Formation of Acetals and Ketals from Carbonyl Compounds: A New and Highly Efficient Method Inspired by Cationic Palladium

Article abstract of DOI:10.1055/s-0039-1690497

The development of a new, highly efficient, and simple method for masking carbonyl groups as acetals and ketals is described. This methodology relies on the nature of the palladium catalyst to direct the acetalization/ketalization reaction. This new protocol is mild and proceed with a very low catalyst loading at ambient temperatures. The method has been extended to a wide variety of different carbonyl compounds with various steric encumbrances to form the corresponding acetals and ketals in excellent yields.

Full text of DOI:10.1055/s-0039-1690497

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© Georg Thieme Verlag Stuttgart · New York
2019, 30, A–E
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E. A. Mensah et al.
Letter
Synlett
Formation of Acetals and Ketals from Carbonyl Compounds:
A New and Highly Efficient Method Inspired by Cationic Palladium
Enoch A. Mensah*
OR'
O
Pd(PhCN)2(OTf)2 (0.5 mol%)
rt, 12–90 min
R'O
R
OR'
H
+
Shawn D. Green
Jesse West
R'O
OR'
R
H
R = Alkyl, Aryl
R' = Me, Et
(1 equiv)
(3 equiv)
Tyler Kindoll
28 examples
up to 98% yield
Brenda Lazaro-Martinez
O
O
O
Pd(PhCN)2(OTf)2 (1 mol%)
MeOH, rt, 1–6 h
O
O
+
School of Natural Sciences, Indiana University Southeast,
4201 Grant Line Road, New Albany, IN 47150, USA
mensahe@ius.edu
O
R
R'
R
R'
R = Alkyl, Aryl
R' = Me, Pr
(1 equiv)
(3 equiv)
10 examples
up to 96% yield
Received: 25.06.2019
Accepted after revision: 09.07.2019
Published online: 23.07.2019
In spite of the existence of many methods that can serve
as viable alternatives for masking carbonyl groups during
organic transformation reactions, some of the methods em-
ploy the use of catalysts that are expensive or moisture sen-
sitive, and some require laborious workup protocols to iso-
late the product. This has therefore necessitated the need
for the development of a new and simple method for mask-
ing carbonyl groups to complement existing methods.
In recent years, the use of cationic palladium com-
pounds, by virtue of their high stability, low toxicity, and
their ease of handling, has attracted much attention in or-
ganic synthesis, and these compounds have been used in
many organic synthesis protocols. For example, the Nguyen
research group reported a novel method that uses cationic
palladium to activate glycosyl trichloroacetimidates to ac-
cess - and -glycosides stereoselectively.27,28 To access cer-
tain classes of bioactive heterocycles, Lu et al. recently re-
ported the use of cationic palladium catalysts in arylative
cyclization of N-(2-formylaryl)alkynamides with various
aryl boronic acids to access functionalized 2-quinolinones,
an important class of heterocycles found present in many
bioactive natural products.29 In utilizing cationic palladium
species in the synthesis of bioactive compounds, Lipshutz
and co-workers demonstrated a cationic palladium-in-
spired Suzuki–Miyaura coupling of arylureas and arylbo-
ronic acids as a key step in a simple synthesis of the pesti-
cide Boscalid, used in controlling several plant pathogens.30
Because of the versatility and excellent catalytic activity
of cationic palladium catalysts in many synthetic organic
transformations, we reasoned that cationic palladium spe-
cies might be employed in activating carbonyl groups and
or trimethyl orthoformates in masking carbonyl com-
pounds as acetals or ketals.
DOI: 10.1055/s-0039-1690497; Art ID: st-2019-k0323-l
Abstract The development of a new, highly efficient, and simple
method for masking carbonyl groups as acetals and ketals is described.
This methodology relies on the nature of the palladium catalyst to di-
rect the acetalization/ketalization reaction. This new protocol is mild
and proceed with a very low catalyst loading at ambient temperatures.
The method has been extended to a wide variety of different carbonyl
compounds with various steric encumbrances to form the correspond-
ing acetals and ketals in excellent yields.
Key words palladium catalysis, acetals, ketals, acetalization, ketaliza-
tion, orthoformates
The formation of acetals and ketals is among the most
widely used protocols for protecting carbonyl groups in
multifunctional substrates during functional-group trans-
formations in organic synthesis.1 Acetalization and ketal-
ization reactions are usually performed by the condensa-
tion of carbonyl compounds with alcohols or diols promot-
ed by acids.1–4 However, long reaction times, high
temperatures, incomplete reactions, and moderate yields
are frequent problems and can potentially limit the utility
of acetalization and ketalization reactions in organic syn-
thesis.
