Acetalization of Carbonyl Compounds and Deprotection of Acetals
FULL PAPERS
À 4.35 (2C); anal. calcd. for C H O Si: C 64.24, H 8.62; found:
1
5
24
3
Experimental Section
C 64.25, H 8.60.
NMR spectra were recorded on a Bruker DPX 300 instrument
1,1-Ethylenedioxy-1-(3-allyloxy)methane (entry 6, Ta-
1
13
À1
at 300 MHz for H and at 75 MHz for C NMR in CDCl3
solutions. IR spectra were measured on a FT-8300 Shimadzu
spectrometer as neat samples. Cyclohexane was distilled over
sodium metal. All reagents and carbonyl compounds were
distilled before use. Indium(III) chloride (98%) was purchased
from Aldrich and was used as such.
ble 1): Colorless liquid; R : 0.50; IR: n 1485, 1263 cm ;
f
1
H NMR: d 7.25 ± 7.36 (m, 1H), 7.05 ± 7.15 (m, 2H), 6.89 ±
6.93 (m, 1H), 5.99 ± 6.17 (m, 1H), 5.79 (s, 1H), 5.25 ± 5.45 (m,
1
3
2H), 4.54 (d, J 5.1 Hz, 2H), 3.99 ± 4.13 (m, 4H); C NMR:
d 160.0, 139.8, 133.3, 129.5, 119.0, 117.7, 115.9, 112.5, 103.6,
69.4, 65.7 (2C); anal. calcd. for C H O : C 69.88, H 6.84; found:
1
2
14
3
C 69.85, H 6.80.
,1-Ethylenedioxydecane (entry 10, Table 1): Colorless liq-
1
À1
1
uid; R : 0.85; IR: n 1465, 1407 cm ; H NMR: d 4.82 (t, J
f
4
.8 Hz, 1H), 3.77 ± 3.99 (m, 4H), 1.25 ± 1.41 (m, 14H), 0.09 (t,
Conversion of 4-Chlorobenzaldehyde to the
Corresponding 1,3-Dioxolane; Typical Procedure
1
3
J 6.8 Hz, 3H); C NMR: d 104.8, 64.9 (2C), 34.0, 31.9, 29.7
(
2C), 29.6, 29.4, 24.1, 22.7, 14.2; anal. calcd. for C H O : C
12 24 2
(
entry 3, Table 1)
7
1.95, H 12.07; found: C 71.94, H 12.03.
3,3-Ethylenedioxypentane (entry 11, Table 1): Colorless
Astirred solution of 4-chlorobenzaldehyde (141 mg, 1 mmol)
and 1,2-ethanediol (93 mg, 1.5 mmol) was heated at reflux (oil
bath 908C) in cyclohexane (10 mL) in the presence of
indium(III) chloride (11 mg, 0.05 mmol, 5 mol % with respect
to aldehyde) using a Dean±Stark water separator. After the
reaction was complete (7 h as indicated by TLC) the reaction
mixture was extracted with ether (3 Â 10 mL) and the ether
extract was washed with brine and dried over Na SO .
Evaporation of solvent followed by column chromatography
of the crude product over silica gel (hexane-Et O, 90:10)
furnished the pure 1,1-ethylenedioxy-1-(4-chlorophenyl)me-
thane as a colorless liquid; yield: 168 mg (91%); R : 0.55; IR:
À1
1
liquid; R : 0.80; IR: n 1463 cm ; H NMR: d 3.89 (s, 4H),
f
1
3
1.58 (q, J 7.5 Hz, 4H), 0.85 (t, J 7.5 Hz, 6H); C NMR: d
112.7, 65.4 (2C), 29.7 (2C), 8.4 (2C); anal. calcd. for C H O : C
7
14
2
64.58, H 10.83; found: C 64.58, H 10.85.
2,2-Ethylenedioxy-4-methylpent-3-ene (entry 13, Table 1):
À1
1
Colorless liquid; R : 0.60; IR: n 1444 cm ; H NMR: d 5.16
f
2
4
(s, 1H), 3.74 ± 3.87 (m, 4H), 1.73 (s, 3H), 1.63 (s, 3H), 1.39 (s,
1
3
3H); C NMR: d 136.4, 127.2, 108.2, 64.2 (2C), 26.7, 25.5,
2
18.4; anal. calcd. for C H O : C 67.57, H 9.92; found: C 67.55, H
8
14
2
9.90.
1,1-Ethylenedioxycyclooctane (entry 16, Table 1): Color-
f
À1
1
À1
1
n 1614, 1249 cm ; H NMR: d 7.42 (d, J 8.4 Hz, 2H), 7.35
less liquid; R : 0.85; IR: n 1471, 1112 cm ; H NMR: d
f
1
3
(
d, J 8.4 Hz, 2H), 5.76 (s, 1H), 3.98 ± 4.10 (m, 4H); C NMR:
3.82 ± 3.84 (m, 4H), 1.71 ± 1.73 (m, 4H), 1.50 ± 1.54 (m, 10H);
1
3
d 136.9, 135.3, 128.9 (2C), 128.4 (2C), 103.4, 65.7 (2C); anal.
