capable of functioning also as HϪ-donors. As mentioned above,
the condensation products of type 2 formed in the RCH2CHO–
TMSI reaction system were not formed in the corresponding
R2CHCHO–TMSI reaction system. The derived alcohol
R2CH–CH2–OH was formed instead. We suggest that the
electrophilic addition of R2CH–CH(I)OTMS to the derived
using SiMe4 as standard using a Bruker AC 200 MHz
spectrometer. The chemical shifts (δ) and J values are given
in ppm and Hz, respectively. Mass and high-resolution mass
spectra were carried out using the EI method on a VG Autospec
250 A mass spectrometer. The melting points were measured
using Fisher–Johns apparatus.
silyl enol ether R C᎐CH–OTMS (cf. Scheme 2) is suppressed
The reaction set-up consisted of a three-neck flask equipped
with a nitrogen inlet and rubber septums. All glass parts,
syringes and needles were dried at 120 ЊC 24 h before use and
assembled while warm.
᎐
2
because of steric hindrance, so that the following competing
HϪ-transfer reaction becomes a favoured one [eqn. (8)].
Solvents and liquid reactants were introduced into the
reaction flask using hypodermic glass syringes. All reactions
were carried out under anhydrous conditions, under an
atmosphere of dry nitrogen. The products were kept under
nitrogen in a refrigerator.
(8)
Formation of the by-product CH3CHPh2 7 in the RCH᎐
᎐
O–TMSI–DPE reaction system might be reasonably due to
an HϪ-transfer reaction to the corresponding carbocation
[eqn. (9)].
A general procedure for the reaction of the RCH(I)OTMS with
the 1,1-diarylethylenes ([RCHO] : [TMSI] : [CH ᎐C(Ar1)Ar2] ؍
᎐
2
1 : 1 : 2 or 5 : 1 : 2)
Iodotrimethylsilane (0.70 g, 3.5 mmol, 0.5 ml) was added to a
stirred solution of the aldehyde (3.5 mmol) in dichloromethane
(1 ml). The reaction mixture was stirred for 15–30 min and the
1,1-diarylethylene (7 mmol) was then added in one portion to
the reaction mixture. Stirring was continued for 2 h at room
temperature. Diethyl ether (10 ml) was then added, followed by
an aqueous saturated solution of sodium thiosulfate (25 ml).
The mixture was stirred for 5 min, the organic layer separated,
and the aqueous layer was extracted with dichloromethane
(3 × 20 ml). The combined organic layers were washed with
water, dried over anhydrous magnesium sulfate, filtered and the
solvent evaporated. The pure product was obtained from
the residue by either crystallization or column chromatography
on silica gel using petroleum ether–ethyl acetate as eluent.
A five-fold amount of aldehyde (17.5 mmol) was used for the
reactions having a concentration ratio of [RCHO] : [TMSI] :
[CH ᎐C(Ar1)Ar2] = 5 : 1 : 2.
(9)
A similar hydride-transfer is involved in the reaction
sequence suggested for the formation of the by-product RCH2–
CH᎐CPh 9 in the RCH᎐O–TMSI–DPE reaction system, under
᎐
᎐
2
conditions aimed at the formation of RCH(–CH᎐CPh )
4
᎐
2
2
(Scheme 5 and compare with Scheme 3).
᎐
2
Scheme 5
A general procedure for the reaction of aldehydes with 1,1-
diarylethylene in the presence of TMSCl–Lewis acid
The protic acid-catalyzed dimerization of CH ᎐CAr to yield
᎐
2
2
the corresponding type-6 dimers, has been reported for 1,1-di-
Chlorotrimethylsilane (0.38 g, 3.5 mmol, 0.4 ml) was added to
a cold solution (0 ЊC) of the SnCl2 (0.07 g, 0.35 mmol) in
dichloromethane (1 ml). The mixture was stirred at 0 ЊC for
an hour, the cooling bath was removed and the aldehyde
(3.5 mmol) was added. After stirring the reaction mixture for
15–30 min the 1,1-diarylethylene (7 mmol) was added in one
portion. Stirring was continued for 2 h at room temperature.
Work up was as described above.
phenylethylene.11 It is, mechanistically, an Hϩ-initiated cationic
polymerization of CH ᎐CAr , followed by one propagation
᎐
2
2
step, and a subsequent β-elimination of a proton from the
carbocationic intermediate, and its transfer to CH ᎐CAr .
᎐
2
2
In conclusion, the results of the present research signifi-
cantly expand the scope of the chemistry of the trialkylsilyl
iodohydrin–electron-rich olefin reaction system. It has been
demonstrated in this study that trialkylsilyl iodohydrin deriva-
tives, which often act as highly reactive electrophilic reactants,
also function as nucleophiles and as HϪ-donors.
Preparation of 1,3,3-triphenyl-1-methylindane 10
A 50% aqueous solution (26.5 ml) of chloroacetaldehyde
(Aldrich) was mixed with chloroform (500 ml) and heated to
reflux. A chloroform–water azeotrope was distilled out until
the solution became anhydrous. A solution (1 ml) of chloro-
acetaldehyde (0.32 g, 4.1 mmol) in chloroform was added to
dichloromethane (1 ml). Iodotrimethylsilane (0.82 g, 4.1 mmol)
was added to this solution. The reaction mixture was stirred for
15–30 min and 1,1-diphenylethylene (8.2 mmol, 1.44 ml) was
then added in one portion to the reaction mixture and stirring
was continued for 2 h at room temperature. Diethyl ether (10
ml) was then added, followed by an aqueous saturated solution
of sodium thiosulfate (25 ml). The mixture was stirred for 5
min, the organic layer separated, and the aqueous layer was
extracted with dichloromethane (3 × 20 ml). The combined
organic layers were washed with water, dried over anhydrous
magnesium sulfate, filtered and the solvent removed. The
residue, which was a viscous yellow oil, solidified after being
kept for several hours in a refrigerator. The solid crude product
was purified by washing it with petroleum ether. The mixture
Experimental
General
Dichloromethane (AR) and acetonitrile (AR) were dried by
refluxing over P2O5 and were distilled from it. The aldehydes
(Aldrich) were purified, distilled and kept under nitrogen in
flasks sealed with rubber septum caps in a refrigerator. Para-
formaldehyde (Merck) was used without any further purifica-
tion. Trimethylchlorosilane (Aldrich) was distilled before use.
Trimethyliodosilane (Aldrich) was stored over copper wire,
under nitrogen in an Aldrich bottle in a refrigerator.
Sodium iodide was dried in an oven at 120 ЊC for 24 h before
use. The 1,1-diarylethylenes, CH ᎐C(Ar1)Ar2 (Ar1 = Ar2,
᎐
2
Ar1 ≠ Ar2) used are all known compounds, prepared by litera-
ture methods. The crude products were purified by column
chromatography on silica gel.
1H (200 MHz) and 13C NMR spectra were obtained in CDCl3
J. Chem. Soc., Perkin Trans. 1, 2002, 434–438
437
Ishai, Eti
