A general alternative to obtain S.S-acetals using taff, a bentonitic clay, as the catalyst

Article abstract of DOI:10.1081/SCC-100104073

A one-pot general alternative to prepare dithioacetals, with excellent yields, via the condensation of 1,3-propanedithiol, benzyl, and n-butyl mercapthanes with several carbonylic compounds using a bentonitic earth as the catalyst is proposed. Also, the a

Full text of DOI:10.1081/SCC-100104073

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A GENERAL ALTERNATIVE TO
OBTAIN S.S-ACETALS USING
TAFF, A BENTONITIC CLAY, AS
THE CATALYST*
René Miranda a , Roberto Osnaya a , Raymundo
Garduñ a , Francisco Delgado b , Cecilio Álvarez c
& Manuel Salmon c
a Universidad Nacional Autónoma de México ,
Av. Primero de Mayo s/n, Cuautitlán Izcalli, C.P,
Estado de México, 54740, México
b Instituto Politécnico Nacional , Departamento de
Quámica Orgánica, Escuela Nacional de Ciencias
Biológicas, Prolongación Carpio y Plan de Ayala,
Casco de Santo Tomás, México D.F., C.P., 11340
c Instituto de Química, Universidad Nacional
Autónoma de México , Circuito Exterior, Ciudad
Universitaria, Coyoacán D.F., C.P., 04510, México
Published online: 02 Aug 2010.
To cite this article: René Miranda , Roberto Osnaya , Raymundo Garduñ , Francisco
Delgado , Cecilio Álvarez & Manuel Salmon (2001) A GENERAL ALTERNATIVE TO
OBTAIN S.S-ACETALS USING TAFF, A BENTONITIC CLAY, AS THE CATALYST* , Synthetic
Communications: An International Journal for Rapid Communication of Synthetic
Organic Chemistry, 31:10, 1587-1597, DOI: 10.1081/SCC-100104073

To link to this article: http://dx.doi.org/10.1081/SCC-100104073
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SYNTHETIC COMMUNICATIONS, 31(10), 1587–1597 (2001)
A GENERAL ALTERNATIVE TO OBTAIN
S.S-ACETALS USING TAFF, A BENTONITIC
CLAY, AS THE CATALYST*
y
Rene Miranda,1, Roberto Osnaya,1 Raymundo Garduno,1
Francisco Delgado,2 Cecilio Alvarez,3
and Manuel Salmon3
1Departamento de Ciencias Quımicas, Facultad de
Estudios Superiores Cuautitlan, Universidad Nacional
Autonoma de Mexico.Av.Primero de Mayo s/n,
Cuautitlan Izcalli C.P. 54740, Estado de Mexico, Mexico
2Departamento de Quımica Organica, Escuela Nacional de
Ciencias Biologicas, Instituto Politecnico Nacional,
Prolongacion Carpio y Plan de Ayala, Casco de
Santo Tomas, Mexico D.F., C.P. 11340
3Instituto de Quımica, Universidad Nacional Autonoma de
Mexico, Circuito Exterior, Ciudad Universitaria,
Coyoacan D.F., C.P. 04510, Mexico
ABSTRACT
A one-pot general alternative to prepare dithioacetals, with
excellent yields, via the condensation of 1,3-propanedithiol,
benzyl, and n-butyl mercapthanes with several carbonylic
compounds using a bentonitic earth as the catalyst
is proposed.Also, the acidic role of the clay in the reaction
* To the memory of Professor Alvaro Leo Ramırez.
y Corresponding author.Fax: 00 52 5623 2056; E-mail: rgmonroy@servidor.
unam.mx
1587
Copyright & 2001 by Marcel Dekker, Inc.
www.dekker.com

