Regioselective transformation of alkynes into cyclic acetals and thioacetals with a gold(I) catalyst: comparison with Br?nsted acid catalysts

Article abstract of DOI:10.1016/j.tet.2008.06.032

Au(I) catalyzes the transformation of alkynes into cyclic acetals and thioacetals at much higher rate than Br?nsted acids. The reaction appears to be general for a range of alkynes and diols or dithiols, which are efficiently transformed with high selectivities. One of the salient features of this reaction process is the high reactivity of the enol ether or enol thioether intermediates, which undergo a rapid isomerization reaction to afford the cyclic acetals or thioacetals, so that isolation or subsequent activation processes are not required. This type of reactions allows us to synthesize a series of fragrances.

Full text of DOI:10.1016/j.tet.2008.06.032

Tetrahedron 64 (2008) 7902–7909
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Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Regioselective transformation of alkynes into cyclic acetals and thioacetals
with a gold(I) catalyst: comparison with Brønsted acid catalysts
*
Laura L. Santos, Violeta R. Ruiz, Maria J. Sabater, Avelino Corma
Instituto de Tecnolog´ıa Qu´ımica, UPV-CSIC, Avenida de Los Naranjos s/n, 46022 Valencia, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
Au(I) catalyzes the transformation of alkynes into cyclic acetals and thioacetals at much higher rate than
Brønsted acids. The reaction appears to be general for a range of alkynes and diols or dithiols, which are
efficiently transformed with high selectivities. One of the salient features of this reaction process is the
high reactivity of the enol ether or enol thioether intermediates, which undergo a rapid isomerization
reaction to afford the cyclic acetals or thioacetals, so that isolation or subsequent activation processes are
not required. This type of reactions allows us to synthesize a series of fragrances.
Received 16 May 2008
Accepted 10 June 2008
Available online 13 June 2008
Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction
AuCl or AuCl3 can also be used as catalysts in the formation of in-
teresting bicyclic ketals by using two intramolecular hydroxyl
Cyclic acetals and thioacetals are important molecules for pro-
tecting carbonyl groups in organic synthesis1 and for the genera-
tion of chiral auxiliaries for asymmetric induction.2 They also have
interest for the production of polymers, pharmaceuticals and fra-
grances.3–5 Classical methods to obtain cyclic acetals involve the
reaction of an aldehyde or ketone with an alcohol with azeotropic
removal of water or transacetalization reactions. When the ketone
is not stable, this procedure involves large excess of reactant and
tedious work-up procedures.1,6 Recently, the direct transformation
of unactivated alkynes into ketones or acetals upon water or alcohol
addition, respectively, has become one of the most useful func-
tionalizations of simple alkynes, and a variety of catalysts have been
extensively studied.7–9 For instance, transition metals salts in-
cluding mercury(II),7 palladium(II)8 as well as a Zeise-type plati-
num compound9 catalyze the hydration of many alkynes to afford
ketones; whereas formation of cyclic acetals has been described to
occur with the assistance of a cationic iridium complex.10 In the
case of gold, it has been recently reported that this metal working
either in homogeneous or heterogeneous phase can efficiently
catalyze reactions involving alkynes.11 Indeed, it has been described
that the use of cationic gold(I) complexes for the direct formation of
dimethyl acetals from alkynes by addition of methanol, and protons
as cocatalyst,12 whereas gold(III) efficiently catalyzes the addition
of water and methanol to nonactivated alkynes forming ketones
and acetals.13 It should be remarked that despite the fact that di-
methyl acetals were successfully obtained with this Au(III) catalyst,
direct conversion of alkynes into cyclic acetals was not possible.
groups as nucleophiles.14 Similarly,
a combination of intra-
molecular and intermolecular additions in the case of a homo-
propargylic alcohol can be catalyzed by AuPPh3Cl/AgBF4, in the
presence of 10% acid.15
In this work we present that gold(I)/AgBF4 can catalyze very
efficiently the formation of cyclic acetals and thioacetals with five
to eight membered ring from alkynes and diols and thiols, without
adding acid. To the best of our knowledge there is no precedent for
forming this last type of compounds from alkynes using gold cat-
alysts. We can oversee interesting applications of this reaction and,
as one example, the synthesis of a molecule with blossom orange
scent is presented. We will show that with this catalyst the for-
mation of cyclic acetals and thioacetals takes place in a direct way
through a two step transformation starting from alkynes and diols
or thiols to afford enol ethers(thioethers) intermediates. In our
reaction system, the intermediate reaction product undergoes
a rapid isomerization to the corresponding cyclic acetal and thio-
acetal so that isolation of the enol ether/thioether is not required.
One of the main advantages of this experimental procedure is that
most of the inconveniences associated with classical acetalization
reactions, such as the use of an excess of reagent or tedious work-up
procedures can be overcome.
2. Results and discussion
2.1. Synthesis of acetals and thioacetals with Au(I)/Ag(I)
system
The reaction of 1,2-ethanediol with a series of alkynes such as
phenylacetylene, benzylacetylene and 1-hexyne was carried out at
* Corresponding author. Tel.: þ34 96 3877800; fax: þ34 96 3877809.
E-mail address: acorma@itq.upv.es (A. Corma).
0040-4020/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2008.06.032

L.L. Santos et al. / Tetrahedron 64 (2008) 7902–7909
7903
Table 1
Au(I)/AgBF4 catalyzed the direct formation of cyclic acetals from alkynes and diolsa
Entry
Alkyne
Diol
Products
Time (h) Alkyne
conversionb
Sb,c (%)
Yieldh
(%)
(%)
O
1
2
3
4
1
2
3
4
100
75 (93)d 87
82 (87)d 76
77 (89)d 79
HO
HO
HO
HO
OH
OH
OH
OH
O
0.33
0.2
3
100
100
15
O
O
O
O
O
2 (68%)
4 (32%)
90
d
O
O
O
O
5
5
4
100
100
100
51
96
82
HO
OH
O
O
60 (83)d 76
OH
6
6
0.5
4e
6f
HO
O
O
7
7
76
88
96
90
68
41
65
78
HO
OH
O
O
8
8
HO
HO
OH
OH
O
Cl
Cl
O
9
9
0.75
1
80
O
MeO
MeO
O
O
10
11
12
13
14
10i (97%)
12i (94%)
14i (66%)
16i
11i (3%)
13i (6%)
15i (34%)
100
O
O
HO
OH
O
O
HO
0.5 (48)g 100
91 (94)d 85
91 (94)d 35
OH
O
O
O
HO
3
60
100
80
O
O
OH
O
O
1.5
6
94
98
94
83
60
84
O
HO
OH
17
O
HO
HO
OH
OH
O
O
15
18
4
100
O
Me
Me
a
Reaction conditions: alkyne (1.1 mmol), diol (1 mmol), AuPPh3Cl (0.02 mmol), AgBF4 (0.02 mmol), toluene (1 mL), 100 ꢀC, N2.
b
c
d
e
f
Calculated by CG using n-dodecane as internal standard.
