A simple and practical synthetic protocol for acetalisation, thioacetalisation and transthioacetalisation of carbonyl compounds under solvent-free conditions

Article abstract of DOI:10.1002/ejoc.200300685

A wide variety of carbonyl compounds can be converted smoothly to the corresponding acetals on treatment with alcohols or diols and triethyl orthoformate in the presence of a catalytic amount of (bromodimethyl)sulfonium bromide at room temperature. Similarly, various carbonyl compounds can be transformed into the corresponding dithioacetals on reaction with thiol or dithiols at room temperature by employing the same catalyst without any solvent. Moreover, O,O-acetals can also be converted into the corresponding dithioacetals under identical conditions. Some of the major advantages are mild reaction conditions, a high degree of efficiency, compatibilty with other protecting groups and the lack of solvents, particularly for thioacetalisation. In addition, no brominations occur at the double bond or α to the keto position or even in the aromatic ring under these experimental conditions. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.

Full text of DOI:10.1002/ejoc.200300685

FULL PAPER
A Simple and Practical Synthetic Protocol for Acetalisation,
Thioacetalisation and Transthioacetalisation of Carbonyl Compounds under
Solvent-Free Conditions
Abu T. Khan,*[a] Ejabul Mondal,[a] Subrata Ghosh,[a] and Samimul Islam[b]
Dedicated to Professor G. Mehta on the occasion of his 60th birthday
Keywords: Protecting groups / Carbonyl compounds / Acetals / Dithioacetals / Solvent-free reactions
A wide variety of carbonyl compounds can be converted
smoothly to the corresponding acetals on treatment with al-
cohols or diols and triethyl orthoformate in the presence of
a catalytic amount of (bromodimethyl)sulfonium bromide at
room temperature. Similarly, various carbonyl compounds
can be transformed into the corresponding dithioacetals on
thioacetals under identical conditions. Some of the major ad-
vantages are mild reaction conditions, a high degree of effici-
ency, compatibilty with other protecting groups and the lack
of solvents, particularly for thioacetalisation. In addition, no
brominations occur at the double bond or α to the keto posi-
tion or even in the aromatic ring under these experimental
reaction with thiol or dithiols at room temperature by em- conditions.
ploying the same catalyst without any solvent. Moreover,
O,O-acetals can also be converted into the corresponding di-
( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2004)
Introduction
presence of trialkyl orthoformates as water scavenger are
Amberlyst-15,[7a] ZrCl4,[7b] DDQ,[7c] NBS,[7d] Sc(NTf2)3,[7e]
and TBATB.[7f] Unfortunately, many of these procedures
have some drawbacks such as longer reaction times, the
need for excess reagents, harsh reaction conditions and the
use of expensive reagents. Similarly, some new catalytic pro-
cedures have recently been developed for thioacetalisation
The protection of a carbonyl functionality as an acetal[1]
or 1,3-dithiane[2] is a very common practice in multi-step
organic syntheses. Protection of carbonyl groups as di-
thioacetals, in particular, is an even more important trans-
formation than to the corresponding acetals due to their
higher stability under both acidic and basic reaction con-
ditions. In addition, they also often serve as masked acyl
anion equivalents[3] or masked methylene functions[4] in
carbonϪcarbon bond-forming reactions. Moreover, various
1,3-dithiane derivatives play an important role as valuable
building blocks in natural product synthesis; this has been
reviewed very recently.[5] For example, 2-styryl-1,3-dithiane
(27) and the 1,3-dithiane derivative 31 have been used
recently as key starting materials for the synthesis of kurzi-
lactone[6a] and bicyclic acetals, a precursor present in
several polyfunctionalised 1,7-dioxaspiro[5.5]undecane
spiroacetal systems,[6b] respectively. Although numerous
methods have been developed both for the acetalisation[1]
and dithioacetalisation[2] of carbonyl compounds over the
years, there is still a need to find better alternatives that
work efficiently under mild conditions. Some of the recently
employed reagents that can catalyse acetalisation in the
using LiBr,[8] LiBF4,[9] InCl3,[10] molecular I2,[11] NBS,[12]
[13]
Sn(OTf)3
and NiCl2.[14] Unfortunately, some of these
methods also require long reaction times, provide low
yields, require a stoichiometric amount of catalyst, involve
expensive reagents, require an inert atmosphere for the
reaction,[8Ϫ12] fail to protect deactivated aromatic sub-
strates[13] and ketonic compounds,[14] or require solvent in
order to carry out the transformations. In light of the grad-
ual changes in current working practices to provide greener
and more environmentally friendly alternatives,[15] there is
a need for a solvent-free and catalytically efficient alterna-
tive for the acetalisation and thioacetalisation of carbonyl
compounds, which might work under mild and cheaper re-
action conditions. As part of our ongoing research project
to develop new synthetic methodologies, particularly for the
protection and deprotection of carbonyl compounds as
oxathioacetals and dithioacetals,[16] we envisioned that
(bromodimethyl)sulfonium bromide, which can generate
HBr in the reaction medium on reaction with alcohol,[17a]
might be a useful catalyst for the protection of carbonyl
compounds as acetals and dithioacetals. Previously,
(bromodimethyl)sulfonium bromide has been utilised for
[a]
Department of Chemistry, Indian Institute of Technology
Guwahati,
Guwahati-781 039, India
[b]
Department of Chemistry,
Visva-Bharati, Santiniketan, West Bengal-731 235, India
2002
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
DOI: 10.1002/ejoc.200300685
Eur. J. Org. Chem. 2004, 2002Ϫ2009

Acetalisation of Carbonyl Compounds under Solvent-Free Conditions
FULL PAPER
the conversion of alcohols to the corresponding alkyl bro- 1,3-dioxolanes derivatives 7, 8, 9 and 10, respectively, in
mides,[17a] enones to their α-bromoenones,[17b] oxidation of fairly good yields. It is noteworthy to mention that the con-
thiols to disulfides[17c] and deprotection of dithioacetals to version can be achieved without affecting other protecting
the corresponding carbonyl compounds.[17d] However, the groups such as allyl and TBS ethers. We have noticed that
versatility of this reagent has not been well studied. Very highly deactivated aromatic aldehydes and acid-sensitive
recently, we have demonstrated the utility of this reagent substrates can also be protected to the corresponding acet-
for tetrahydropyranylation/depyranylation of alcohols and als in very good yields. Cetylaldehyde does not react with
phenols.[18] Here we wish to report for the first time a ethylene glycol under the above conditions, but it could be
simple and practical synthetic protocol for acetalisation, converted smoothly to the corresponding acyclic acetal 11
thioacetalisation and transthioacetalisation using (bromo- on treatment with dry methanol under identical conditions.
dimethyl)sulfonium bromide as a new catalyst under sol-
vent-free conditions (Scheme 1).
Next, we switched our attention to the protection of vari-
ous ketonic compounds under identical reaction conditions.
By extending our protocol, various 1,3-dioxolane deriva-
tives 12, 13, 14, 15, 16, 17 and 18 were prepared from the
respective ketones 3-octanone, acetophenone, cyclopenta-
none, cyclohexanone, cycloheptanone, cyclooctanone and
cyclododecanone. The results are summarised in the Table 1
and the products were fully characterised by IR and 1H
1
NMR spectroscopy and elemental analysis. The H NMR
spectroscopic data of the compounds 1, 2, 9, 10, 13, 14,
15, and 16 were also compared with those of the reported
compounds in the literature.[19] The results shown in Table 1
clearly indicate the scope and generality of the reaction with
respect to various carbonyl compounds. It is also important
to highlight that no brominations occur α to the keto posi-
tions.
