ortho Substituent effect on a 1,5-H shift reaction during thermal decomposition of aryltriazenes

Article abstract of DOI:10.1016/j.tetlet.2006.08.017

An ortho substituent group has a significant effect on thermal decomposition of aryltriazenes. When the ortho methoxy-substituted phenyltriazenes were treated with methyl iodide at 110-130 °C, 1,5-H shift products were obtained in fair to moderate yields.

Full text of DOI:10.1016/j.tetlet.2006.08.017

Tetrahedron Letters 47 (2006) 7343–7347
ortho Substituent effect on a 1,5-H shift reaction during
thermal decomposition of aryltriazenes
*
Michael Harmata, Xuechuan Hong and Pinguan Zheng
Department of Chemistry, University of Missouri-Columbia, Columbia, MO 65211, United States
Received 27 June 2006; revised 4 August 2006; accepted 7 August 2006
Available online 1 September 2006
Abstract—An ortho substituent group has a significant effect on thermal decomposition of aryltriazenes. When the ortho methoxy-
substituted phenyltriazenes were treated with methyl iodide at 110–130 ꢀC, 1,5-H shift products were obtained in fair to moderate
yields.
ꢁ
2006 Elsevier Ltd. All rights reserved.
We have been investigating the synthesis of enantio-
merically pure 2,1-benzothiazines as part of a program
directed toward the synthesis of chiral ligands and natural
1
products. Most relevant here is the chemistry involving
the stereoselective, intramolecular Michael addition of
2
sulfoximine carbanions to a,b-unsaturated esters,
which provides a novel way to establish benzylic stereo-
centers with a high selectivity. This methodology was
applied in the total syntheses of (+)-curcuphenol, (+)-
3
4
5
curcumene, erogorgiaene, and pseudopteroxazole (1).
During the course of our total synthesis of pseudopter-
5
oxazole (1), we examined some aryltriazene chemistry
as a method to introduce an iodide into the aromatic
ring. In our initial approach toward pseudopteroxazole,
we needed to install the iodide present in compound 2,
which would be obtained by the thermal decomposition
of triazene 3 (Scheme 1).
Thus, a reductive desulfurization of 4 with Na/Hg pro-
6
vided aniline 5 in a 90% yield (Scheme 2). Aniline 5 was
then converted to 1-aryl-3,3-diethyltriazene 3 in 87%
7
yield under standard conditions. However, decomposi-
Scheme 1.
tion of 3 in neat methyl iodide in a sealed tube at 120–
1
30 ꢀC for 0.5 h generated 1,5-hydrogen atom transfer
tion, since triazene derivatives are widely used in organic
and medicinal chemistry. Triazenes have found use as
product 6 in a 61% yield and not the aryl iodide we
desired (Scheme 2).8,9
1
0
11
metal complexes, chelating agents, hydrogenation
1
2
catalysts, iodo-masking groups in the preparation of
The formation of 1,5-hydrogen atom transfer product 6
prompted us to carry out a broader study of this reac-
1
3
N-containing heterocycles and in the synthesis of mac-
1
4
romolecules. Triazine derivatives possess varied and
1
5
strong biological and pharmacological activities such
1
6
*
Corresponding author. Tel.: +1 573 882 1097; fax: +1 573 882
754; e-mail: harmatam@missouri.edu
as functioning as alkylating agents in tumor therapy.
While the 1,5-hydrogen atom transfer of several
2
0040-4039/$ - see front matter ꢁ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2006.08.017

7344
M. Harmata et al. / Tetrahedron Letters 47 (2006) 7343–7347
Scheme 2.
ortho-substituted aryl iodides has been achieved ther-
decomposition of ortho-methoxy-substituted aryltri-
azene 8c provided not only aryl iodide 9c in 45% yield,
but 1,5-hydrogen atom transfer product 10c as well in
40% yield (Table 2, entry 3). Thus, the replacement of
an ortho hydrogen by a methoxy group has a great effect
on the decomposition of triazene. Further studies
showed this reaction to be very general. Treatment of
various triazenes 8d–f with methyl iodide in a sealed
tube at 120–130 ꢀC gave 1,5-hydrogen atom transfer
products and aryl iodides in excellent yields and the
yields of 1,5-hydrogen atom transfer products depended
on the particular system. However, treatment of 8g with
1
7
mally, to the best of our knowledge the related reac-
tion using triazene chemistry has not been reported in
the literature. Herein we report the ortho substituent ef-
fect on 1,5-H shift reactions by the thermal decomposi-
tion of aryltriazenes.
