Hypervalent iodine mediated synthesis of carbamate protected p-quinone monoimine ketals and p-benzoquinone monoketals

Article abstract of DOI:10.1039/c2ob25089f

A simple and efficient method for the synthesis of p-quinone monoimide ketals and p-benzoquinone monoketals by using a hypervalent iodine reagent, diacetoxyiodobenzene, has been developed. These two types of ketals are achieved from a single starting material by varying the reaction conditions.

Full text of DOI:10.1039/c2ob25089f

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PAPER
Hypervalent iodine mediated synthesis of carbamate protected p-quinone
monoimine ketals and p-benzoquinone monoketals†‡
Naganjaneyulu Bodipati and Rama Krishna Peddinti*
Received 12th January 2012, Accepted 3rd April 2012
DOI: 10.1039/c2ob25089f
A simple and efficient method for the synthesis of p-quinone monoimide ketals and p-benzoquinone
monoketals by using a hypervalent iodine reagent, diacetoxyiodobenzene, has been developed. These two
types of ketals are achieved from a single starting material by varying the reaction conditions.
p-quinone monoimide ketals by using a hypervalent iodine
reagent, iodosylbenzene. However, their procedure was used for
Introduction
Quinone imines and bisimines are remarkably versatile starting
materials in the synthesis of natural products1,2 and in the syn-
thesis of 5-methoxyindoles,3 benzofused heterocycles4 and
tropone ring systems.5 The major applications of these entities
are in nucleophilic additions promoted by both acids and
bases.6–8 The stability of these reactive species is a function of
the nature of the substitution on the nitrogen atom. Simple p-
benzoquinone imines and N-alkyl-p-benzoquinone imines are
highly unstable compounds and are prone to rapid hydrolysis.
As a result, an electron-withdrawing group on the nitrogen atom
of the p-benzoquinone imine is necessary to prevent decompo-
sition. The methods most commonly used today to generate such
synthons mostly rely on electrochemical oxidation of p-methox-
yanilides or p-phenylenediamides.9–12 The reported methods
involve the use of N-arylsulfonyl and N-benzoyl groups as
amide linkage.13 The necessity for strongly acidic conditions for
the removal of these groups during synthetic manipulation of the
quinone imides limits their use.
On the contrary, the carbamate protected quinone imine ketals
can be more easily hydrolysed than other imides and are stable
enough under the hydrolysis conditions. Swenton et al.
reported14 an electrochemical method for the generation of car-
bamate protected quinone imine ketals, and later it was improved
by Carreño and Ribagorda.15 However, only a few chemical
methods16,17 for the generation of p-quinone imine ketals are
reported in literature. No reports for the chemical generation of
carbamate protected quinone imine ketals are available. Barret
and Daudon18 described a method for the generation of
N-arylsulfonyl and N-benzoyl-p-methoxyanilides and suffers
from moderate yields. Herein we report for first time the chemi-
cal generation of carbamate protected p-quinone monoimide
ketals by the diacetoxyiodobenzene (DIB) mediated oxidation of
N-tert-butoxycarbonyl-p-methoxyanilides. We also extended this
protocol for the oxidation of N-acyl-p-methoxyanilides, N-tert-
butoxycarbonylanilides and N-acetylanilides into the correspond-
ing N-protected p-benzoquinone imine ketals.
Results and discussion
Inspired by the protocols for obtaining the reactive orthobenzo-
quinone monoketals19 and orthobenzoquinone monoimines20
generated by the oxidation of 2-methoxyphenols and 2-amino-
phenols with hypervalent iodine reagents,19b,c,20–22 we became
interested to employ this strategy for the generation of N-tert-
butoxycarbonyl-p-quinone imine ketals by oxidative dearomati-
zation of N-tert-butoxycarbonyl-p-methoxyanilides. In our initial
experiments, 1 mmol of p-methoxyanilide 1a was treated with
1.2 mmol of DIB in methanol (5 mL) at room temperature to
obtain the desired product, p-quinone imide ketal 4a in low
yield. This low yield of 4a may be attributed to the presence of
acetic acid, which was released during the progress of the reac-
tion. To neutralize the acetic acid, we performed the reaction in
the presence of the base KHCO3. Indeed, as can be seen from
entry 2, Table 1, the chemical yield was considerably improved
with the introduction of KHCO3. To gauge the effect of the base,
the reaction was performed in the presence of different bases, the
results of which are summarized in Table 1.