To circumvent these problems, many alternative reac-
tion protocols for masking carbonyl groups have been re-
ported over the years, some of which include the use of
clays,5 InCl3,6 In(OTf)3/(MeO)3CH,7–9 Sc(OTf)3/(MeO)3CH,10
Bi(OTf)3/(MeO)3CH,11 CeCl3/(MeO)3CH,12 LaCl3/(MeO)3CH,13
LiBF4/(MeO)3CH,14 TiCl4/NEt3CH,15 I2,16 Cu(BF4)2.xH2O,17
N,N′-bis[3,5-bis(trifluoromethyl)phenyl]thiourea,18 decab-
orane,19 DDQ,20 FeCl3/(EtO)3CH,21 ZrCl4,22 RuCl3,23 CoCl2,24
tetrabutylammonium tribromide,25 or pyridinium ions.26
Our recent report on the excellent catalytic activity of
the cationic palladium(II) species bis(benzonitrile)palladi-
um(II) bistriflate [Pd(PhCN)2(OTf)2] in activating acetic
© 2019. Thieme. All rights reserved. — Synlett 2019, 30, A–E
Georg Thieme Verlag KG, Rüdigerstraße 14, 70469 Stuttgart, Germany

B
E. A. Mensah et al.
Letter
Synlett
anhydride in the acetylation of alcohols and polyols31
prompted us to begin this study by using this catalyst. To
the best of our knowledge, this represents the first instance
of the use of a cationic palladium(II) species in catalyzing
the masking of carbonyl groups as acetals or ketals. We re-
port a novel and highly efficient method that employs the
use of the cationic palladium(II) species Pd(PhCN)2(OTf)2 as
a catalyst in masking carbonyl groups as the corresponding
acetals or ketals.
After a series of extensive preliminary studies with 4-
bromobenzaldehyde as our model substrate in the presence
of trimethyl orthoformate (3 equiv), we discovered that 0.5
mol% of cationic Pd(PhCN)2(OTf)2 catalyzed the transforma-
tion of 4-bromobenzaldehyde into the corresponding di-
methyl acetal 1 within a short reaction time and in excel-
lent yield. This result was significant, as it demonstrates the
ability of Pd(PhCN)2(OTf)2 to activate an aldehyde and
trimethyl orthoformate, resulting in rapid transformation
into the corresponding dimethyl acetal with a low catalyst
loading.
groups. Silyl protecting groups, although acid labile, have
been used extensively to mask hydroxy groups in many or-
ganic synthetic transformations. In this instance, when a si-
lyl-protected benzaldehyde was used as the substrate, it
was gratifying to note that the acid-labile silyl group sur-
vived and the corresponding dimethyl acetal 10 was ob-
tained in excellent yield (Scheme 1). Also noteworthy was
the facile transformation of acid-sensitive 2-furaldehyde
into the corresponding dimethyl acetal 8 in excellent yield
(Scheme 1). These results suggest not only that this cationic
Pd(II)catalyst is highly efficient, but that the reaction proto-
col is also mild.
The efficacy of this new method was also evaluated by
comparing it with other reported methods for masking car-
bonyl groups as dimethyl acetals. With benzaldehyde as a
starting substrate, De and Gibbs reported that ruthenium
(III) chloride catalyzed a transformation into benzaldehyde
dimethyl acetal in good yield, although a long reaction time
was required.23 With pyridinium salts as catalysts, Procu-
ranti and Connon26 reported the transformation of benzal-
dehyde into its dimethyl acetal after 24 hours. On the other
hand, with the same starting aldehyde, our new cationic
palladium(II) method resulted in a rapid transformation
into the dimethyl acetal 2 in a shorter reaction time (40
min) and with an excellent yield (90%; Scheme 1).
In a recent report, Lei and co-workers successfully uti-
lized visible light to induce the acetalization of aldehydes
with alcohols;32 however, when 4-bromobenzaldehyde and
4-nitrobenzaldehyde were used as substrates, the respec-
tive dimethyl acetals were isolated only after a long reac-
tion time of 12 hours. In contrast, with our new protocol,
the acetalization reactions of these aldehydes were rapid,
affording the acetals 1 and 5, respectively, in excellent
yields and in relatively short reaction times of 15 and 12
minutes (Scheme 1). It is gratifying to note that our new
method for masking carbonyl groups is not only rapid, but
also proceeds with a relatively low catalyst loading at room
temperature.