In most cases, synthesis of triazenes through the reac-
tion of diazonium salts with secondary aliphatic amines
like diethylamine is straightforward. 1-Aryl-3,3-diethyl-
triazenes 8a–g were prepared by reacting salts 7a–g with
diethylamine in Et O/THF/CH CN/H O, in the pres-
2
3
2
7
19
ence of potassium carbonate at 0–5 ꢀC (Table 1). The
reactions proceeded rapidly to completion and the yields
of the triazenes were consistently high, usually greater
similar conditions gave only decomposition (entry 7).
More than likely, 1,5-H shift reactions of the thermal
decomposition of aryltriazenes can be attributed to a
radical mechanism as outlined in Scheme 3. Accord-
ingly, we formulated a possible mechanism for the reac-
tion of triazene 8c. Initial reaction of the nitrogen lone
pair of triazene 8c with methyl iodide gives intermediate
11, which can follow one of two possible pathways:
pathway 1 leads to the formation of product 9c through
nucleophilic attack by iodide, while pathway 2 is the
1
8
than 90% (Table 1).
Our initial evaluation of ortho substituent effects on 1,5-
H shift reactions of aryltriazenes was carried out with
hydrogen as an ortho substituent (Table 2, entries 1
and 2). The thermal decomposition of 8a–b in neat
methyl iodide in a sealed tube at 110–130 ꢀC resulted
in only aryl iodides 9a and 9b in 80% and 78% yields,
respectively (Table 2, entries 1 and 2). Interestingly, no
7
a
radical pathway. For pathway 2, the formation of
1
,5-H shift products were observed. However, the
radical 13 occurs through diazonium cation formation
Table 1. Synthesis of 1-aryl-3,3-diethyltriazenes
Entry
Aniline
Yield (%)
1
2
3
4
5
6
7
7a: R
7b: R
1
= Me (S), R2À4 = H, R
= Me, R2À5 = H, R = vinyl
= H, R = MeO, R
= H, R = MeO, R
= H, R = MeO, R
= H, R = MeO, R
= H, R = MeO, R
5
= Me, R
6
= OH
90
87
95
92
94
96
95
1
6
7c: R1À3 = R
7d: R1À3 = R
7e: R1À3 = R
7f: R1À3 = R
7g: R1À3 = R
5
4
6
= vinyl
= CH OH
5
4
6
2
5
4
6
= ethynyl
5
4
6
= TMSethynyl
5
4
6
= CHCHCO
2
Et

M. Harmata et al. / Tetrahedron Letters 47 (2006) 7343–7347
Table 2. Reaction of aryltriazenes with methyl iodide
7345
Entry
Triazene
Reaction conditions
R
7
9 Yield (%)
10 Yield (%)
1
2
3
8a
8b
8c
CH
CH
CH
3
3
3
I, 130 ꢀC, 0.5 h
I, 110–120 ꢀC, 24 h
I, 120–130 ꢀC, 24 h
—
—
80
78
45
0
0
40
–CH@CHCH
2
I
4
5
8d
8e
CH
CH
3
I, 120–130 ꢀC, 0.5 h
I, 120–130 ꢀC, 1 h
59
14
—
a
3
74 (41/59)
a
6
7
8f
CH
3
3
I, 120–130 ꢀC, 0.5 h
I, 110–120 ꢀC, 1 h
79 (42/58)
—
b
b
8g
CH
—
a
Mixture of 9:10 in ratio shown.
Decomposition observed.
b
and single electron transfer. 1,5-Hydrogen atom transfer
of 13 and subsequent reaction of the allyl radical with
iodine anion at the terminus affords 10c (pathway 2b);
another route is that of the formation of iodide 9c via
radical 13 and iodine anion (pathway 2a).
results obviously showed that the ortho methoxy group
has a significant effect on 1,5-H shift reactions and
iodination. 1,5-H shift products were obtained in mod-
erate yields when the ortho methoxy-substituted tri-
azenes were treated with methyl iodide at 110–130 ꢀC.
Further investigations regarding the scope and applica-
tion of benzothiazine chemistry will be reported in due
course.
In summary, we have studied the thermal decomposition
of triazenes with and without ortho substituents. The
Scheme 3.

