Silylated cyclohexadienes in radical chain hydrosilylations

Article abstract of DOI:10.1002/1522-2675(200210)85:10<3559::AID-HLCA3559>3.0.CO;2-6

A new method for the mild radical hydrosilylation of alkenes and alkynes is described. Silylated cyclohexadienes that can be readily prepared on large scale are used as radical hydrosilylating reagents. Nonactivated alkenes and alkynes are hydrosilylated in high yields. The reaction can be combined with C-C bond formation, as demonstrated for the preparation of silylated cycloalkanes from the corresponding dienes. Furthermore, radical hydrosilylations in combination with β-fragmentation reactions for the synthesis of allylsilanes and hydrosilylations of aldehydes and ketones providing protected alcohols can be readily performed by this strategy.

Full text of DOI:10.1002/1522-2675(200210)85:10<3559::AID-HLCA3559>3.0.CO;2-6

Helvetica Chimica Acta Vol. 85 (2002)
3559
Silylated Cyclohexadienes in Radical Chain Hydrosilylations
by Stephan Amrein1) and Armido Studer*
Fachbereich Chemie der Universit‰t Marburg, Hans-Meerwein-Stra˚e, D-35032 Marburg
(fax: ‡4964212825629; e-mail: studer@mailer.uni-marburg.de)
Dedicated to Professor Dieter Seebach on the occasion of his 65th birthday
A new method for the mild radical hydrosilylation of alkenes and alkynes is described. Silylated
cyclohexadienes that can be readily prepared on large scale are used as radical hydrosilylating reagents. Non-
activated alkenes and alkynes are hydrosilylated in high yields. The reaction can be combined with CÀC bond
formation, as demonstrated for the preparation of silylated cycloalkanes from the corresponding dienes.
Furthermore, radical hydrosilylations in combination with b-fragmentation reactions for the synthesis of
allylsilanes and hydrosilylations of aldehydes and ketones providing protected alcohols can be readily
performed by this strategy.
1. Introduction. The radical chain hydrosilylation of alkenes in the presence of
simple trialkylsilanes in an inefficient reaction and, therefore, rarely used in
preparative synthesis. It is well-known that the addition of a silyl radical to an alkene
is a fast process [1][2]. However, the subsequent reduction of the resulting b-silylalkyl
radical with a trialkylsilane is a slow reaction at ambient temperatures (Scheme 1,a).
This inefficient reduction generally leads to chain termination. Therefore, there are not
many procedures known for successful radical chain hydrosilylations. By using more
reactive silanes, however, the reduction of the b-silylalkyl radical should be feasible.
Indeed, tris(trimethylsilyl)silane [3], with its more reactive SiÀH bond compared to
regular trialkyl silanes, has been successfully used in radical hydrosilylation reactions
[4 6]. Moreover, the surface modification of porous silicon that contains reactive
SiÀH bonds has also been achieved via radical hydrosilylation reactions [7].
Scheme 1
R3SiH
R''SH
fast
R3Si
R3Si
R3Si
a)
R3Si
+
R'
R'
R'
R'
R'
R'
R3Si
b)
c)
R3Si
R''S
+
+
R''S
R3SiH
+
R''SH
R3Si
1
)
Part of the Ph.D. Thesis of S. A.

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Helvetica Chimica Acta Vol. 85(2002)
In elegant work, Roberts showed that the radical hydrosilylation with non-activated
trialkylsilanes can be conducted in the presence of thiols as polarity-reversal catalysts
[8]. Here, the direct abstraction of H from the silane by the b-silylalkyl radical is
replaced by a H-transfer reaction from a thiol (Scheme 1,b). The thiyl radical
generated is then reduced by the silane to provide the chain-carrying silyl radical along
with the thiol (Scheme 1,c). Both types of H-transfer reactions benefit from favorable
polar effects. Matsumoto and Ito generated silyl radical by selective SiÀB bond
homolysis of bis(diisopropylamino)organosilylboranes and used them in non-chain
radical hydrosilylation reactions [9].
Recently, we introduced silylated cyclohexadienes as new Sn-free radical reducing
reagents [10]. Various typical radical reactions, e.g., dehalogenations, deselenations,
deoxygenations, and intermolecular additions were performed with the aid of these
new reagents. The cyclohexadiene CH2 moiety acts as the H donor in these radical
.
chain reactions [11]. Reduction of a radical R with reagent 1 affords a cyclohexadienyl
radical 2 (Scheme 2). Re-aromatization of the latter provides the corresponding silyl
radical, which is able to propagate the chain by reaction with the starting halide,
xanthate, or phenyl selenide RÀX. As a by-product, the methylated resorcin diether 3
is formed. In a preliminary communication, we reported the successful application of
silylated cyclohexadienes of type 1 in hydrosilylation reactions [12]. The silyl radical
formed in the re-aromatization of 2 is allowed to react with an alkene to form a b-
silylalkyl radical that is subsequently reduced with the cyclohexadiene 1 to yield 2 and
the corresponding hydrosilylation product.
Scheme 2
Si
MeO
OMe
tBuMe2SiX
R
1
R–X
R–H
tBuMe2Si
Si
MeO
OMe
MeO
OMe
2
3
The hydrosilylation of alkenes can formally be regarded as a transfer-hydro-
silylation since the reagent is transformed into the corresponding arene in a reverse
hydrosilylation process. Here, we present in full detail our results on the radical

Helvetica Chimica Acta Vol. 85(2002)
3561
hydrosilylation of various unsaturated substrates with the aid of silylated cyclo-
hexadienes.
2. Results and Discussion. Hydrosilylations of Alkenes. The reagents 1 and 5 7
can be readily prepared from cyclohexadiene 4 [13] in a one-pot procedure (Scheme 3).
The regioselective metallation [14] of 4 is accomplished with tBuLi in tetrahydrofurane
(THF) with either hexamethylphosphortriamide (HMPA) or the nontoxic N,N,N',N'-
tetramethylethylenediamine (TMEDA) as an additive at À788. Silylation with the
commercially available chlorosilanes ClSiMe2(tBu), ClSiMe2Ph, ClSi(iPr)3 or with
ClSiMe2(NEt2) [15] provided the corresponding silylated cyclohexadienes that, again,
underwent metalation upon BuLi addition. Methylation with dimethyl sulfate provided
the reagents 1 and 5 7 in moderate to high yields (44 90%). Reagent 8 was prepared
analogously, starting from cyclohexa-1,4-diene treated with sBuLi and TMEDA (63%)
[16]. The trimethylsilyl derivative prepared from cyclohexadiene 4 (not shown) is not
stable and was, therefore, not used in radical hydrosilylation reactions.
Scheme 3
1. tBuLi, TMEDA or
HMPA, THF
E
MeO
OMe
MeO
OMe
2. E-Cl
3. BuLi
4. (MeO)2SO2
t
4
1 E = SiMe2 Bu (78%)
5 E = Si(iPr)3 (44%)
6 E = SiMe2Ph (74%)
7 E = SiMe2NEt2 (90%)
SiMe3
1. sBuLi, TMEDA
2. ClSiMe3
3. sBuLi
4. (MeO)2SO2
8 (63%)
The radical hydrosilylation of non-activated CˆC bonds in the presence of
cyclohexadiene 1 was studied first. From our previous work, we knew that hexane is the
solvent of choice to perform radical chain reactions with tin hydride substituents of type
1 [10]. We were pleased to find that the hydrosilylation of allyl acetate with reagent 1
worked well in hexane (0.25m) when a,a-azoisobutyronitrile (AIBN) was used as an
initiator (sealed tube, 80 858) (Scheme 4). Best results were obtained with 1.5equiv. of
1 and 0.3 equiv. of AIBN. Under these conditions, the silylated product 9 was isolated in
54% yield. Under analogous conditions, compound 10 was hydrosilylated to afford the
tetraalkylsilane 11 in 55% yield. Our method is not restricted to the hydrosilylation of
terminal CˆC bonds, as demonstrated by the transformation of cyclohexene to the
silylated cyclohexane derivative 12 (60%). However, the hydrosilylation of tetrasub-