This excellent result prompted us to investigate the
scope of this catalyst by using a variety of aldehydes as sub-
strates (Scheme 1). Several aldehyde substrates with vari-
ous activating or deactivating groups underwent rapid ac-
etalization to give the corresponding dimethyl acetals 2–14
in excellent yields.
O
O
Pd(PhCN)2(OTf)2 (0.5 mol%)
rt
O
O
+
O
O
R
H
R
H
(1 equiv)
(3 equiv)
O
O
O
O
H
O O
O
O
H
H
H
Br
1 (15 min, 97%)
2 (40 min, 90%)
3 (45 min, 92%)
4 (30 min, 91%)
O
O
O
O
O
O
H
H
O
O
H
O
O
H
O2N
NO2
O
One key problem encountered with this protocol was
the consistently low isolated yields obtained due to partial
deprotection of the product when the reaction mixture was
concentrated in vacuo before purification. A similar issue
was observed by Gregg et al.7 with indium triflate. To cir-
cumvent this problem, after the reaction was completed,
the reaction mixture was directly purified by flash column
chromatography with elution by hexanes–ethyl acetate
containing 1% triethylamine to give excellent yields of the
isolated products.
Although there are many methods for masking alde-
hydes as the corresponding dimethyl acetals, relatively few
methods have been reported for transforming aldehydes
into the corresponding diethyl acetals.7–9,11,14,17,21–25 To
study the versatility of our protocol in masking carbonyl
groups, we next examined the conversion of aldehydes into
the corresponding diethyl acetals by treatment with
5 (12 min, 95%)
6 (20 min, 90%)
7 (20 min, 94%)
8 (40 min, 96%)
O
O
O
H
O
O
O
H
O
O
H
H
TBDMSO
10 (30 min, 90%)
12 (15 min, 88%)
11 (15 min, 92%)
9 (90 min, 92%)
O
O
H
O
O
H
13 (20 min, 91%)
14 (20 min, 90%)
Scheme 1 Acetalization of aldehydes with trimethyl orthoformate cat-
alyzed by Pd(PhCN)2(OTf)2. Pd(PhCN)2(OTf)2 was generated in situ from
Pd(PhCN)2Cl2 (1 equiv) and Ag(OTf) (2 equiv) in dried CH2Cl2 (0.0125
M).
As a result of these encouraging results, we next investi-
gated the compatibility of our new acetalization protocol
with acid-labile protecting groups, such as silyl protecting
© 2019. Thieme. All rights reserved. — Synlett 2019, 30, A–E

C
E. A. Mensah et al.
Letter
Synlett
triethyl orthoformate. With various aldehydes as sub-
strates, the reaction proceeded smoothly and rapidly in all
cases to afford the corresponding diethyl acetals 15–28 in
good to excellent yields (Scheme 2).
O
O
Pd(PhCN)2(OTf)2 (1 mol%)
MeOH, rt, 1–6h
O
O
+
O
O
R
R'
R
R'
R = Alkyl, Aryl
R' = Me, Pr
1 equiv
3 equiv
O
O
O
O
O
O
O O
O
O
Pd(PhCN)2(OTf)2 (0.5 mol%)
rt
O
O
+
O
O
R
H
R
H
O
NO2
32 (89%)
(1 equiv)
(3 equiv)
29 (90%)
30 (96%)
31 (88%)
O
O
O
O
O
O
O
O
O
O
H
O
O
O
O
H
H
H
O O
Br
Cl
15 (20 min, 92%)
16 (30 min, 91%)
17 (60 min, 93%)
18 (30 min, 90%)
Cl
34 (85%)
O
O
33 (94%)
35 (87%)
36 (92%)
O
O
O
O
H
H
O
O
O
O
O
O
H
O
O
H
O2N
O
NO2
20 (25 min, 91%)
37 (88%)
38 (90%)
19 (15 min, 98%)
21 (30 min, 93%)
22 (45 min, 90%)
Scheme 3 Protection of ketones with trimethyl orthoformate cata-
lyzed by Pd(PhCN)2(OTf)2. Pd(PhCN)2(OTf)2 was generated in situ from
Pd(PhCN)2Cl2 (1 equiv) and Ag(OTf) (2 equiv) in dried CH2Cl2 (0.0125
M).