7346
M. Harmata et al. / Tetrahedron Letters 47 (2006) 7343–7347
18. Triazene synthesis. General procedure: To a 50 mL round
Acknowledgments
bottomed flask was added aniline (0.9 mmol), 4.5 M aq
HCl (0.9 mL), and Et O/THF/CH CN 7:6:1 (5 mL). The
This work was supported by the NIH (1R01-AI59000-
2
3
mixture was chilled to 5 ꢀC in an ice bath. A solution of
0
1A1), to whom we are grateful.
NaNO (211 mg, 3.06 mmol) in CH CN/H O 2:3 (4 mL)
2
3
2
was added and the reaction mixture was stirred at 0–5 ꢀC
for 1 h. A second 50 mL round bottomed flask was
charged with diethylamine (464 lL, 4.5 mmol), K
2 3
CO
Supplementary data
(
621 mg, 4.5 mmol), and CH CN/H O 2:1 (5 mL), which
3
2
was chilled to 0–5 ꢀC in an ice bath. The solution of aniline
was transferred over 15 min to the first flask, and stirred
for an additional 1 h at 0–5 ꢀC. The solution was extracted
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/
j.tetlet.2006.08.017.
2
with 3 · 10 mL Et O. The combined organic phases were
dried over Na SO , filtered, and concentrated in vacuo, to
2
4
give a brown oil. Purification of the product by basic
References and notes
aluminum oxide chromatography (5% Et O/pentane)
2
afforded a colorless oil in excellent yield. Compound 8b:
1
1
. (a) Harmata, M.; Ghosh, S. K. Org. Lett. 2001, 3, 3321;
b) Harmata, M. Chemtracts 2003, 16, 660; (c) Harmata,
M.; Pavri, N. Angew. Chem., Int. Ed. 1999, 38, 2419.
. Harmata, M.; Hong, X. J. Am. Chem. Soc. 2003, 125,
5
H NMR (250 MHz, CDCl ): d 7.32–7.36 (m, 2H), 7.20–
3
(
7.24 (m, 1H), 7.08–7.15 (m, 2H), 5.74–5.81 (m, 1H), 4.94
(d, J = 18.7 Hz, 1H), 4.88 (d, J = 12.1 Hz, 1H), 3.73 (q,
J = 7.1 Hz, 4H), 3.60 (q, J = 7.1 Hz, 1H), 1.95–2.03 (m,
2H), 1.60–1.80 (m, 2H), 1.18–1.27 (m, 9H); C NMR
(62.5 MHz, CDCl ): d 148.2, 139.2, 126.2, 126.0, 125.3,
116.5, 113.8, 37.0, 32.2, 32.0, 21.1. Compound 8c:
NMR (500 MHz, CDCl ): d 7.05 (t, J = 7.9 Hz, 1H), 6.81–
6.85 (m, 2H), 5.81–5.87 (m, 1H), 5.03 (dt, J = 17.2, 1.7 Hz,
1H), 4.97 (dt, J = 10.2, 0.9 Hz, 1H), 3.77–3.81 (m, 7H),
2.59 (dd, J = 7.7, 7.7 Hz, 2H), 2.09 (q, J = 7.4 Hz, 2H),
2
3
1
3
754.
. Harmata, M.; Hong, X.; Barnes, C. L. Tetrahedron Lett.
003, 44, 7261.
3
1
2
H
4
5
. Harmata, M.; Hong, X. Tetrahedron Lett. 2005, 46, 3847.
. (a) Harmata, M.; Hong, X.; Barnes, C. L. Org. Lett. 2004,
3
6, 2201; (b) Harmata, M.; Hong, X. Org. Lett. 2005, 7,
3581.
1
3
6
7
. Harmata, M.; Kahraman, M. Synthesis 1994, 142.
. (a) Ku, H.; Barrio, J. R. J. Org. Chem. 1981, 46, 5239; (b)
Satyamurthy, N.; Barrio, J. R. J. Org. Chem. 1983, 43,
1.63–1.69 (m, 2H), 1.31 (t, J = 7.1 Hz, 6H); C NMR
(125 MHz, CDCl ): d 151.8, 139.9, 138.7, 136.3, 124.9,
122.1, 114.2, 109.9, 56.0, 33.6, 31.2, 29.8. Compound 8d:
3
1
4394.
