A new variant of Reformatsky-Claisen rearrangement mediated by indium chloride

Article abstract of DOI:10.1055/s-0029-1217716

A new variant of Reformatsky - Claisen rearrangement is described. The reaction of an allyl a-bromo ester in the presence of indium(I) chloride provides a general entry into the functionalized synthon. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-0029-1217716

LETTER
2351
A New Variant of Reformatsky–Claisen Rearrangement Mediated by Indium
Chloride
A
N
ew V
a
u
riant of
R
efo
n
rmatsky–Claisen
R
I
earrange
s
ment hihara,* Noriko Koyama, Yukihiro Nishino, Keisuke Takahashi, Susumi Hatakeyama*
Graduate School of Biomedical Sciences, Nagasaki University, 1-14 Bunkyo-machi, Nagasaki 852851, Japan
Fax +81(95)8192426; E-mail: jishi@nagasaki-u.ac.jp
Received 22 May 2009
the reaction in MeCN resulted in significant improve-
Abstract: A new variant of Reformatsky–Claisen rearrangement is
described. The reaction of an allyl a-bromo ester in the presence of
indium(I) chloride provides a general entry into the functionalized
synthon.
ment, affording 2 in 60% yield (entries 4 and 5). Indium(I)
chloride turned out to be effective in the Reformatsky–
Claisen rearrangement of 1 (entry 6). It was found that the
use of a mixture of In and InCl3 improved the yield of 2 to
72% (entry 7). In addition, we were pleased to find that the
reaction under ultrasonication at 10–30 °C brought us the
satisfying results, giving 2 in 80% yield (entry 8).
Key words: indium, Claisen rearrangement, Reformatsky reaction,
carboxylic acid, a-bromo ester
Next, the reactions of linear a-bromo esters 4a–d were ex-
amined under the optimized reaction conditions (Table 2).
Although the reaction of 4a, a-bromodifluoroacetate 4b,
and a-bromopropionate 4c (entries 1–3) did not give the
corresponding rearranged products 5a–c, the reaction of
The Claisen rearrangement often proceeds with high ste-
reoselectivity and gives synthetically useful products, and
therefore it has been widely used for the synthesis of nat-
ural products.1 The synthetic utility prompted the devel-
opment of a considerable number of variants of Claisen
rearrangement.2 For instance, zinc-mediated [3,3]-sigma-
tropic rearrangement of a-halo esters proceeds through
zinc enolates, which was referred as Reformatsky–
Claisen rearrangement.3 This rearrangement also pro-
ceeds in the presence of a silylating agent via the silyl
ketene acetal.4 A vast number of Ireland–Claisen-type re-
arrangements were reported,2a,4,5 whereas only a few ex-
amples of Reformatsky–Claisen rearrangement have
appeared so far.6 Herein we report an improved method
for the Reformatsky–Claisen rearrangement which is me-
diated by indium.
Table 1 Reformatsky–Claisen Rearrangement of Compound 1
O
O
COOH
Br
H
O
O
1
2
3
Entry Condition
Yield of 2 Yield of 3
(%)
(%)
1
2
3
4
5
6
7
8
Zn (2 equiv), TMSCl (2.5 equiv),
Et3N (2.5 equiv), PhMe,
r.t. to reflux, 9 h
0
96
In the course of our synthetic study of natural products,
we needed to explore a Claisen rearrangement under
nonbasic conditions. Therefore, we were interested in a
Reformatsky–Claisen rearrangement which can be exe-
cuted under mild conditions. First, we examined the reac-
tion using 1 as a substrate (Table 1). When a-bromo ester
1 was treated with Zn and TMSCl–Et3N in benzene or
THF, the protonated product 3 was obtained exclusively
(entries 1 and 2). On the other hand, when MeCN was
used as a solvent, the rearrangement proceeded to gener-
ate product 2, but the yield was moderate (entry 3). Be-
sides activated zinc, indium is also known to react readily
with a-halo ester to cause the Reformatsky-type reac-
tions.7 Thus, Baba et al. reported that In(I)X is effective
for the Reformatsky-type reactions of a-bromo esters and
ketones to afford b-hydroxy ketones diastereoselectively.8
This report prompted us to investigate the indium-mediat-
ed rearrangement of 1. Treatment of 1 with indium in the
presence of TMSCl in THF gave 2 in 20% yield, whereas
Zn (2 equiv), TMSCl (2.5 equiv),
Et3N (2.5 equiv), THF,
r.t. to reflux, 9 h
0
30
20
60
52
72
80
100
57
79
36
43
25
8
Zn (2.5 equiv), TMSCl (2 equiv),
Et3N (2 equiv), MeCN,
r.t. to reflux, 3 h
In (2 equiv), TMSCl (4 equiv),
Et3N (4 equiv), THF,
r.t. to reflux, 8 h
In (2 equiv), TMSCl (4 equiv),
Et3N (4 equiv), MeCN,
r.t. to reflux, 7 h
InCl (2 equiv), TMSCl (4 equiv),
Et3N (4 equiv), MeCN,
r.t. to reflux, 4 h
In (2 equiv), InCl3 (2 equiv),
TMSCl (4 equiv), Et3N (4 equiv),
MeCN, reflux, 3 h
SYNLETT 2009, No. 14, pp 2351–2355
x
x
.x
x
.2
0
0
9
In (2 equiv), InCl3 (2 equiv),
TMSCl, Et3N, MeCN,
Advanced online publication: 31.07.2009
DOI: 10.1055/s-0029-1217716; Art ID: U05509ST
© Georg Thieme Verlag Stuttgart · New York
10–30 °C, ultrasound, 3 h

