzuki. R. Noyori, Tetruhedron Lett. 1980, 21. 71 - 74; b) H.
Sakurai, K. Sasaki, A. Hosomi, ihid. 1981, 22. 745-748; c) T. Mukaiyama, H.
Nagaoka, M. Murakami, M. Ohshima, Chem. Lett. 1985, 977-980.
[S) a) Gmeljn-Institut for Inorganic Chemistry of the Max-Phnck-Gesellschaft L u r
Forderung der Wissenschaften. Gmelin-Hundhuch der Anorgunischen Chemie,
Schwefeloxide, Vol. 3, 8th ed., Springer, Berlin. 1980, p. 95: b) M . Begtrup. J.
CAem. Educ. 1987, 64, 974.
[6] a) U. von der Briiggen. R. Lammers. H. Mayr, J. Org. C h m . 1988, 53, 29202925; b) H. Mayr, I-P. Dau-Schmidt, Cliem. Ber. 1994, 127. 213 - 217.
171 a) J:P. Dau-Schmidt, H. Mayr, Chem. Ber. 1994, 127, 205-212; b) H . Mayr.
A n g w . Chem. 1981, 93, 202-204; Angew. Chrm. I n t . Ed. Engl. 1981. 20. 184186; c) H. Mayr, W Stnepe. J1 Org. Chem. 1983, 48, 159- 1165
[XI a) H. Mayr, R. Pock, Tetrahedron 1986,42,4211-4214; b) G . Hagen, H. Mayr.
J. Am. Chem. SOC.1991, 113. 4YS4-4961.
[9] H. F. Mark, N. G. Gaylord, N. M. Bikales, Encyclopediu o/ Piilvmer Sciiwvuna
Technology, Vol. 9, Intersience Publ., New York, 1968.
VCH Verlugs~i~sell~~chafi
mhH, D-6Y451 Weinhelm, 1994
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dioxide, allylsilanes, alkylation, sulfur, solvents, acidic, alkoxyalkylation, lewis, liquid
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