PAPER
Chemoselective Acetalization of Carbonyl Compounds
787
2-(3-Nitrophenyl)-1,3-dioxane (Entry 7)
clization of this intermediate then lead to cyclic acetal,
hexamethyldisiloxane (HMDS) and concomitant release
of I2 that reenter the catalytic cycle (Scheme 3). The for-
mation of stable HMDS could be considered as the driv-
ing force for the reactions. Nevertheless, the actual
mechanism of this transformation should be studied in de-
tail.
1H NMR (250 MHz, CDCl3, TMS): = 7.98–8.28 (d, J = 9.0 Hz, 2
H), 7.62–7.73 (d, J = 9.0 Hz, 2 H), 5.54 (s, 1 H), 4.24–4.51 (dd, J =
5, 13.8 Hz, 2 H), 3.94–4.05 (pseudo-t, J = 13.8 Hz, 2 H), 2.13–2.25
(tq, J = 5 Hz, J = 13.3 Hz, 1 H), 1.43–1.50 (quintet, J = 1.1, 13.3
Hz, 1 H).
13C NMR (63 MHz, CDCl3, TMS): = 154.5, 147.05, 132.33,
127.50, 102.52, 67.80, 34.5.
O
2-Methyl-2-phenyl-1,3-dioxane (Entry 12)
TMSO
R
O
OTMS
TMSO
OTMS
1H NMR (250 MHz, CDCl3, TMS): = 7.16–7.37 (m, 5 H), 3.66–
3.78 (m, 4 H), 1.94–2.08 (tq, J = 5.4, 12.9 Hz 1 H), 1.44 (s, 3
H), 1.11–1.19 (quintet, J = 1.2, 12.9 Hz, 1 H).
R
R
R
I2
3
13C NMR (63 MHz, CDCl3, TMS): = 141.63, 129.10, 128.99,
128.24, 100.92, 61.62, 32.84, 25.89.
TMS
I2
TMSO
O
O
I
3
4
I
R
R
2-Methyl-2-(2-phenylethyl)-1,3-dioxane (Entry 16)
1H NMR (250 MHz, CDCl3, TMS): = 6.91–7.38 (m, 5 H), 3.79–
3.89 (m, 4 H), 2.73–2.79 (m, 2 H), 1.98–2.05 (m, 2 H), 1.97–1.73
(m, 1 H), 1.48–1.68 (m, 1 H), 1.44 (s, 3 H).
13C NMR (63 MHz, CDCl3, TMS): = 139.01, 129.63, 129.65,
126.02, 100.85, 58.09, 41.50, 34.13, 23.67 18.27
4
R
R
O
O
I2
1,5-Dioxaspiro[5.11]heptadecane (Entry 17)
1H NMR (250 MHz, CDCl3, TMS): = 3.57–3.79 (m, 4 H), 1.59–
1.66 (m, 6 H), 1.16–1.26 (br m, 18 H).
TMSOTMS
Scheme 3
13C NMR (63 MHz, CDCl3, TMS): = 100.77, 60.28, 60.03, 40.30
(two peaks), 36.50, 30.29 (7 peaks), 19.25 (two peaks).
In conclusion, we have developed a remarkably mild and
catalytic protocol for the acetalization of a relatively wide
range of carbonyl compounds. To the best of our knowl-
edge this is the first example of such a transformation un-
der neutral aprotic conditions. Further investigations on
the development of organic transformations under neutral
aprotic conditions using iodine and other neutral catalyst
are ongoing in our laboratories.
9-Phenyl-1,5-dioxaspiro[5.5]undecane (Entry 18)
1H NMR (500 MHz, CDCl3, TMS): = 7.29–7.32 (m, 2 H), 7.24–
7.26 (m, 2 H), 7.18–7,22 (tt, J = 1.4, 7.2 Hz, 5 H), 3.97–4.00 (t,
J = 5.7 Hz, 2 H), 3.93–3.95 (t, J = 5.7 Hz, 2 H), 2.56–2.60 (tt,
J = 4.4, 11.7 Hz, 1 H), 2.40–2.45 (m, 2 H), 1.74–1.80 (m, 6 H),
1.47–1.54 (m, 2 H).
13C NMR (125 MHz, CDCl3, TMS): = 154.93, 128.23, 126.57,
98.36, 55.01, 66.81, 33.73, 29.76, 28.36, 28.35.
1H NMR and 13C NMR spectra were recorded on a Bruker 250 or
500 MHz spectrometer in CDCl3 as the solvent and TMS as internal
standard at 25 °C. The majority of the products are known and all of
the isolated products gave satisfactory IR spectra.