A complex mixture was formed when pyridine was used as
the base (entry 3, Table 1). Among the bases tested, triethyl-
amine was found to produce p-quinone imide ketal 4a in optimal
yield (entry 4, Table 1). When the reaction was carried out at
50 °C in the presence of triethylamine, the product was obtained
in 81% yield (entry 7, Table 1). Since the products are sensitive
towards silica gel, they were isolated on silica gel column
Department of Chemistry, Indian Institute of Technology, Roorkee-247
667, Uttarakhand, India. E-mail: rkpedfcy@iitr.ernet.in, ramakpeddin-
ti@gmail.com; Fax: (+) 91 13 3227 3560; Tel: (+) 91 13 3228 5438
†Dedicated to our esteemed colleague Professor Gurudas Bhattacharjee
on the occasion of his retirement.
‡Electronic supplementary information (ESI) available: Copies of 1H
NMR and 13C NMR spectra are provided. See DOI: 10.1039/
c2ob25089f
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Table 1 Optimization of the oxidation of N-tert-butoxycarbonyl-p-
methoxyanilide (1a) by using DIBa
Table 2 (Contd.)
Entry Substrate
7
Time (h) Product
1
Yielda (%)
Entry
Baseb
Yieldc (%)
1g
1h
4g 94
1
2
3
4
5
6
7
—
21
46
Trace
92
54
KHCO3
Pyridine
Et3N
DBU
DABCO
Et3N
8
1
4h 96
4i 82
4j 79
4k 93
4l 89
62
81d
a All reactions were carried out under aerobic conditions. b 3 equiv of
base used. c Yield of isolated products. d Reactions were carried out at
50 °C.
9
1i 2.5
10
11
12
1j
2
2
Table 2 DIB Mediated oxidation of differently substituted p-
methoxyanilides
1k
1l 2.5
Entry Substrate
1
Time (h) Product
1
Yielda (%)
4a 92
1a
1b
1c
a Yield of pure and isolated products. b cis/trans mixture.
neutralized with triethylamine and stored in a freezer below
0 °C. With a consistent set of conditions in hand, we extended
this procedure to differently substituted N-tert-butoxycarbonyl-p-
methoxyanilides 1b–1f (Table 2). The 2-substituted p-methoxya-
nilides 1b and 1e upon oxidation provided the products 4b and
4e as single isomers in 95 and 96% yield, respectively. On the
other hand, the p-methoxyanilides 1c and 1d under the same
conditions, as a result of steric reasons, gave mixtures of cis and
trans imides 4c and 4d in 91 and 92% yield, respectively. The
naphthalene amide 1f underwent smooth oxidation to provide
the corresponding imide 4f in 83% yield.
2
3
1
2
4b 95
4c 91b
4
1d
2
4d 92b
Since there is much interest in the oxidation products of acy-
lated aromatic amines,23 we adopted the above protocol to
oxidize N-acetyl-p-methoxyanilides 1g–1l. When we attempted
to purify the reaction mixture on silica gel, it led to a complex
mixture of decomposed products in which noticeable amount of
p-benzoquinone monoketal was present. Consequently, we
purified p-benzoquinone monoimide ketals 4g–4l in good yields
(Table 2) on a silica gel column neutralized with triethylamine.