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Helvetica Chimica Acta Vol. 85(2002)
stituted alkenes failed. Tetramethylethene (2,3-dimethylbut-2-ene), e.g., was recovered
almost quantitatively.
Scheme 4
1 (1.5 equiv.)
AIBN (0.3 equiv.)
Si
Si
O
O
Hexane (0.25M)
O
O
9 (54%)
1 (1.5 equiv.)
AIBN (0.6 equiv.)
Hexane (0.25M)
10
11 (55%)
1 (1.5 equiv.)
AIBN (0.3 equiv.)
Si
Hexane (0.25M)
12 (60%)
Hydrosilylations of Alkynes. We next focused on the hydrosilylation of alkynes,
which were reacted under the optimized conditions described above (1.5equiv. of
reagent in hexane (0.25m), 0.3 equiv. of AIBN, 80 858, sealed tube). Hydrosilylation
of phenylacetylene with reagent 1 afforded the vinylsilane 13 in 73% yield as a 25:1
mixture of diastereoisomers (Scheme 5). An even higher yield (88%) was obtained for
15, arising from the hydrosilylation of hex-1-yne. However, the stereoselectivity of the
reaction dropped markedly ((Z)/(E) 21:10). It is well-known that Ph-substituted vinyl
radicals can be stereoselectively reduced [17]. These p-type vinyl radicals are linear,
and the stereoselectivity of the reduction is determined by the size of the substituent in
b-position. However, alkyl-substituted (nonconjugated) vinyl radicals are sp2-hybri-
dized and invert at very low energy barriers [18]. The product ratio depends on the
equilibrium constant of the two interconverting vinyl radicals and on the rate constant
of the reduction. In general, lower selectivities are obtained for the reduction of these
s-type vinyl radicals compared to the reduction of Ph-substituted vinyl radicals, as
observed in our experiments.
Hydrosilylation of alkyne 17 with reagent 1 provided the vinylsilane 18 in 66% yield.
Hydrosilylation of phenylacetylene with reagent 6 (instead of 1) led to 14 in only 19%
yield. Thus, hydrosilylation of phenylacetylene with the (tert-butyl)dimethylsilyl reagent 1
is much more efficient than with the phenyl(dimethyl)silyl-derived reagent 6. We believe
that the vinyl radical 19, formed after phenyl(dimethyl)silyl radical addition, reacts with
the Ph substituent at the Si-atom to afford the cyclohexadienyl radical 20 (Scheme 5). The
latter is rather stable and, thus, cannot propagate the chain reaction. Indeed, with
0.6 equiv. of AIBN, the yield of 14 could be slightly increased to 34%. However, further

Helvetica Chimica Acta Vol. 85(2002)
3563
Scheme 5
1 or 6 (1.5 equiv.)
AIBN (0.3 or 0.6 equiv.)
R
Si
Hexane (0.25M)
13 R = tBu (73%, (Z)/(E) 25:1)
14 R = Ph (34%, (Z)/(E) 25:1)
1 or 6 (1.5 equiv.)
AIBN (0.3 or 0.6 equiv.)
R
Si
Hexane (0.25M)
15 R = tBu (88%, (Z)/(E) 21:10)
16 R = Ph (28%, (Z)/(E) 22:10)
1 (2 equiv.)
AIBN (1.1 equiv.)
OTr
Si
OTr
OMe
OMe
Hexane (0.25M)
17
18 (66%, (Z)/(E) 21:10)
Tr = Trityl
H
R
H
R
Si
Si
Chain termination
19
20
increase of the initiator concentration (0.9 equiv.) does not lead to higher yields. A similar
result was obtained for the hydrosilylation of hex-1-yne with cyclohexadiene 6. The vinyl
silane 16 was isolated in 28% yield upon adding 0.6 equiv. of AIBN.
Hydrosilylations can also be performed without AIBN by using O2 (air) as an
initiator. Thus, reaction of phenylacetylene with reagent 1 in hexane under an
atmosphere of O2 provided 13 in 55% yield (reflux, 24 h). Attempted room-
temperature hydrosilylation with Et3B/O2, however, failed.
Hydrosilylation/Cyclization. The hydrosilylation/cyclization of dienes in the
presence of transition-metal catalysts is a well-studied reaction [19]. From an
ecological point of view, however, it would be favorable if one had not to rely on
transition metals. We, therefore, tested our reagents in the hydrosilylation of dienes
21 25 and 31 (cf. Scheme 6 and the Table).
Reaction of diene 21 with reagent 1 afforded product 26 in 80% yield as a 43 :10
mixture of diastereoisomers. The initially formed b-silylalkyl radical undergoes a 5-exo-

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Helvetica Chimica Acta Vol. 85(2002)
Scheme 6
Si
1 (1.5 equiv.)
AIBN (0.3 equiv.)
Hexane (0.25M)
X
X
21–25
26–30
Si
1 (1.5 equiv.)
AIBN (0.6 equiv.)
Hexane (0.25M)
CO2Et
CO2Et
EtO2C
EtO2C
31
32 (61%)
cis/trans 1:1
Table. Hydrosilylation/Cyclization of Various Dienes
X
Starting material
Yield [%]
Product
cis/trans
C(CO2Et)2
O
21
80
71
76
62
26
27
28
29
43 : 10
25: 10
20 : 10
23 : 10
22
NÀTs
23a)
24b)
C(CH2OH)2
O
25
72
30
26 : 10
C
O
a) The reaction was complete in 7 h. b) 3 Equiv. of 6 and 0.6 equiv. of AIBN were used.
cyclization to a primary radical that is reduced by 1 to the five-membered ring of 26.
The isomer ratio was determined by gas chromatography (GC). The assignment of the
1
relative configuration is based on comparison of the H-NMR data with literature
values [20]. All compounds were identified in this way. The formation of the cis-
compound as the major isomer is in accordance with the Beckwith Houk model for 5-
exo-cyclizations [21]. Similarly, the diallyl ether 22 was readily transformed into the
furan derivative 27 in 71% yield, with a diastereoisomer ratio (dr) of 25:10. The
tosylated pyrrolidine 28 was obtained in 76% yield from sulfonamide 23 (dr 20 :10).
The hydrosilylation of diol 24 did not go to completion under standard conditions.
However, with 3 equiv. of 1 and 0.6 equiv. of AIBN product 29 was obtained in 62%
yield (dr 23 :10). Hydrosilylation of acetal 25 led to the cyclization product 30 in 72%
yield (dr 26 :10).
We have previously shown that reagent 1 reduces primary C-radicals about 55 times
slower than Bu3SnH does [10]. This should allow us to study slow radical chain

Helvetica Chimica Acta Vol. 85(2002)
3565
reactions. For instance, the hydrosilylation/cyclization of diene 31 worked well, and the
product 32 was isolated in 61% yield (dr 1:1). The silyl radical addition occurs highly
regioselectively at the less-hindered terminal CˆC bond and is followed by a rather
slow 6-exo-cyclization. The product of a mono hydrosilylation was not observed.
Since the reduction of the initially formed b-silylalkyl radical with reagent 1 is a
slow process, it should be possible to combine it with other radical reactions, e.g., b-
fragmentations. This would directly lead to allylsilanes
highly versatile carbon
nucleophiles in organic synthesis [22]. We, therefore, studied the hydrosilylation of b-
pinene. The expected product 33 was isolated in 70% yield (Scheme 7). Hydrosilylation
can also be combined with the cleavage of a carbonÀheteroatom bond, as shown for
the transformation of vinyloxirane to the corresponding allyl alcohol 34 (61%)
(Scheme 7). A lower yield (35%) was obtained for the analogous reaction performed
with reagent 6 leading to 35.
Scheme 7
Our synthetic strategy for the preparation of hydrosilylating reagents basically
allows the introduction of any silyl group (cf. Scheme 3). To demonstrate this potential,
the hydrosilylation/cyclization of diene 36 was studied with the Si reagents 1 and 5 8
(Scheme 8). It turned out that the nature of the silyl group influences the outcome of
the reaction. With the standard reagent 1, under typical conditions (1.5equiv. of Si
reagent, 0.3 equiv. of AIBN, hexane (0.25m)), the cyclization product 37 was obtained
in 84% yield (dr 38 :10). The reaction with the phenyl(dimethyl)silyl-derived reagent 6
was less efficient and led to 38 in 57% yield (dr 44 :10). Reaction of 36 with the bulky
triisopropylsilyl derivative 5 provided the hydrosilylation/cyclization product 39 in only
44% yield (dr 38 :10). Finally, with reagent 8, lacking the methoxy substituents, the
hydrosilylation/cyclization of 36 could not be accomplished, and the cyclopentane
dicarboxylate 40 was not observed at all. However, we found that the hydrosilylation/
cyclization reaction of 36 with reagents 5 and 8 works well at 1408 in the presence of
di(tert-butyl) peroxide as the initiator. The reactions were conducted in hexane in
sealed tubes. Under these modified conditions, compound 39 was obtained in 82%

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Helvetica Chimica Acta Vol. 85(2002)
yield, but with a slightly lower selectivity (dr 26 :10). The corresponding reaction with
the trimethylsilyl derivative 8 at 1408 provided 40 in 81% yield as a 31:10 mixture of
diastereoisomers.
Scheme 8
R
a)
MeO2C
CO2Me
MeO2C
CO2Me
37 R = tBuMe2Si (84%, dr: 38:10)
38 R = PhMe2Si (57%, dr: 44:10)
39 R = iPr3Si (82%, dr: 26:10)
40 R = Me3Si (81%, dr: 31:10)
36
Et2N
Si
OiPr
Si
b)
c)
36
MeO2C
CO2Me
MeO2C
42 (53%, dr: 15:10)
OH
CO2Me
41
d)
38
MeO2C
CO2Me
43 (74%, dr: 40:10)
dr = Diastereoisomer ratio
a) 1, 5, 6, or 8 (1.5 2.2 equiv.), AIBN (0.3 0.9 equiv.) or ( tBuO)2 (0.5equiv.), hexane (0.25 m). b) 7 (1.5equiv.),
i
AIBN (0.3 equiv.), hexane (0.25m). c) PrOH, NH4Cl. d) Hg(OAc)2, AcOOH.
Reagent 7 is an interesting compound, since such aminosilanes can be regarded
both as electrophilic and radical silylation reagents. The hydrosilylation of diene 36
with 7, under standard conditions, provided 41 in a clean reaction (Scheme 8).
However, it was difficult to isolate the product. We, therefore, treated the crude
i
reaction mixture with PrOH in the presence of NH4Cl [23], which afforded the
silylether 42 in 53% yield (dr 15 :10).
The phenyl(dimethyl)silyl reagent 6 is synthetically very useful, because the
corresponding hydrosilylation products can be easily converted to alcohols by Tamao
Fleming oxidation [24]. The cyclization product 38, e.g., was oxidized to the alcohol 43
in 73% yield [25]. Formally, the above hydrosilylation process can, thus, be regarded as
a radical anti-Markovnikov hydration.
Hydrosilylation of CˆC Bonds. Finally, we studied the radical hydrosilylation of
various aldehydes in the presence of 1 [26]. With AIBN as the initiator at 808 in hexane,