Selectivity (%).
Results in parentheses refer to reactions with starting reagents dried on activated molecular sieves (4 Å).
Reaction was carried out at 60 ꢀC.
Reaction was carried out at 120 ꢀC.
Reaction was carried out at 25 ꢀC.
g
h
i
Isolated yield of main product.
Mixture of diastereoisomers.

7904
L.L. Santos et al. / Tetrahedron 64 (2008) 7902–7909
100 ꢀC, in the presence of AuPPh3Cl/AgBF4. In all cases, the main
reaction product was the corresponding cyclic acetal, together with
minor amounts of ketones (entries 1–3, Table 1). The addition of the
diol takes place almost exclusively at the most substituted carbon
atom of the alkyne to produce the expected cyclic acetal. This
transformation should involve the initial regioselective formation
of an enol ether intermediate, which would undergo a rapid ther-
mal isomerization to the more stable cyclic acetal (Scheme 1).
and the results are given in Table 1 (entries 8 and 9). The electro-
donor or withdrawing ability of the substituent at the aromatic
position did not influence the very high regioselectivity to the
Markovnikov substitution. Nonetheless, the conversion towards
the cyclic acetal improved significantly with the p-methoxyaryl
acetylene with respect to the p-halogenaryl substituted derivative,
owing to the higher electron density in the acetylenic group in the
former case.12
The reactivity of aliphatic and aromatic alkynes is compared in
Figure 1 and Table 1 (entries 3 and 9). The experimental results
show that aliphatics react faster than aromatic alkynes, while in
both cases selectivity towards the cyclic acetal formation remains
constant during the experiments, confirming the stability of both
products in the reaction media.
n
n
OH
O
OH
HO
n
O
O
R2
R1
R2
Au1+/Ag1+
R1
R2
R1
Scheme 1. Gold(I) catalyzes the transformation of alkynes into cyclic acetals.
The gold catalytic system also catalyzes efficiently the addition of
secondary alcohols such as 2,3-butanediol to terminal acetylenic
groups (entry 10 in Table 1), being the secondary alcohols more re-
active than primary, in contrast what it occurs during the formation
of acyclic acetals.12 Furthermore, the addition of 1,2-butanediol to
internal and terminal alkynes, i.e., 1-methyl-2-phenylacetylene and
1-phenylacetylene, leads to formation of interesting mixed or
asymmetric cyclic acetals with high conversions and selectivities
(entries 11 and 12 in Table 1), and turnover frequencies in the order
of 250 mmol alkyne per mmol of catalyst per hour (Table 2). As can
Control experiments showed that the formation of cyclic acetals
did not occur with AgBF4 or AuPPh3Cl alone. This indicates that
AgBF4 is necessary to generate a cationic gold(I) in solution that,
otherwise, may not exist in a free form but coordinated with
whatever donor molecules (alkynes, diols) are present in solution.12
Additional experiments were carried out with catalytic amounts
of a Brønsted acid (p-TsOH) to compare its effect on reactivity (see
Section 2.2).
The formation of minor amounts of ketones can be explained by
the hydrolysis of the acetals and/or by hydration of the alkyne. To
check this, we carried out the reaction under anhydrous conditions
by drying the reactants with molecular sieves (4 Å). The results
obtained show that a decrease in the yield to the ketone is observed
(entries 1–3 and 6, Table 1). Moreover, control experiments with
(a)
100
phenylacetylene, water (in the absence of the diol) and the Auþ1
/
Agþ1 catalyst were carried out and in this case the aromatic ketone
was detected only at the level of traces. Similar results were also
found when using iridium complexes as catalysts.10 We can then
conclude that gold in the AuPPh3Cl/AgBF4 system can efficiently
catalyze the formation of a five membered ring cyclic acetal by
reacting 1,2-ethanediol with a series of alkynes and the ketone
obtained as subproduct is formed by the hydrolysis of the acetal if
water is present in the reaction media.
80
60
40
1-hexyne
It appears that the process presented here could be used to
synthesize cyclic acetals with six or more membered rings by
properly selecting the diol. Results from Table 1 (entries 1–7) show
that cyclic acetals with five and six membered rings can be effi-
ciently formed and they are perfectly stable, provided that there is
not water and acid present. In the case of seven and eight mem-
bered ring cyclic acetals, the results from Table 1 (entries 6 and 7)
indicate that they can also be formed. The lower yield (w80%)
obtained in this case can be due to the typical ring strains of larger
cyclic molecules, which make cyclic acetals with larger ring less
stable and very prone to undergo undesired ring opening re-
actions. Nevertheless, we have seen that gold can catalyze the
formation of cyclic acetals with, at least, five to eight membered
rings. From the point of view of the alkyne reactivity, it is in-
teresting to notice that the rate of addition of 1,2-ethanediol to the
aliphatic alkyne (1-hexyne) was much faster than to the aromatic
one (1-phenylacetylene) (entries 1 and 3 in Table 1). This could be
explained not only taking into account the relative electrophilicity
of the sp hybridization towards the hydroxyl group of the diol but,
presumably, also because of steric effects. These steric effects
might contribute to slow down the addition to the alkyne, espe-
cially when bulky substituents such as a phenyl group, are directly
bound to the triple bond.
20
0
p-methoxyphenylacetylene
0
10
20
30
40
Time (min)
50
60
70
80
(b)
100
80
60
40
20
0
1-hexyne
p-methoxyphenylacetylene
0
10
20
30
Time (min)
40
50
In order to explore the scope of the catalytic process presented
here, we have studied a series of reactions involving different
combinations of alkynes and diols. Various p-aryl substituted
acetylenic compounds (Cl, OCH3) with different electrodonor or
electron withdrawing properties were reacted with 1,2-ethanediol
Figure 1. Evolution of conversion/selectivity with time for the acetalization reaction of
1-hexyne and p-methoxyphenylacetylene with 1,2-ethanediol catalyzed by AuPPh3Cl/
AgBF4.

L.L. Santos et al. / Tetrahedron 64 (2008) 7902–7909
7905
Table 2
carbonyl compounds as dithioacetals is an important trans-
formation due to the higher stability of these sulfur compounds
with respect to cyclic acetals under both acidic and basic condi-
tions. In addition, they also very often serve as masked acyl anion
equivalents or masked methylene functions in carbon–carbon bond
forming reactions. Moreover, various 1,3-dithiane derivatives play
an important role as valuable building blocks in natural product
synthesis.17
The results in Table 3 indicate that phenylacetylene can be easily
and regioselectively converted into cyclic thioacetals by reacting
the alkyne with the corresponding dithiol in the presence of
AuPPh3Cl/AgBF4 under similar reaction conditions than the diols.