1588
MIRANDA ET AL.
is discussed.The product structures were established by 1H
and 13C NMR, as well as by the corresponding EIMS and
HRMS data.
INTRODUCTION
The hydrolytic stability of dithioacetals and the highly specific con-
ditions used for their removal from masked carbonyls have afforded invalu-
able applications in synthesis.1 In this sense, there are important strategic
reasons why cyclic S.S-acetals in general, and 1,3-dithianes in particular
attracted the attention of synthetic chemists.2 For instance, the above
class of compounds is easily metallated with alkyllithium solutions, and
the resulting carbanions employed as effective nucleophiles in C-C bond-
forming reactions.In addition to its role in the synthon and umpolung
concepts,3,4 another interesting fact for some 1,3-dithianes is the presence
of the anomeric effect.5,6
The standard procedures to prepare 1,3-dithianes involves the Lewis
or Bronsted acid-catalyzed derivatization of carbonylic substrates or their
corresponding O.O-acetals with 1,3-propane dithiols;7 also, the reaction of
1,3-propanedithiol with gem-diiodo alkanes affords the access to 1,3-dithia-
cyclohexanes.8 However, the literature reports provide scarce information
for this purpose using montmorillonites.15
Related to our research program16–18 on the use of TAFF, a commer-
cial bentonitic clay,19 as the catalyst or support of inorganic molecules, we
have also provided in some cases alternatives to produce heterocyclic com-
pounds.16 Thus, using this clay, the aim of this work deals with the results of
a set of experiments performed to achieve a general alternative for the
catalytic heterogeneous preparation of S.S-acetals.
RESULTS AND DISCUSSION
Chemical
The results of a set of reactions performed with 1,3-propanedithiol and
various aldehydes and ketones using TAFF as catalyst are summarized
in Table 1.As it can be seen, this material is a convenient catalyst for the
synthesis of useful thio-organic molecules like the 1,3-dithianes 1–11 and
several acyclic dithioacetals as 12–15 (Scheme 1).These results also
demonstrated that the reaction is applicable to aromatic and aliphatic alde-
hydes and ketones, as well as aliphatic enones.In general, the condensation

S.S-ACETALS
1589
Table 1. 2-Substituted-1,3-dithianes Obtained Using TAFF as the Cayalyst
Yield
(%)a
Melting or boiling
point (ꢀC)b
Mol.weight/
Elemental composition
Time
(h)
Compound
1
90
95
95
90
60
90
60
95
90
90
95
68–69
(70–71)7,10,13,15
196.0380c 196.0380d
C10H12S2
3
3
3
3
3
3
3
5
5
5
5
2
3
81–82
(84–85)15
C10H11S2Cl
142–143
(140–142)10
241.0235c 241.0231d
C10H11O2NS2
241.0226c 241.0231d
C10H11O2NS2
226.0292c 226.0486d
C11H14OS2
240.0293c 240.0279d
C11H12O2S2
240.1002c 240.1006d
C13H20S2
228.0451c 228.0443d
C11H13FS2
240.0641c 240.0643d
C12H16OS2
272.0720c 272.0693d
C16H16S2
4
122–124
(123–125)10
5
123–125
(127–128)10–13
6
85–86
(84–86)14
Oile
(bp 110/100 mm Hg)
7
8
50–51e
9
Oile
(bp 90/110 mm Hg)
10
11
Oil
(bp 110/110 mm Hg)9
Oil11
162.0546c 162.0537d
C7H14S2
b
c
d
e
aIsolated pure products; uncorrected; observed (HR); estimated; new products.
of thiols with carbonylic substrates was completed in short reaction times
with very good yields in refluxing toluene.In addition, it is relevant to note
several reaction advantages of this catalytic method over other reported
procedures.It can be prepared without azeotropic separation of water, in
general pure compounds are obtained, the work-up is easy, mild, and
remarkably inexpensive.23 Recourse to a natural, environment-friendly
clay offers a valuable alternative to the numerous efficient catalytic systems
that have already been proposed for this type of reaction (Vide supra).
Moreover, the generality of this alternative is well-documented by
the various examples (1–15) presented in this paper, together with those
previously reported by us for several dithiolanes.17 Furthermore, as it was
previously mentioned, there is scant information about the employment of a