O
H
O
O
O
O
O
H
O
O
H
TBDMSO
H
26 (17 min, 92%)
23 (90 min, 90%)
24 (30 min, 92%)
25 (15 min, 90%)
hyde with trimethyl orthoformate in the absence of a cata-
lyst, there was no significant formation of the correspond-
ing dimethyl acetal 1, even after stirring the reaction mix-
ture for five hours (Table 1, entry 1). The result from this
control experiment suggests a likely role of the catalyst in
the observed transformation. Because the catalyst used was
generated in situ from 0.5 mol% of the neutral Pd(II) species
Ph(PhCN)2Cl2 and 1 mol% of AgOTf, another control experi-
ment was carried out with 0.5 mol% of the neutral Pd(II)
species Ph(PhCN)2Cl2 as the catalyst. In this case, the reac-
tion also did not result in any significant formation of the
desired product 1, even when the reaction mixture was
stirred for a number of hours (entry 2). In view of earlier re-
ports on the use of AgOTf as a catalyst in many organic
transformations,33–38 as well its use in generating the cat-
ionic Pd(II) catalyst in this study, we conducted another
control experiment in the presence of 1 mol% AgOTf to in-
vestigate the influence of AgOTf on the observed catalytic
activity. In this instance, the acetalization reaction was also
sluggish, with no significant product isolation. (entry 3).
Upon running the acetalization reaction with 0.5 mol% of
the cationic Pd(II) species, Ph(PhCN)2(OTf)2 generated in
situ from 0.5 mol% of the neutral Pd(II) species
Ph(PhCN)2Cl2 and 1 mol% of AgOTf, the reaction proceeded
smoothly to afford the desired dimethyl acetal 1 in excel-
lent yield (entry 4). These results confirm that the cationic
Pd(II) catalyst, rather than AgOTf or the neutral Pd(II) spe-
cies Pd(PhCN)2Cl2, played a role in the observed transforma-
tion.
O
O
H
O
O
H
27 (22 min, 88%)
28 (20 min, 93%)
Scheme 2 Acetalization of aldehydes with triethyl orthoformate cata-
lyzed by Pd(PhCN)2(OTf)2. Pd(PhCN)2(OTf)2 was generated in situ from
Pd(PhCN)2Cl2 (1 equiv) and Ag(OTf) (2 equiv) in dried CH2Cl2 (0.0125
M).
To investigate the scope and efficacy of the cationic pal-
ladium(II) catalyst in more detail, the method was extended
to a variety of relatively less reactive carbonyl compounds,
such as aliphatic and aromatic ketones. As expected, the ac-
etalization reactions were sluggish. However, the reaction
was driven to completion to afford the corresponding ketals
29–38 in good to excellent yields when the catalyst loading
was increased to 1 mol% and methanol was used as the sol-
vent (Scheme 3).
Of particular note was the transformation of acetophe-
none into the corresponding ketal 29. Whereas both Gregg
et al.7 and Smith and Graham8 reported either low yields or
long reaction times to access the ketal, our new reaction
protocol afforded the desired ketal 29 in good yield and in a
relatively short reaction time of 2.5 hours (Scheme 3).
As a result of these encouraging results and observa-
tions, we examined the origin of the observed catalytic ac-
tivity. In this instance, a number of control experiments
were conducted by using 4-bromobenzaldehyde as the
model substrate (Table 1). Upon treating 4-bromobenzalde-
© 2019. Thieme. All rights reserved. — Synlett 2019, 30, A–E

D
E. A. Mensah et al.
Letter
Synlett
Table 1 Control Experiment with 4-Bromobenzaldehyde as a Model
(6) Ranu, B. C.; Jana, R.; Samanta, S. Adv. Synth. Catal. 2004, 346,
446.
Substratea
(7) Gregg, B. T.; Golden, K. C.; Quinn, J. F. Tetrahedron 2008, 64,
3287.
(8) Smith, B. M.; Graham, A. E. Tetrahedron Lett. 2006, 47, 9317.
(9) Smith, B. M.; Graham, A. E. Tetrahedron Lett. 2007, 48, 4891.
(10) Ishihara, K.; Karumi, Y.; Kubota, M.; Yamamoto, H. Synlett 1996,
839.
O
O
O
O
Catalyst
rt
H
+
H
O
O
Br
Br
(1 equiv)
(3 equiv)
1
(11) Leonard, N. M.; Oswald, M. C.; Freiberg, D. A.; Nattier, B. A.;
Smith, R. C.; Mohan, R. S. J. Org. Chem. 2002, 67, 5202.
(12) Smith, A. B. III.; Fukui, M.; Vaccaro, H. A.; Empfield, J. R. J. Am.