Nonetheless, it is necessary to remark that higher amounts of cat-
alyst and longer reaction times were required for the synthesis of
cyclic thioacetals. Moreover, anti-Markovnikov products are
formed in ratio 10–20% (entries 1, 3 and 4, Table 3). This ratio is
much higher than that in the case of diols. On the other hand, the
stability of six and seven membered ring thioacetals is higher than
the corresponding cyclic acetals, but selectivities are lower than for
cyclic acetals because of the slower reaction rate for the synthesis of
cyclic thioacetals that gives further possibilities to polymerization
of alkynes to proceed.
TON and TOF (hꢁ1) values calculated for the acetalization reaction of 1-phenyl-
acetylene and 1,2-butanediol with 0.02 mmol of catalyst AuPPh3Cl/AgBF4
AuPPh3Cl/AgBF4
Toluene, 100 °C
+
HO
OH
Substrates (mmol)
Time (h)
Conversion (%)
100
100
80
TOFa (hꢁ1
)
TONb
1
2
4
0.5
0.75
5
117
172
265
50
100
164
a
Calculated as mmol of alkyne transformed/mmol of catalyst/h.
Calculated as mmol of alkyne transformed/mmol of catalyst.
b
be seen in Table 1, when reacting 2,3-butanediol and 1,2-butanediol
with 1-phenylacetylene, minor amounts of anti-Markovnikov
products are formed (entries 10 and 11).
The scope of the reaction has been extended to different alkynes
with steric hindrance. The reaction of 3,3-dimethyl-1-butyne and
2-ethynyltoluene with 1,2-ethanediol occurred to high conversion
at 100 ꢀC over 4–6 h in toluene to form the corresponding cyclic
acetals (entries 14 and 15, Table 1). High selectivities were observed
in both cases (98% and 94%, respectively).
The catalytic properties of other gold salts have been studied by
reacting phenylacetylene and 1,2-ethanediol in the presence of
AuCl, AuCl3 and NaAuCl4. In these conditions the reaction does not
proceed even in the presence of AgBF4 or CuCl2,16 which has been
shown to stabilize the Au(III) (AuCl3) during the addition of alcohols
to alkenes.
2.2. Catalysis by Au(I)/Ag(I) system versus catalysis
by p-TsOH
There are a few gold-catalyzed reactions in the literature that
can be alternatively catalyzed by Brønsted acids.18,19 However,
there are many more examples in which Brønsted acids act as gold
cocatalysts.12,15,18
The catalytic process described here could be applied to the
synthesis of fructone (ethyl 2-methyl-1,3-dioxolane-2-acetate)5b
and blossom orange fragrances.5a We show this possibility by
synthesizing 2-methyl-2-naphthyl-4-methyl-1,3-dioxolane, which
is a fragrance with blossom orange scent. The commercial synthesis
of this compound is carried out by acetalization reaction between
methyl naphthyl ketone and propylene glycol using liquid5c or solid
acids.5a We have successfully performed the synthesis of this
compound by reacting naphthylene-2-acetylene and propylene
glycol in the presence of Au(I)/AgBF4 under similar reaction con-
ditions than for other cyclic acetals (entry 13 in Table 1). Total
conversion is obtained after 1.5 h at 100 ꢀC with high selectivity.
After the successful synthesis of cyclic acetals from alkynes and
diols catalyzed by Au(I)/AgBF4 we have explored the possibility to
synthesize cyclic thioacetals using the same catalyst. Protection of
In order to explore how a Brønsted acid affects the acetalization/
thioacetalization reaction, we have described few examples carried
out in the presence of Au(I)/AgBF4 and a catalytic amount of p-TsOH
as cocatalyst, as well as only with the Brønsted acid (Tables 4 and 5).
The results obtained when reacting diols are shown in Table 4.
According to the literature, an increase of the reaction rate was
observed when p-TsOH was added together with the gold cata-
lyst.12,15,18 For example, the rate of reaction for 1-phenylacetylene
with 1,2-ethanediol increases by w1 order of magnitude when
adding p-TsOH to the reaction in the presence of gold. Similarly,
when p-methoxyphenylacetylene was used as substrate, the re-
action was completed in 0.33 h (0.75 h without Brønsted acid) with
total conversion of the alkyne (entry 9, Table 1 and entry 2, Table 4).
Table 3
Au(I)/AgBF4 catalyzed the direct formation of dithiolanes from alkynes and dithiolsa
Entry
Alkyne
Dithiol
Products
Time (h)
Alkyne
S
b,c (%)
Yieldd (%)
conversionb (%)
S
S
1
2
3
19 (92%)
20 (8%)
22e (3%)
24 (20%)
20
24
30
100
95
70
60
55
45
51
35
HS
SH
SH
S
S
S
S
21e (97%)
23 (80%)
S
S
HS
S
S
90
HS
SH
S
S
S
S
SH
4
25 (91%)
26 (9%)
10
98
40
26
HS
S
S
a
Reaction conditions: alkyne (1.1 mmol), dithiol (1 mmol), AuPPh3Cl (0.05 mmol), AgBF4 (0.05 mmol), toluene (1 mL), 100 ꢀC, N2.
Calculated by CG using n-dodecane as internal standard.
Selectivity (%).
Isolated yield of main product.
Mixture of diastereoisomers.
b
c
d
e

7906
L.L. Santos et al. / Tetrahedron 64 (2008) 7902–7909
Table 4
Influence of p-TsOH for acetalization reactions
Entry
Alkyne
Diol
Au(I)/AgBF4/p-TsOHa
p-TsOHb
Products
Time (h)
0.5
Alkyne
Sc,d (%)
Products
Time (h)
24
Alkyne
Sc,d (%)
conversionc (%)
conversionc (%)
1
2
1
100
85
1
4
d
HO
HO
OH
OH
9
0.33
21e
100
100
87
82
9
28
24
25
84
MeO
HO
3
12h (94%)/13h (6%)
12h (94%)/13h (6%)
0(10)f(18)g
d
OH
a
Reaction conditions: alkyne (1.1 mmol), diol (1 mmol), AuPPh3Cl (0.02 mmol), AgBF4 (0.02 mmol), p-TsOH (0.02 mmol), toluene (1 mL), 100 ꢀC, N2.
b
c
Reaction conditions: alkyne (1.1 mmol), diol (1 mmol), p-TsOH (0.02 mmol), toluene (1 mL), 100 ꢀC, N2.
Calculated by CG using n-dodecane as internal standard.
Selectivity (%).
d
e
f
Reaction was carried out at 25 ꢀC.
Results refer to reaction at 100 ꢀC.
Results refer to reaction with p-TsOH (0.05 mmol).