2352
J. Ishihara et al.
LETTER
a-bromomethylpropionate 4d brought about the Refor- lating agents such as TBSCl and TBSOTf were not
matsky–Claisen rearrangement successfully to give 5d in suitable for the capture of indium enolates.
good yield. The result shows that this reaction has an ad-
vantage in installing a quaternary center in a carbon
framework. It should be also noted that an acetoxy group
To test the generality of this method, a-bromo esters 7a–
c were subjected to the optimized reaction conditions
(Table 3). The benzyl and TBS ethers were also not af-
was tolerated under the reaction conditions, which is in
fected at all under the conditions; however, the THP group
stark contrast with the Ireland–Claisen rearrangement.
was susceptible owing to the Lewis acidity of InCl3. The
Furthermore we evaluated the solvent effect (entries 5–9). indium-mediated rearrangement of (Z)-allyl bromo ester
When the reaction of 4d was run in benzene, only the pro- 7d also occurred to give 5d in moderate yield.
tonated product 6d was obtained (entry 5). On the other
hand, the rearrangement successfully proceeded in a polar
solvent. For example, the reactions in THF and isobuty-
ronitrile gave 5d in 42% and 35% yield, respectively (en-
The aromatic compounds 9a–e underwent rearrangement
efficiently to the carboxylic acids 10a–e (Table 4). Cin-
namyl alcohol esters 9a, 9b and 9c as well as 3-furylpro-
penol ester 9e reacted very smoothly. Interestingly, 4-
tries 6 and 7). Employing propionitrile as a solvent, the
nitrocinnamyl derivative 9d was recovered completely.
yield of 5d increased to 74% (entry 8), but did not exceed
Table 5 shows the result of more functionalized com-
that obtained in MeCN (entry 4). In addition, heating a
pounds. Entries 1 and 3 exhibit an advantage of this meth-
od which allows us to assemble two contiguous
quaternary centers. Furthermore it can be seen that prop-
mixture of 4d, In–InCl3 and TMSCl in MeCN without ul-
trasonication at 90 °C gave 5a in 63% yield, but it required
longer time compared to the reaction under ultrasonica-
tion (entry 9).
Table 3 Indium-Mediated Reformatsky–Claisen Rearrangement of
7a–c
Table 2 Indium-Mediated Reformatsky–Claisen Rearrangement of
O
In, InCl3
4a–d and Solvent Effect
TMSCl–Et3N
RO
Br
RO
COOH
O
O
In, InCl3
MeCN,
AcO
Br TMSCl–Et3N
AcO
COOH
R1 R2
5a–d
O
4a R1 = R2 = H
10–30 °C
4–6 h
7a R = Bn
7b R = TBS
7c R = THP
8a R = Bn
R1 R2
8b R = TBS
8c R = THP
5d R = Ac
4b
4c
4d
R
1 = R2 = F
R
R
1 = H, R2 = Me
1 = Me, R2 = Me
Substrate
Product
8a
Yield (%)
+
O
O
AcO
R2
7a
7b
7c
55
78
23
53
AcO
O
O
R1
8b
2
6e
6a–d
8c
Entry
Substrate Solvent
Time
(h)
Yield of 5 Yield of 6
(%)
5d
O
O
(%)
100
16
9
Br
AcO
1
2
3
4
5
6
7
8
9a
4a
4b
4c
4d
4d
4d
4d
4d
4d
MeCN
MeCN
MeCN
MeCN
benzene
THF
7.5
2.5
6
0
0
7d
0
Table 4 Indium-Mediated Reformatsky–Claisen Rearrangement of
Aromatic Compounds 9a–e
3
80
0
8
O
In, InCl3
TMSCl–Et3N
6
100
42
50
23
12
Br
COOH
R
O
R
MeCN,
6
42
35
74
63
10–30 °C
4–6 h
9a R = Ph
10a R = Ph
i-PrCN
EtCN
6
10b R = 4-MeOC6
10c R = 4-BrC6H4
10d R = 4-O2NC6H4
10e R = 3-fur
H4
9b R = 4-MeOC6H4
9c R = 4-BrC6H4
9d R = 4-O2NC6H4
9e R = 3-fur
6
MeCN
23
Substrate
Product
Yield (%)
a The reaction mixture was heated at 90 °C without ultrasonication.
9a
9b
9c
9d
9e
10a
10b
10c
10d
10e
96
Baldwin et al. reported that Reformatsky–Claisen rear-
rangements mediated by zinc proceeded smoothly with-
out a silylating agent;3 however, in our case TMSCl was
essential for the rearrangement. Exposure of 4d to In and
InCl3 without TMSCl furnished the corresponding homo-
coupling product in 82% yield in place of 5d. Other sily-
94
71
No reaction
80
Synlett 2009, No. 14, 2351–2355 © Thieme Stuttgart · New York