2-(4-Benzoyloxyphenyl)-1,3-dioxane (Entry 22)
1H NMR (500 MHz, CDCl3, TMS): = 8.20-8.22 (dd, J = 8.4, 1.4
Hz, 2 H), 7.61–7.65 (tt, J = 7.4, 1.4 Hz, 1 H), 7.56–7.59 (d, J = 8.4
Hz, 2 H), 7.49–7.53 (t, J = 7.4 Hz, 2 H), 7.23–7.26 (dd, J = 8.4, 1.4
Hz, 2 H), 5.54 (s, 1 H), 4.27–4.30 (dd, J = 11.0, 3.6 Hz, 2 H), 3.98–
4.03 (pseudo-t, J = 11.0 Hz, 2 H), 2.20–2.27 (tq, J = 5.0, 13.3 Hz, 1
H), 1.44–1.48 (quintet, J = 1.3, 13.3 Hz, 1 H).
Iodine-Catalyzed Acetalization of Carbonyl Compounds; Gen-
eral Procedure
To a solution of carbonyl compound (2 mmol), BTSP (4–6 mmol)
in anhyd CH2Cl2 (20 mL) was added I2 (0.06–0.14 mmol), and the
resulting solution was stirred at r.t. After completion of the reaction
(TLC or GC), a cold 10% aq solution of NaOH (25 mL) was added
and the mixture was extracted with CH2Cl2 (3 15 mL). The organ-
ic extracts were washed successively with Na2S2O3 solution (5%, 15
mL), H2O (2 15 mL) and dried (Na2SO4). Evaporation of the sol-
vent under reduced pressure gave almost pure product(s). Further
purification was proceeded by vacuum distillation or recrystalliza-
tion in appropriate solvent to afford pure acetals (Table).
13C NMR (125 MHz, CDCl3, TMS): = 165.08, 151.29, 136.58,
133.68, 130.25, 129.62, 128.65, 127.38, 121.55, 101.05, 67.45,
25.82.
2-[3-(Tetrahydropyran-2-yloxy)phenyl]-1,3-dioxane (Entry 24)
1H NMR (500 MHz, CDCl3, TMS): = 7.15–7.17 (t, J = 7.9 Hz, 1
H), 7.01–7.04 (d, J = 7.9 Hz, 1 H), 6.88–6.89 (t, J = 2.2 Hz, 1 H),
6.69–6.71 (dd, J = 7.9, 2.2 Hz, 1 H), 5.38 (s, 1 H), 4.52–4.53 (m, 1
H), 4.15–4.18 (dd, J = 11.0, 5.0 Hz, 2 H), 4.00–4.03 (m, 2 H), 3.86–
3.91 (pseudo-t, J = 11.0 Hz, 2 H), 2.10–2.15 (tq, J = 5.0, 12.7 Hz, 1
H), 1.96–2.02 (m, 1 H), 1.81–1.85 (m, 1 H), 1.47–1.50 (m, 3 H),
1.34–1.37 (m, 1 H), 1.23–1.27 (m, 1 H).
13C NMR (125 MHz, CDCl3, TMS): = 156.58, 140.11, 129.28,
119.13, 117.50, 115.83, 102.29, 98.79, 67.27, 66.81, 30.68, 30.67,
25.44, 19.51.
Some representative spectral data are as follows:
2-(4-Chlorophenyl)-1,3-dioxane (Entry 3)
1H NMR (250 MHz, CDCl3, TMS): = 7.40–7.49 (d, J = 8.0 Hz, 2
H), 7.30–7.34 (d, J = 8.0 Hz, 2 H), 5.44 (s, 1 H), 4.20–4.26 (dd,
J = 5.0, 11.3 Hz, 2 H), 3.88–3.98 (pseudo-t, J = 11.3 Hz, 2
H), 2.14–2.23 (tq, J = 5, 13.2 Hz, 1 H), 1.37–1.43 (quintet, J = 1.2,
13.2 Hz 1 H).
tert-Butyl-[3-(1,3-dioxane-2-yl)phenoxy]dimethylsilane (Entry
26)
13C NMR (63 MHz, CDCl3, TMS): = 137.70, 134.95, 128.81,
127.91, 101.19, 67.78, 26.09.
1H NMR (500 MHz, CDCl3, TMS): = 7.22–7.25 (t, J = 7.9 Hz, 1
H), 7.02–7.11 (d, J = 7.9 Hz, 1 H), 7.01 (t, J = 2.0 Hz, 1 H), 6.82–
Synthesis 2002, No. 6, 784–788 ISSN 0039-7881 © Thieme Stuttgart · New York