Mixture of diastereoisomers.
g
h
Table 5
Influence of p-TsOH for thioacetalization reactions
Entry
Alkyne
Diol
Au(I)/AgBF4/p-TsOHa
p-TsOHb
Products
Time (h)
Alkyne
S
c,d (%)
Time (h)
Products
Alkyne
Sc,d (%)
conversionc (%)
conversionc (%)
1
2
3
19 (96%)/20 (4%)
21e (92%)/22e (8%)
23 (85%)/24 (15%)
3
10
9
100
95
70
75
75
14
50
15
19 (80%)/20 (20%)
21e (49%)/22e (51%)
23 (80%)/24 (20%)
99
75
98
80
HS
HS
SH
SH
60
100
75
HS
SH
SH
4
25 (88%)/26 (12%)
2.5
100
40
40
25 (20%)/26 (80%)
100
40
HS
a
Reaction conditions: alkyne (1.1 mmol), dithiol (1 mmol), AuPPh3Cl (0.05 mmol), AgBF4 (0.05 mmol), p-TsOH (0.05 mmol), toluene (1 mL), 100 ꢀC, N2.
b
c
Reaction conditions: alkyne (1.1 mmol), dithiol (1 mmol), p-TsOH (0.05 mmol), toluene (1 mL), 100 ꢀC, N2.
Calculated by CG using n-dodecane as internal standard.
Selectivity (%).
Mixture of diastereoisomers.
d
e
The reaction described in entry 3 (Table 4) was carried out at 25 ꢀC
noteworthy that when the catalyst is a Brønsted acid longer re-
action times are required (14–50 h) and led to a different ratio of
thioacetal products than when using gold catalyst. When using only
a Brønsted acid as catalyst, anti-Markovnikov products were
formed in higher ratio being the reactions less regioselective. For
example, the reaction of 1-phenylacetylene with 2,3-buthanedi-
thiol gave a w1:1 ratio of Markovnikov and anti-Markovnikov
products, 21 and 22, respectively (entry 2), whereas with 1,4-
butanedithiol, the main product was anti-Markovnikov compound
26 (80%) (entry 4).
In summary, these experiments have proven that addition of
a catalytic amount of p-toluenesulphonic acid to Au(I)/Ag(I) system
accelerates the acetalization and thioacetalization reactions serving
the Brønsted acid as cocatalyst. However, the use of p-TsOH alone
(2–5 mol %) to acetals formation yields very low conversions. Fi-
nally, p-toluenesulphonic acid catalyzes the thioacetalization re-
actions but in almost all cases, it is less regioselective than gold
giving more of the anti-Markovnikov products.
over 21 h whereas without acid 48 h was required (entry 11, Table
1). In all cases, the selectivity decreases with respect to the re-
actions without acid. When the reactions were performed with p-
TsOH alone (2 mol %), the conversions were significantly lower than
with gold or even no reaction occurs (entries 1–3 in Table 4). An
increase of the p-TsOH from 2 to 5 mol % and working at 100 ꢀC gave
only 20% conversion (entry 3).
The comparative studies of thioacetals formation with addition
of p-TsOH are illustrated in Table 5. The reaction of 1-phenyl-
acetylene and different thiols with 5 mol % of AuPPh3Cl/AgBF4 and
5 mol % of p-TsOH gives high conversion at 100 ꢀC in 3–10 h,
demonstrating that the presence of Brønsted acid accelerates these
reactions. Furthermore, the selectivities were similar (entries 1 and
4, Table 5) or higher than the reaction without acid (entries 2 and 3,
Table 5). We have also performed these reactions with p-TsOH
alone (5 mol %), observing in this case that it is possible to obtain
high conversions, in contrast to what was observed with diols. It is

L.L. Santos et al. / Tetrahedron 64 (2008) 7902–7909
7907
3. Conclusion
14.4 (–CH2CH2CH2CH3). MS (80 eV): m/z (%)¼144 [Mþ], 87 (100),
129 (49), 85 (22), 57 (20), 55 (11), 88 (10), 71 (6), 72 (5), 130 (4).
In conclusion, Au(I) as AuPPh3Cl in combination with AgBF4
efficiently catalyzes the direct and regioselective formation of cyclic
acetals and thioacetals with five to eight membered rings from
alkynes and diols or dithiols. p-Toluenesulphonic acid can be used
as an effective cocatalyst. The results obtained clearly indicate the
generality of the reaction with respect to both the alkyne and the
diol or dithiol. There are not severe limitations on the use of dif-
ferent substrates since highly reactive electrophilic bonds are not
necessary in the current reaction system and severe reaction con-
ditions are not required. The addition of the diol or dithiol takes
place almost exclusively at the most substituted carbon atom of the
alkyne to produce the cycle. This procedure represents an efficient
alternative to other processes involving ketones, specially when
cyclic acetals and thioacetals with more than six membered ring
atoms have to be obtained.
4.2.4. 2-Methyl-2-phenyl-1,3-dioxane (5)
Isolated yield 82%, >95% pure by GC. 1H NMR (CDCl3, 300 MHz):
d
7.34 (m, 5H, 5CHar), 3.75 (m, 4H, O–CH2CH2), 2.02, 1.12 (m, m, 1H
each, O–CH2CH2), 1.43 (s, 3H, Cq–CH3). 13C NMR (CDCl3, 75 MHz):
141.6 (Cqar), 129.1, 128.0, 127.2 (CHar), 100.9 (Cq–CH3), 61.6 (O–
d
CH2CH2), 32.8 (Cq–CH3), 25.9 (O–CH2CH2). MS (80 eV): m/z (%)¼177
[Mþ], 163 (100), 105 (88), 101 (42), 77 (25), 164 (10).
4.2.5. 2-Methyl-2-phenyl-1,3-dioxepane (6)
Isolated yield 76%, >95% pure by GC. 1H NMR (CDCl3, 300 MHz):
d
7.52, 7.30 (m, m, 2:3, 5CHar), 3.80, 3.60 (m, m, 2H each, O–
CH2CH2), 1.65, 1.59 (m, m, 2H each, O–CH2CH2), 1.50 (s, 3H, Cq–CH3).
13C NMR (CDCl3, 75 MHz):
145.2 (Cqar), 128.3, 127.7, 126.2 (CHar),
d
103.0 (Cq–CH3), 63.5 (O–CH2CH2), 29.9 (Cq–CH3), 27.8 (O–CH2CH2).
MS (80 eV): m/z (%)¼192 [Mþ],136 (100), 121 (90), 87 (42), 103 (25),
137 (20), 77 (19), 59 (17). Anal. Calcd for C12H16O2: C, 75.00; H, 8.33.
Found: C, 75.19; H, 8.11.