H NMR (300 MHz, CDCl ): d 7.00 (t, J = 7.9 Hz, 1H),
3
8
. Cary, J. M.; Moore, J. S. Org. Lett. 2002, 4, 4663.
6.74–6.79 (m, 2H), 3.71–3.76 (m, 7H), 3.52–3.54 (m, 2H),
9
. Moore, J. S.; Weinstein, E. J.; Wu, Z. Tetrahedron Lett.
2.53 (t, J = 7.2 Hz, 2H), 1.99 (s, 1H), 1.48–1.57 (m, 4H),
1.25 (t, J = 7.1 Hz, 6H). Compound 8e: H NMR
1
1991, 32, 2465.
1
1
1
1
1
0. Paul, P.; Tyagi, B.; Bilakhiya, A. K.; Dastidar, P.; Suresh,
E. Inorg. Chem. 2000, 39, 14.
1. Lee, C. H.; Yamamoto, T. Bull. Chem. Soc. Jpn. 2002, 75,
(300 MHz, CDCl ): d 7.02 (t, J = 7.9 Hz, 1H), 6.79 (td,
3
J = 7.3, 1.1 Hz, 2H), 3.76 (s, 3H), 3.75 (q, J = 7.1 Hz, 4H),
2.66 (t, J = 7.6 Hz, 2H), 2.16 (td, J = 7.1, 2.6 Hz, 2H),
1.94 (t, J = 2.6 Hz, 1H), 1.76 (dt, J = 7.6, 7.3 Hz, 2H),
6
15.
2. Santra, P. K.; Sagar, P. J. Mol. Catal. A: Chem. 2003, 197,
7.
1
3
1.27 (t, J = 7.1, 6H); C NMR (75 MHz, CDCl
): d 151.8,
3
3
139.9, 135.3, 124.9, 122.2, 110.1, 84.3, 68.2, 56.0, 30.6,
1
3. Wirshun, M.; Winkler, K. L.; Jochims, J. C. J. Chem. Soc.,
Perkin Trans. 2 1998, 1755.
3
29.1, 18.0. Compound 8f: H NMR (250 MHz, CDCl ): d
7.00 (t, J = 7.8 Hz, 1H), 6.78–6.83 (m, 2H), 3.75 (s, 3H),
3.76 (q, J = 7.1 Hz, 4H), 2.65 (t, J = 7.5 Hz, 2H), 2.20 (t,
J = 7.2 Hz, 2H), 1.75 (dt, J = 14.9, 7.5 Hz, 2H), 1.28 (t,
4. (a) Young, J. K.; Nelson, J. C.; Moore, J. S. J. Am. Chem.
Soc. 1994, 116, 10841; (b) Jones, L.; Schumm, J. S.; Tour,
J. M. J. Org. Chem. 1997, 62, 1388; (c) Moore, J. S. Acc.
Chem. Res. 1997, 30, 402; (d) Br a¨ se, S.; Enders, D.;
K o¨ bberling, J.; Avemaria, F. A. Angew. Chem., Int. Ed.
1
3
J = 7.1 Hz, 6H), 0.16 (s, 9H); C NMR (62.5 MHz,
CDCl ): d 151.9, 140.0, 135.5, 125.0, 122.3, 110.3, 107.5,
84.4, 56.1, 30.8, 29.3, 19.5, 0.14. Compound 8g: H NMR
(250 MHz, CDCl ): d 6.88–7.05 (m, 2H), 6.76–6.80 (m,
3
1
1998, 37, 3413; (e) Nicolaou, K. C.; Boddy, C. N. C.; Li,
3
H.; Koumbis, A. E.; Hughes, R.; Natarajan, S.; Jain, N.
F.; Ramanjulu, J. M.; Br a¨ se, S.; Soloman, M. E. Chem.
Eur. J. 1999, 5, 2602; (f) Nicolaou, K. C.; Boddy, C. N. C.;
Br a¨ se, S.; Winssinger, N. Angew. Chem., Int. Ed. 1999, 38,
2H), 5.78 (dt, J = 15.6, 1.4 Hz, 1H), 4.16 (q, J = 7.1 Hz, 2
H), 3.70–3.79 (m, 7H), 2.56 (dd, J = 6.9, 6.9 Hz, 2H), 2.17
(q, J = 7.2 Hz, 2H), 1.68 (td, J = 15.1, 7.6 Hz, 2H), 1.23–
1
3
3
1.30 (m, 9H); C NMR (62.5 MHz, CDCl ): d 166.6,
2097.