We then turned our attention to whether the same cata-
lyst can be used for thioacetalisation. When a mixture of
benzaldehyde (1 mmol) and 1,3-propanedithiol (1.1 mmol)
was treated with a catalytic amount of (bromodimethyl)sul-
fonium bromide (0.05 mmol) without any solvent at room
temperature, it was smoothly transformed into the corre-
Scheme 1
Results and Discussion
sponding 2-phenyl-1,3-dithiane (19) in very good yield.
1
(Bromodimethyl)sulfonium bromide was prepared by fol- Compound 19 was characterised by IR, H NMR and 13C
lowing a literature procedure.[17d] As per our expectation, a NMR spectroscopy and elemental analysis. This result en-
mixture of benzaldehyde (5 mmol), 1,2-ethanediol [A] couraged us to investigate further the usefulness of the cata-
(6 mmol) and triethyl orthoformate (6 mmol) in the pres- lyst. In a similar manner, 4-chlorobenzaldehyde was con-
ence of (bromodimethyl)sulfonium bromide (0.05 mmol) at verted into the corresponding 1,3-dithiane derivative of 4-
room temperature was converted smoothly to the desired 2- chlorobenzaldehyde 20 under identical reaction conditions.
phenyl-1,3-dioxolane (1) in 82% yield. Similarly, a mixture Likewise, various aromatic aldehydes were converted easily
of benzaldehyde (5 mmol), 1,3-propanediol [B] (6 mmol) and chemoselectively into the corresponding acyclic or cyc-
and triethyl orthoformate (6 mmol) provided the corre- lic dithioacetals 21, 22, 23, 24, 25, 26, 27, 28 and 29, on
sponding 2-phenyl-1,3-dioxane (2) in 78% yield at room treatment with thiol or dithiol in the presence of the same
temperature with a catalytic amount of (bromodimethyl)- catalyst in solvent-free mode without affecting the other
sulfonium bromide. Likewise, 4-methoxybenzaldehyde was protecting groups such as benzoyl, allyl, cyclohexenyl and
transformed into the 1,3-dioxane derivative
identical reaction conditions. Subsequently, various aro-
3
under TBS ether. These results are summarised in Table 2.
Next we converted phenylacetaldehyde, furfural, heptanal
matic aldehydes such as 4-chlorobenzaldehyde and 4-nitro- and 5-(tert-butyldiphenylsilyloxy)pentanal into the corre-
benzaldehyde were converted into the corresponding 1,3- sponding dithioacetals 30, 31, 32 and 33, respectively, under
dioxolane derivatives 4 and 5 in good yields, on treatment identical reaction conditions depending upon the 1,2-di-
with 1,2-ethanediol in the presence of triethyl orthoformate thiol or 1,3-dithiol used. Moreover, various dithioacetals
(which acts as water scavenger) and a catalytic amount of derivatives 34Ϫ42 were obtained in very good yields from
(bromodimethyl)sulfonium bromide at room temperature. the corresponding ketones and diketones by employing the
By following the above reaction procedure, a wide variety same catalyst under solvent-free conditions. Remarkably, by
of aldehydes such as phenylacetaldehyde, 4-(tert-butyldi- using our protocol both aliphatic and aromatic aldehydes,
methylsilyloxy)benzaldehyde, 4-(allyloxy)benzaldehyde, cin- and various ketones can be transformed easily into the cor-
namaldehyde and the highly acid-sensitive substrate 2-fural- responding dithioacetals without non-aqueous work up. All
dehyde were efficiently transformed into the corresponding the results are summarised in Table 2. All the products were
Eur. J. Org. Chem. 2004, 2002Ϫ2009
www.eurjoc.org
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2003

A. T. Khan, E. Mondal, S. Ghosh, S. Islam
FULL PAPER
compounds 20, 23, 24, 27, 35, 36 and 42 were compared
with the reported data.[12,20] It is important to mention that
no brominations occur at the double bond, at the α-position
of the ketone or even in the highly electron-rich aromatic
ring. It is pertinent to mention that a highly acid-sensitive
substrate, furfural, can be easily protected under identical
conditions at a much faster rate and in much higher yield
than reported recently.[11] These results clearly demonstrate
the efficiency and generalisation of the procedure. It is
worthwhile to mention that thioacetalisation can be carried
out with larger amounts of the carbonyl compounds. For
Table 1. Protection of carbonyl compounds to the corresponding
acetals by employing 0.01 equiv. of (bromodimethyl)sulfonium
bromide as catalyst
example, when
a mixture of 4-methoxybenzaldehyde
(1.36 g, 10 mmol) and 1,2-ethanedithiol (0.84 mL,
10 mmol) was treated with (bromodimethyl)sulfonium bro-
mide (0.111 g, 0.5 mmol), it was smoothly converted within
3 min into the corresponding 1,3-dithiolane derivative of 4-
methoxybenzaldehyde 43. The product was obtained by
recrystallisation without column chromatography in 93%
yield (1.98 g), and was characterised by its melting point,
and IR and NMR spectra. The capability of (bromodime-
thyl)sulfonium bromide to promote thioacetalisation on a
large scale was also investigated to establish the potential
scope of the procedure. To this end, 4-methoxybenzal-
dehyde (13.6 g, 100 mmol), 1,2-ethanedithiol (8.4 mL,
100 mmol) and (bromodimethyl)sulfonium bromide (1.1 g,
5 mmol) were mixed together at room temperature afford-
ing complete conversion in 2Ϫ3 min. The pure protected
compound was obtained in 95% yield after recrystallisation.
Interestingly, this procedure can be applied for the
chemoselective acetalisation of an aldehyde group in the
presence of a ketone. For example, when an equimolar mix-
ture of benzaldehyde and 3-octanone, triethyl orthoformate
and 1,2-ethanediol was allowed to react in the presence of
a catalytic amount of (bromodimethyl)sulfonium bromide
only the 1,3-dioxolane derivative of benzaldehyde was ob-
tained in 75% yield with 90% recovery of the 3-octanone
(Scheme 2).
Scheme 2
Furthermore, the aldehyde group of the keto aldehyde 44
was chemoselectively protected to the corresponding di-
thioacetals 45 in the presence of 0.05 equivalents of the
same catalyst in 90% yield under solvent-free conditions, as
shown in Scheme 3.
[a] Diol used: A ϭ HOCH2CH2OH, B ϭ HOCH2CH2CH2OH, C ϭ
[b]
1
MeOH.
Products were characterised by IR, H NMR and 13C
[c]
NMR spectroscopy and elemental analysis. Isolated yield. [d] 1H
NMR spectroscopic data of the products were compared with the
reported literature data.
Moreover, we have also noticed that the catalyst is equ-
ally efficient for the transthioacetalisation of O,O-acetals
characterised by recording their IR, 1H NMR and 13C and O,O-ketals, as represented in Scheme 4.