1590
MIRANDA ET AL.
8
6
2
1
S
6
9
2´
5
R
3´
4
1´
6´
S
4
5
7
2
3
3
1
S
4´
10
15
5´
R
S
11
14
1
2
3
4
5
H
4-Cl
4-NO2
2-NO2
2-OMe
12
13
7
O
6
3,4-CH2
O
R
2
6
1
S
R´
4
S
5
3
R
R´
Me
Me
φ
Et
8
9
10
4-Fφ
4-MeOφ
φ
11 Me
Φ
S
5´
2´
S
6´
3´
4´
Φ
6
3
1´
S
1
5
S
R
4
2
R
R
R
14 4-Cl
12 4-Cl
O
15 3,4-CH2
O
O
O
13
3,4-CH2
Scheme 1.
montmorillonitic material to obtain S.S-acetals; in this sense, only the KSF
montmorillonite from Sud Chemie has been employed16 for such purposes.
However, it is worth mentioning that only one-seventh of the amount of
TAFF is required, compared to the amount of KSF.This must be due to the
great difference of surface properties between both catalysts (Table 2).From

S.S-ACETALS
Table 2. Comparative Surface Properties of Montmorillonitic Catalysts
1591
Catalyst
S (cm2/g)
Pv (cm2/g)
Dp (A)
pH
L
BL
TAFF19
KSF21
198.7
9.0
0.032
0.011
77.8
50
3
1.5
2.52
0.59
0.25
2.35
S specific surface area; Pv pore volume; Dp average pore diameter; pH in suspension
(10% in water); L and BL Lewis and Bronsted acidity corresponding to the relative
intensities of the infrared bands of adsorbed pyridine at 393ꢀK.
the mechanistic point of view, the catalytic action of TAFF should enhance
the electrophylic character of the carbonylic substrates, facilitating the
nucleophilic action of the thiol; this might be due to the protonated and
unprotonated active sites corresponding to the acidic Bronsted and Lewis
character of the clay (Scheme 2).
TAFF
Si
BL
TAFF
Al
L
O
O
H
O
Scheme 2. Enhancement of the elctrophylic character of a carbonylic substrate by
means of TAFF: L as a Lewis and BL as acidic Bronsted-Lowry catalyst.
Characterization
For the structural attribution of the heterocyclic molecules, first, we
envisaged by mass spectrometry that the high-resolution data of the mol-
ecular radical ions were in agreement with the exact molecular weights.
This information is important since the mass measurement of an ion
with sufficient accuracy provides an unequivocal identification of its ele-
mental composition.In addition, the respective dithiane mass spectra
showed analogous fragments, suggesting
a common fragmentation
pattern: [M-33]þ, [M-43]þ, [M-65]þ, [M-74]þ, [M-75-H]þ, [M-75-15]þ and
C3H6Sþ.
When the corresponding nuclear magnetic resonance data was analy-
zed for the monosubstituted compounds (1–7), the 1,3-dithiane moieties
became evident, since these S.S cyclic acetals showed analogous coupl-
ing patterns on 1H NMR: dtt 1.81–1.99 ppm Ha-5, dtt 1.99–2.22 ppm

1592
MIRANDA ET AL.
He-5, ddd 2.7–2.9 He 4-6, and ddd 2.9–3.15 Ha-4,6 with coupling constant
values of J4a/4e ꢁ J5a/5e ꢁ 13–14 Hz; J4a/5a ¼ 10–12 Hz; J4a/5e ꢁ J4e/5a
¼
2.6–3.4 Hz; J4e,5e¼4–6 Hz.In addition, these monosubstituted molecules
showed anancomeric structures with H-2 in axial configuration, as demon-
strated by a set of NOE-differential experiments.However, the correspond-
ing disubstituted compounds (8–11) are in a dynamic equilibrium, as
1
detected by H NMR (Ha-4,6 collapsed with He-4,5 and Ha-5 with He-5).
In general, the corresponding chemical shifts acquired by 13C NMR were in
agreement with the heterocyclic frame, showing signals between 22.59–26.2
and 26.05–33.5 corresponding to C-5 and C-4, 6; the C-2 signals appear
between 30.58 and 46.95 ppm.
In addition to the NMR and MS data of the new molecules, semi-
empirical electronic structure calculations were carried out to obtain a more
detailed characterization, thus the minimum energy conformations of
compounds, 7, 8, and 9 were achieved (Scheme 3) and compared with the
1H NMR experimental results, obtaining good fitness.The computations
were done using the Austin Method (AM1) parameterization,22 which has
Scheme 3. Stereostructures of new 2-substituted-1,3-ditianes: myrthenyl (7);
methy, p-fluorophenyl (8); methyl, p-methoxyphenyl (9).