It occurred to us that if we developed a method for the synthesis
of p-benzoquinone monoketals from the same starting material,
it would be a valuable addition to p-benzoquinone chemistry
5
6
1e
1f
3
2
4e 96
4f 83
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Fig. 1 p-Methoxyanilides.
Table 3 Synthesis of p-benzoquinone monoketals from p-
methoxyanilides
Scheme 1 Double oxidation of anilides.
limitation of this procedure is non-availability of variously sub-
stituted 4-methoxyanilides/phenols.24 In an effort to increase the
library of precursors for p-quinone monoimide ketals and p-
quinone monoketals, we attempted the reaction of simple ani-
lides 2 and 3 with 2.4 equiv. of DIB in methanol at room temp-
erature; the reaction went smoothly to furnish the corresponding
ketals 4a, 4f, 4g, 4l in good yields (Scheme 1).
Entry
Substrate
Time (h)
Product
Yielda (%)
1
2
3
4
5
6
7
8
1a
1b
1c
1d
1e
1f
1g
1h
1i
5
4
6
6
5
4
4
4
5
5
5
4
5a
5b
5c
5d
5e
5f
5a
5b
5c
5d
5e
5f
74
81
60
59
61
75b
84
89
71
76
74
82b
Conclusion
In summary, we have developed a new and facile chemical
method for the synthesis of carbamate and acetyl protected
quinone imine ketals and p-benzoquinone monoketals from
various p-methoxyanilides and from simple anilides. The
method is operationally simple and high yielding at room temp-
erature and circumvents purification problems.
9
10
11
12
1j
1k
1l
a Yield of pure and isolated products. b Yield of 1,4-naphthoquinone.
Experimental section
since these molecular entities are extremely valuable building
blocks in natural product synthesis, particularly halogen substi-
tuted ketals.24 Thus we carried out the reaction of 1g in the
absence of triethylamine, expecting that the released acetic acid
would help to hydrolyze the imide ketal into quinone monoketal,
but obtained N-acetyl-3,4-dimethoxyaniline (6a) in 81% yield
instead of quinone ketal 5a. This transformation took place due
to the migration of one of the methoxy groups of p-quinone
monoimide ketal 4g. When we extended this protocol to anilides
1h–1k, surprisingly we recovered only starting compounds
instead of methoxy substituted p-methoxyanilides such as 6
(Fig. 1).
In subsequent studies we performed the oxidation of 1a in the
presence of silica gel and triethylamine. To our delight, p-
quinone monoketal 5a was obtained in good yield. Here triethyl-
amine assisted the neutralization of acetic acid and silica gel
facilitated the hydrolysis of imide ketal 3a affording the quinone
monoketal 5a in a controlled manner. Under these conditions
various p-methoxyanilides 1a–1l were oxidized to the corre-
sponding p-quinone monoketals 5a–5f (Table 3). The reaction
procedure worked better with acetylated p-methoxyanilides 1g–
1l than with the carbamate protected anilides. In general, the syn-
thesis of p-quinone monoimide ketals and p-benzoquinone
monoketals was achieved from the oxidation of the correspond-
ing 4-methoxy substituted anilides and phenols. The main
General information
Unless otherwise noted, chemicals were purchased at the highest
purity grade available and were used without further purification.
Methanol was distilled by using magnesium cake. Column
chromatography was carried out using silica gel
(100–200 mesh). Analytical thin layer chromatography was per-
formed on 0.25 mm silica gel plates (60F-254) using UV light
as visualizing agent. 1H NMR spectra were recorded at 500 MHz
and were recorded relative to the peak for CDCl3 (δ 7.26) or
TMS (δ 0.00). High-resolution mass spectra (HRMS) were
recorded on Jeol JMS600H spectrometer. 1H NMR coupling
constants (J) are reported in Hertz, and multiplicities are indi-
cated as follows: s (singlet), d (doublet), t (triplet), q (quartet), m
(multiplet).