NMR spectra and elemental analysis. The NMR spectro-
The formation of acetals and dithioacetals from the car-
scopic data of the compounds as well as melting points of bonyl compounds can be explained as follows. The (bromo-
2004
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
Eur. J. Org. Chem. 2004, 2002Ϫ2009

Acetalisation of Carbonyl Compounds under Solvent-Free Conditions
FULL PAPER
Table 2. Protection of various carbonyl compounds to the corresponding dithioacetals using (bromodimethyl)sulfonium bromide as cata-
lyst
[a]
Thiol or dithiol used: A ϭ HSCH2CH2CH2SH, B ϭ EtSH, C ϭ HSCH2CH2SH. [b] Products were characterised by IR, 1H NMR and
13C NMR spectroscopy and elemental analysis. [c] Isolated yield. [d] The reaction was carried out with 0.05 equivalents of catalyst. [e] The
reaction was carried out with 0.15 equivalents of catalyst. [f] The reaction was carried out with 0.30 equivalents of catalyst. [g] The reaction
was carried out on a 100 mmol scale. [h] 1H NMR spectroscopic data of the products were compared with the reported literature data.
dimethyl)sulfonium bromide catalyst, on reaction with the
diol, thiol or dithiol, gives HBr in the reaction medium,
which is the actual catalyst for the acetalisation or thioacet-
alisation. We have also found that the pH of the reaction
mixture drops to about 2Ϫ3 while carrying out the reaction.
Scheme 3
Conclusion
In conclusion, various carbonyl compounds were ef-
ficiently converted into the corresponding acetals at room
temperature using triethyl orthoformate as a water scaven-
ger, and (bromodimethyl)sulfonium bromide as a new and
efficient catalyst. We have also demonstrated that both
acyclic and cyclic dithioacetals can be prepared in very high
yields from the corresponding carbonyl compounds using
Scheme 4
the same catalyst under solvent-free reaction conditions.
Eur. J. Org. Chem. 2004, 2002Ϫ2009
www.eurjoc.org
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2005

A. T. Khan, E. Mondal, S. Ghosh, S. Islam
FULL PAPER
1132, 1061, 1015 cmϪ1. 1H NMR (300 MHz, CDCl3): δ ϭ 2.94 (d,
J ϭ 5.7 Hz, 2 H, CHCH2), 3.40Ϫ3.50 (m, 2 H, OCH2), 3.57Ϫ3.73
(m, 2 H, OCH2), 4.64 (t, J ϭ 5.7 Hz, 1 H, CH), 7.23 (m, 5 H, ArH)
ppm. C10H12O2 (164.20): calcd. C 73.15, H 7.37; found C 73.30,
H 7.22.
This methodology can also be applied on a large scale with-
out the need for solvents or chromatographic separation. In
addition, this methodology can be applied for the chemose-
lective protection of an aldehyde group by acetalisation or
thioacetalisation in the presence of a ketone. It is note-
worthy that no bromination takes place under these exper- 2-[4Ј-(tert-Butyldimethylsilyloxy)phenyl]-1,3-dioxolane (7): 1.0 g,
72%. Colourless liquid. IR (neat): ν˜ ϭ 2986, 2935, 2883, 1609,
1532, 1347, 1209, 1107, 1055, 1020, 856 cmϪ1. 1H NMR (400 MHz,
CDCl3): δ ϭ 0.16 [s, 6 H, Si(CH3)2], 0.92 [s, 9 H, SiC(CH3)3], 3.84
(m, 4 H, 2 ϫ OCH2), 5.36 (s, 1 H, ArCH), 6.82 (d, J ϭ 8.5 Hz, 2
H, ArH), 7.31 (d, J ϭ 8.5 Hz, 2 H, ArH) ppm. C15H24O3Si
(280.44): calcd. C 64.24, H 8.63; found C 64.53, H 8.56.
imental conditions and the reaction can be performed in
the presence of other protecting groups without affecting
them. Transthioacetalisation is also possible by using the
same catalyst.
Experimental Section
2-[4Ј-Allyloxyphenyl]-1,3-dioxolane (8): 0.770 g, 75%. Colourless
liquid. IR (neat): ν˜ ϭ 2970, 2883, 1655, 1613, 1555, 1373, 1306,
1
1244, 1091, 1050, 1029, 994, 927, 835 cmϪ1. H NMR (400 MHz,
Melting points were recorded with a Büchi B-545 melting point
apparatus and are uncorrected. IR spectra were recorded in KBr
or neat with a Nicolet Impact 410 spectrophotometer. 1H NMR
and 13C NMR spectra were recorded with a Bruker 200, Bruker
300 or Jeol 400 MHz spectrometer in CDCl3 using TMS as internal
CDCl3): δ ϭ 3.93 (m, 4 H, 2 ϫ OCH2), 4.50 (m, 2 H, CH2OAr),
5.24 (dd, J ϭ 1.4, J ϭ 10.5 Hz, 1 H, CH2ϭC), 5.29 (dd, J ϭ 1.5,
J ϭ 17.3 Hz, 1 H, CH2ϭC), 5.89 (s, 1 H, OCHO), 6.04 (m, 1 H,
CHϭC), 6.85 (d, J ϭ 8.7 Hz, 2 H, ArH), 7.35 (d, J ϭ 8.6 Hz, 2 H,
ArH) ppm. C12H14O3 (206.24): calcd. C 69.89, H 6.84; found C
69.74, H 6.76.
reference. Elemental analyses were carried out with
a
PerkinϪElmer 2400 automatic carbon, hydrogen, nitrogen and sul-
fur analyser. Column chromatographic separations were done on
SRL silica gel (60Ϫ120 mesh).
Cetylaldehyde Dimethyl Acetal (11): 1.070 g, 75%. Colourless
liquid. IR (neat): ν˜ ϭ 2924, 2852, 1464, 1383, 1126, 1055 cmϪ1. 1H
NMR (300 MHz, CDCl3): δ ϭ 0.87 (t, J ϭ 6.5 Hz, 3 H, CH3),
1.18Ϫ1.25 (br. s, 26 H, CH2), 1.55Ϫ1.60 (m, 2 H, CHCH2), 3.30
(s, 6 H, 2 ϫ OCH3), 4.35 (t, J ϭ 5.7 Hz, 1 H, CH) ppm. C18H38O2
(286.50): calcd. C 75.46, H 13.37; found C 75.18, H 13.48.
General Procedure for Acetalisation: A catalytic amount of (bromo-
dimethyl)sulfonium bromide (0.011 g, 0.05 mmol) was added to a
mixture of the appropriate carbonyl compound (5 mmol), triethyl
orthoformate (1 mL, 6 mmol) and 1,2-ethanediol (0.350 mL,
6 mmol) or 1,3-propanediol (0.420 mL, 6 mmol) at room tempera-
ture and the mixture stirred until the starting material had disap-
peared, as monitored by TLC. After completion of the reaction, it
was neutralised with NaHCO3 solution and extracted with CH2Cl2
(2 ϫ 25 mL), washed with water (2 ϫ 15 mL) and dried with anhy-
drous Na2SO4. The organic extract was concentrated on a rotary
evaporator and the crude residue was finally purified by alumina
column chromatography or by distillation under reduced pressure
to obtain the desired protected compound.
2-Ethyl-2-pentyl-1,3-dioxolane (12): 0.690 g, 80%. Colourless liquid.
IR (neat): ν˜ ϭ 3068, 3037, 2975, 2935, 2889, 1470, 1372, 1214,
1176, 1050, 989, 753 cmϪ1. 1H NMR (400 MHz, CDCl3): δ ϭ 0.84
(t, J ϭ 6.8 Hz, 3 H , CH3), 0.93 (t, J ϭ 6.8 Hz, 3 H, CH3),
1.20Ϫ1.40 (m, 6 Η, CH2), 1.55Ϫ1.65 (m, 4 Η, CH2), 3.91Ϫ3.96
(m, 4 H, 2 ϫ OCH2) ppm. C10H20O2 (172.27): calcd. C 69.73, H
11.70; found C 69.91, H 11.62.