4. Experimental
4.1. General
4.2.6. 2-Methyl-2-phenyl-1,3-dioxocane (7)
Isolated yield 68%, >95% pure by GC. 1H NMR (CDCl3, 300 MHz):
Commercially available reagents including AuPPh3Cl and AgBF4
were purchased from Sigma–Aldrich. 1,2-Ethanediol, 1,4-butane-
diol and 1,2-butanediol were dried on activated molecular sieves
(4 Å). GC/MS analyses were performed on an Agilent 5973N spec-
trometer equipped with the same column and in the same condi-
tions as GC. 1H NMR and 13C NMR were recorded in CDCl3 with TMS
as an internal standard at 25 ꢀC on a Bruker Avance 300.
d
7.42, 7.12 (m, m, 2:3, 5CHar), 3.50, 3.55 (m, m, 2H each, O–CH2CH2),
1.54, 1.46, 1.45 (m, m, m, 2H each, O–CH2CH2CH2), 1.50 (s, 3H, Cq–
CH3). 13C NMR (CDCl3, 75 MHz):
142.8 (Cqar), 129.4, 128.4, 126.6
d
(CHar), 101.4 (Cq–CH3), 61.5 (O–CH2CH2), 30.3, 30.2, 29.9 (O–
CH2CH2CH2), 27.5 (Cq–CH3). MS (80 eV): m/z (%)¼206 [Mþ], 161
(100), 105 (100), 121 (49), 191 (40), 77 (36), 169 (22), 162 (15), 120
(10). Anal. Calcd for C13H18O2: C, 75.73; H, 8.74. Found: C, 75.25; H,
8.36.
4.2. General procedure for acetalization reactions
4.2.7. 2-(4-Chlorophenyl)-2-methyl-1,3-dioxolane (8)
Catalytic reactions were carried out under N2 atmosphere in
a closed glass reactor (2.5 mL) equipped with a micro-syringe
trough, which can take a sample to analysis. To a catalytic amount
of AuPPh3Cl (0.02 mmol, 0.0099 g)/AgBF4 (0.02 mmol, 0.0039 g),
a mixture of the appropriate alkyne (1.1 mmol) and the diol
(1 mmol) in 1 mL of toluene was added. The reaction mixture was
stirred at 100 ꢀC and monitored by gas chromatography. When the
reaction was completed, the solvent was evaporated under vacuo.
The crude product was purified by PLC chromatography on silica
gel, using a 99:1 mixture of hexane/Et2O as eluent.
Isolated yield 41%, >95% pure by GC. 1H NMR (CDCl3, 300 MHz):
d
7.34, 7.22 (d, d, 3JHH¼7.5 Hz, 2H each, 4CHar), 3.96, 3.68 (m, m, 2H
each, O–CH2CH2–O),1.56 (s, 3H, Cq–CH3). 13C NMR (CDCl3, 75 MHz):
d
142.3 (Cqar), 134.1 (Cqar–Cl), 128.7, 127.2 (CHar), 108.8 (Cq–CH3),
64.9 (O–CH2CH2–O), 27.9 (Cq–CH3). MS (80 eV): m/z (%)¼198 [Mþ],
183 (100), 139 (100), 185 (74), 141 (41), 87 (34), 111 (33), 75 (23), 184
(22), 103 (19), 167 (15).
4.2.8. 2-(4-Methoxyphenyl)-2-methyl-1,3-dioxolane (9)
Isolated yield 65%, >95% pure by GC. 1H NMR (CDCl3, 300 MHz):
d
7.32, 6.79 (d, d, 3JHH¼7.3 Hz, 2H each, 4CHar), 3.94, 3.70 (m, m, 2H
4.2.1. 2-Methyl-2-phenyl-1,3-dioxolane (1)
each, O–CH2CH2–O), 3.72 (s, 3H, Ar–OCH3), 1.57 (s, 3H, Cq–CH3). 13
C
Isolated yield 87%, >95% pure by GC. 1H NMR (CDCl3, 300 MHz):
NMR (CDCl3, 75 MHz): d 159.6 (Cqar–OCH3), 135.9 (Cqar), 126.9, 113.9
d
7.41, 7.26 (m, m, 2:3, 5CHar), 3.96, 3.70 (m, m, 2H each, O–CH2),
(CHar), 109.2 (Cq–CH3), 64.8 (O–CH2CH2–O), 55.6 (–OCH3), 28.0 (Cq–
CH3). MS (80 eV): m/z (%)¼194 (4) [Mþ], 179 (100), 135 (56), 180
(11), 77 (10), 87 (8), 92 (7), 163 (6), 136 (5), 91 (5), 107 (5). Anal.
Calcd for C11H14O3: C, 68.04; H, 7.22. Found: C, 67.93; H, 7.11.
1.58 (s, 3H, Cq–CH3). 13C NMR (CDCl3, 75 MHz):
d
143.7 (Cqar), 128.6,
128.2,125.6 (CHar), 109.2 (Cq–CH3), 64.8 (O–CH2), 28.0 (Cq–CH3). MS
(80 eV): m/z (%)¼164 (10) [Mþ], 105 (100), 163 (90), 101 (50), 77
(32), 51 (11), 73 (10), 106 (8), 78 (4), 91 (4).
4.2.9. 2-Methyl-2-phenyl-4,5-dimethyl-1,3-dioxolane (10)
4.2.2. 2-Benzyl-2-methyl-1,3-dioxolane (2)
Isolated yield 78%, >95% pure by GC. Mixture of dia-
Isolated yield 76%, >95% pure by GC. 1H NMR (CDCl3, 300 MHz):
stereoisomers. 1H NMR (CDCl3, 300 MHz):
d 7.45, 7.23 (m, m, 2:3,
3
d
7.18 (m, 5H, 5CHar), 3.81, 3.67 (m, m, 2H each, O–CH2CH2–O), 2.84
(s, 2H, Ph–CH2), 1.22 (s, 3H, Cq–CH3). 13C NMR (CDCl3, 75 MHz):
137.3 (Cqar), 130.9, 128.3, 126.7 (CHar), 110.1 (Cq–CH3), 65.2 (O–
5CHar), 3.71, 3.42 (dq, dq, 1H each, JHH¼6.0, 8.3 Hz, O–
CH(Me)CH(Me)–O), 1.57 (s, 3H, Cq–CH3), 1.22, 1.11 (d, d, 3H each,
3JHH¼6.0 Hz, O-CH(CH3)CH(CH3)–O). 13C NMR (CDCl3, 75 MHz):
d
CH2CH2–O), 45.7 (Ph–CH2), 24.7 (Cq–CH3). MS (80 eV): m/z (%)¼179
d 145.6 (Cqar), 128.4, 127.9, 125.5 (CHar), 108.2 (Cq–CH3), 79.3, 78.6
[Mþ], 87 (100), 91 (38), 65 (12), 88 (9), 105 (6).