S.S-ACETALS
1593
been previously reported to be good in order to obtain minimum energy
conformations.
EXPERIMENTAL
General Features
Toluene (Aldrich) was dried prior to use (Na0/benzophenone).The
carbonylic substrates and the mercaptanes employed were also purchased
from Aldrich and used as received.The catalytic material was obtained from
Tonsil Mexicana and analyzed prior to use with a Siemens D-5000 X-ray
difractometer using the Cu Ka1 radiation.Purified products were character-
1
ized by spectroscopic means. H NMR spectra were recorded in a Varian
Gemini-300 spectrometer using CDCl3 as solvent and TMS as internal
reference; EIMS (70 ev) spectra and the HRMS data were obtained using
JEOL MS AX 505 HA and MS-SM 102 mass spectrometers.Thin layer
chromatographic analyses were performed using Merck precoated plates
(silica gel 60 F254, 0.25 mm); for the corresponding column chromato-
graphies (flash) silica gel Merck 230–400 mesh was employed.The melting
points were determinated in a Fisher-Johns apparatus and are uncorrected.
General Procedure
3,4-Methylene dioxybenzaldehyde (350 mg, 2.3 mmol), 5 mmol of
benzylmercaptane or n-BuSH or 2.5 mmol of 1,3-propanedithiol were dis-
solved with 20 mL of anhydrous toluene and refluxed (105ꢀC/585 mm Hg) in
the presence of 250 mg of TAFF during 3 h.The reactions were monitored
by TLC (n-hexane/EtOAc 7:3; CeSO4 1% 2N H2SO4), the reaction mixtures
were filtered over celite and the resulting solutions washed with NaOH
10% (3 Â 20 mL) then water (3 Â 20 mL) and dried (Na2SO4).Finally, the
solvent was removed under vacuum and the residue, if necessary (TLC), was
purified by column chromatography.
Spectroscopic and physical data of pure isolated products
Compound 1.Yield 90%; mp.:. 68 ꢀ–69ꢀC; MW [elemental composi-
tion]: 196.038a/196.0380b [C10H12S2]; EIMS m/z (ra %): 196 (100) [M]þ, 163
(5) [M-33]þ, 153 (12) [M-43]þ, 131 (36) [M-65]þ, 122 (83) [M-74]þ; 1H NMR:
7.49–7.25 (m, 5H, Ar-H), 5.19 (s, 1H, H-2), 3.07 (ddd, 2H, Ha-4, 6), 2.92