1,4-Dioxaspiro[4.7]dodecane (17): 0.740 g, 87%. Colourless gummy
liquid. IR (neat): ν˜ ϭ 2924, 2873, 1470, 1444, 1378, 1244, 1152,
2-[4Ј-Methoxyphenyl]-1,3-dioxane (3): 0.780 g, 80%. Colourless
liquid. IR (neat): ν˜ ϭ 2965, 2842, 1603, 1521, 1465, 1429, 1393,
1111, 1050, 968 cmϪ1
. δ ϭ
1H NMR (400 MHz, CDCl3):
1321, 1250, 1163, 1106, 1035, 988 cmϪ1 1H NMR (400 MHz,
.
1.30Ϫ1.42 (m, 10 Η, CH2), 1.50Ϫ1.64 (m, 4 H, CH2), 3.91 (s, 4 H,
2 ϫ OCH2) ppm. C10H18O2 (170.25): calcd. C 70.55, H 10.66;
found C 70.36, H 10.54.
CDCl3): δ ϭ 1.81 (m, 1 H, OCH2CHaHbCH2O), 2.21 (m, 1 H,
OCH2CHaHbCH2O), 3.59 (s, 3 H, OCH3), 3.80 (m, 4 H, 2 ϫ
OCH2), 5.20 (s, 1 H, ArCH), 6.84 (d, J ϭ 8.7 Hz, 2 H, ArH), 7.41
(d, J ϭ 8.7 Hz, 2 H, ArH) ppm. C11H14O3 (194.23): calcd. C 68.02,
H 7.26; found C 68.19, H 7.16.
1,4-Dioxaspiro[4.11]hexadecane (18): 0.990 g, 88%. Low melting
solid. IR (neat): ν˜ ϭ 2929, 2847, 1470, 1444, 1332, 1224, 1122,
1086, 1055, 1015, 953 cmϪ1 1H NMR (400 MHz, CDCl3): δ ϭ
.
1.30Ϫ1.42 (m, 18 Η, CH2), 1.50Ϫ1.64 (m, 4 H, CH2), 3.91 (s, 4 H,
2 ϫ OCH2) ppm. C14H26O2 (226.36): calcd. C 74.29, H 11.58;
found C 74.01, H 11.65.
2-[4Ј-Chlorophenyl]-1,3-dioxolane (4): 0.690 g, 75%. Colourless
liquid. IR (neat): ν˜ ϭ 2975, 2930, 2883, 1603, 1490, 1444, 1403,
1
1342, 1209, 1116, 1096, 1060, 1014, 922, 846, 809 cmϪ1. H NMR
(400 MHz, CDCl3): δ ϭ 4.08 (m, 4 Η, OCH2), 5.80 (s, 1 H, ArCH),
7.23 (d, J ϭ 8.6 Hz, 2 H, ArH), 7.44 (d, J ϭ 8.4 Hz, 2 H, ArH)
ppm. C9H9ClO2 (184.62): calcd. C 58.55, H 4.91; found C 58.73,
H 4.85.
General Procedure for Thioacetalisation: A catalytic amount of
(bromodimethyl)sulfonium bromide (as indicated in Table 2) was
added to a mixture of the carbonyl compound (1 mmol) and thiol
(2.2 mmol) or dithiol (1.1 mmol) and the mixture stirred at room
temperature. After completion of the reaction, it was neutralised
with two drops of saturated NaHCO3 solution. Then, the reaction
mixture was passed directly through a silica gel column without
aqueous work up to get the desired dithioacetal. In the case of a
large-scale reaction (10Ϫ100 mmol), the product can be obtained
by direct recrystallisation instead of chromatographic separation if
the product is solid.
2-[4Ј-Nitrophenyl]-1,3-dioxolane (5): 0.880 g, 90%. Light yellow
solid. IR (KBr): ν˜ ϭ 2986, 2935, 2883, 1609, 1532, 1347, 1209,
1107, 1055, 1020, 856 cmϪ1 1H NMR (400 MHz, CDCl3): δ ϭ
.
4.10 (m, 4 H, 2 ϫ OCH2), 5.90 (s, 1 H, ArCH), 7.66 (d, J ϭ 8.4 Hz,
2 H, ArH), 8.24 (d, J ϭ 8.4 Hz, 2 H, ArH) ppm. C9H9NO4
(195.17): calcd. C 55.39, H 4.65, N 7.18; found C 55.28, H 4.59,
N 7.01.
2-[Benzyl]-1,3-dioxolane (6): 0.530 g, 65%. Colourless liquid. IR
(neat): ν˜ ϭ 2981, 2930, 2884, 1609, 1496, 1460, 1378, 1352, 1214,
2-Phenyl-1,3-dithiane (19): 0.176 g, 90%. White solid; m.p. 74 °C;
SiO2-TLC (hexane/EtOAc, 19:1), Rf ϭ 0.94. IR (KBr): ν˜ ϭ 3037,
2006
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
Eur. J. Org. Chem. 2004, 2002Ϫ2009

Acetalisation of Carbonyl Compounds under Solvent-Free Conditions
FULL PAPER
2940, 2894, 2827, 1593, 1491, 1429, 1281, 1183, 1066, 912, 728, 2940, 2894, 2807, 1609, 1516, 1450, 1363, 1250, 1173, 1112, 851,
1
1
697 cmϪ1. H NMR (400 MHz, CDCl3): δ ϭ 1.85Ϫ1.96 (m, 1 H,
774 cmϪ1. H NMR (400 MHz, CDCl3): δ ϭ 1.85Ϫ1.96 (m, 1 H,
SCH2CHaHbCH2S), 2.09Ϫ2.16 (m, H, SCH2CHaHbCH2S), SCH2CHaHbCH2S), 2.12Ϫ2.19 (m,
1
1
H, SCH2CHaHbCH2S),
2.85Ϫ2.90 (m, 2 H, SCH2), 2.99Ϫ3.07 (m, 2 H, SCH2), 5.16 (S, 1 2.86Ϫ2.92 (m, 2 H, SCH2), 3.01Ϫ3.08 (m, 2 H, SCH2), 5.12 (S, 1
H, ArCH), 7.24Ϫ7.35 (m, 3 H, ArH), 7.45Ϫ7.47 (m, 2 H, ArH) H, ArCH), 6.77 (d, J ϭ 8.2 Hz, 2 H, ArH), 7.31 (d, J ϭ 8.3 Hz, 2
ppm. 13C NMR (100 MHz, CDCl3): δ ϭ 24.96, 31.95 (2 C), 51.34, H, ArH) ppm. 13C NMR (100 MHz, CDCl3): δ ϭ 25.06, 32.18 (2
127.61 (2 C), 128.29, 128.59 (2 C), 138.99 ppm. C10H12S2 (196.34):
calcd. C 61.17, H 6.16, S 32.66; found C 61.95, H 6.14, S 32.49.
C), 50.74, 115.58 (2 C), 129.18 (2 C), 131.45, 155.61 ppm.
C10H12OS2 (212.34): calcd. C 56.56, H 5.70, S 32.20; found C 56.34,
H 5.63, S 32.01.
4Ј-Methoxyphenyl Diethyl Dithioacetal (21): 0.208 g, 86%. White
solid; m.p. 43 °C; SiO2-TLC (hexane/EtOAc, 19:1), Rf ϭ 0.94. IR
(KBr): ν˜ ϭ 2965, 2928, 1609, 1510, 1447, 1301, 1261, 1174, 1106,
2-[4Ј-(Benzoyloxy)phenyl]-1,3-dithiane (29): 0.297 g, 94%; m.p.