(–O–CH(Me)CH(Me)–O), 29.4 (Cq–CH3), 17.5, 16.9 (–O–
CH(CH3)CH(CH3)–O). MS (80 eV): m/z (%)¼192 [Mþ], 177 (100), 105
(81), 147 (25), 104 (22), 77 (20). Anal. Calcd for C12H16O2: C, 74.97;
H, 8.39. Found: C, 75.20; H, 7.86.
4.2.3. 2-n-Butyl-2-methyl-1,3-dioxolane (3)
Isolated yield 79%, >95% pure by GC. 1H NMR (CDCl3, 300 MHz):
d
3.86 (m, 4H, O–CH2CH2–O), 1.54, 1.27 (m, m, 2:4,
–CH2CH2CH2CH3), 1.24 (s, 3H, Cq–CH3), 0.83 (s, 3H,
–CH2CH2CH2CH3). 13C NMR (CDCl3, 75 MHz):
110.6 (Cq–CH3), 64.9
(O–CH2CH2–O), 39.3, 26.6, 23.3 (–CH2CH2CH2CH3), 24.1 (Cq–CH3),
4.2.10. 2-Methyl-2-phenyl-4-ethyl-1,3-dioxolane (12)
d
Isolated yield 85%, >95% pure by GC. Mixture of dia-
stereoisomers (ratio 12a/12b¼1.8:1). Compound 12a: 1H NMR

7908
L.L. Santos et al. / Tetrahedron 64 (2008) 7902–7909
(CDCl3, 300 MHz):
m, 1H each, O–CH2), 4.07 (m, 1H, O–CH), 1.56 (s, 3H, Cq–CH3),
d
7.44, 7.25 (m, m, 2:3, 5CHar), 4.09, 3.30 (m,
133.3 (Cqar), 128.6, 128.4, 128.0, 126.5, 126.4, 124.2, 124.1 (CHar),
109.5 (Cq–CH3), 72.3 (O–CH), 71.3 (O–CH2), 28.8 (Cq–CH3), 19.4 (O–
CH–CH3). MS (80 eV): m/z (%)¼228 (15) [Mþ], 213 (100), 155 (86),
127 (37), 101 (17), 214 (15), 156 (10). Compound 16b: 1H NMR
3
1.48, 1.30 (m, m, 1H each, –CH2CH3), 0.85 (t, 3H, JHH¼7.5 Hz,
–CH2CH3). 13C NMR (CDCl3, 75 MHz):
d 145.1 (Cqar), 128.4, 128.0,
125.5 (CHar), 109.3 (Cq–CH3), 79.0 (O–CH), 70.1 (O–CH2), 28.6 (Cq–
CH3), 26.9 (–CH2CH3), 10.5 (–CH2–CH3). MS (80 eV): m/z (%)¼192
[Mþ], 177 (100), 105 (78), 55 (48), 43 (35), 123 (34), 77 (32).
(CDCl3, 300 MHz): d 7.89, 7.73, 7.50, 7.35 (m, m, m, m, 1:3:1:2,
7CHar), 4.28 (m, 1H, O–CH–CH3), 4.04, 3.21 (dd, dd, 1H each,
3JHH¼5.8 Hz, 2JHH¼8.1 Hz, O–CH2), 1.60 (s, 3H, Cq–CH3), 1.07 (d, 3H,
Compound 12b: 1H NMR (CDCl3, 300 MHz):
d
7.41, 7.31 (m, m,
3JHH¼6.0 Hz, O–CH–CH3). 13C NMR (CDCl3, 75 MHz):
d 142.5, 133.3,
2:3, 5CHar), 3.80, 3.53 (m, m, 1H each, O–CH2), 3.77 (m, 1H, O–
133.3 (Cqar), 128.7, 128.3, 128.0, 126.4, 126.3, 124.2, 124.1 (CHar),
109.5 (Cq–CH3), 723.6 (O–CH), 71.5 (O–CH2), 28.7 (Cq–CH3), 18.7 (O–
CH–CH3). MS (80 eV): m/z (%)¼228 (13) [Mþ], 213 (100), 155 (90),
127 (39), 214 (16), 101 (11), 156 (11). Anal. Calcd for C15H16O2: C,
78.92; H, 7.06. Found: C, 78.41; H, 7.01.
CH), 1.62, 1.54 (m, m, 1H each, –CH2CH3), 1.58 (s, 3H, Cq–CH3),
3
0.88 (t, 3H, JHH¼7.5 Hz, –CH2CH3). 13C NMR (CDCl3, 75 MHz):
d
144.3 (Cqar), 128.5, 128.0, 125.6 (CHar), 109.3 (Cq–CH3), 77.4 (O–
CH), 69.4 (O–CH2), 28.7 (Cq–CH3), 27.0 (–CH2CH3), 10.1 (–CH2CH3).
MS (80 eV): m/z (%)¼192 [Mþ], 177 (100), 105 (94), 55 (47), 123
(41), 77 (36), 43 (30). Anal. Calcd for C12H16O2: C, 74.97; H, 8.39.
Found: C, 75.22; H, 8.10.
4.2.14. 2-Methyl-2-tert-butyl-1,3-dioxolane (17)
Isolated yield 60%, >95% pure by GC. 1H NMR (CDCl3, 300 MHz):
d
3.87, 3.82 (m, m, 2H each, O–CH2CH2–O), 1.17 (s, 3H, O–Cq–CH3),
4.2.11. 2-Benzyl-2-methyl-4-ethyl-1,3-dioxolane (14)
0.90 (s, 9H, Cq–(CH3)3). 13C NMR (CDCl3, 75 MHz):
d
112.95 (O–Cq–
Isolated yield 35%, >95% pure by GC. Mixture of dia-
CH3), 64.9 (O–CH2CH2–O), 37.9 (Cq–(CH3)3), 24.2 (Cq–(CH3)3), 18.2
(Cq–O–CH3). MS (80 eV): m/z (%)¼144 [Mþ], 87 (100), 43 (46), 129
(17), 57 (15), 41 (14), 29 (7), 39 (7), 99 (7), 69 (5), 27 (5).