1594
MIRANDA ET AL.
(ddd, 2H, He-4, 6), 2.2 (dtt, 1H, He-5), 1.95 (dtt, 1H, Ha-5); 13C NMR: 25.05
(C-5), 32.04 (C-4, 6), 51.41 (C-2), 127.69 (C-20, 60), 128.38 (C-30, 50), 128.67
(C-40), 139.05 (C-10).
Compound 2. Yield 95%; m.p.: 81ꢀ–82ꢀC; MW [elemental composi-
tion] [C10H11S2Cl]; EIMS m/z (ra %): 232 (40) [Mþ2]þ, 230(100) Mþ, 197
(5) [M-33]þ, 187 (7) [M-43]þ, 165 (22) [M-65]þ, 156 (71) [M-74]þ; 1H NMR:
7.49–7.30 (AA0BB0, 4H, Ar-H), 5.18 (s, 1H, H-2), 3.06 (ddd, 2H, Ha-4, 6),
2.93 (ddd, 2H, He-4, 6), 2.19 (dtt, 1H, He-5), 1.95 (dtt, 1H, Ha-5).
Compound 3. Yield 95%; m.p.: 142ꢀ–143ꢀC; MW [elemental composi-
tion]: 241.0235a/241.0231b [C10H11O2NS2]; EIMS m/z (ra %): 241 (100)
[M]þ, 208 (3) [M-33]þ, 176 (12) [M-65]þ, 167 (12) [M-74]þ; 1H NMR:
7.95 (AA0BB0, 4H, Ar-H), 5.26 (s, 1H, H-2), 3.08 (ddd, 2H, Ha-4, 6), 2.96
(ddd, 2H, He-4, 6), 2.21 (dtt, 1H, He-5), 1.95 (dtt, 1H, Ha-5); 13C NMR: 26.01
(C-5), 32.51 (C-4, 6), 51.90 (C-2), 125.60 (C-20, 60), 132.00 (C-30, 50), 147.15
(C-10), 147.50 (C-40).
Compound 4. Yield 90%; m.p.: 122ꢀ–124ꢀC; MW [elemental composi-
tion]: 241.0226a/241.0231b [C10H11O2NS2]; EIMS m/z (ra %) 241 (22) [M]þ,
167 (12) [M-74]þ, 167 (12) [M-74]þ, 166 (42) [M-74-H]þ, 106 (100)
[C3H6S2]þ; H NMR: 7.95 (dd, 1H, Jo, m, H-30), 7.90 (dd, 1H, Jo, m, H-60),
1
7.65 (ddd, 1H, Jo, m, H-50), 7.45 (ddd, Jo, m, H-40), 5.91 (s, 1H, H-2), 3.11
(ddd, 2H, Ha-4, 6), 2.92 (ddd, 2H, He-4, 6), 2.22 (dtt, 1H, He-5), 1.97 (dtt,
1H, Ha-5); 13C NMR: 24.40 (C-5), 32.50 (C-4, 6), 45.90 (C-2), 122.90 (C-40),
128.90 (C-50), 132.81 (C-60), 134.20 (C-30), 148.32 (C-10), 148.48 (C-20).
a
Compound 5.Yield 60%; oil; MW [elemental composition]: 226.0292
/
226.0486b [C11H14OS2]; EIMS m/z (ra %): 226 (100) [M]þ, 193 (5) [M-33]þ,
161 (6) [M-65]þ, 152 (51) [M-74]þ; H NMR: 7.61 (dd, 1H, Jo, m, H-60),
1
7.27 (ddd, 1H, Jo, o, m, H-40), 6.98 (ddd, 1H, Jo, o, m, H-50), 6.89 (dd, 1H, Jo, m
,
H-30), 5.72 (s, 1H, H-2), 3.88 (s, 3H, OMe), 3.10 (ddd, 2H, Ha-4, 6); 2.89
(ddd, 2H, He-4, 6), 2.21 (dtt, 1H, He-5), 1.98 (dtt, 1H, Ha-5); 13C NMR:
26.15 (C-5), 33.01 (C-4, 6), 44.15 (C-2), 56.45 (-OMe), 110.62 (C-30), 121.85
(C-50), 127.95 (C-20), 129.85 (C-60), 131.2 (C-40), 156.15 (C-10).
Compound 6. Yield 90%; m.p.: 85ꢀ–86ꢀC; MW [elemental composi-
tion]: 240.0293a/240.0279b [C11H12O2S2]; EIMS m/z (ra %): 240 (90) [M]þ,
207 (3) [M-33]þ, 197 (5) [M-43]þ, 175 (8) [M-65]þ, 166 (100) [M-74]þ;
1H NMR: 6.95 (dd, 1H, Jo, m, H-60), 6.91 (d, 1H, Jm, H-20), 6.74 (d, 1H,
Jo, H-50), 5.93 (s, 2H, CH2O2), 5.07 (s, 1H, H-2), 3.15 (ddd, 2H, Ha-4, 6);
2.91 (ddd, 2H, He-4, 6), 2.19 (dtt, 1H, He-5), 1.92 (dtt, 1H, Ha-5); 13C NMR:
25.05 (C-5), 32.16 (C-4, 6), 51.17 (C-2), 101.25 (-CH2O2), 108.38 (C-20, 50),
121.32 (C-60), 132.81 (C-30, 40), 147.95 (C-10).
a
Compound 7.Yield 60%; oil; MW [elemental composition]: 240.1002
/
240.1006b [C13H20S2]; EIMS m/z (ra %): 225 (4) [M-15]þ, 207 (3) [M-33]þ,
197 (46) [M-43]þ, 166 (11) [M-74]þ, 165 (62) [M-74-H]þ; 1H NMR: 5.71 (m,