General procedure for p-quinone monoimide ketals
A solution of DIB (1.2 mmol) in methanol (2 mL) was added
drop-wise to a solution of p-methoxyanilide (1, 1 mmol) and tri-
ethylamine (3 mmol) in methanol (3 mL) at room temperature.
The reaction mixture was stirred at the same temperature for the
time indicated in Table 2. After completion of the reaction the
solvent was removed under reduced pressure and the crude reac-
tion mixture was loaded directly onto a silica gel column
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1
(100–200 mesh) neutralized with triethylamine. The product was
eluted by using ethyl acetate in hexanes. The known products
were characterized by comparison of their spectral data (1H and
13C NMR) with those of authentic samples.11,14,15
968, 847 cm−1; H NMR (CDCl3, 500 MHz): δ 6.39 (brd, J =
12.0 Hz, 2H), 5.74 (s, 1H), 3.80 (s, 3H), 3.29 (s, 6H), 1.57 (s,
9H) ppm; 13C NMR (CDCl3, 125 MHz): δ 152.8, 150.5, 132.0,
122.0, 120.9, 118.0, 95.0, 83.2, 56.0, 51.1 (2C), 27.7 (3C) ppm;
HRMS (FAB+, m/z), calcd for C14H21NO5Na+ [M + Na]+:
306.1317, found 306.1315.
General procedure for p-benzoquinone monoketals 5
N-(tert-Butoxycarbonyl)-2-methoxy-p-benzoquinone imine di-
methyl acetal (4e). Colorless oil; IR (film): 3050, 1689, 955,
A solution of DIB (1.2 mmol) in methanol (2 mL) was added
drop-wise to a mixture of p-methoxyanilide (1, 1 mmol), tri-
ethylamine (2.4 mmol) and silica gel (0.5 g, 100–200 mesh) in
methanol (3 mL) at room temperature. The reaction mixture was
stirred at the same temperature for the time indicated in Table 3.
After completion of the reaction, the contents were filtered and
the solvent was removed under reduced pressure and the crude
reaction mixture was loaded directly onto a silica gel column
(100–200 mesh). The product was eluted by using ethyl acetate
in hexanes.
1
918 cm−1; H NMR (CDCl3, 500 MHz): δ 6.48–6.43 (m, 1H),
6.33–6.29 (m, 1H), 5.48 (s, 1H), 3.71 (s, 3H), 3.30 (s, 6H), 1.52
(s, 9H) ppm; 13C NMR (CDCl3, 125 MHz): δ 186.1, 153.1,
139.3, 134.0, 129.5, 103.9, 99.9, 80.1, 56.1, 50.3 (2C), 28.0
(3C) ppm; HRMS (FAB+, m/z), calcd for C14H21NO5Na+ [M +
Na]+: 306.1317, found 306.1309.
N-(tert-Butoxycarbonyl)-1,4-naphthoquinone imine dimethyl
acetal (4f). Colorless oil; IR (film): 3056, 1680, 1209, 1193,
1
1095 cm−1; H NMR (CDCl3, 500 MHz): δ 8.27 (dd, J = 1.0,
9.0 Hz, 1H), 8.21 (dd, J = 1.0, 8.0 Hz, 1H), 7.84 (d, J = 8.5 Hz,
1H), 6.75 (d, J = 8.0 Hz, 1H), 6.71 (d, J = 10.5 Hz, 1H), 6.59
(d, J = 10.5 Hz, 1H), 3.13 (s, 6H), 1.60 (s, 9H) ppm; 13C NMR
(CDCl3, 125 MHz): δ 162.0, 155.7, 139.9, 137.7, 132.2, 129.0,
126.6, 125.7, 125.2, 122.5, 95.4, 82.7, 55.5, 51.2, 28.1 (3C)
ppm; HRMS (FAB+, m/z), calcd for C17H21NO4Na+ [M + Na]+:
326.1368, found 326.1362.
