466 J. CHEM. RESEARCH (S), 1998
J. Chem. Research (S),
1998, 466±467$
Efficient and Catalytic Conversion of Epoxides to
1,3-Dioxolanes with TiO(TFA)2 or TiCl3(OTf)$
N. Iranpoor* and B. Zeynizadeh
Chemistry Department, College of Sciences, Shiraz University, Shiraz 71454, Iran
TiO(TFA)2 or TiCl3(OTf) catalyses the efficient reaction of epoxides with acetone to give the corresponding
1,3-dioxolanes in excellent yields. The reaction of chiral styrene oxide was found to be highly stereospecific.
Direct conversion of an epoxide into
a 1,3-dioxolane
with acetone instead of adding water to form a diol with
subsequent elimination is a subject of interest due to the im-
portance of 1,3-dioxolanes as widely used protecting groups
for diols1,2 and particularly for carbohydrates and steroid
chemistry. In addition, they are very suitable derivatives
of diols for GC, GLC and mass spectrometry.3 This trans-
formation has been studied only with a few reagents.
Among these, anhydrous copper sulfate3 has been reported
to produce the dioxolanes, but the yields in most cases
are low with relatively long reaction times. The use of
Scheme 1 R or epoxide: a Ph, b n-C4H9, c CH21CHCH2OCH2,
d PhOCH2, e ClCH2OCH2, f (CH3)2CHOCH2, g clyclohexene
oxide, h cyclopentene oxide
The results obtained are shown in Table 1.
The reaction of R-()-styrene oxide in the presence of
0.02 mol equiv. of TiCl3(OTf ) was found to be highly
stereospeci®c with inversion of con®guration9b (Scheme 2).
4c
zeolite,4a KSF clay,4b HBF4 and some Lewis acids has
been studied for this transformation. Most of the Lewis
acids failed to give the desired product. Anhydrous zinc5
and magnesium halides5,6 have been reported to give
7
rearranged products. The same reaction with both FeCl3 or
Me3SiCl8 gave the corresponding halohydrins, and SnCl4
and TiCl4 produced little or no product.9a However, the use
of TiCl4 for conversion of only aryl-substituted epoxides
into their corresponding acetals in moderate yield has been
reported.9b
Scheme 2
Among Lewis acids, BF3ÁOEt2 has been successfully used
for conversion of dierent types of carbonyl compounds
into their corresponding 1,3-dioxolane derivatives with only
ethylene and propylene oxides.9a There was no reaction of
epoxides carrying electron-releasing groups. Although TiCl4
In conclusion this catalytic method can be applied for
conversion of dierent classes of epoxides into their corre-
sponding 1,3-dioxolanes. Excellent yields and stereo-
speci®city, short times, simple work-up and mild reaction
conditions make this a useful procedure for this trans-
formation.
10
also gave no reaction, we observed that TiO(TFA)2 and
TiCl3(OTf)11 can catalyse the ecient reaction of epoxides
with acetone to give 1,3-dioxolanes in excellent yields. These
two known solid titanium(IV) compounds are stable and
can be prepared from TiCl4. Epoxides with both electron-
releasing and withdrawing groups were treated with these
catalysts in acetone. It was observed that TiCl3(OTf ) is
more ecient than TiO(TFA)2. Its reactions with epoxides
and acetone occur at room temperature and only 0.02 molar
equivalent of the catalyst is enough to convert epoxides into
their corresponding 1,3-dioxolanes within 10 min in 92±98%
yields (Scheme 1).
Experimental
Products were characterised by comparison of their physical data,
IR, NMR and mass spectra with those of authentic samples.
Infrared spectra were recorded on a Perkin-Elmer 781 spectrometer,
NMR spectra on a Bruker Avance DPX-250 and mass spectra on a
Shimadzu GCMS-QP 1000 EX. The purity determination of the
substrates and reaction monitoring were by TLC on polygram
SILG/UV 254 silica gel plates or GLC on a Shimadzu GC-10A
instrument.
Table 1 Conversion of epoxides into 1,3-dioxolanes catalysed with TiO(TFA)2 or TiCl3(OTf) in acetone
Reaction with TiCl3(OTf) at r.t. Reaction with TiO(TFA)2 under reflux
Epoxide
Producta/yield (%)b
Molar equiv. of cat./time (min)
Product/yield (%)
Molar equiv. of cat./time (h)
1a
1b
1c
1d
1e
1f
2a/98
2b/93
2c/96
2d/97
2e/92
2f/95
2g/95
2h/93
0.02/10
0.02/10
0.02/10
0.02/10
0.02/10
0.02/10
0.02/10
0.02/10
2a/90
2b/80
2c/90
2d/91
2e/78
2f/89
2g/85
2h/83
0.06/0.6
0.2/2
0.15/1.3
0.3/5
0.2/1.4
0.3/6
0.1/0.6
0.15/0.7
1gc
1h
aProducts were identified by comparison with known samples. bIsolated yield. cThe stereochemistry of the product was found to be
trans; confirmed by hydrolysis of the product and isolation of the corresponding trans-1,2 diol according to the literature.12
Reaction of Styrene Oxide with Acetone in the presence of
TiO(TFA)2, Typical Procedure.ÐStyrene oxide (0.121 g, 1 mmol)
and TiO(TFA)2 (0.06 mmol, 17.3 mg) were re¯uxed in dry acetone
(3 ml) for 36 min. The reaction mixture was cooled to room
*To receive any correspondence.
$This is a Short Paper as de®ned in the Instructions for Authors,
Section 5.0 [see J. Chem. Research (S), 1998, Issue 1]; there is there-
fore no corresponding material in J. Chem. Research (M).
Iranpoor