stereoisomers (ratio 14a/14b¼1.25:1). Compound 14a: 1H NMR
(CDCl3, 300 MHz): d 7.19 (m, 5H, CHar), 3.86, 3.42 (dd, dd, 1H each,
3
2JHH¼7.3 Hz, JHH¼5.8, 6.2 Hz resp., O–CH2), 3.72 (q, 1H, O–
CHCH2CH3), 2.83 (s, 2H, Ph–CH2), 1.56, 1.43 (m, m, 1H each, –O–
4.2.15. 2-Methyl-2-(2-methylphenyl)-1,3-dioxolane (18)
3
CHCH2CH3), 1.26 (s, 3H, Cq–CH3), 0.83 (t, 3H, JHH¼7.5 Hz, –O–
Isolated yield 84%, >95% pure by GC. 1H NMR (CDCl3, 300 MHz):
CHCH2CH3). 13C NMR (CDCl3, 75 MHz):
d
137.5 (Cqar), 130.8, 128.3,
d
7.47 (m, 1H, CHar), 7.09 (m, 3H, CHar), 3.95, 3.65 (m, m, 2H each, O–
CH2), 2.42 (s, 3H, Cqar–CH3), 1.61 (s, 3H, Ar–Cq–CH3). 13C NMR
(CDCl3, 75 MHz): 139.5, 134.6 (Cqar), 130.9, 126.9, 125.0, 124.6
126.7 (CHar), 110.4 (Cq–CH3), 78.2 (O–CHCH2CH3), 69.8 (O–CH2),
45.8 (Ph–CH2), 26.8 (–O–CHCH2CH3), 25.8 (Cq–CH3), 10.2 (–O–
CHCH2CH3). MS (80 eV): m/z (%)¼206 [Mþ], 115 (100), 55 (66), 43
(63), 91 (32), 61 (11), 65 (8), 105 (8), 116 (7), 39 (5), 117 (5).
d
(CHar), 108.4 (Cq–CH3), 63.1 (O–CH2), 25.2 (Ar–Cq–CH3), 19.8 (Cqar
–
CH3). MS (80 eV): m/z (%)¼178 [Mþ],163 (100),119 (45), 91 (25),164
Compound 14b: 1H NMR (CDCl3, 300 MHz):
d
7.19 (m, 5H, CHar),
(12), 65 (8), 39 (5), 105 (5), 115 (5), 120 (4), 77 (3). Anal. Calcd for
3.92, 3.09 (dd, dd, 1H each, O–CH2), 3.86 (m, 1H, –O–CHCH2CH3),
2.86 (s, 2H, Ph–CH2), 1.56, 1.44 (m, m, 1H each, –O–CHCH2CH3),
1.23 (s, 3H, Cq–CH3), 0.80 (t, 3H, –O–CHCH2CH3). 13C NMR (CDCl3,
C11H14O2: C, 74.16; H, 7.87. Found: C, 73.97; H, 7.91.
75 MHz):
d
135.3 (Cqar), 128.8, 126.2, 124.7 (CHar), 108.2 (Cq–CH3),
4.3. General procedure for thioacetalization reactions
75.8 (O–CHCH2CH3), 68.0 (O–CH2), 44.7 (Ph–CH2), 24.3 (–O–
CHCH2CH3), 23.0 (Cq–CH3), 8.3 (–O–CHCH2CH3). MS (80 eV): m/z
(%)¼206 [Mþ], 115 (100), 55 (63), 43 (56), 91 (37), 61 (10), 65 (8),
105 (8), 116 (7), 117 (5), 39 (5). Anal. Calcd for C13H18O2: C, 75.73;
H, 8.74. Found: C, 75.31; H, 8.96.
These catalytic reactions were carried out under analogous
conditions to acetalization reactions. To a catalytic amount of
AuPPh3Cl (0.05 mmol, 0.025 g)/AgBF4 (0.05 mmol, 0.010 g), a mix-
ture of the appropriate alkyne (1.1 mmol) and the dithiol (1 mmol)
in 1 mL of toluene was added. The reaction mixture was stirred at
100 ꢀC and monitored by gas chromatography. When the reaction
was completed, the solvent was evaporated under vacuo. The crude
product was purified by PLC chromatography on silica gel, using
a 99:1 mixture of hexane/Et2O as eluent.
4.2.12. 2-Ethyl-2-phenyl-4-ethyl-1,3-dioxolane (15)
Mixture of diastereoisomers (ratio 15a/15b¼3:1). Compound
15a: 1H NMR (CDCl3, 300 MHz):
d 7.38, 7.23 (m, m, 2:3, 5CHar), 3.78,
3.51 (m, m, 1H each, O–CH2), 3.77 (m, 1H, O–CH), 1.83 (c, 2H,
3JHH¼7.5 Hz, Cq–CH2CH3), 1.65, 1.52 (m, m, 1H each, O–CH–CH2CH3),
3
0.88 (t, 3H, JHH¼7.3 Hz, O–CH–CH2CH3), 0.82 (t, 3H, Cq–CH2CH3).
4.3.1. 2-Methyl-2-phenyl-1,3-dithiolane (19)
13C NMR (CDCl3, 75 MHz):
d
141.2 (Cqar), 125.9, 125.8, 123.8 (CHar),
Isolated yield 45%, >95% pure by GC. 1H NMR (CDCl3, 300 MHz):
108.7 (Cq–CH2CH3), 74.8 (O–CH), 67.2 (O–CH2), 31.8 (Cq–CH2CH3),
24.4 (O–CH–CH2CH3), 7.7 (O–CH–CH2CH3), 5.8 (Cq–CH2CH3). MS
(80 eV): m/z (%)¼206 [Mþ], 177 (100), 105 (78), 123 (42), 55 (36), 77
(29), 147 (17), 117 (13), 178 (12), 57 (10), 129 (8). Compound 15b: 1H
d
7.66, 7.19 (d, m, 2:3, 3JHH¼7.2 Hz, 5CHar), 3.35, 3.26 (m, m, 2H each,
S–CH2CH2), 2.06 (s, 3H, Cq–CH3). 13C NMR (CDCl3, 75 MHz):
d 146.4
(Cqar), 128.5, 127.5, 127.3 (CHar), 69.1 (Cq–CH3), 40.8 (S–CH2CH2),
34.4 (Cq–CH3). MS (80 eV): m/z (%)¼196 (62) [Mþ], 181 (100), 121
(93), 167 (86), 196 (62), 103 (60), 168 (46), 77 (34), 136 (28), 59 (17),
51 (12). Anal. Calcd for C10H12S2: C, 61.22; H, 6.12. Found: C, 61.31;
H, 6.32.
NMR (CDCl3, 300 MHz): d 7.41, 7.27 (m, m, 2:3, 5CHar), 4.07, 3.27 (m,
m, 1H each, O–CH2), 4.03 (m, 1H, O–CH), 1.79 (c, 2H, Cq–CH2CH3),
1.30, 1.18 (m, m, 1H each, O–CH–CH2CH3), 0.85 (t, 3H, O–CH–
CH2CH3), 0.79 (t, 3H, Cq–CH2CH3). 13C NMR (CDCl3, 75 MHz):
d 142.0
(Cqar), 125.5, 125.4, 123.7, (CHar), 108.8 (Cq–CH2CH3), 75.2 (O–CH),
67.7 (O–CH2), 32.1 (Cq–CH2CH3), 24.6 (O–CH–CH2CH3), 8.1 (O–CH–
CH2CH3), 5.9 (Cq–CH2CH3).