General procedure for double oxidation
A solution of DIB (2.4 mmol) in methanol (4 mL) was added
drop-wise to a solution of anilides (2 or 3, 1 mmol) and triethyl-
amine (5 mmol) in methanol (4 mL) at room temperature. The
reaction mixture was stirred at the same temperature for 4 h.
After completion of the reaction, the solvent was removed under
reduced pressure and the crude reaction mixture was loaded
directly onto a silica gel column (100–200 mesh) neutralized
with triethylamine. The product 4 was eluted by using ethyl
acetate in hexanes.
N-Acetyl-p-benzoquinone imine dimethyl acetal (4g). Color-
1
less oil; IR (film): 3050, 2944, 1695, 1461, 963, 827 cm−1; H
NMR (CDCl3, 500 MHz): δ 6.62 (d, J = 10.0 Hz, 2H), 6.33 (d,
J = 10.0 Hz, 2H), 3.31 (s, 6H), 2.21 (s, 3H) ppm; 13C NMR
(CDCl3, 125 MHz): δ 185.9, 151.7, 143.2, 139.1, 129.9, 126.4,
92.9, 50.1 (2C), 25.4 ppm; HRMS (FAB+, m/z), calcd for
C10H13NO3H+ [M + H]+: 196.0974, found 196.0978.
N-(tert-Butoxycarbonyl)-p-benzoquinone
imine
dimethyl
acetal (4a). Colorless oil; IR (film): 3062, 2926, 1694, 1606,
1
951, 835 cm−1; H NMR (CDCl3, 500 MHz): δ 6.53 (br, 2H),
6.41 (d, J = 10.5 Hz, 2H), 3.25 (s, 6H), 1.55 (s, 9H) ppm; 13C
NMR (CDCl3, 125 MHz): δ 160.9, 156.1, 137.2, 130.0, 127.2,
113.8, 92.8, 82.5, 49.9 (2C), 27.8 (3C) ppm; HRMS (FAB+, m/
z), calcd for C13H19NO4Na+ [M + Na]+: 276.1212, found
276.1219.
N-Acetyl-2-methyl-p-benzoquinone imine dimethyl acetal (4h).
1
Colorless oil; IR (film): 3060, 1675, 1465, 1071, 909 cm−1; H
NMR (CDCl3, 500 MHz): δ 6.50 (dd, J = 2.5, 10.0 Hz, 1H),
6.39 (q, J = 1.5 Hz, 1H), 6.29 (d, J = 10.0 Hz, 1H), 3.37 (s, 6H),
2.23 (s, 3H), 2.04 (s, 3H) ppm; 13C NMR (CDCl3, 125 MHz): δ
186.1, 152.1, 139.1, 135.9, 134.9, 123.1, 93.2, 49.9 (2C), 25.4,
17.1 ppm; HRMS (FAB+, m/z), calcd for C11H15NO3Na+ [M +
Na]+: 232.0950, found 232.0959.
N-(tert-Butoxycarbonyl)-2-methyl-p-benzoquinone imine di-
methyl acetal (4b). Colorless oil; IR (film): 3062, 1664, 976,
1
848 cm−1; H NMR (CDCl3, 500 MHz): δ 7.27 (br, 1H), 6.71
(s, 1H), 6.12 (s, 1H), 3.76 (s, 6H), 2.22 (s, 3H), 1.51 (s, 9H)
ppm; 13C NMR (CDCl3, 125 MHz): δ 161.7, 153.6, 138.7,
136.7, 134.9, 115.5, 93.1, 82.4, 55.0 (2C), 28.1 (3C), 17.7 ppm;
HRMS (FAB+, m/z), calcd for C14H21NO4Na+ [M + Na]+:
290.1368, found 290.1374.
N-Acetyl-3-chloro-p-benzoquinone imine dimethyl acetal (4i).