151.9, 149.1, 140.0, 135.7, 125.0, 122.1, 121.3, 110.3, 60.0,
1
5. (a) Iino, Y.; Karakida, T.; Sugamata, N.; Andoh, T.;
Takei, H.; Takahashi, M.; Yaguchi, S.; Matsumo, Y.;
Takehara, M.; Sakato, M.; Kawashina, S.; Morishita, Y.
Anticancer Res. 1998, 18, 171; (b) Burkhard, K.; Steward,
M.; Barret, M. P.; Brun, R.; Gilbert, I. H. J. Med. Chem.
56.1, 31.9, 31.1, 28.8, 14.2.
19. General procedure for decomposition of triazenes: A 10 mL
sealed tube under Ar was charged with triazene
(0.076 mmol) in methyl iodide (2 mL). The solution was
degassed, sealed, and stirred at 110–130 ꢀC for 20 h. The
methyl iodide was removed under reduced pressure and
2001, 44, 3440; (c) Nishimura, N.; Kato, A.; Maeba, I.
Carbohydr. Res. 2001, 331, 77.
the red residue was dissolved in Et
with saturated Na solution, water, and dried over
MgSO . Removal of the solvent gave a crude product.
2
O (10 mL), washed
1
1
6. Rouzer, C. A.; Sabourin, M.; Skinner, T. L.; Thompson,
E. J.; Wood, T. O.; Chmurny, G. N.; Klose, J. R.; Roman,
J. M.; Smith, R. H., Jr.; Michejda, C. J. Chem. Res.
Toxicol. 1996, 9, 172.
S O
2 2 3
4
Purification of the product by flash chromatography (20%
EtOAc/pentanes) afforded two colorless oils. However, the
1
7. (a) Curran, D. P.; Fairweather, N. J. Org. Chem. 2003, 68,
products were not always separable. Compound 9b: H
2972; (b) Beckwith, A. L. J.; Meijs, G. F. J. Org. Chem.
3
NMR (500 MHz, CDCl ): d 7.81 (dd, J = 7.9, 1.2 Hz, 1H),
1987, 52, 1922; (c) Abeywickrema, A. N.; Beckwith, A. L.
7.30 (td, J = 7.4, 1.2 Hz, 1H), 7.18 (dd, J = 7.8, 1.6 Hz,
J. J. Chem. Soc., Chem. Commun. 1986, 464.
1H), 6.88 (td, J = 7.5, 1.8 Hz, 1H), 5.80–5.81 (m, 1H),

M. Harmata et al. / Tetrahedron Letters 47 (2006) 7343–7347
7347
1
3
4
.92–5.00 (m, 2H), 3.08 (q, J = 7.0 Hz, 1H), 2.06 (m, 1H),
C NMR (62.5 MHz, CDCl
3
): d 159.7, 142.0, 129.5,
1
.98 (m, 1H), 1.73–1.75 (m, 1H), 1.43–1.63 (m, 1H), 1.19
120.8, 114.3, 111.5, 68.5, 55.1, 40.6, 37.5, 35.3. Compound
1
3
1
(
d, J = 6.8 Hz, 3H); C NMR (125 MHz, CDCl ): d
9e: H NMR (250 MHz, CDCl ): d 7.17–7.24 (m, 1H),
3
3
1
3
49.2, 139.5, 138.5, 128.5, 127.7, 126.5, 114.5, 101.8, 42.8,
6.7, 31.6, 21.3. Compound 9c: H NMR (250 MHz,
6.86 (dd, J = 7.5, 1.1 Hz, 1H), 6.65 (dd, J = 7.7, 0.9 Hz,
1H), 3.87 (s, 3H), 2.90 (dd, J = 7.9, 7.5 Hz, 2H), 2.24 (td,