163Ϫ164 °C; SiO2-TLC (hexane/EtOAc, 9:1), Rf ϭ 0.36. IR (KBr):
ν˜ ϭ 3068, 2955, 2894, 1731, 1593, 1506, 1424, 1265, 1204, 1168,
1071, 1020, 886, 769, 707 cmϪ1. 1H NMR (400 MHz, CDCl3): δ ϭ
1.88Ϫ1.98 (m, 1 H, SCH2CHaHbCH2S), 2.15Ϫ2.18 (m, 1 H,
SCH2CHaHbCH2S), 2.89Ϫ2.93 (m, 2 H, SCH2), 3.03Ϫ3.09 (m, 2
H, SCH2), 5.20 (S, 1 H, ArCH), 7.20 (d, J ϭ 8.8 Hz, 2 H, ArH),
7.51 (m, 2 H, ArH), 7.53 (d, J ϭ 8.5 Hz, 2 H, ArH), 7.63 (m, 1 H,
ArH), 8.18 (m, 2 H, ArH) ppm. 13C NMR (100 MHz, CDCl3): δ ϭ
25.04, 32.03 (2 C), 50.72, 121.95 (2 C), 128.57 (2 C), 129.03 (2 C),
129.43, 130.17 (2 C), 133.64, 136.74, 150.80, 164.95 ppm.
C17H16O2S2 (316.44): calcd. C 64.53, H 5.10, S 20.27; found C
64.35, H 5.03, S 20.01.
1
1025 cmϪ1. H NMR (400 MHz, CDCl3): δ ϭ 1.22 (t, J ϭ 7.3 Hz,
6 H, 2 ϫ SCH2CH3), 2.46Ϫ2.63 (m, 4 H, 2 ϫ SCH2CH3), 3.80 (s,
3 H, OCH3), 4.91 (s, 1 H, ArCH), 6.85 (d, J ϭ 8.6 Hz, 2 H, ArH),
7.37 (d, J ϭ 8.5 Hz, 2 H, ArH) ppm. 13C NMR (100 MHz, CDCl3):
δ ϭ 14.24 (2 C), 26.15 (2 C), 51.69, 55.22, 113.75 (2 C), 128.77 (2
C), 132.37, 159.00 ppm. C12H18OS2 (242.41): calcd. C 59.46, H
7.48, S 26.46; found C 59.65, H 7.59, S 26.22.
2-[2Ј,4Ј-Dimethoxyphenyl]-1,3-dithiane (22): 0.246 g, 96%. White
solid; m.p. 103 °C; SiO2-TLC (hexane/EtOAc, 9:1), Rf ϭ 0.83. IR
(KBr): ν˜ ϭ 2996, 2939, 2893, 2837, 1618, 1505, 1454, 1424, 1326,
1290, 1116, 1039, 992 cmϪ1 1H NMR (300 MHz, CDCl3): δ ϭ
.
1.85Ϫ1.92 (m, 1 H, SCH2CHaHbCH2S), 2.12Ϫ2.17 (m, 1 H,
SCH2CHaHbCH2S), 2.84Ϫ2.90 (m, 2 H, SCH2), 3.05Ϫ3.16 (m, 2
H, SCH2), 3.78 (s, 3 H, OCH3), 3.83 (s, 3 H, OCH3), 5.61 (S, 1 H,
ArCH), 6.42 (d, J ϭ 2.4 Hz, 1 H, ArH), 6.48 (dd, J ϭ 2.4, J ϭ
8.5 Hz, 1 H, ArH), 7.48 (d, J ϭ 8.5 Hz, 1 H, ArH) ppm. 13C NMR
(75 MHz, CDCl3): δ ϭ 25.20, 32.41 (2 C), 43.10, 55.30, 55.60,
98.50, 104.70, 119.80, 129.70, 156.40, 160.60 ppm. C12H16O2S2
(256.39): calcd. C 56.22, H 6.29, S 25.01; found C 56.01, H 6.36,
S 25.14.
2-Benzyl-1,3-dithiolane (30): 0.165 g, 84%. Colourless liquid; SiO2-
TLC (hexane/EtOAc, 9:1), Rf ϭ 0.36. IR (neat): ν˜ ϭ 3037, 2925,
2843, 1598, 1501, 1424, 1286, 1132, 1030, 846, 738 cmϪ1. 1H NMR
(400 MHz, CDCl3): δ ϭ 3.04 (d, J ϭ 7.1 Hz, 2 H, PhCH2),
3.08Ϫ3.21 (m, 4 H, 2 ϫ SCH2), 4.66 (t, J ϭ 7.1 Hz, 1 H,
PhCH2CH), 7.16Ϫ7.26 (m, 5 H, ArH) ppm. C10H12S2 (196.34):
calcd. C 61.17, H 6.16, S 32.66; found C 61.31, H 6.10, S 32.43.
2-Furfuryl-1,3-dithiane (31): 0.182 g, 98%. Pale yellow liquid; SiO2-
TLC (hexane/EtOAc, 19:1), Rf ϭ 0.63. IR (neat): ν˜ ϭ 2899, 1495,
1424, 1275, 1163, 1014, 748 cmϪ1 1H NMR (400 MHz, CDCl3):
.
2-[4Ј-Allyloxyphenyl]-1,3-dithiane (25): 0.239 g, 95%. White solid;
m.p. 81 °C; SiO2-TLC (hexane/EtOAc, 99:1), Rf ϭ 0.66. IR (KBr):
ν˜ ϭ 2914, 1603, 1506, 1429, 1245, 1183, 1015, 779 cmϪ1. 1H NMR
(400 MHz, CDCl3): δ ϭ 1.84Ϫ1.97 (m, 1 H, SCH2CHaHbCH2S),
2.11Ϫ2.17 (m, 1 H, SCH2CHaHb CH2S), 2.86Ϫ2.91 (m, 2 H,
SCH2), 3.00Ϫ3.14 (m, 2 H, SCH2), 4.50Ϫ4.52 (m, 2 H, OCH2CHϭ
CH2), 5.13 (s, 1 H, ArCH), 5.27 (dd, J ϭ 3.0, J ϭ 10.6 Hz, 1 H,
OCH2CHϭCHaHb), 5.39 (dd, J ϭ 3.2, J ϭ 17.1 Hz, 1 H,
OCH2CHϭCHaHb), 5.98Ϫ6.08 (m, 1 H, OCH2CHϭCHaHb), 6.87
(d, J ϭ 8.8 Hz, 2 H, ArH), 7.38 (d, J ϭ 8.8 Hz, 2 H, ArH) ppm.
13C NMR (100 MHz, CDCl3): δ ϭ 24.97, 32.10 (2 C), 50.66, 68.81,
114.86 (2 C), 118.26, 128.86 (2 C), 131.34, 133.03, 158.49 ppm.
C13H16OS2 (252.40): calcd. C 61.86, H 6.39, S 25.41; found C 61.69,
H 6.32, S 25.18.
δ ϭ 1.92Ϫ2.01 (m, 1 H, SCH2CHaHbCH2S), 2.08- 2.16 (m, 1 H,
SCH2CHaHbCH2S), 2.88Ϫ2.93 (m, 4 H, 2 ϫ SCH2), 5.20 (s, 1 H,
SCHS), 6.32 (dd, J ϭ 2.0, J ϭ 3.2 Hz, 1 H, H-4), 6.37 (d, J ϭ
3.1 Hz, 1 H, H-3), 7.34 (d, J ϭ 1.9 Hz, 1 H, H-5) ppm. 13C NMR
(100 MHz, CDCl3): δ ϭ 25.22, 30.24 (2 C), 41.99, 107.83, 110.56,
142.27, 151.66 ppm. C8H10OS2 (186.30): calcd. C 51.58, H 5.41, S
34.42; found C 51.39, H 5.33, S 34.23.