Helvetica Chimica Acta Vol. 85(2002)
3567
Scheme 9
1 (1.5 equiv.)
(tBuO)2 (0.3 equiv.)
Si
O
O
R
H
Hexane (0.25M), 140°, 5 h
R
44 R = cyclohexyl
46 R = tBu
48 R = iPr
45 R = cyclohexyl (99%)
47 R = tBu (99%)
49 R = iPr (70%)
50 R = PhCH2CH2
52 R = BnO(CH2)3
51 R = PhCH2CH2 (88%)
53 R = BnO(CH2)3 (67%)
Si
O
O
1 (1.5 equiv.)
(tBuO)2 (0.3 equiv.)
Hexane (0.25M), 140°, 5 h
54 (62%)
low yields of the corresponding hydrosilylation products were obtained. However, at
1408 in sealed tubes and in the presence of (tBuO)2, all reactions went to completion,
and the desired tert-butyldimethylsilyl- (TBDMS) protected alcohols were isolated in
high yields (Scheme 9). Cyclohexanecarbaldehyde (44) and pivalaldehyde (46) were
quantitatively converted to the corresponding silyl ether 45 and 47. Hydrosilylation of
isobutyraldehyde (48) afforded 49 in 70% yield. Thereby, some product was lost during
the purification process (volatile compound). Attempted hydrosilylations of benzal-
dehyde failed. Under standard conditions (1.5equiv. of 1, 0.3 of (tBuO)2, 1408), the
starting material was mostly recovered. The benzylic radical generated upon addition
of the silyl radical is obviously too stable to be reduced by reagent 1. Somewhat lower
yields were obtained for the reductions of the aliphatic aldehydes 50 and 52 leading to
51 (88%) and 53 (67%), respectively. Here, the addition of the silyl radical to the Ph
group, a process that would lead to chain termination, probably competes with the
desired hydrosilylation. Finally, it should be pointed out that our hydrosilylation
method is not restricted to aldehydes. Cyclohexanone, e.g., was converted to the silyl
ether 54 in 62% yield.
3. Conclusions. We have presented a new method for the radical hydrosilylation of
alkenes, alkynes, aldehydes, and ketones with the aid of silylated cyclohexadienes. The
reaction can formally be regarded as a transfer-hydrosilylation, since the reagent is
transformed into the corresponding arene by a reverse hydrosilylation reaction, a
process not known so far. The synthesis of the silylated cyclohexadiene reagent is
straightforward and allows the variation of the silyl group. Various unsaturated
substrates are efficiently hydrosilylated with these new reagents in an environmentally
benign process. In the hydrosilylation of acetylenes, high stereoselectivities can be

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Helvetica Chimica Acta Vol. 85(2002)
obtained. The hydrosilylation of hepta-1,6-diene derivatives leads to silylated cyclo-
pentanes. Thus, our new method nicely complements hydrosilylation/cyclization
reactions performed with (toxic) transition metal catalysts. Vinyl-substituted cyclo-
propanes and vinyl oxirane are transformed into allyl silanes, useful nucleophiles in
synthetic organic chemistry. In addition, the radical hydrosilylation of aldehydes can
also be efficiently achieved with our new reagent.
We thank the Swiss National Science Foundation (2100-055280.98/1) for funding our work.
Experimental Part
General. Solvents were purified by standard methods. Air- and moisture-sensitive compounds were handled
under Ar gas using Schlenk techniques. TLC: Merck silica gel 60 F254 plates; UV detection or staining with a
soln. of KMnO4 (1.5g) in 1m NaOH (333 ml) or with a soln. of Ce(SO4)2 ¥ H2O (10 g), phosphormolybdic acid
hydrate (25g), conc. H 2SO4 (60 ml), and H2O (940 ml), followed by heating. FC: Merck or Fluka silica gel 60
(40 63 mm) at ca. 0.4 bar. GC: Hewlett Packard 5890 chromatograph using Hewlett Packard HP-5 or Supelco m-
DEX-120 columns. M.p.: B¸chi 510 apparatus; uncorrected. IR: Perkin Elmer 782 or Bruker IFS-200
1
spectrophotometer, in cmÀ1. H- and 13C-NMR: Bruker AMX-500, AMX-400, AC-300, or Varian Gemini 300.
Chemical shifts d in ppm rel. to SiMe4 as internal standard, J in Hz.
General Procedure 1 (GP 1) for the Synthesis of Si Reagents 1, 6, and 7. 1,5-Dimethoxycyclohex-1,4-diene
(4) [13] was dissolved in THF. The soln. was cooled to ca. À708. After addition of tBuLi and stirring for 10 min,
HMPA (hexamethylphosphortriamide) or TMEDA (N,N,N',N'-tetramethylethylenediamine) was added. The
resulting red or orange soln. was stirred for 60 min at À708. A soln. of the chlorosilane in THF was slowly added.
The soln. was stirred at À5 0 toÀ708 for 60 min before BuLi was added. After stirring for another 60 min at the
same temp., (MeO)2SO2 was added. The cooling bath was removed and the mixture was allowed to warm to r.t.
Pentane was added, followed by H2O. The org. layer was separated, washed with H2O and brine, and dried
(MgSO4). The crude products were purified by FC, distillation, or recrystallization.
(tert-Butyl)(2,6-dimethoxy-1-methylcyclohexa-2,5-dienyl)dimethylsilane (1). Prepared according to GP 1
from 4 (21 g, 0.15mol) in THF (450 ml), tBuLi (94 ml, 1.76m in pentane, 0.165mol), TMEDA (24.7 ml,
0.165mol), tBuMe2SiCl (24.9 g, 0.165mol) in THF (30 ml), BuLi (102.5ml, 1.61 m in hexane, 0.165mol), and
(MeO)2SO2 (15.7 ml, 0.165 mol). Distillation (1.2 mbar, 858) and recrystallization (MeOH) afforded 1 (31.46 g,
78%). M.p. 32 338. IR (CHCl3): 2934s, 2855s, 1677s, 1643w, 1464m, 1344m, 1127s, 1076m, 977w. 1H-NMR
(500 MHz, CDCl3): 4.46 (t, J ˆ 3.7, 2 CH); 3.45( s, 2 MeO); 2.83 2.82 (m, CH2); 1.32 (s, Me); 0.85( s, tBu); 0.00
(s, Me2Si). 13C-NMR (125MHz, CDCl 3): 158.9 (Cq); 88.4 (CH); 53.7 (Me); 35.7 (Cq); 27.3 (Me); 24.5(CH 2);
‡
‡
19.8 (Me); 19.3 (Cq); À4.9 (Me). EI-MS: 268.2 (15, M ), 253.1 (7, [M À Me] ), 179.1 (4), 153.1 (29), 152.1 (55),
138.1 (9), 122.1 (21), 121.1 (12), 107.0 (19), 91.0 (11), 89.0 (20), 73.0 (100), 59.0 (16). Anal. calc. for C15H28O2Si
(268.47): C 67.11, H 10.51; found: C 67.16, H 10.69.
(2,6-Dimethoxy-1-methylcyclohexa-2,5-dienyl)triisopropylsilane (5). Cyclohexadiene 4 (4.0 g, 28 mmol)
was dissolved in THF (100 ml). The soln. was cooled to ca. À708. After addition of tBuLi (20 ml, 1.6m in hexane,
30 mmol) and stirring for 1 h, HMPA (6.0 ml, 33 mmol) was added. The resulting red soln. was stirred for 10 min
at À708. (iPr)3SiCl (6.68 ml, 30 mmol) was added slowly. The red color of the mixture disappeared. After 5min,
the cooling bath was removed and the mixture was allowed to warm to r.t. Pentane was added, followed by H2O.
The phases were separated, and the org. layer was washed with H2O (2Â) and brine and dried over MgSO4.
Removal of the solvent in vacuo and distillation (908, 0.2 mbar) afforded (2,6-dimethoxycyclohexa-2,5-
dienyl)triisopropylsilane (7.4 g, 25mmol, 89%) as a colorless oil. The crude product (1.20 g, 4.0 mmol) was
dissolved in THF (15ml). The soln. was cooled to ca. À208, BuLi (5ml, 1.63 m in hexane, 8.0 mmol) was added,
and stirring was continued for 3 h at À208. HMPA (1.4 ml, 8.0 mmol) was added, and the resulting orange soln.
was stirred for 30 min at À308. (MeO)2SO2 (0.76 ml, 8.0 mmol) was added, whereupon the color of the mixture
disappeared. After 5min, the cooling bath was removed and the soln. was allowed to warm to r.t. Pentane was
added, followed by H2O, the org. layer was separated, washed with H2O (2Â) and brine, and dried (MgSO4).
Removal of the solvent in vacuo and purification by FC (pentane) afforded 5 (605mg, 49%; 44% over two
steps) as a colorless amorphous solid. IR (CHCl3): 2947s, 2866s, 2831s, 1681s, 1642m, 1581w, 1465s, 1343m, 1128s,
980m, 882m. 1H-NMR (400 MHz, CDCl3): 4.47 (t, J ˆ 3.6, 2 CH); 3.47 (s, 2 MeO); 2.86 2.83 (m, CH2); 1.44
(s, Me); 1.26 1.06 (m, 3 Me2CH); 1.09 (d, J ˆ 6.6, 3 Me2CH). 13C-NMR (100 MHz, CDCl3): 159.3 (Cq); 88.4