Chem. Soc. 1991, 113, 2071.
(13) Gemal, A. L.; Luche, J.-L. J. Org. Chem. 1979, 44, 4187.
(14) Hamada, N.; Kazahaya, K.; Shimizu, H.; Sato, T. Synlett 2004,
1074.
(15) Clerici, A.; Pastori, N.; Porta, O. Tetrahedron 1998, 54, 15679.
(16) Banik, B. K.; Chapa, M.; Marquez, J.; Cardona, M. Tetrahedron
Lett. 2005, 46, 2341.
(17) Kumar, R.; Chakraborti, A. K. Tetrahedron Lett. 2005, 46, 8319.
(18) Kotke, M.; Schreiner, P. R. Tetrahedron 2006, 62, 434.
(19) Lee, S. H.; Lee, J. H.; Yoon, C. M. Tetrahedron Lett. 2002, 43, 2699.
(20) Babak, K.; Miri, A. A. Chem. Lett. 1999, 1199.
(21) Bornstein, J.; Bedell, S. F.; Drummond, P. E.; Kopsloski, C. L.
J. Am. Chem. Soc. 1956, 78, 83.
(22) Firouzabadi, H.; Iranpoor, N.; Karimi, B. Synlett 1999, 321.
(23) De S, K.; Gibbs, R. A. Tetrahedron Lett. 2004, 45, 8141.
(24) Velusamy, S.; Punniyamurthy, T. Tetrahedron Lett. 2004, 45,
4917.
(25) Gopinath, R.; Hasque, S. J.; Patel, B. K. J. Org. Chem. 2002, 67,
5842.
(26) Procuranti, B.; Connon, S. J. Org. Lett. 2008, 10, 4935.
(27) Yang, J.; Cooper-Vanosdell, C.; Mensah, E. A.; Nguyen, H. M.
J. Org. Chem. 2008, 73, 794.
(28) Mensah, E. A.; Azzarelli, J. M.; Nguyen, H. M. J. Org. Chem. 2009,
74, 1650.
Entry Catalyst
Loading
Additive Time
Yielda (%)
1
2
3
4
5
–
–
–
5 h
5 h
5 h
< 1
< 1
< 5
97
Pd(PhCN)2Cl2
AgOTf
0.5 mol%
1.0 mol%
0.5 mol%
0.5 mol%
–
–
b
b
Pd(PhCN)2(OTf)2
Pd(PhCN)2(OTf)2
–
15 min
20 min
Hg(0)
93
a Isolated yield.
b Pd(PhCN)2(OTf)2 was generated in situ from Pd(PhCN)2Cl2 (0.5 equiv) and
AgOTf (1 equiv) in dried CH2Cl2 (0.0125 M).
There are numerous recent reports on the use of Pd(0)
or palladium nanoparticles (Pd-NPs) as catalysts in C–C
bond-forming reactions.39–42 To ensure that the origin of the
observed catalysis was not due to Pd(0) or to Pd-NPs, we
conducted another control experiment in the presence of
mercury (the mercury drop test). In this case, the reaction
still proceeded smoothly to afford the corresponding di-
methyl acetal 1 in excellent yield (Table 1, entry 5). This re-
sult suggests that the observed acetalization reaction in-
volves neither Pd(0) nor Pd-NPs.
In summary, a new method has been developed for
masking carbonyl compounds as their corresponding dial-
kyl acetals through catalysis with a cationic palladium(II)
species.43 This method is mild, versatile, and highly efficient
and it requires low catalyst loading at room temperature.
(29) Zhang, X.; Han, X.; Chen, J.; Lu, X. Tetrahedron 2017, 73, 1541.
(30) Nishikata, T.; Abela, A. R.; Huang, S.; Lipshutz, B. H. Beilstein J.
Org. Chem. 2016, 12, 1040.
(31) Mensah, E. A.; Reyes, F. R.; Standiford, E. S. Catalysts 2016, 6, 27.
(32) Yi, H.; Niu, L.; Wang, S.; Liu, T.; Singh, A. K.; Lei, A. Org. Lett.
2017, 19, 122.
Acknowledgment
(33) Yu, X.; Ye, S.; Wu, J. Adv. Synth. Catal. 2010, 352, 2050.
(34) Briones, J. F.; Davies, H. M. L. Org. Lett. 2011, 13, 3984.
(35) Jiang, L.; Yu, X.; Fang, B.; Wu, J. Org. Biomol. Chem. 2012, 10,
8102.
(36) Das, R.; Chakraborty, D. Synthesis 2011, 1621.