J = 7.0, 2.6 Hz, 2H), 2.00 (t, J = 2.6 Hz, 1H), 1.84 (q,
1
CDCl
3
): d 7.20 (t, J = 7.8 Hz, 1H), 6.83 (dd, J = 7.6,
1
3
1
1
1
.1 Hz, 1H), 6.64 (dd, J = 8.1, 1.1 Hz, 1H), 5.81–5.92 (m,
J = 7.5 Hz, 1H); C NMR (62.5 MHz, CDCl ): d 158.2,
3
H), 5.05 (dd, J = 8.1, 1.1 Hz, 1H), 5.00 (d, J = 11.8 Hz,
H), 3.87 (s, 3H), 2.78 (dd, J = 7.8, 7.8 Hz, 2H), 2.14 (q,
146.1, 128.8, 122.1, 108.5, 92.0, 84.0, 68.8, 56.4, 29.0, 28.6,
1
17.9. Compound 10e: H NMR (250 MHz, CDCl
3
):
1
3
J = 7.1 Hz, 2H), 1.63–1.75 (m, 2H); C NMR (62.5 MHz,
CDCl ): d 158.1, 147.0, 138.4, 128.8, 121.9, 114.8, 108.2,
2.8, 56.4, 40.6, 33.3, 29.2. Compound 10c: H NMR
250 MHz, CDCl ): d 7.16–7.25 (m, 1H), 6.71–6.77 (m,
H), 5.71–5.76 (m, 2H), 3.84–3.87 (m, 2H), 3.79 (s, 3H),
d 7.20 (t, J = 8.0 Hz, 1H), 6.73–6.80 (m, 3H), 5.69
(dt, J= 5.7, 2.5 Hz, 1H), 5.12 (td, J = 6.4, 5.9 Hz, 1H),
3.80 (s, 3H), 2.74 (t, J = 7.6 Hz, 2H), 2.40–2.49 (m, 2H);
3
1
9
(
3
2
1
3
3
C NMR (62.5 MHz, CDCl
3
): d 205.3, 159.6, 142.6,
129.3, 120.7, 114.4, 111.4, 95.5, 55.1, 39.9, 35.9, 34.6.
1
3
1
.63–2.71 (m, 2H), 2.31–2.43 (m, 2H);
): d 159.5, 142.9, 133.9, 129.2, 128.4,
20.7, 114.1, 111.1, 55.1, 35.1, 33.5, 6.40. Compound 9d:
C
NMR
3
Compound 9f: H NMR (250 MHz, CDCl ): d 7.20–7.27
(
62.5 MHz, CDCl
3
(m, 1H), 6.90 (dd, J = 7.6, 1.2 Hz, 1H), 6.67 (dd, J = 8.1,
1.1 Hz, 1H), 3.89 (s, 3H), 2.75–2.95 (m, 2H), 2.21–2.34
(m, 2H), 1.85 (dt, J = 15.2, 7.6 Hz, 2H), 0.21 (s, 9H);
1
1
H NMR (250 MHz, CDCl ): d 7.19 (t, J = 7.8 Hz, 1H),
3
1
3
6
.83 (dd, J = 7.6, 1.2 Hz, 1H), 6.64 (dd, J = 8.1, 1.2 Hz,
3
C NMR (62.5 MHz, CDCl ): d 158.1, 146.2, 128.8,
1
2
H), 3.86 (s, 3H), 3.67 (t, J = 5.8 Hz, 2H), 2.77–2.83 (m,
122.1, 108.4, 106.9, 92.7, 85.1, 56.4, 40.0. Compound 10f:
1
3
1
H), 1.63–1.71 (m, 4H), 1.59 (s, 1H);
C
NMR
H NMR (250 MHz, CDCl ): d 7.23 (td, J = 7.6, 1.8 Hz,
3
(
9
(
62.5 MHz, CDCl ): d 158.0, 146.8, 128.8, 121.8, 108.3,
2.7, 62.6, 56.4, 40.7, 32.2, 26.2. Compound 10d: H NMR
1H), 6.78–6.83 (m, 3H), 4.47 (t, J = 6.9 Hz, 1H), 3.82
3
1
(s, 3H), 2.75–2.95 (m, 2H), 2.21–2.34 (m, 2H), 0.21
1
3
250 MHz, CDCl ): d 7.17–7.25 (m, 1H), 6.73–6.81 (m,
3
3
(s, 9H); C NMR (62.5 MHz, CDCl ): d 159.7, 141.5,
3
2
H), 4.11–4.14 (m, 1H), 3.79 (s, 3H), 3.70–3.77 (m, 2H),
.82–2.88 (m, 1H), 2.66–2.74 (m, 1H), 1.97–2.19 (m, 3H);
129.5, 120.8, 114.3, 111.5, 106.0, 91.7, 55.1, 42.3, 35.1, 9.8,
À0.29.