2-Hexyl-1,3-dithiolane (32): 0.123 g, 65%. Colourless liquid; SiO2-
TLC (hexane/EtOAc, 99:1), Rf ϭ 0.4. IR (neat): ν˜ ϭ 2960, 2929,
1
2852, 1465, 1429, 1383, 1275, 1102, 979, 855, 728 cmϪ1. H NMR
(400 MHz, CDCl3): δ ϭ 0.85 (t, J ϭ 6.6 Hz, 3 H, CH3), 1.25Ϫ1.42
(m, 8 H, CH2), 1.76Ϫ1.82 (m, 2 H, CH2CHS), 3.14Ϫ3.25 (m, 4 H,
2 ϫ SCH2), 4.44 (t, J ϭ 7.08 Hz, 1 H, SCHS) ppm. C9H18S2
(190.37): calcd. C 56.78, H 9.53, S 33.69; found C 56.49, H 9.46,
S 33.51.
2-[4Ј-(Cyclohexenyloxy)phenyl]-1,3-dithiane (26): 0.266 g, 91%.
White solid; m.p. 103Ϫ104 °C; SiO2-TLC (hexane/ /EtOAc, 99:1),
1
Rf ϭ 0.45. IR (KBr): ν˜ ϭ 2933, 1605, 1509, 1242, 1168 cmϪ1. H
2-[4Ј-(tert-Butyldiphenylsilyloxy)butane]-1,3-dithiane (33): 0.314 g,
NMR (400 MHz, CDCl3): δ ϭ 1.57Ϫ1.65 (m, 2 H, CH2),
1.76Ϫ1.89 (m, 2 H, CH2), 1.91Ϫ2.03 (m, 1 H, SCH2CHaHbCH2S),
2.05Ϫ2.18 (m, 3 H, SCH2CHaHb CH2S and CH2), 2.84Ϫ2.92 (m,
2 H, SCH2), 3.01Ϫ3.15 (m, 2 H, SCH2), 3.54Ϫ3.55(m, 1 H, CHϭ
CHCHO), 5.10 (s, 1 H, ArCH), 5.81 (dd, J ϭ 2.0, J ϭ 10.0 Hz, 1
H, CHϭCHCHO), 6.03Ϫ6.08 (m, 1 H, CH2CHϭCHCHO), 6.87
(d, J ϭ 8.8 Hz, 2 H, ArH), 7.37 (d, J ϭ 8.8 Hz, 2 H, ArH) ppm.
13C NMR (100 MHz, CDCl3): δ ϭ 21.37, 24.93, 25.04, 29.80, 32.24
(2 C), 38.08, 50.94, 116.38, 126.87, 128.95, 129.36, 131.00, 131.18
(2 C), 154.14 ppm. C16H20OS2 (292.47): calcd. C 65.71, H 6.89, S
21.93; found C 65.52, H 6.81, S 21.79.
73%. Colourless liquid; SiO2-TLC (hexane/EtOAc, 95:5), Rf
ϭ
0.70. IR (neat): ν˜ ϭ 3068, 2935, 2863, 1588, 1434, 1260, 1107, 835,
748, 707. 1H NMR (300 MHz, CDCl3): δ ϭ 1.04 [s, 9 H,
SiC(CH3)3], 1.57Ϫ1.59 (m, 2 H, CH2), 1.75Ϫ1.79 (m, 3 H, CH2
and SCH2CHaHbCH2S), 1.83Ϫ1.93 (m, 1 H, SCH2CHaHbCH2S),
2.58Ϫ2.69 (m, 4 H, SCH2 and CH2), 2.71Ϫ2.83 (m, 2 H, SCH2),
3.65 (t, J ϭ 5.8 Hz, 2 H, OCH2), 4.00 (t, J ϭ 7.1 Hz, 1 H, CH),
7.34Ϫ7.42 (m, 5 H, ArH), 7.64Ϫ7.67 (m, 5 H, ArH) ppm.
C24H34OS2Si (430.75): calcd. C 66.92, H 7.96, S 14.89; found C
66.78, H 7.84, S 15.02.
2-[4Ј-Hydroxyphenyl]-1,3-dithiane (28): 0.201 g, 95%; m.p. 158 °C; 2-Ethyl-2-pentyl-1,3-dithiolane (34): 0.177 g, 87%. Colourless
SiO2-TLC (hexane/EtOAc, 9:1), Rf ϭ 0.36. IR (KBr): ν˜ ϭ 3370, liquid; SiO2-TLC (hexane/EtOAc, 19:1), Rf ϭ 0.83. IR (neat): ν˜ ϭ
Eur. J. Org. Chem. 2004, 2002Ϫ2009
www.eurjoc.org
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2007

A. T. Khan, E. Mondal, S. Ghosh, S. Islam
FULL PAPER
2960, 2930, 2853, 1465, 1373, 1276, 1148, 984, 892, 851, 810, 733,
7.6 Hz, PhCOCH2), 2.96 (t, J ϭ 7.3 Hz, 2 H, CH2CHO), 7.46 (t,
692 cmϪ1. H NMR (400 MHz, CDCl3): δ ϭ 0.85 (t, J ϭ 7.0 Hz, J ϭ 7.6 Hz, 2 H, ArH), 7.54Ϫ7.57 (m, 1 H, ArH), 7.95 (d, J ϭ
3 H, CH3), 0.99 (t, J ϭ 7.30 Hz, 3 H, CH3), 1.21Ϫ1.31 (m, 4 H, 8.6 Hz, 2 H, ArH), 9.76 (s, 1 H, CHO) ppm. C14H18O2 (218.29):
CH2), 1.38Ϫ1.46 (m, 2 H, CH2), 1.84Ϫ1.93 (m, 4 H, CH2), 3.21 calcd. C 77.03, H 8.31; found C 77.23, H 8.25.
(br. s, 4 H, SCH2) ppm. 13C NMR (100 MHz, CDCl3): δ ϭ 11.16,
1
Keto Dithioacetal 45: 0.265 g, 90%. Colourless liquid. IR (neat):
14.01, 22.53, 26.58, 31.95, 36.12, 39.37 (2 C), 42.88, 72.41 ppm.
C10H20S2 (204.40): calcd. C 58.76, H 9.86, S 31.38; found C 58.54,
H 9.79, S 31.09.
ν˜ ϭ 2930, 2853, 1685, 1598, 1450, 1368, 1276, 1209, 1102, 1086,
1035, 974, 758 cmϪ1. 1H NMR (400 MHz, CDCl3): δ ϭ 1.18Ϫ1.30
(m, 8 H, CH2), 1.63Ϫ177 (m, 2 H, CH2), 2.77Ϫ2.83 (m, 2 H,
PhCOCH2), 2.87Ϫ2.94 (m, 2 H, SCH2), 3.11Ϫ3.21 (m, 2 H, SCH2),
4.40 (t, J ϭ 7.0 Hz, 1 H, CH2CHS), 7.39 (t, J ϭ 7.6 Hz, 2 H, ArH),
7.48 (t, J ϭ 7.3 Hz, 1 H, ArH), 7.89 (d, J ϭ 7.3 Hz, 2 H, ArH)
ppm. C16H22OS2 (294.48): calcd. C 65.26, H 7.53, S 21.78; found
C 65.01, H 7.45, S 21.58.