(37) Rao, V. K.; Rao, M. S.; Jain, N.; Panwar, J.; Kumar, A. Org. Med.
Chem. Lett. 2011, 1, 10.
(38) Zheng, D.; Li, S.; Wu, J. Org. Lett. 2012, 14, 2655.
(39) Pérez-Lorenzo, M. J. Phys. Chem. Lett. 2012, 3, 167.
(40) Sawai, K.; Tatumi, R.; Nakahodo, T.; Fujihara, H. Angew. Chem.
Int. Ed. 2008, 47, 6917.
We gratefully acknowledge the financial support of Indiana Universi-
ty Southeast. This research is also supported by Indiana University
Southeast Research Support Program and the Indiana University
Southeast Large Grant Program.
Supporting Information
Supporting information for this article is available online at
https://doi.org/10.1055/s-0039-1690497.
S
u
p
p
orit
n
gInformati
o
n
S
u
p
p
orti
n
gInformati
o
n
(41) Sawoo, S.; Srimani, D.; Dutta, P.; Lahiri, R.; Sarkar, A. Tetrahe-
dron 2009, 65, 4367.
References and Notes
(42) Lu, F.; Ruiz, J.; Astruc, D. Tetrahedron Lett. 2004, 45, 9443.
(43) 4-Bromobenzaldehyde Dimethyl Acetal (1); Typical Procedure
An oven-dried, argon-flushed, 10 mL round-bottomed flask was
charged with 4-bromobenzaldehyde (92.5 mg, 0.5 mmol, 1.0
equiv) and HC(OMe)3 (0.16 mL, 1.5 mmol, 3.0 equiv). To this
mixture was added a preformed solution of Pd(PhCN)2(OTf)2
(0.2 mL, 0.0025 mmol, 0.5 mol%), generated in situ from
Pd(PhCN)2Cl2 (0.96 mg, 0.0025 mmol, 0.5 mol%) and AgOTf
(1.29 mg, 0.005 mmol, 1 mol%) in anhyd CH2Cl2 (0.2 mL). The
(1) Meskens, F. A. J. Synthesis 1981, 501.
(2) Greene, T. W.; Wuts, P. G. M. Protecting Groups in Organic Syn-
thesis, 3rd ed; Wiley-Interscience: New York, 1999.
(3) Cameron, A. F. B.; Hunt, J. S.; Oughton, J. F.; Wilkinson, P. A.;
Wilson, B. M. J. Chem. Soc. 1953, 3864.
(4) Wenkert, E.; Goodwin, T. E. Synth. Commun. 1977, 7, 409.
(5) (a) Taylor, E. C.; Chiang, C.-S. Synthesis 1977, 467. (b) Mizugake,
T.; Ebitani, K.; Kaneda, K. Tetrahedron Lett. 2001, 42, 8329.
© 2019. Thieme. All rights reserved. — Synlett 2019, 30, A–E

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E. A. Mensah et al.
Letter
Synlett
resulting mixture was stirred at r.t. until the reaction was com-
plete (TLC) then directly purified by flash column chromatogra-
phy [silica gel, hexanes–EtOAc (4:1) + Et3N (1%)] to give a color-
less oil; yield: 112 mg (97%).
Acetophenone Dimethyl Acetal (29)
Colorless oil; yield: 74.8 mg (90%). IR (film): 3002, 2991, 2943,
2831, 1447, 1372, 1276, 1197, 1146, 1091, 1040, 909 cm–1 1H
NMR (600 MHz, CDCl3):  = 7.54–7.52 (m, 1 H), 7.52–7.51 (m, 1
H), 7.38–7.34 (m, 2 H), 7.31 – 7.27 (m, 1 H), 3.21 (s, 6 H), 1.56 (s,
3 H). 13C NMR (150 MHz, CDCl3):  = 142.9, 128.0, 127.5, 126.2,
101.6, 48.9, 26.1.
.
IR (film): 3005, 2936, 1593, 1485, 1398, 1349, 1205, 1099, 1051,
1011, 984 cm–1 1H NMR (600 MHz, CDCl3):  = 7.48 (d, J = 8.5
.
Hz, 2 H), 7.31 (d, J = 8.3 Hz, 2 H), 5.34 (s, 1 H), 3.29 (s, 6 H). 13
NMR (150 MHz, CDCl3):  = 137.1, 131.3, 128.5, 122.5, 102.2, 52.5.
C
© 2019. Thieme. All rights reserved. — Synlett 2019, 30, A–E