C NMR: d 112.7, 64.5 (2C), 34.4 (2C), 28.3 (2C), 25.0, 22.5
calcd. for C H O Cl: C 58.55, H 4.91; found: C 58.52, H 4.88.
(2C); anal. calcd. for C H O : C 70.55, H 10.65; found: C 70.43,
9
9
2
10 18
2
This procedure is followed for the conversion of all the
carbonyl compounds to the corresponding 1,3-dioxolanes
listed in Table 1.
H 10.62.
1,1-Diethoxydecane (entry 10, Table 2): Colorless liquid; R :
0.75; IR: n 1467 cm ; H NMR: d 4.42 (t, J 5.7 Hz, 1H),
f
À1
1
3
1
1
1
7
.38 ± 3.65 (m, 4H), 1.51 ± 1.58 (m, 2H), 1.16 ± 1.21 (m, 14H),
1
3
.14 (t, J 7.0 Hz, 6H), 0.82 (t, J 6.8 Hz, 3H); C NMR: d
03.3, 61.1 (2C), 33.9, 32.2, 29.8, 29.7, 29.6, 25.1, 23.0, 15.6 (2C),
4.4 (2C); anal. calcd. for C H O : C 72.98, H 13.12; found: C
Conversion of 4-Chlorobenzaldehyde to the
Corresponding Dimethyl Acetal; Typical Procedure
14 30
2
2.85, H 13.10.
,1-Diethoxycycloheptane (entry 16, Table 2): Colorless
1
(
entry 3, Table 2)
À1
1
liquid; R : 0.85. IR: n 1456, 1444 cm ; H NMR: d 3.38
f
The procedure reported in the previous experiment for the
formation of 1,3-dioxolanes was followed using trimethyl
orthoformate (1 mmol) in place of 1,2-ethanediol and a
mixture of cyclohexane and methanol (3:1, 10 mL) instead
of pure cyclohexane. The corresponding dimethyl acetal was
obtained as a colorless oil whose identity was established by
(q, J 7.1 Hz, 4H), 1.73 ± 1.76 (m, 4H), 1.46 ± 1.50 (m, 8H), 1.11
1
3
(t, J 7.1 Hz, 6H); C NMR: d 104.7, 55.5 (2C), 37.4 (2C),
29.5 (2C), 22.1 (2C), 15.9 (2C); anal. calcd. for C H O : C
1
1
22
2
70.92, H 11.90; found: C, 70.84; H, 12.01.
1
comparison of its spectroscopic data (IR, H NMR) with those
Deprotection of 1,3-Dioxolanes and Dialkyl Acetals;
Typical Procedure
reported;[ yield: 178 mg (96%).
2a]
This procedure is followed for the protection of all the
carbonyl compounds as dialkyl acetals listed in Table 2. The
known compounds are identified by comparison of their
Astirred solution of 1-(4-chlorophenyl)-1,1-dimethoxyme-
thane (entry 2, Table 4) (186 mg, 1 mmol) in aqueous meth-
anol (1:1, 3 mL) was heated at reflux (908C) in the presence of
indium(III) chloride (11 mg, 0.05 mmol, 5 mol %) for 1 h
(TLC). The reaction mixture was then extracted with ether
and the ether extract was washed with brine, dried (Na SO )
1
13
spectroscopic data (IR, H, C NMR) with those reported. The
1
13
spectral (IR, H and C NMR) data and elemental analyses of
the compounds which are not readily found are provided
below.
2
4
1
,1-Ethylenedioxy-1-(3-ter-butyldimethylsilyloxy)methane
and evaporatedto leave the crude product. This was purified by
(
entry 5, Table 1): Colorless liquid; R : 0.55; IR: n 1602,
column chromatography over silica gel (hexane-Et O, 90:10)
f
2
À1
1
1
1
3
1
487 cm ; H NMR: d 7.17 ± 7.27 (m, 1H), 7.03 (t, J 8.5 Hz,
to provide pure 4-chlorobenzaldehyde which was identified by
H), 6.86 ± 6.93 (m, 1H), 6.61 ± 6.65 (m, 1H), 5.57 (s, 1H), 3.82 ± comparison with an authentic sample.
1
3
.92 (m, 4H), 0.73 (s, 9H), 0.03 (s, 6H); C NMR: d 155.6,
This procedure was followed for the deprotection of all 1,3-
dioxolanes and dialkyl acetals listed in Tables 3 and 4. The
40.4, 133.5, 128.9, 128.6, 128.2, 125.6, 64.8 (2C), 64.1, 28.1 (3C),
Adv. Synth. Catal. 2004, 346, 446 ± 450
asc.wiley-vch.de
¹ 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
449