Helvetica Chimica Acta Vol. 85(2002)
3569
‡
‡
(CH); 53.5 (Me); 24.9 (CH2); 21.8 (CH); 19.6 (Me); 13.0 (CH). EI-MS: 310.3 (24, M ), 294.2 (5, [M À Me] ),
267.2 (12), 251.2 (16), 195.1 (10), 157.2 (41), 153.1 (20), 152.1 (100), 115.1 (47), 87.1 (11). Anal. calc. for
C18H34O2Si (310.55): C 69.62, H 11.03; found: C 69.43, H 11.16.
(2,6-Dimethoxy-1-methylcyclohexa-2,5-dienyl)(dimethyl)phenylsilane (6). Prepared according to GP 1
from 4 (280 mg, 2 mmol) in THF (7 ml), tBuLi (1.4 ml, 1.6m in hexane, 2.2 mmol), HMPA (0.42 ml, 2.4 mmol),
(chloro)dimethyl(phenyl)silane (0.37 ml, 2.2 mmol) in THF (2 ml), BuLi (1.6 ml, 1.5m in pentane, 2.4 mmol),
and (MeO)2SO2 (0.2 ml, 2.1 mmol). Purification by FC (pentane/Et2O 20 :1) afforded 6 (427 mg, 74%) as a
colorless oil. IR (CHCl3): 3068w, 2998m, 2952m, 2903m, 2831m, 1677s, 1643w, 1451m, 1427m, 1346m, 1127s,
1
1076w, 979w. H-NMR (400 MHz, CDCl3): 7.42 7.39 (m, 2 arom. H); 7.29 7.20 (m, 3 arom. H); 4.39 (dd, J1 ˆ
4.6, J2 ˆ 2.7, 2 CH); 3.31 (s, 2 MeO); 2.62 (dt, J1 ˆ 20.3, J2 ˆ 4.6, 1 H, CH2); 2.42 (dt, J1 ˆ 20.3, J2 ˆ 2.7, 1 H, CH2);
1.28 (s, Me); 0.26 (s, 2 Me2Si). 13C-NMR (100 MHz, CDCl3): 157.5 (Cq); 138.6 (Cq); 134.1 (CH); 128.5(CH);
‡
126.9 (CH); 89.1 (CH); 53.8 (Me); 36.4 (Cq); 24.3 (CH2); 17.1 (Me); À3.93 (Me). EI-MS: 288.2 (31, M ), 271.1
(3), 195.1 (15), 180.1 (3), 163.0 (3), 152.1 (50), 135.0 (100), 122.0 (22), 107.0 (28), 91.0 (11), 77.0 (7). Anal. calc.
for C17H24O2Si (288.46): C 70.78, H 8.39; found: C 70.73, H 8.24.
[(2,6-Dimethoxy-1-methylcyclohexa-2,5-dienyl)dimethylsilyl]diethylamine (7). Prepared according to GP 1
with 4 (4.20 g, 30 mmol) in THF (100 ml), tBuLi (22.3 ml, 1.48m in hexane, 33 mmol), HMPA (5.77 ml,
33 mmol), (Et2N)Me2SiCl [15] (5.46 g, 33 mmol), BuLi (20.5 ml, 1.61m in pentane, 33 mmol) and (MeO)2SO2
(2.85ml, 30 mmol). Distillation (80 8, 1 mbar) afforded 7 (7.63 g, 90%) as a colorless oil. IR (nujol): 2964s, 2904s,
2868m, 2829s, 1678s, 1345m, 1248m, 1211s, 1177m, 1127s, 1031m, 811s, 766m. 1H-NMR (300 MHz, CDCl3): 4.52
(t, J ˆ 3.4, 2 CH); 3.51 (s, 2 MeO); 2.87 (dd, J1 ˆ J2 ˆ 3.4, CˆCHÀCH2); 2.81 (q, J ˆ 7.0, 2 CH2N); 1.32 (s, Me);
0.99 (t, J ˆ 7.0, 2 MeCH2); 0.12 (s, Me2Si). 13C-NMR (75MHz, CDCl 3): 158.7 (Cq); 88.2 (CH); 53.9 (Me); 41.0
‡
(CH2); 38.5(C q); 24.5(CH 2); 17.3 (CH3); 16.3 (Me); À2.7. EI-MS: 283 (2, M ), 268 (4), 197 (9), 152 (22), 132
(47), 131 (69), 130 (100), 117 (15), 116 (84), 103 (37), 88 (19), 73 (20), 72 (31), 70 (24), 59 (58), 58 (32), 57
‡
‡
(12). HR-EI-MS: 283.1965( M , C15H29NO2Si ; calc. 283.1968).
Trimethyl(1-methylcyclohexa-2,5-dienyl)silane (8). Cyclohexa-1,4-diene (0.94 ml, 10 mmol) was dissolved
in THF (16 ml) and cooled to ca. À 608. sBuLi (8.4 ml, 1.31m in cyclohexane, 11 mmol) was added. The resulting
yellow soln. was treated with TMEDA (1.54 ml, 10 mmol). The mixture was allowed to warm to À358 in 2 h.
After addition of Me3SiCl (1.39 ml, 11 mmol), the soln. was stirred for 1 h at r.t. After cooling to À608, sBuLi
(8.4 ml, 1.31m in cyclohexane, 11 mmol) was added. The mixture was allowed to warm to À40 to À358. Stirring
was continued for 2 h at this temp. before (MeO)2SO2 (1.04 ml, 11 mmol) was added. After 5min, the cooling
bath was removed, and the mixture was allowed to warm to r.t. H2O and Et2O were added. The org. layer was
separated, washed with H2O (2Â), sat. NH4Cl soln., and brine, and dried (MgSO4). Removal of the solvent in
vacuo and distillation (16 mbar, 538) afforded 8 (1.04 g, 63%) as a colorless oil. IR (CHCl3): 3008m, 2957s,
2863m, 2821m, 1662w, 1616w, 1461m, 1432m, 1404w, 1366w, 1333w, 1095w, 999w, 95 m9 , 925m. 1H-NMR
(400 MHz, CDCl3): 5.58 5.54 (m, 2 CH2CH); 5.48 5.44 (m, 2 CH); 2.73 2.55 (m, CH2); 1.09 (s, MeC); À0.01
(s, Me3Si). 13C-NMR (100 MHz, CDCl3): 132.37 (CH); 120.80 (CH); 45.83 (Cq); 26.52 (CH2); 22.61 (Me);
‡
À4.72 (Me). EI-MS: 166.2 (<1, M ), 107.1 (2), 105.1 (2), 93.0 (1), 92.0 (3), 91.0 (2), 79.0 (3), 78.0 (2), 73.0 (21),
59.0 (2), 39.9 (3), 31.9 (29), 27.9 (100), 17.9 (5). Anal. calc. for C10H18Si (166.34): C 72.21, H 10.91; found:
C 71.97, H 10.90.
General Procedure 2 (GP 2) for Hydrosilylation Reactions. In a pressure-stable glass tube, substrate, Si
reagent, and radical initiator were dissolved in hexane. After flushing with Ar, the tube was sealed and heated to
80 858. After cooling down, the solvent was evaporated in vacuo, and the crude product was purified by FC.
The diastereoisomer ratio of the products was determined by gas chromatography taking samples of the crude
mixture.
3-[(tert-Butyl)dimethylsilyl]propyl Acetate (9). Prepared according to GP 2 from allyl acetate (100 mg,
1 mmol), reagent 1 (400 mg, 1.5mmol), and AIBN (50 mg, 0.3 mmol) in hexane (4 ml); 4.5h. FC (pentane/
tBuOMe 40 :1) afforded 9 (116 mg, 54%) as a colorless oil. IR (nujol): 2953s, 2930s, 2885m, 2857m, 1744s,
1468m, 1363m, 1236s, 1048m, 835m. 1H-NMR (300 MHz, CDCl3): 4.02 (t, J ˆ 6.96, CH2O); 2.05( s, MeCO);
1.67 1.56 (m, CH2CH2CH2); 0.87 (s, tBu); 0.53 0.47 (m, CH2Si); À0.05( s, Me2Si). 13C-NMR (75MHz,
CDCl3): 171.0 (Cq); 67.68 (CH2); 26.92 (Me); 23.99 (CH2); 21.42 (Me); 16.90 (Cq); 8.63 (CH2); À6.01 (Me). EI-
t
‡
MS: 159.2 (14, [M À Bu] ), 118.1 (8), 117.2 (92), 76.0 (7), 75.0 (100), 73.1 (13), 43.0 (14), 28.0 (5). HR-EI-MS:
t
‡
‡
119.0841 ([M À Bu] , C7H15O2Si ; calc. 119.0841).
(tert-Butyl)dimethyl(4-phenylbutyl)silane (11). Prepared according to GP 2 from (but-3-enyl)benzene (10)
[27] (132 mg, 1 mmol), 1 (407 mg, 1.5mmol), and AIBN (50 mg, 0.3 mmol) in hexane (4 ml); 4 h. Additional
AIBN (50 mg, 0.3 mmol) was added. The soln. was stirred for another 4 h at 908. FC (pentane) afforded 11
(136 mg, 55%) as a colorless oil. IR (nujol): 2952s, 2927s, 2882m, 2855s, 1466m, 1251s, 830s, 803m, 746m, 698s.