1
Colorless oil; IR (film): 3054, 1694, 1080, 958 cm−1; H NMR
(CDCl3, 500 MHz): δ 6.51 (dd, J = 3.0, 10.0 Hz, 1H), 6.41 (q, J
= 1.5 Hz, 1H), 6.34 (d, J = 10.0 Hz, 1H), 3.37 (s, 6H), 2.28 (s,
3H) ppm; 13C NMR (CDCl3, 125 MHz): δ 186.1, 152.1, 139.1,
135.9, 134.9, 123.1, 93.2, 49.9 (2C), 25.4 ppm; HRMS (FAB+,
m/z), calcd for C10H1235ClNO3H+ [M + H]+: 230.0584, found
230.0589; calcd for C10H1237ClNO3H+ [M + H]+: 232.0555
found 232.0561.
N-(tert-Butoxycarbonyl)-3-chloro-p-benzoquinone imine di-
methyl acetal (4c). Colorless oil; IR (film): 3065, 1665, 1249,
1
967, 865 cm−1; H NMR (CDCl3, 500 MHz): δ 6.70–6.69 (m,
1H), 6.59–6.55 (m, 1H), 6.44–6.42 (m, 1H), 3.24 (s, 6H), 1.55
(s, 9H) ppm; 13C NMR (CDCl3, 125 MHz): δ 158.7, 148.7,
136.8, 132.0, 131.9, 96.0, 94.2, 81.8, 51.1 (2C), 27.7 (3C) ppm;
HRMS (FAB+, m/z), calcd for C13H1835ClNO4Na+ [M + Na]+:
310.0822, found 310.0818; calcd for C13H1837ClNO4Na+
[M + Na]+: 312.0793 found 312.0794.
N-Acetyl-3-methoxy-p-benzoquinone imine dimethyl acetal
(4j). Colorless oil; IR (film): 3046, 1689, 959, 818, 744 cm−1
;
1H NMR (CDCl3, 500 MHz): δ 6.35 (dd, J = 1.5, 10.0 Hz, 1H),
6.31 (d, J = 10.0 Hz, 1H), 5.52 (d, J = 1.5 Hz, 1H), 3.73 (s, 3H),
3.21 (s, 6H), 2.17 (s, 3H) ppm; 13C NMR (CDCl3, 125 MHz): δ
185.8, 164.3, 153.4, 156.8, 128.4, 98.0, 93.9, 55.4, 50.9 (2C),
N-(tert-Butoxycarbonyl)-3-methoxy-p-benzoquinone imine di-
methyl acetal (4d). Colorless oil; IR (film): 3046, 1685, 1080,
4552 | Org. Biomol. Chem., 2012, 10, 4549–4553
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25.1 ppm; HRMS (FAB+, m/z), calcd for C11H15NO4H+ [M +
1,4-Naphthoquinone (5f). Colorless oil; IR (film): 3056,
1675, 946, 731 cm−1; 1H NMR (CDCl3, 500 MHz): δ 8.11–8.07
(m, 2H), 7.79–7.75 (m, 2H), 6.69 (s, 2H) ppm; 13C NMR
(CDCl3, 125 MHz): δ 185.1, 138.7, 134.1, 131.9, 126.5 ppm;
HRMS (FAB+, m/z), calcd for C10H6O2H+ [M + H]+: 159.0446,
found 159.0441.
H]+: 226.1079, found 226.1071.
N-Acetyl-2-methoxy-p-benzoquinone imine dimethyl acetal
(4k). Colorless oil; IR (film): 3062, 1694, 951, 881, 752 cm−1
;
1H NMR (CDCl3, 500 MHz): δ 6.44 (dd, J = 2.5, 10.0 Hz, 1H),
6.22 (d, J = 10.0 Hz, 1H), 5.40 (d, J = 2.5 Hz, 1H), 3.63 (s, 3H),
3.25 (s, 6H), 2.19 (s, 3H) ppm; 13C NMR (CDCl3, 125 MHz): δ
184.4, 149.5, 146.3, 138.4, 126.6, 106.9, 96.3, 55.1, 50.0 (2C),
24.8 ppm; HRMS (FAB+, m/z), calcd for C11H15NO4Na+ [M +
Na]+: 248.0899, found 248.0892.