1,4-Dithiaspiro[4.4]nonane (37): 0.144 g, 90%. Colourless liquid;
SiO2-TLC (hexane), Rf ϭ 0.92. IR (neat): ν˜ ϭ 2960, 2924, 2878,
1
1449, 1275, 1168, 1101, 978, 851, 692 cmϪ1. H NMR (400 MHz,
CDCl3): δ ϭ 1.74Ϫ1.77 (m, 4 H, CH2), 2.07Ϫ2.14 (m, 4 H, CH2),
3.30 (s, 4 H, 2 ϫ SCH2) ppm. 13C NMR (100 MHz, CDCl3): δ ϭ
24.48 (2 C), 39.37 (2 C), 43.92 (2 C), 70.86 ppm. C7H12S2 (160.30):
calcd. C 52.45, H 7.55, S 40.00; found C 52.12, H 7.50, S 39.85.
General Procedure for Transthioacetalisation: A catalytic amount of
(bromodimethyl)sulfonium bromide (as indicated in Scheme 4) was
added to a mixture of O,O-acetal or O,O-ketal (1 mmol) and dithiol
(1.1 mmol) and the mixture stirred at room temperature. After
completion of the reaction, it was neutralised by addition of two
drops of saturated NaHCO3 solution. Then, the reaction mixture
was purified through a silica gel column to get the required di-
thioacetal.
1,4-Dithiaspiro[5.5]decane (38): 0.175 g, 93%. Colourless Liquid;
SiO2-TLC (hexane/ethyl acetate, 99:1); Rf ϭ 0.75. IR (neat): ν˜ ϭ
1
2930, 2853, 1440, 1265, 1127, 1015, 907, 861, 764 cmϪ1. H NMR
(400 MHz, CDCl3): δ ϭ 1.43Ϫ1.49 (m, 2 H, CH2), 1.60Ϫ1.67 (m,
4 H, CH2), 1.96Ϫ2.02 (m, 6 H, SCH2CH2CH2S and 2 ϫ CH2),
2.79Ϫ2.83 (m, 4 H, 2 ϫ SCH2) ppm. 13C NMR (100 MHz, CDCl3):
δ ϭ 21.97 (2 C), 25.79 (2 C), 25.87, 26.12, 37.86 (2 C), 50.32 ppm.
C9H16S2 (188.36): calcd. C 57.39, H 8.56, S 34.05; found C 57.14,
H 8.50, S 34.23.
2-[4Ј-Nitrophenyl]-1,3-dithiolane (46): 0.204 g, 90%; yellow low
melting solid; SiO2-TLC (hexane/EtOAc, 9:1), Rf ϭ 0.85. IR (neat):
ν˜ ϭ 2930, 2853, 1603, 1521, 1424, 1352, 1317, 1291, 1245, 1112,
1
1015, 984, 876, 830, 784 cmϪ1. H NMR (300 MHz, CDCl3): δ ϭ
1,4-Dithiaspiro[4.6]undecane (39): 0.156 g, 83%. White solid; m.p.
56 °C; SiO2-TLC (hexane); Rf ϭ 0.75. IR (KBr): ν˜ ϭ 2919, 2842,
3.37Ϫ3.43 (m, 2 H, SCH2), 3.45Ϫ3.55 (m, 2 H, SCH2), 5.65 (s, 1
H, ArCH), 7.66 (d, J ϭ 8.6 Hz, 2 H, ArH), 8.17 (d, J ϭ 8.7 Hz, 2
H, ArH) ppm. C9H9NO2S2 (227.31): calcd. C 47.56, H, 3.99, N
6.16, S 28.21; found C 47.29, H 3.95, N 6.01, S 28.01.
1
1460, 1424, 1275, 1244, 1234, 1152, 1101, 963, 846, 692 cmϪ1. H
NMR (400 MHz, CDCl3): δ ϭ 1.57 (m, 8 H, CH2), 2.17Ϫ2.19 (m,
4 H, CH2), 3.26 (s, 4 H, SCH2) ppm. 13C NMR (100 MHz, CDCl3):
δ ϭ 25.62 (2 C), 28.55 (2 C), 38.84 (2 C), 46.11 (2 C), 71.88 ppm.
C9H16S2 (188.36): calcd. C 57.39, H 8.56, S 34.05; found C 57.18,
H 8.48, S 33.87.
2-Methyl-2-phenyl-1,3-dithiolane (47): 0.176 g, 90%; gummy liquid;
SiO2-TLC (hexane/EtOAc, 9.9:0.1), Rf ϭ 0.9. IR (neat): ν˜ ϭ 2971,
2935, 1598, 1491, 1445, 1276, 1071, 1030, 774, 702 cmϪ1. 1H NMR
(400 MHz, CDCl3): δ ϭ 2.14 (s, 3 H, CH3), 3.31Ϫ3.47 (m, 4 H, 2
ϫ SCH2), 7.19Ϫ7.23 (m, 1 H, ArH), 7.28Ϫ7.32 (m, 2 H, ArH);
7.72Ϫ7.75 (m, 2 H, ArH) ppm. 13C NMR (100 MHz, CDCl3): δ ϭ
33.81, 40.22 (2 C), 68.52, 126.68 (2 C), 126.99, 127.90 (2 C),
145.82 ppm. C10H12S2 (196.34): calcd. C 61.17, H 6.16, S 32.66;
found C 61.01, H 6.09, S 32.43.
1,4-Dithiaspiro[4.11]hexadecane (40): 0.232 g, 90%. White solid;
m.p. 88 °C; SiO2-TLC (hexane); Rf ϭ 0.81. IR (KBr): ν˜ ϭ 2955,
1
2858, 1470, 1440, 1045, 799, 738, 687 cmϪ1. H NMR (400 MHz,
CDCl3): δ ϭ 1.18Ϫ1.51 (m, 18 H, CH2), 1.95 (dd, J ϭ 7.6, J ϭ
8.3 Hz, 4 H, CH2), 3.22 (s, 4 H, SCH2) ppm. C14H26S2 (258.49):
calcd. C 65.05, H 10.14, S 24.81; found C 65.30, H 10.06, S 24.63.
1,3-Dithiolanes 41 of cis-Bicyclo[3.3.0]octane-3,7-dione: 0.266 g,
92%. White solid; m.p. 176Ϫ177 °C; SiO2-TLC (hexane); Rf ϭ 0.62.
Acknowledgments
1
IR (KBr): ν˜ ϭ 2957, 2920, 2843, 1426, 1275, 1210, 974 cmϪ1. H
A. T. K. acknowledges to the Department of Science and Technol-
ogy (DST), New Delhi for a research grant (Grant No. SP/S1/G-
35/98). E. M. is thankful to the CSIR for a Senior Research Fellow-
ship and S. G is grateful to IITG for his research fellowship. We
are also grateful to the Head of the Department of Chemistry for
giving permission to Samimul Islam to work as a guest researcher
and to the Director, IITG for general facilities to carry out our
research work. We are also very grateful for the referees’ valuable
comments and suggestions.
NMR (400 MHz, CDCl3): δ ϭ 2.05 (dd, J ϭ 7.1, J ϭ 13.2 Hz, 4
H, CH2), 2.37Ϫ2.40 (dd, J ϭ 7.1, J ϭ 13.2 Hz, 4 H, CH2),
2.79Ϫ2.87 (m, 2 H, CH2), 3.26Ϫ3.34 (m, 8 H, SCH2) ppm.
C12H18S4 (290.54): calcd. C 49.61, H 6.24, S 44.15; found C 49.43,
H 6.18, S, 44.10.
2-[4Ј-Methoxyphenyl]-1,3-dithiolane (43): 20.14 g, 95%. White solid;
m.p. 65 °C; SiO2-TLC (hexane/EtOAc, 95:5), Rf ϭ 0.88. IR (KBr):
Ϫ1
.