3570
Helvetica Chimica Acta Vol. 85(2002)
1H-NMR (300 MHz, CDCl3): 7.25 7.19 ( m, 2 arom. H); 7.15 7.14 ( m, 3 arom. H); 2.63 2.58 (m, PhCH2);
1.69 1.59 (m, CH2); 1.41 1.30 (m, CH2); 0.86 (s, tBu); 0.56 0.51 (m, CH2Si); À0.09 (s, Me2Si). 13C-NMR
(75MHz, CDCl 3): 143.3 (Cq); 128.8 (CH); 128.6 (CH); 125.9 (CH); 36.1 (CH2); 36.1 (CH2); 27.0 (Me); 24.5
‡
t
‡
(CH2); 17.0 (Cq); 12.7 (CH2); À5.9 (Me). EI-MS: 233.2 (<1, [M À Me] ), 192.1 (18), 191.2 (100, [M À Bu] ),
189.1 (18), 187.2 (9), 135.2 (8), 91.1 (12), 87.0 (21), 73.1 (40), 59.1 (65), 28.0 (13). HR-EI-MS: 191.1262 ([M À
‡
‡
tBu] , C12H19Si ; calc. 191.1256).
(tert-Butyl)(cyclohexyl)dimethylsilane (12). Prepared according to GP 2 from cyclohexene (82 mg,
1 mmol), 1 (400 mg, 1.5mmol), and AIBN (50 mg, 0.3 mmol) in hexane (4 ml); 15h. FC (pentane) afforded
12 (119 mg, 60%) as a colorless oil. IR (nujol): 2955s, 2926s, 2852s, 1471m, 1446m, 1362w, 1254m, 1247m, 1097w,
888w, 85 0m, 827m, 799m, 765m. 1H-NMR (500 MHz, CDCl3): 1.80 1.68 (m, 5H, CH 2); 1.32 1.11 (m, 5 H,
CH2); 0.92 (s, tBu); 0.81 0.73 (m, CHSi); À0.08 (s, Me2Si). 13C-NMR (125MHz, CDCl 3): 28.92 (CH2); 28.55
‡
(CH2); 27.55 (Me); 27.18 (CH2); 24.22 (CH); 17.50 (Cq); À7.54 (Me). EI-MS: 198.4 (4, M ), 142.5(15), 141.4
‡
(86), 113.3 (8), 99.2 (7), 81.3 (48), 74.2 (5), 73.2 (62), 60.2 (7), 59.2 (100), 28.0 (11). HR-EI-MS: 198.1795 ( M ,
‡
C12H26Si ; calc. 198.1804).
(tert-Butyl)(dimethyl)[(Z)-2-phenylethenyl]silane (13). Prepared according to GP 2 from phenylacetylene
(102 mg, 1 mmol), 1 (400 mg, 1.5mmol), and AIBN (50 mg, 0.3 mmol) in hexane (4 ml); 4 h. FC (pentane)
afforded 13 (159 mg, 73%) as a colorless oil. Diastereoisomer ratio: (Z)/(E) 25:1. IR (nujol): 2953 m, 2926s,
2855m, 1591w, 1572w, 1492w, 1463m, 1251m, 824s, 777m, 699m. 1H-NMR (300 MHz, CDCl3): 7.48 (d, J ˆ 15.2,
SiÀCHˆCH); 7.32 7.21 (m, 5arom. H); 5.87 ( d, J ˆ 15.2, SiÀCHˆCH); 0.91 (s, tBu); À0.07 (s, Me2Si).
13C-NMR (75MHz, CDCl 3): 147.7 (CH); 140.3 (Cq); 129.8 (CH); 128.1 (CH); 127.8 (CH); 127.2 (CH); 26.5
‡
t
‡
(Me); 22.4 (Cq); À4.4 (Me). EI-MS: 203 (<1, [M À Me] ), 162 (28), 161 (100, [M À Bu] ), 146 (9), 145(77),
‡
‡
t
‡
135 (31), 73 (21), 59 (59). HR-EI-MS: 203.1249 ([M À Me] , C13H19Si ; calc. 203.1256), 161.0782 ([M À Bu] ,
‡
C10H13Si ; calc. 161.0787).
(Z)-Dimethyl(phenyl)(2-phenylethenyl)silane (14). Prepared according to GP 2 from phenylacetylene
(102 mg, 1.0 mmol), 6 (432 mg, 1.5mmol), and AIBN (50 mg, 0.3 mmol) in hexane (4 ml); overnight. FC
(pentane) afforded 14 (80 mg, 34%) as a colorless oil. Diastereoisomer ratio: (Z)/(E) 25:1. The spectroscopic
data are in agreement with those reported in [28].
(tert-Butyl)(hex-1-enyl)(dimethyl)silane (15). Prepared according to GP 2 from hex-1-yne (112 ml,
1 mmol), reagent 1 (400 mg, 1.5mmol), and AIBN (50 mg, 0.3 mmol) in hexane (4 ml); 4.5h. FC (pentane)
afforded 15 (174 mg, 88%) as a colorless oil. Diastereoisomer ratio: (Z)/(E) 21:10. The NMR-data for the (Z)-
1
isomer are in agreement with those reported in [29]. H-NMR (300 MHz, CDCl3): (E)-15: 6.04 (dt, J1 ˆ 18.6,
J2 ˆ 6.1, SiÀCHˆCH); 5.61 (br. d, J ˆ 18.5, SiÀCHˆCH), 2.13 (dt, J1 ˆ J2 ˆ 6.2, CH2ÀCHˆCH); 1.38 1.23
t
(m, 2 CH2); 0.95 0.85 ( m, MeCH2); 0.87 (s, Bu); 0.00 (s, Me2Si). 13C-NMR (75MHz, CDCl 3): (E)-15: 148.8
(CH); 126.6 (CH); 36.7 (CH2); 31.1 (CH2); 26.4 (Me); 22.3 (CH2); 16.9 (Cq); 14.1 (Me); À6.0 (Me).
Dimethyl(hex-1-enyl)(phenyl)silane (16). Prepared according to GP 2 from hex-1-yne (112 ml, 1 mmol), 6
(432 mg, 1.5mmol), and AIBN (50 mg, 0.3 mmol) in hexane (4 ml); overnight. FC (pentane) afforded 16
(66 mg, 28%) as a colorless oil. Diastereoisomer ratio: (Z)/(E) 22 :10. The spectroscopic data are in agreement
with those reported in [30].
(tert-Butyl)[(4S)-4-ethoxy-5-(triphenylmethoxy)pent-1-enyl]dimethylsilane (18). Prepared according to
GP 2 from 4-methoxy-5-(triphenylmethoxy)-1-pentyne (17)2) (89.0 mg, 0.25mmol), reagent 1 (133 mg,
0.50 mmol), and AIBN (25 mg, 0.15 mmol) in hexane (1.5 ml); overnight. After cooling to r.t., the mixture
was treated with additional AIBN (25mg, 0.15mmol) and stirred for another 24 h at 80 85 8. FC (pentane/
Et2O/Et3N 100 :2 :1) afforded 18 (78.2 mg, 66%) as a colorless oil. Diastereoisomer ratio: (Z)/(E) 21:10. IR
(nujol): 2952s, 2927s, 2881m, 2855m, 1449m, 1076m, 827s, 775s, 705s. 1H-NMR (300 MHz, CDCl3): (Z)-18: 7.49
7.46 (m, 6 arom. H); 7.33 7.21 (m, 9 arom. H); 6.34 (dt, J1 ˆ 14.3, J2 ˆ 7.3, CH2ÀCHˆCH); 5.54 (d, J ˆ 14.3,
CHˆCHSi); 3.42 (s, MeO); 3.42 3.34 (m, CHO); 3.16 3.12 (m, CH2O); 2.41 2.36 (m, CH2ÀCHˆCH); 0.87
(s, tBu); 0.05( s, Me2Si); (E)-18: 7.49 7.46 (m, 6 arom. H); 7.33 7.21 (m, 9 arom. H); 5.95 (dt, J1 ˆ 18.5, J2 ˆ 6.8,
CH2ÀCHˆCH); 5.65 (d, J ˆ 18.6, CHˆCHSi); 3.43 (s, MeO); 3.42 3.34 (m, CHO); 3.16 3.12 (m, CH2O);
2.41 2.36 (m, CH2ÀCHˆCH); 0.81 (s, tBu); À0.05( s, Me2Si). 13C-NMR (75MHz, CDCl 3): (Z)-18: 145.4
(CH); 144.1 (Cq); 128.2 (CH); 128.7 (CH); 127.7 (CH); 126.9 (CH); 86.6 (Cq); 80.8 (CH); 65.4 (CH2); 58.0
(Me); 36.0 (CH2); 26.4 (Me); 16.8 (Cq); À4.2 (Me). 13C-NMR (75MHz, CDCl 3): (E)-18: 142.7 (CH); 144.1
(Cq); 129.9 (CH); 128.7 (CH); 127.7 (CH); 126.9 (CH); 86.5(C q); 80.4 (CH); 65.1 (CH2); 58.0 (Me); 39.4 (CH2);
2
)
Kindly provided by H. Wehlan and U. Koert.