S.S-ACETALS
1595
1H, H-3), 4.62 (s, 1H, H-10), 2.92 (m, 4H, H-12, 14), 2.41 (m, 1H, H-1), 2.31
(m, 1H, He-7), 2.11 (m, 3H, H-5, 13), 1.84 (m, 2H, H-4), 1.32 (s, 3H, Me-9),
1.20 (d, 1H, Ha-7, J¼10 Hz); 0.89 (s, 3H, Me-8); 13C NMR: 144.72 (C-
2), 121.06 (C-3), 52.03 (C-10), 44.80 (C-1), 40.31 (C-5), 37.95 (C-4), 31.61
(C-6), 31.03 (C-7), 30.62 (C-12, 14), 27.07 (C-9), 25.81 (C-13), 21.30 (C-8).
Compound 8. Yield 95%; m.p.: 50ꢀ–51ꢀC MW [elemental composi-
tion]: 228.0451a/228.0443b [C11H13FS2]; EIMS m/z (ra %): 228 (67) [M]þ,
213 (7) [M-15]þ, 195 (8) [M-33]þ, 185 (5) [M-43]þ, 154 (100) [M-74]þ,
139(96) [M-74-15]þ; H NMR: 7.99–7.15 (AA0BB0, 4H, Ar-H), 2.69 (m,
1
4H, H-4, 6), 1.92 (m, 2H, H-5), 1.76 (s, 3H, Me); 13C NMR: 24.56 (C-5),
28.04 (C-4, 6), 32.79 (Me), 53.28 (C-2), 115.14 (C-20, 60; J ¼ 20.8 Hz), 129.65
(C-30, 50; J ¼ 7.7 Hz), 139.55 (C-10), 161.17 (C-40; J ¼ 248.8 Hz).
a
/
Compound 9.Yield 90%; oil; MW [elemental composition]: 240.0641
240.0643b [C12H16OS2]; EIMS m/z (ra %): 240(81) [M]þ, 225(11)[M-15]þ,
207 (15)[M-33]þ, 197 (3) [M-43]þ, 166(100) [M-74]þ, 151(75) [M-74-15]þ; 1H
NMR: 7.80–6.32 (AA0BB0, 4H, Ar-H), 3.75 (s, 3H, OMe), 2.65 (m, 4H, H-4,
6), 1.87 (m, 2H, H-5), 1.76 (s, 3H, C2-Me); 13C NMR: 22.59 (C-5), 24.51
(C-4, 6), 27.88 (C2-Me), 53.14 (C-2), 54.99 (OMe), 113.46 (C-30, 50), 128.75
(C-20, 60), 135.49 (C-10), 158.30 (C-40).
Compound 10.Yield 90%; oil; bp. 110 ꢀC; MW [elemental composi-
tion]:272.0720a/272.0693b [C16H16S2];EIMSm/z(ra %):272(46)[M]þ,229(3)
[M-43]þ, 211 (8) [M-61]þ, 198 (100) [M-74]þ, 165 (95), 121 (45) [M-74-77]þ;
1H NMR: 7.90–7.15 (m, 10H, Ar-H), 2.78 (m, 4H, H-4, 6), 1.99 (m, 2H, H-
5); 13C NMR: 24.34 (C-5), 29.23 (C-4, 6), 62.65 (C-2), 127.41–129.18 (Ar).
Compound 11.Yield 95%; oil; MW [elemental composition]:
162.0546a/162.0537b [C7H14S2]; EIMS m/z (ra %): 163(7) [MþH]þ, 147(7)
[M-15]þ, 133 (3) [M-29]þ, 119 (3) [M-43]þ, 106 (100) [C3H6S2]þ 1H NMR:
2.70 (m, 4H, H-4, 6), 1.81 (m, 4H, H-5 and CH2Me), 1.45 (s, 3H, C2-Me),
0.89 (t, 3H, CH2Me); 13C NMR: 8.74 (CH2Me), 25.04 (C-5), 26.06 (CH2-
Me), 26.82 (C2-Me), 33.92 (C-4, 6).
Compound 12.Yield 75%; oil; EIMS m/z (ra %): 304 (03.) [M þ2]þ,
302 (1) [M]þ, 247 [Mþ2-57]þ, 245 [M-57]þ, 215 (33) [Mþ2-SBu]þ, 213 (100)
[M-SꢂBu]þ, 157 (24) [C7H5SCl]þ; 1H NMR: 7.45–7.20 (AA0BB0, 4H, Ar-H),
4.82 (s, 1H, CHS.S), 2.54 (m, 4H, 2CH2S), 0.88 (t, 6H, 2CH3).
Compound 13.Yield 70%; oil; EIMS m/z (ra %): 312 (1) [M] þ, 255 (3)
[M-57]þ, 223 (100) [M-SBu]þ, 167 (28) [M-SBu-56]þ; 1H NMR: 7.01 (d, 1H,
Jm, H-2) 6.86 (dd, 1H, Jo, m, H-6), 6.72 (d, 1H, Jo, H-5), 5.95 (s, 2H, CH2O2),
4.79 (s, 1H, CHS.S), 2.54 (m, 4H, 2CH2S), 1.49 (m, 8H, 2CH2CH2), 0.88
(t, 6H, 2CH3).
Compound 14. Yield 80%; m.p.: decompose; EIMS m/z (ra %): 372
(1) [Mþ2]þ, 370 (3) [M]þ, 281 (2) [Mþ2-91]þ, 279 (6) [M-91]þ, 249 (25)