Acknowledgements
The authors thank Council for Scientific and Industrial Research
[CSIR 01(2297)/09/EMR-II], New Delhi for financial support.
NB thanks CSIR for a research fellowship.
N-Acetyl-1,4-naphthoquinone imine dimethyl acetal (4l). Col-
orless oil; IR (film): 3070, 1698, 1652, 1594, 972, 810 cm−1; 1H
NMR (CDCl3, 500 MHz): δ 8.05 (d, J = 8.0 Hz, 1H), 7.63 (d, J
= 8.0 Hz, 1H), 7.50 (t, J = 8.0 Hz, 1H), 7.36 (t, J = 8.0 Hz, 1H),
6.56 (s, 2H), 3.07 (s, 6H), 2.23 (s, 3H) ppm; 13C NMR (CDCl3,
125 MHz): δ 186.2, 150.7, 139.9, 137.7, 131.8, 130.6, 128.8,
126.4, 125.4 (2C), 95.0, 50.9 (2C), 25.6 ppm; HRMS (FAB+, m/
z), calcd for C14H15NO3H+ [M + H]+: 246.1130, found
246.1135.
Notes and references
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Chem., 1993, 58, 867–878.
p-Benzoquinone dimethyl acetal (5a). Colorless oil; IR (film):
3062, 1682, 1461, 1072, 964 cm−1
;
1H NMR (CDCl3,
500 MHz): δ 6.80 (dd, J = 1.5, 10.0 Hz, 2H), 6.25 (dd, J = 1.5,
10.0 Hz, 2H), 3.35 (s, 6H) ppm; 13C NMR (CDCl3, 125 MHz):
δ 185.0, 143.2, 129.9, 92.4, 50.3 (2C) ppm; HRMS (FAB+, m/
z), calcd for C8H10O3 [M] +: 154.0630, found 154.0637.
2-Methyl-p-benzoquinone dimethyl acetal (5b). Colorless oil;
IR (film): 3066, 1694, 964, 810 cm−1 1H NMR (CDCl3,
;
500 MHz): δ 6.73 (dd, J = 3.0, 10.0 Hz, 1H), 6.54 (dd, J = 1.5,
3.0 Hz, 1H), 6.19 (d, J = 10.0 Hz, 1H), 3.29 (s, 6H), 1.84 (d, J =
1.5 Hz, 3H) ppm; 13C NMR (CDCl3, 125 MHz): δ 185.7, 143.0,
138.5, 136.8, 129.9, 92.9, 50.2 (2C), 15.7 ppm; HRMS (FAB+,
m/z), calcd for C9H12O3Na+ [M + Na]+: 191.0684, found
191.0678.
13 T. J. Holmes, Jr. and R. G. Lawton, J. Org. Chem., 1983, 48, 3146–3150.
14 J. S. Swenton, B. R. Bonke, C.-P. Chen and C.-T. Chou, J. Org. Chem.,
1989, 54, 51–58.
15 M. C. Carreño and M. Ribagorda, J. Org. Chem., 2000, 65, 1231–1234.
16 T. A. Engler, W. Chai and K. O. Lynch, Jr., Tetrahedron Lett., 1995, 36,
7003–7006.
3-Chloro-p-benzoquinone dimethyl acetal (5c). Colorless oil;
IR (film): 3058, 1689, 955, 723 cm−1
;
1H NMR (CDCl3,
500 MHz): δ 6.73 (dd, J = 1.0, 10.5 Hz, 1H), 6.55–6.54 (m,
1H), 6.40 (dd, J = 2.0, 10.0 Hz, 1H), 3.24 (s, 6H) ppm; 13C
NMR (CDCl3, 125 MHz): δ 182.2, 151.7, 142.8, 130.7, 130.5,
93.9, 50.5 (2C) ppm; HRMS (FAB+, m/z), calcd for
C8H935ClO3H+ [M + H]+: 189.0318, found 189.0314; calcd for
C8H937ClO3H+ [M + H]+: 191.0289 found 191.0296.