Helvetica Chimica Acta Vol. 85(2002)
3571
26.4 (Me); 16.8 (Cq); À6.1 (Me). EI-MS: 287 (4), 244 (9), 243 (45), 184 (37), 147 (32), 115 (11), 99 (19), 98
‡
‡
(100), 87 (10), 81 (20), 73 (53). HR-ESI-MS: 495.2710 ([M ‡ Na] , C31H40NaO2Si ; calc. 495.2695).
Diethyl 3-{[(tert-Butyl)dimethylsilyl]methyl}-4-methylcyclopentane-1,1-dicarboxylate (26; representative
example for hydrosilylation/cyclization reactions of dienes; cf. Table). Prepared according to GP 2 from
malonate 21 (242 mg, 1 mmol), 1 (400 mg, 1.5mmol), and AIBN (50 mg, 0.3 mmol) in hexane (4 ml); 4 h. FC
(pentane/tBuOMe 30 :1) afforded 26 (286 mg, 0.80 mmol, 80%) as a colorless oil. Diastereoisomer ratio: cis/
1
trans 43 :10. IR (nujol): 2954s, 2930s, 2857s, 1732s, 1255s, 1201m, 1179m, 1150m, 1099m, 828s, 810m. H-NMR
(500 MHz, CDCl3): cis-26: 4.19 4.11 (m, MeCH2); 2.38 2.33 (m, 2 H, CH2, CH); 2.10 2.01 (m, 3 H, CH2,
CH); 1.87 (dd, J1 ˆ 13.4, J2 ˆ 9.8, 1 H, CH2); 1.23 (t, J ˆ 7.1, 2 MeCH2); 0.85( s, tBu); 0.82 (d, J ˆ 6.6, MeCH);
0.61 (dd, J1 ˆ 14.7, J2 ˆ 4.5, 1 H, SiCH2); 0.42 (dd, J1 ˆ 14.7, J2 ˆ 9.3, 1 H, SiCH2); À0.04 (2s, 2 MeSi). 1H-NMR
(500 MHz, CDCl3): trans-26: 4.19 4.11 (m, 2 MeCH2); 2.56 (dd, J1 ˆ 13.5, J2 ˆ 6.9, 1 H, CH2); 2.49 (dd, J1 ˆ
13.4, J2 ˆ 7.0, 1 H, CH2); 1.69 1.62 (m, 2 H, CH2); 1.48 1.35( m, 2 H, CH2, CH); 1.23 (t, J ˆ 7.1, 2 MeCH2); 0.95
(d, J ˆ 6.3, MeCH); 0.85( s, tBu); 0.93 0.85( m, 1 H, SiCH2); 0.23 (dd, J1 ˆ 14.5, J2 ˆ 11.1, 1 H, SiCH2); À0.04
(2s, 2 MeSi). 13C-NMR (133 MHz, CDCl3): cis-26: 173.17 (Cq); 172.17 (Cq); 61.21 (CH2); 59.00 (Cq); 41.10
(CH2); 40.67 (CH2); 39.01 (CH); 37.83 (CH); 26.48 (Me); 16.55 (Cq); 14.87 (Me); 14.02 (Me); 11.98 (CH2);
À5.10 (Me); À5.89 (Me). 13C-NMR (133 MHz, CDCl3): trans-26: 173.17 (Cq); 172.17 (Cq); 61.21 (CH2); 58.29
(Cq); 43.54 (CH); 43.69 (CH); 42.90 (CH2); 41.96 (CH2); 26.48 (Me); 17.26 (Me); 16.55 (Cq); 15.75 (CH2); 14.02
‡
t
‡
(Me); À4.73 (Me); À6.12 (Me). EI-MS: 311.2 (4, [M À EtO] ), 300.3 (21), 299.3 (100, [M À Bu] ), 182.1 (6),
181.1 (41), 73.0 (11), 32.0 (6), 28.0 (52). Anal. calc. for C19H36O4Si (356.57): C 64.00, H 10.18; found: C 63.74,
H 10.03.
Diethyl But-2-enyl(but-3-enyl)malonate (31). Na (230 mg, 10 mmol) was dissolved in EtOH (7 ml). The
soln. was treated with ethyl hex-4-enoate [31] (1.46 g, 6.8 mmol) and stirred for 1 h at r.t. 4-Bromobut-1-ene
(1.01 ml, 10 mmol) was added, and the mixture was refluxed overnight. The solvent was removed in vacuo, and
the residue was dissolved in tBuOMe. The soln. was washed with sat. NH4Cl soln. and brine, and dried (MgSO4).
Removal of the solvent in vacuo and purification by FC (pentane/tBuOMe 25:1) afforded 31 (521 mg, 29%) as a
colorless oil. IR (nujol): 3470w (br.), 2980m, 2937w, 1732s, 1447m, 1385w, 1367w, 1298w, 1266m, 1240m, 1203s,
1134m, 1096w, 1035w. 1H-NMR (300 MHz, CDCl3): 5.86 5.72 (m, 1 H, CH2ˆCH); 5.57 5.45 (m, 1 H,
CHˆCH); 5.30 5.20 (m, 1 H, CHˆCH); 5.05 4.94 (m, CH2ˆCH); 4.17 (q, J ˆ 7.1, 2 CH2O); 2.58 (d, J ˆ 7.3,
CHˆCHCH2); 2.02 1.87 (m, CH2CH2); 1.64 (d, J ˆ 6.4, MeCHˆCH); 1.24 (t, J ˆ 7.1, 2 MeCH2). 13C-NMR
(125MHz, CDCl 3): 171.7 (Cq); 138.1 (CH2); 129.9 (CH); 125.1 (CH); 115.3 (CH); 61.4 (CH2); 57.7 (Cq); 36.2
‡
(CH2); 31.8 (CH2); 28.7 (CH2); 18.4 (Me); 145(Me). EI-MS: 268.2 (2, M ), 213.2 (34), 194.2 (31), 167.1 (42),
153.1 (100), 127.1 (25), 125.1 (24), 122.1 (52), 121.2 (40), 107.1 (23), 81.1 (29), 79.1 (24), 55.1 (31), 29.1 (53),
‡
‡
28.0 (37). HR-EI-MS: 268.1687 (M , C15H24O4 ; calc. 268.1675).
Diethyl 4-{[(tert-Butyl)dimethylsilyl]methyl}-3-ethylcyclohexane-1,1-dicarboxylate (32). Prepared accord-
ing to GP 2 from 31 (110 mg, 1 mmol), 1 (400 mg, 1.5mmol), and AIBN (50 mg, 0.3 mmol) in hexane (4 ml);
4 h. Additional AIBN (50 mg, 0.3 mmol) was added. The mixture was stirred for another 4 h at 80 858. FC
(pentane/tBuOMe 50 :1) afforded cis,trans-32 (233 mg, 61%), ca. 95% pure, as a colorless oil. Diastereoisomer
ratio: cis/trans 1 :1. IR (nujol): 2955s, 2932s, 2857s, 1733s, 1464m, 1365w, 1299w, 1247s, 1158m, 1133w, 1096w,
1038w, 860w, 828m, 808w. 1H-NMR (400 MHz, CDCl3): 4.22 4.13 (m, 8 H); 2.41 2.27 (m, 2 H); 2.09 2.04
(m, 2 H); 1.83 1.58 (m, 8 H); 1.40 1.11 (m, 20 H); 0.88 0.83 (m, 6 H); 0.85( s, tBu); 0.83 (s, tBu); 0.48 0.42
(m, 2 H); 0.14 0.06 (m, 2 H); À0.04 (s, 3 H, (CH2)2Si); À0.05( s, 3 H, (CH2)2Si); À0.07 (s, 3 H, (CH2)2Si);
À0.10 (s, 3 H, (CH2)2Si). 13C-NMR (100 MHz, CDCl3): 172.8; 171.3; 61.2; 61.0; 60.9; 55.3; 42.3; 40.3; 37.1; 36.1;
32.0; 31.6; 31.3; 30.9; 28.4; 26.5; 26.1; 25.6; 25.5; 16.0; 14.1; 14.0; 11.5; 10.4; À4.0; À4.3; À5.4; À5.8. EI-MS: 369
‡
t
‡
(<1, [M À Me] ), 327 (66, [M À Bu] ), 224 (36), 196 (25), 180 (21), 103 (15), 81 (16), 80 (14), 79 (14), 75 (48),
‡
‡
73 (71), 67 (15), 66 (100), 59 (17), 41 (14), 40 (35). HR-EI-MS: 369.2468 ([ M À Me] , C20H37O4Si ; calc.
t
‡
‡
369.2461), 327.1993 ([M À Bu] , C17H31O4Si ; 327.1992).
(tert-Butyl)[((S)-4-isopropylcyclohex-1-enyl)methyl]dimethylsilane (33). Prepared according to GP 2
from (À)-(1S)-b-pinene (136 mg, 1 mmol), 1 (400 mg, 1.5mmol), and AIBN (50 mg, 0.3 mmol) in hexane
(4 ml); 3 h. FC (pentane) afforded 33 (177 mg, 70%) as a colorless oil. IR (nujol): 2954s, 2928s, 2881m, 2856m,
1663w, 1468m, 1437w, 1386w, 1363w, 1250m, 1172m, 1149w, 1007w, 828s, 807m, 746w. 1H-NMR (400 MHz,
CDCl3): 5.23 5.18 (m, CˆCH); 2.02 0.82 (m, 16 H); 0.87 (s, tBu); À0.05( s, Me); À0.06 (s, Me). 13C-NMR
(100 MHz, CDCl3): 135.31 (Cq); 119.07 (CH); 40.15(CH); 32.35(CH); 31.97 (CH 2); 29.23 (CH2); 26.78 (CH2);
‡
26.48 (Me); 23.15(CH 2); 20.01 (Me); 19.74 (Me); 16.78 (Cq); À5.53 (Me); À5.89 (Me). EI-MS: 252.6 (9, M ),
t
‡
196.4 (15), 195.5 (97, [ M À Bu] ), 167.4 (11), 139.3 (8), 99.2 (10), 74.2 (8), 73.2 (100), 59.1 (16), 28.0 (14). HR-
‡
‡
EI-MS: 252.2277 (M , C16H32Si ; calc. 252.2273).