1596
MIRANDA ET AL.
1
[Mþ2-SCH2f]þ, 247 (76) [M-SCH2f]þ, 91 (100) [C7H7]þ; H NMR: 7.35–
7.10 (m, 14H, Ar-H), 4.42 (s, 1H, CHS.S), 3.67 (AB, 4H, J ¼ 13.5 Hz, 2CH2f).
Compound 15. Yield 80%; m.p.: 66ꢀ–68ꢀC; EIMS m/z (ra %): 380
(1) [M]þ, 289 (7) [M-91]þ, 257 (100) [M-SCH2f]þ; 91 (90) [C7H7]þ;
1H NMR: 7.41–6.63 (m, 13H, Ar-H), 5.83 (s, 2H, CH2O2), 4.36 (s, 1H,
CHS2), 3.64 (AB, 4H J ¼ 13.5 Hz, 2CH2f).
ACKNOWLEDGMENTS
We thank Ing.Luis Velasco and MSc Javier Pe rez for recording the MS
experiments.Contract/grant sponsor: DGAPA-UNAM.Contract/grant
number PAPIIT-IN215598 and CONACYT-UNAM Contract/grant
number CONACyT 25267-A.
REFERENCES AND NOTES
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S.S-ACETALS
1597
19.Tonsil Actisil FF (TAFF), a commercial Mexican bentonitic clay, is
easily available from Tonsil Mexicana S.A.de C.V.Mexico City,
Mexico at US$ 1.30/kg. Examined with x-ray fluorescence, this clay
proved to have the following composition (in percent): SiO2, 74.5;
Al2O3, 9.3; MgO, 0.4; Fe2O3, 1.3; CaO, 4.0; K2O, 0.4; TiO2, 0.4;
H2O, 9.7. When x-ray thermodiffractograms were run, the laminar
structure was found to be unstable above 150ꢀC.Quartz and cristo-
balite are also important components in the clay composition as
observed by x-ray diffraction.The corresponding BET surface area
was 198.718 m2gꢃ1 and the pore volume and average pore diameter
were 32.04 Â 10ꢃ2 cm3 gꢃ1 and 77.8 A, respectively.It is worth men-
tioning that a detailed characterization of the clay (29Si and 27Al
MAS-NMR, SEM, IR-Py, DTA, and TG, Ho) is under review.
Miranda, R.; Rıos, H.; Salmon, M.; Cogordan, J.A.; Cabrera, A.
J.Appl.Cat. 2000.
20. Miranda, R.; Cervantes, H.; Joseph-Nathan, P. Synth. Commun. 1990,
20, 153.
21.Cseri, T; .Be
kassy, S.B.; Figueras, F.; Cseke, E.; de Menorval, L.C.;
1995, 132, 141.
22. Lipkowitz, K.B.; Boyd, D.B. Reviews in Computational Chemistry,
Dutartre, R.J.Appl.Cat.A: General,
VHC Publishers: New York, 1991, Vol.2, 313.
Received in the USA July 24, 2000