17 R. Adams and J. H. Looker, J. Am. Chem. Soc., 1951, 73, 1145–1149;
and references therein.
18 R. Barret and M. Daudon, Tetrahedron Lett., 1991, 32, 2133–2134.
19 (a) C.-C. Liao and R. K. Peddinti, Acc. Chem. Res., 2002, 35, 856–866;
(b) S. R. Surasani, V. S. Rajora, N. Bodipati and R. K. Peddinti, Tetrahe-
dron Lett., 2009, 50, 773–775; (c) S. R. Surasani and R. K. Peddinti, Tet-
rahedron Lett., 2011, 52, 4615–4618.
3-Methoxy-p-benzoquinone dimethyl acetal (5d). Colorless
20 N. Bodipati and R. K. Peddinti, Org. Biomol. Chem., 2012, 10, 1958–
1961.
1
oil; IR (film): 3047, 1692, 1463, 1295 cm−1; H NMR (CDCl3,
21 For reviews on hypervalent iodine reagents, see: (a) S. F. Kirsch and
A. Duschek, Angew. Chem., Int. Ed., 2011, 50, 1524–1552; (b) V.
V. Zhdankin, Chem. Rev., 2008, 108, 5299–5358; (c) L. Pouysegu,
D. Deffieux and S. Quideau, Tetrahedron, 2010, 66, 2235–2261;
(d) V. Satam, A. Harad, R. Rajule and H. Pati, Tetrahedron, 2010, 66,
7659–7706.
22 For the applications of DIB, see: (a) W. Liu, C. Chen and Q. Zhang,
Org. Biomol. Chem., 2011, 9, 6484–6486; (b) P.-H. Lu, C.-S. Yang,
B. Devendar and C.-C. Liao, Org. Lett., 2010, 12, 2642–2645;
(c) Y. Zhao and Y.-Y. Yeung, Org. Lett., 2010, 12, 2128–2131;
(d) R. Akula, M. Galligan and H. Ibrahim, Chem. Commun., 2009,
6991–6993.
500 MHz): δ 6.49 (d, J = 10.0 Hz, 1H), 6.19 (d, J = 9.0 Hz,
1H), 5.52 (s, 1H), 3.68 (s, 3H), 3.17 (s, 6H) ppm; 13C NMR
(CDCl3, 125 MHz): δ 186.1, 164.4, 153.6, 140.1, 130.9, 98.2,
55.6, 51.1 (2C) ppm; HRMS (FAB+, m/z), calcd for
C9H12O4Na+ [M + Na]+: 207.0633, found 207.0632.
2-Methoxy-p-benzoquinone dimethyl acetal (5e). Colorless
1
oil; IR (film): 3058, 1689, 955, 723 cm−1; H NMR (CDCl3,
500 MHz): δ 6.51 (d, J = 10.0 Hz, 1H), 6.21 (d, J = 9.0 Hz,
1H), 5.54 (s, 1H), 3.67 (s, 3H), 3.15 (s, 6H) ppm; 13C NMR
(CDCl3, 125 MHz): δ 186.2, 164.6, 153.7, 137.0, 131.0, 98.3,
55.9, 51.2 (2C) ppm; HRMS (FAB+, m/z), calcd for
C9H12O4Na+ [M + Na]+: 207.0633, found 207.0638.
23 C.-P. Chen, C.-T. Chou and J. S. Swenton, J. Am. Chem. Soc., 1987, 109,
946–948; and references therein.
24 D. R. Hookins and R. J. K. Taylor, Tetrahedron Lett., 2010, 51, 6619–
6621; and references therein.
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Org. Biomol. Chem., 2012, 10, 4549–4553 | 4553