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Helvetica Chimica Acta Vol. 85(2002)
4-[(tert-Butyl)dimethylsilyl]but-4-en-1-ol (34). Prepared according to GP 2 from 2-vinyloxirane (80.5 ml,
1.0 mmol), reagent 1 (402 mg, 1.5mmol), and AIBN (50 mg, 0.3 mmol) in pentane (4 ml); 6 h. FC (pentane/
Et2O 8 :2) afforded 34 (114 mg, 61%) as a colorless oil. Diastereoisomer ratio: (E)/(Z) 22 :10. IR (nujol):
3343m (br.), 2953s, 2929s, 2883m, 2858s, 1470m, 1404w, 1362w, 1252m, 1154w, 1005m, 967m, 827s, 804m, 749w.
1H-NMR (300 MHz, CDCl3): (E)-34: 5.75 5.46 (m, CHˆCH); 4.02 (d, J ˆ 6.3, CH2OH); 1.73 (s, OH); 1.51
(d, J ˆ 8.3, CH2Si); 0.88 (s, tBu); À0.05( s, Me2Si). 1H-NMR (300 MHz, CDCl3): (Z)-34: 5.75 5.46
(m, CHˆCH); 4.16 (d, J ˆ 6.6, CH2OH); 1.73 (s, OH); 1.55 1.50 (m, CH2Si); 0.88 (s, tBu); À0.05( s, Me2Si).
13C-NMR (75MHz, CDCl 3): (E)-34: 131.1 (CH); 127.5(CH); 64.2 (CH 2); 26.5(Me); 23.5(C q); 18.8 (CH2);
t
‡
À6.5(Me). EI-MS: 132 (3), 129 (2, [ M À Bu] ), 76 (7), 75(100), 73 (32), 54 (5), 40 (8). HR-EI-MS: 129.0726
‡
‡
([M tBu] , C6H13OSi ; calc. 129.0736).
4-[Dimethyl(phenyl)silyl]but-2-en-1-ol (35). Prepared according to GP 2 from 2-ethenyloxirane (95 ml,
1.2 mmol), 6 (514 mg, 1.8 mmol), and AIBN (60 mg, 0.4 mmol) in hexane (4 ml); 5 h. FC (pentane/Et2O 8 :2)
afforded 35 (84 mg, 35%) as a colorless oil. Diastereoisomer ratio: (E)/(Z) 44 :10. The NMR-data for the (E)-
isomer are in agreement with those reported in [32]. 1H-NMR (200 MHz, CDCl3): (Z)-35: 7.54 7.46
(m, 2 arom. H); 7.37 7.33 (m, 3 arom. H); 5.75 5.42 (m, CHˆCH); 3.95( d, J ˆ 6.2, CH2OH); 1.78 1.71
(m, CH2Si); 0.31 (s, Me2Si). 13C-NMR (75MHz, CDCl 3): (Z)-35: 138.4 (Cq); 133.6 (CH); 129.2 (CH); 128.5
(CH); 127.8 (CH); 126.6 (CH); 58.3 (CH2); 18.4 (CH2); À3.4 (Me).
Dimethyl 3-Methyl-4-[(triisopropylsilyl)methyl]cyclopentane-1,1-dicarboxylate (39, representative exam-
ple, cf. Scheme 8): Prepared according to GP 2 from 36 (217 mg, 1.02 mmol), 5 (666 mg, 2.15mmol), and
(tBuO)2 (100 ml, 0.54 mmol) in hexane (4 ml); 6 h, 1408. FC (pentane/tBuOMe 40 :1) afforded 39 (311 mg,
0.84 mmol, 82%) as a colorless oil. Diastereoisomer ratio: cis/trans 26 :10. IR (nujol): 2944s, 2891m, 2866s,
1736s, 1362m, 1435m, 1254s, 1202m, 1153m, 882m. 1H-NMR (300 MHz, CDCl3): cis-39: 3.70 (s, MeO); 3.69
(s, MeO); 2.41 (dd, J1 ˆ 13.1, J2 ˆ 6.4, 1 H, CH2); 2.38 2.33 (m, 1 H, CH2); 2.20 2.00 (m, 3 H, CH2, CH); 1.91
(dd, J1 ˆ 13.1, J2 ˆ 10.4, 1 H, CH2); 1.11 0.98 (m, 3 Me2CH); 1.03 (br. s, 3 Me2CH); 0.85( d, J ˆ 6.9, MeCH);
0.69 (dd, J1 ˆ 15.0, J2 ˆ 3.5, 1 H, CH2Si); 0.49 (dd, J1 ˆ 14.9, J2 ˆ 10.3, 1 H, CH2Si). 1H-NMR (300 MHz, CDCl3):
trans-39: 3.70 (s, MeO); 3.69 (s, MeO); 2.62 (dd, J1 ˆ 14.1, J2 ˆ 8.2, 1 H, CH2); 2.50 (dd, J1 ˆ 13.6, J2 ˆ 6.9, 1 H,
CH2); 1.73 1.63 (m, 2 H, CH, CH2); 1.52 1.44 (m, 2 H, CH, CH2); 1.11 0.98 (m, Me2CH); 1.03 (br. s,
3 Me2CH); 0.85( d, J ˆ 6.9, MeCH); 0.76 (dd, J1 ˆ 15.0, J2 ˆ 3.4, 1 H, CH2Si); 0.36 (dd, J1 ˆ 15.0, J2 ˆ 11.3,
CH2Si). 13C-NMR (75MHz, CDCl 3): cis-39: 173.6 (Cq); 173.4 (Cq); 59.0 (Cq); 52.6 (Me); 41.0 (CH2); 40.6 (Me);
38.4 (2 CH); 18.8 (Me); 14.8 (Me); 11.4 (CH); 8.9 (CH2). 13C-NMR (75MHz, CDCl 3): trans-39: 173.6 (Cq);
173.4 (Cq); 58.2 (Cq); 52.6 (Me); 44.1 (CH); 43.2 (CH); 42.0 (2 CH2); 24.4 (Me); 18.2 (Me); 11.4 (CH); 9.3
i
‡
(CH2). EI-MS: 329.1 (8), 328.2 (25), 327.1 (100, [M À Pr] ), 325.1 (26), 145.1 (14), 117.1 (16), 75.0 (12), 28.0
‡
‡
(34). HR-EI-MS: 327.1992 ([M À C3H7] , C17H31O4Si ; calc. 327.1991).
Dimethyl 3-{[(Isopropyloxy)dimethylsilyl]methyl}-4-methylcyclopentane-1,1-dicarboxylate (42). Prepared
according to GP 2 from 36 (212 mg, 1.0 mmol), 7 (425mg, 1.5mmol), and ( tBuO)2 (55 ml, 0.30 mmol) in hexane
(4 ml); 4 h, 1408. The solvent was removed in vacuo, the residue was dissolved in iPrOH (2 ml), and the resulting
soln. was treated with a cat. amount of NH4Cl and stirred overnight at r.t. The solvent was removed in vacuo, and
H2O and Et2O were added. The org. phase was separated, washed with brine, and dried (MgSO4). Purification
by FC (pentane/Et2O 40 :1) afforded 42 (175mg, 53%) as a colorless oil. Diastereoisomer ratio: cis/trans 15:10.
IR (nujol): 2956m, 2874w, 1736s, 1436w, 1381w, 1368w, 1253s, 1199m, 1172m, 1126m, 1027s, 882m, 840m.
1H-NMR (400 MHz, CDCl3): cis-42: 3.99 3.93 (m, Me2CH); 3.69 (s, 2 MeO); 2.41 2.34 (m, 2 H, CH, CH2);
2.15 2.04 ( m, 2 H, CH, CH2); 2.00 (dd, J1 ˆ 13.6, J2 ˆ 4.2, 1 H, CH2); 1.91 (dd, J1 ˆ 13.3, J2 ˆ 9.6, 1 H, CH2); 1.12
(d, J ˆ 6.1, Me2CH); 0.81 (d, J ˆ 6.6, Me); 0.64 (dd, J1 ˆ 14.6, J2 ˆ 4.7, 1 H, CH2Si); 0.51 (dd, J1 ˆ 14.6, J2 ˆ 9.2,
1
1 H, CH2Si); 0.10 (s, Me2Si). H-NMR (400 MHz, CDCl3): trans-42: 3.99 3.93 (m, Me2CH); 3.69 (s, 2 MeO);
2.59 (dd, J1 ˆ 13.6, J2 ˆ 6.7, 1 H, CH2); 2.48 (dd, J1 ˆ 13.3, J2 ˆ 6.4, 1 H, CH2); 1.73 1.64 (m, 2 H, CH, CH2);
1.38 1.15( m, 2 H, CH, CH2); 1.13 (d, J ˆ 6.0, Me2CH); 0.94 (d, J ˆ 5.9, Me); 0.90 0.82 (m, 1 H, CH2Si); 0.35
(dd, J1 ˆ 15.6, J2 ˆ 10.8, 1 H, CH2Si); 0.10 (s, Me2Si). 13C-NMR (100 MHz, CDCl3): cis-42: 173.40 (Cq); 64.77
(CH); 58.87 (Cq); 52.56 (Me); 43.38 (CH); 42.13 (CH2); 41.21 (CH2); 38.13 (CH); 25.78 (Me); 16.92 (CH2);
14.90 (Me); À0.57 (Me); À0.64 (Me). 13C-NMR (100 MHz, CDCl3): trans-42: 173.57 (Cq); 64.80 (CH); 58.13
(Cq); 52.56 (Me); 42.69 (CH); 42.69 (CH2); 40.55 (CH2); 37.57 (CH); 25.78 (Me); 20.38 (CH2); 17.14 (Me);
‡
À0.81 (Me). EI-MS: 330 (2, M ), 315 (68), 271 (60), 270 (100), 257 (85), 197 (80), 189 (83), 154 (49), 145 (48),
140 (65), 123 (40), 117 (75), 108 (86), 107 (45), 95 (34), 91 (53), 81 (38), 75 (45), 45 (30). HR-EI-MS: 330.1856
‡
‡
(M , C16H30O5Si ; calc. 330.1863).
Dimethyl 3-(Hydroxymethyl)-4-methylcyclopentane-1,1-dicarboxylate (43). Ac2O (5.4 ml, 57 mmol) was
treated with 3 drops of conc. H2SO4 and cooled to 08. To this soln., H2O2 (3.60 ml, 35% in H2O, 42 mmol) was
added. The resulting soln. was stirred at r.t. for 30 min. Silane 38 (171 mg, 0.49 mmol) was dissolved in 6 ml of