1H NMR (400 MHz,
˜
ν ϭ 1608, 1520, 1256, 1180, 1028 cm
CDCl3): δ ϭ 3.28Ϫ3.35 (m, 2 H, SCH2), 3.44Ϫ3.51 (m, 2 H,
SCH2), 3.77 (s, 3 H, OCH3), 5.62 (S, 1 H, ArCH), 6.83 (d, J ϭ
8.56 Hz, 2 H, ArH), 7.44 (d, J ϭ 8.76 Hz, 2 H, ArH) ppm. 13C
NMR (100 MHz, CDCl3): δ ϭ 40.02 (2 C), 55.19, 55.94, 113.74 (2
C), 129.04 (2 C), 131.69, 159.25 ppm. C10H12OS2 (212.33): calcd.
C 56.57, H 5.70, S 30.20; found C 56.70, H 5.58, S 30.35.
[1]
T. W. Greene, P. G. M. Wuts, Protective Groups in Organic Syn-
thesis, 3rd ed., John Wiley & Sons, Inc., New York, 1999,
pp.307Ϫ312.
T. W. Greene, P. G. M. Wuts, Protective Groups in Organic Syn-
thesis, 3rd ed., John Wiley & ons, Inc., New York, 1999,
[2]
pp.329Ϫ344.
[3] [3a]
[3b]
S. D. Rychnovsky, Chem. Rev. 1995, 95, 2021Ϫ2040.
A.
Keto Aldehyde 44: Colourless liquid. IR (neat): ν˜ ϭ 2930, 2853,
B. III Smith, S. M. Condon, J. A. McCauley, Acc. Chem. Res.
1998, 31, 35Ϫ46.
1726, 1685, 1598, 1450, 1409, 1363, 1276, 1214, 1178, 1076, 1009,
1
753 cmϪ1. H NMR (400 MHz, CDCl3): δ ϭ 1.26Ϫ1.33 (m, 6 H,
[4]
[4a] D. Seebach, Angew. Chem. Int. Ed. Engl. 1969, 8, 639Ϫ649.
[4b]
[4c]
CH2), 1.69Ϫ177 (m, 2 H, CH2), 2.42 (ddd, 2 H, J ϭ 2.0, J ϭ
B. T. Grobel, D. Seebach, Synthesis 1977, 357Ϫ402.
P.
2008
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org Eur. J. Org. Chem. 2004, 2002Ϫ2009

Acetalisation of Carbonyl Compounds under Solvent-Free Conditions
FULL PAPER
J. H. Clark, Chemistry of Minimisation, Chapman and Hall,
London, 1995.
[15]
C. Bulman Page, M. B. van Niel, J. C. Prodger, Tetrahedron
1989, 45, 7643Ϫ7677. [4d] G. R. Pettit, E. E. van Tamelen, Org.
React. 1962, 12, 356.
[16] [16a]
[16b]
E. Mondal, G. Bose, A. T. Khan, Synlett 2001, 785Ϫ786.
E. Mondal, G. Bose, P. R. Sahu, A. T. Khan, Chem. Lett.
[5]
M. Yus, C. Najera, F. Foubelo, Tetrahedron 2003, 59,
[16c]
6147Ϫ6212.
2001, 1158Ϫ1159.
A. T. Khan, J. Boruwa, E. Mondal, G.
[6] [6a]
[16d]
V. A. Keller, J. R. Martinelli, E. R. Strieter, S. D. Burke,
Bose, Indian J. Chem. Sec B 2001, 40B, 1039Ϫ1042.
E.
[6b]
Org. Lett. 2002, 4, 467Ϫ470.
P. Wipf, J. T. Reeves, Chem.
Mondal, P. R. Sahu, G. Bose, A. T. Khan, Tetrahedron Lett.
2002, 43, 2843Ϫ2846. [16e] E. Mondal, P. R. Sahu, A. T. Khan,
Synlett 2002, 463Ϫ467. [16f] A. T. Khan, E. Mondal, P. R. Sahu,
Synlett 2003, 377Ϫ381.
[17] [17a]
Commun. 2002, 2066Ϫ2067.
[7] [7a]
[7b]
S. A. Patwardhan, S. Dev, Synthesis 1974, 348Ϫ349.
H.
Firuouzabadi, N. Iranpoor, B. Karimi, Synlett 1999, 321Ϫ323.
[7c]
B. Karimi, A. M. Ashtiani, Chem. Lett. 1999, 1199Ϫ1200.
B. Karimi, G. R. Ebrahimian, H. Seradj, Org. Lett. 1999,
N. Furukawa, T. Inoue, T. Aida, S. Oae, J. Chem. Soc.,
[7d]
Chem. Commun. 1973, 212. [17b] Y. L. Chow, B. H. Bakker, Can.
1, 1737Ϫ1739. [7e] K. Ishihara, Y. Karumi, M. Kubota, H. Ya-
mamoto, Synlett 1996, 839Ϫ841. [7f] R. Gopinath, S. J. Haque,
B. K. Patel, J. Org. Chem. 2002, 67, 5842Ϫ5846.
H. Firouzabadi, N. Iranpoor, B. Karimi, Synthesis 1999,
58Ϫ60.
J. Chem. 1982, 60, 2268.
G. A. Olah, M. Arvanaghi, Y. D.
[17c]
Vankar, Synthesis 1979, 721. [17d] G. A. Olah, Y. D. Vankar, M.
Arvanaghi, G. K. Suraya Prakash, Synthesis 1979, 720Ϫ721.
A. T. Khan, E. Mondal, B. M. Borah, S. Ghosh, Eur. J. Org.
Chem. 2003, 4113Ϫ4117.
[8]
[9]
[18]
[19] [19a]
J. S. Yadav, B. V. S. Reddy, S. K. Pandey, Synlett 2001,
238Ϫ239.
S. Mathuswamy, S. Arulananda Babu, C. Gunanathan, Tetra-
hedron Lett. 2001, 42, 359Ϫ362.
S. Samajdar, M. K. Basu, F. F. Becker, B. K. Banik, Tetra-
hedron Lett. 2001, 42, 4425Ϫ4427.
A. Kamal, G. Chouhan, Synlett 2002, 474Ϫ476.
A. Kamal, G. Chouhan, Tetrahedron Lett. 2002, 43,
1347Ϫ1350.
S.-B. Lee, S.-D. Lee, T. Takata, T. Endo, Synthesis 1991,
[19b]
368Ϫ370.
6756Ϫ6765.
son, J. M. Wetzel, J. Org. Chem. 1987, 52, 188Ϫ191.
B. Bartels, R. Hunter, J. Org. Chem. 1993, 58,
[10]
[11]
[19c]
J. R. Hwu, L. Leu, J. A. Robl, D. A. Ander-
[19d]
D.
S. Torok, J. J. Figueroa, W. J. Scott, J. Org. Chem. 1993, 58,
7274Ϫ7276. [19e] H. Sakurai, K. Sasaki, J. Hayashi, A. Hosomi,
J. Org. Chem. 1984, 49, 2808Ϫ2809.
[12]
[13]
[20] [20a]
[20b]
B. S. Ong, Tetrahedron Lett. 1980, 21, 4225Ϫ4228.
H.
Firouzabadi, N. Iranpoor, H. Hazarkhani, J. Org. Chem. 2001,
[14]
A. T. Khan, E. Mondal, P. R. Sahu, S. Islam, Tetrahedron Lett.
2003, 44, 919Ϫ922.
66, 7527Ϫ7529.
Received October 29, 2003
Eur. J. Org. Chem. 2004, 2002Ϫ2009
www.eurjoc.org
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2009