4.3.2. 2-Methyl-2-phenyl-4,5-dimethyl-1,3-dioxolane (21)
Isolated yield 51%, >95% pure by GC. Mixture of dia-
stereoisomers. 1H NMR (CDCl3, 300 MHz):
d 7.67, 7.19 (m, m, 2:3,
5CHar), 3.54, 3.41 (m, m, 1H each, S–CH(Me)CH(Me)–S), 2.07 (s, 3H,
4.2.13. 2-Methyl-2-naphthyl-4-methyl-1,3-dioxolane (16)
Cq–CH3), 1.31, 1.29 (d, d, 3H each, S–CH(Me)CH(Me)–S). 13C NMR
Isolated yield 83%, >95% pure by GC. Mixture of di-
(CDCl3, 75 MHz): d 146.0 (Cqar), 128.4, 127.3, 127.0 (CHar), 67.0
astereoisomers (ratio 16a/16b¼2:1). Compound 16a: 1H NMR
(Cq–CH3), 37.0 (S–CH(CH3)CH(CH3)–S), 36.1 (Cq–CH3), 17.2 (S–
CH(Me)CH(Me)–S). MS (80 eV): m/z (%)¼224 (25) [Mþ], 167 (100),
168 (94), 121 (50), 103 (40), 169 (18), 77 (17), 59 (16), 209 (15),
136 (10). Anal. Calcd for C12H16S2: C, 64.28; H, 7.14. Found: C, 64.67;
H, 7.31.
(CDCl3, 300 MHz):
d 7.85, 7.69, 7.47, 7.33 (m, m, m, m, 1:3:1:2,
7CHar), 3.94 (m, 1H, O–CH–CH3), 3.79, 3.45 (dd, dd, 1H each,
3JHH¼6.8 Hz, 2JHH¼7.5 Hz, O–CH2), 1.64 (s, 3H, Cq–CH3), 1.21 (d, 3H,
3JHH¼6.03 Hz, O–CH–CH3). 13C NMR (CDCl3, 75 MHz):
d 141.6, 133.4,

L.L. Santos et al. / Tetrahedron 64 (2008) 7902–7909
7909
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8. (a) Harman, W. D.; Dobson, J. C.; Taube, H. J. Am. Chem. Soc. 1989, 111, 3061–
3062; (b) Imi, K.; Imai, K.; Utimoto, K. Tetrahedron Lett. 1987, 28, 3127–3130; (c)
Utimoto, K. Pure Appl. Chem. 1983, 55, 1845–1852.
4.3.3. 2-Methyl-2-phenyl-1,3-dithiane (23)
Isolated yield 35%, >95% pure by GC. 1H NMR (CDCl3, 300 MHz):
3
d
7.86, 7.30, 7.18 (d, t, t, 2:2:1, JHH¼7.5 Hz, 5CHar), 2.65 (m, 4H, S–
3
CH2CH2), 1.87 (q, 2H, JHH¼5.0 Hz, S–CH2CH2), 1.72 (s, 3H, Cq-CH3).
13C NMR (CDCl3, 75 MHz):
d
144.2 (Cqar), 129.0, 128.2, 127.5 (CHar),
54.4 (Cq–CH3), 33.2 (Cq–CH3), 28.5 (S–CH2CH2), 25.1 (S–CH2CH2).
MS (80 eV): m/z (%)¼210 (58) [Mþ], 136 (100), 121 (80), 103 (30), 77
(22), 59 (13), 149 (9). Anal. Calcd for C11H14S2: C, 62.86; H, 6.67.
Found: C, 62.67; H, 6.72.
4.3.4. 2-Methyl-2-phenyl-1,3-dithiepane (25)
Isolated yield 26%, >95% pure by GC. 1H NMR (CDCl3, 300 MHz):
d
7.72, 7.26, 7.15 (d, t, t, 2:2:1, 3JHH¼7.5 Hz, 5CHar), 2.84, 2.70 (m, m,
2H each, S–CH2CH2), 1.92 (m, 4H, S–CH2CH2), 1.88 (s, 3H, Cq–CH3).
13C NMR (CDCl3, 75 MHz):
d 147.6 (Cqar), 130.1, 128.9, 128.6 (CHar),
50.4 (Cq–CH3), 35.3 (Cq–CH3), 31.9 (S–CH2CH2), 25.9 (S–CH2CH2).
MS (80 eV): m/z (%)¼224 (22) [Mþ], 136 (100), 121 (95), 87 (50), 103
(28), 77 (24), 59 (23), 224 (22),137 (19),119 (14), 88 (14). Anal. Calcd
for C12H16S2: C, 64.28; H, 7.14. Found: C, 64.16; H, 6.97.
4.3.5. 2-Benzyl-1,3-dithiepane (26)
1H NMR (CDCl3, 300 MHz):
d
7.33 (m, 5H, CHar), 4.4 (t,1H, S–CH),
3.14 (d, 2H, Cqar–CH2), 2.85, 2.75 (m, m, 2H each, S–CH2CH2), 2.00
(m, 4H, S–CH2CH2). 13C NMR (CDCl3, 75 MHz):
138.9 (Cqar), 129.8,
d
128.8, 128.7, 127.2, 125.9 (CHar), 54.4 (S–CH), 43.8 (Cqar–CH2), 32.1
(S–CH2CH2), 31.5 (S–CH2CH2). MS (80 eV): m/z (%)¼224 (7) [Mþ],
133 (100), 91 (27), 135 (24), 55 (14), 87 (12), 134 (10), 65 (7), 77 (5),
104 (5).
9. Hiscox, W. C.; Jennings, P. W. Organometallics 1990, 9, 1997–1999.
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´
11. (a) Hashmi, A. S. K. Chem. Rev. 2007, 107, 3180–3211; (b) Gonzalez-Arellano, C.;
Abad, A.; Corma, A.; Garcı´a, H.; Iglesias, M.; Sanchez, F. Angew. Chem., Int. Ed.
´
2007, 46, 1536–1538; (c) Gonzalez-Arellano, C.; Corma, A.; Iglesias, M.; Sanchez,
4.4. General procedure for acetalization and thioacetalization
reactions with p-toluenesulphonic acid
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These catalytic reactions were carried out under similar condi-
tions to acetalization/thioacetalization reactions with the addition
of the corresponding amount of p-TsOH.
´
Corma, A.; Gonzalez-Arellano, C.; Iglesias, M.; Sanchez, F. Angew. Chem., Int. Ed.
2007, 46, 7820–7822.
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9976–9977.
Acknowledgements
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Financial support by the Spanish CICYT (MAT2006-14274-C02-
01 and 02) is gratefully acknowledged. V.R. thanks to CSIC for an
I3-P fellowship.
References and notes
18. Hashmi, A. S. K. Catal. Today 2007, 122, 211–214.
19. Rosenfeld, D. C.; Shekhar, S.; Takemiya, A.; Utsunomiya, M.; Hartwig, J. F. Org.
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