Helvetica Chimica Acta Vol. 85(2002)
3573
the above soln. and treated with Hg(OAc)2 (263 mg, 0.79 mmol) [33]. The soln. was stirred for 5h at r.t. Et 2O
(80 ml) was added, the org. phase was separated, washed with sat. Na2S2O3 soln., H2O, NaHCO3 soln., and brine,
and dried (MgSO4). Filtration and removal of the solvent in vacuo yielded the crude product, which was purified
by FC (pentane/tBuOMe 1 :1) to afford pure 43 (83 mg, 0.36 mmol, 74%) as a colorless oil. Diastereoisomer
ratio: cis/trans 4 :1. The NMR data for the trans-isomer are in agreement with those reported in [25]. cis-43:
1H-NMR (300 MHz, CDCl3): 3.65( s, 2 MeO); 3.60 (dd, J1 ˆ 11.0, J2 ˆ 5.6, 1 H, CHOH); 3.45( dd, J1 ˆ 10.7, J2 ˆ
6.3, 1 H, CH2OH); 2.43 (dd, J1 ˆ 13.4, J2 ˆ 6.8, 1 H, CH2); 2.33 2.09 (m, 4 H, CH2, CH); 1.86 (dd, J1 ˆ 13.4, J2 ˆ
7.3, 1 H, CÀCH2); 1.81 (br. s, 1 H, OH); 0.88 (d, J ˆ 6.8, MeCH). 13C-NMR (75MHz, CDCl 3): 173.9 (Cq); 173.6
(Cq); 63.1 (CH2); 59.4 (Cq); 53.1 (Me); 53.0 (Me); 44.8 (CH); 42.2 (CH2); 36.7 (CH2); 35.6 (CH); 15.1 (Me).
(tert-Butyl)(cyclohexylmethoxy)dimethylsilane (45). Prepared according to GP 2 from cyclohexane-
carbaldehyde (44; 121 ml, 1 mmol), 1 (400 mg, 1.5mmol), and ( tBuO)2 (55 ml, 0.3 mmol) in hexane (4 ml);
5h, 140 8. FC (pentane/NEt3 100 :1) afforded 45 (225mg, 99%) as a colorless oil. The spectral data are in
agreement with those reported in [34].
(tert-Butyl)[(tert-butyl)methoxy]dimethylsilane (47). Prepared according to GP 2 from pivalaldehyde (46)
(108 ml, 1 mmol), 1 (400 mg, 1.5mmol), and ( tBuO)2 (55 ml, 0.3 mmol) in hexane (4 ml); 5h, 140 8. FC (pentane/
Et2O 100 :1) afforded 47 (201 mg, 99%) as a colorless oil. IR (neat): 2955s, 2718w, 1473s, 1362s, 1257s, 1103s,
1029m, 1006m, 936w, 837s, 667m. 1H-NMR (300 MHz, CDCl3): 3.21 (s, CH2O); 0.90 (s, tBu); 0.86 (s, tBu); 0.02
(s, Me2Si). 13C-NMR (75MHz, CDCl 3): 73.1 (CH2); 31.6 (Cq); 26.2 (Me); 25.9 (Me); 22.7 (Cq); À5.5 (Me). EI-
‡
‡
‡
MS: 202 (33, M ), 189 (1), 188 (23), 187 (100), 40 (39). HR-EI-MS: 201.1669 ([MÀH] , C11H25OSi ; calc.
201.1675).
(tert-Butyl)[(isopropyl)methoxy]dimethylsilane (49). Prepared according to GP 2 from 2-methylpropanal
(48, 91 ml, 1 mmol), 1 (400 mg, 1.5mmol), and ( tBuO)2 (55 ml, 0.3 mmol) in hexane (4 ml); 5h, 140 8. FC
(pentane/NEt3 100 :1) afforded 47 (131 mg, 70%) as a colorless oil. The spectral data are in agreement with
those reported in [35].
(tert-Butyl)dimethyl(3-phenylpropoxy)silane (51). Prepared according to GP 2 from 3-phenylpropanal
(50; 134 mg, 1 mmol), 1 (400 mg, 1.5mmol), and ( tBuO)2 (55 ml, 0.3 mmol) in hexane (4 ml); 5h, 140 8. FC
(pentane/Et3N 100 :1) afforded 51 (221 mg, 88%) as a colorless oil. The spectral data are in agreement with
those reported in [36].
[4-(Benzyloxy)butoxy](tert-butyl)dimethylsilane (53). Prepared according to GP 2 from 4-(benzyloxy)-
butanal (523); 178 mg, 1 mmol), 1 (400 mg, 1.5mmol), and ( tBuO)2 (55 ml, 0.3 mmol) in hexane (4 ml); 5h, 140 8.
FC (pentane/Et2O 100 :1) afforded 53 (198 mg, 67%) as a colorless oil. IR (neat): 3030w, 2953s, 2856s, 1472m,
1
1361m, 1256s, 1203w, 1098s, 1029w, 1006w, 836s, 775s. H-NMR (200 MHz, CDCl3): 7.36 7.26 (m, 5arom. H);
4.50 (s, CH2); 3.63 (t, J ˆ 6.3, CH2O); 3.49 (t, J ˆ 6.4, CH2O); 1.75 1.51 ( m, 2 CH2), 0.89 (s, tBu); 0.04
(s, Me2Si). 13C-NMR (75MHz, CDCl 3): 138.6 (Cq); 128.3 (CH); 127.6 (CH); 127.5(CH); 72.8 (CH 2); 70.3
‡
(CH2); 63.0 (CH2); 29.5(CH 2); 26.2 (CH2); 26.0 (Me); 18.3 (Cq); À5.3 (Me). EI-MS: 294 (<1, M ), 237 (2), 145
‡
‡
(19), 131 (4), 92 (28), 91 (100), 75(5), 73 (7), 71 (7). HR-EI-MS: 294.2020 ( M , C17H30O2Si ; calc. 294.2015).
(tert-Butyl)(cyclohexyloxy)dimethylsilane (54). Prepared according to GP 2 from cyclohexanone (98 mg,
1 mmol), 1 (400 mg, 1.5mmol), and ( tBuO)2 (55 ml, 0.3 mmol) in hexane (4 ml); 5h, 140 8. FC (pentane/NEt3
100 :1) afforded 54 (132 mg, 62%) as a colorless oil. The spectral data are in agreement with those reported in
[37].
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Received May 29, 2002