LETTER
A New Variant of Reformatsky–Claisen Rearrangement
2353
Table 5 Indium-Mediated Reformatsky–Claisen Rearrangement of 11, 13, 15, 17, 19, and 21
Entry
1
Substrate
Product
Yield (%)
63
O
COOH
COOH
Br
O
O
12
11
2
66
O
AcO
Br
AcO
13
15
14
3
4
91
60
O
COOH
Br
O
O
16
•
Br
O
BnO
COOH
BnO
17
18
5
6
15
35
O
COOH
O
Br
20
19
O
O
AcO
O
AcO
COOH
AcO
AcO
Br
22
O
21
argyl ester 17 was converted to allenic compound 18 in The proposed mechanism is shown in Scheme 1. It has
60% yield. Unfortunately, application of this method to been reported that a mixture of In and InCl3 generates in
the cyclic allyl esters 19 and 21 gave the corresponding situ InCl(I), which readily reacts with a-bromo ester 23 to
carboxylic acids 20 and 22 in low yields. These results can afford a-In(III) intermediate 24 or a-In(I) 25.8 The a-indi-
be rationalized by the transition states which involve um intermediate can be transformed to indium enolate 26,
strained boat forms.
which is converted to silyl ketene acetal 27 by transmetal-
In + InCl3
InCl
R2
O
R2
O
R2
O
InX
Br
InBrX
In
R1
O
R1
O
R1
O
23
24
25
InBrX2
SiMe3
InXn
rearrangement
R2
O
R2
O
R1 R2
Me3SiCl
COOH
R1
O
R1
O
26
n = 0 or 2
InClXn
28
27
Scheme 1 Proposed mechanism for the Reformatsky–Claisen rearrangement
Synlett 2009, No. 14, 2351–2355 © Thieme Stuttgart · New York

2354
J. Ishihara et al.
LETTER
mmol of TMSCl) was added to a mixture of dried InCl3 (158
mg, 0.72 mmol) and In (82 mg, 0.72 mmol) in MeCN (2
mL). To the stirred mixture was added a solution of 4d (100
mg, 0.36 mmol) in MeCN (3 mL) and the reaction mixture
was stirred at 10–30 °C for 3 h under ultrasonication. The
stirred mixture was diluted with sat. NH4Cl (4 mL), and the
aqueous layer was extracted with EtOAc (2 × 20 mL).
Drying over MgSO4, concentration, and silica gel
lation with TMSCl. Since no rearrangement was observed
in the absence of TMSCl, the direct rearrangement of in-
dium enolates would be unlikely to occur. Finally, the
rearrangement of 27 would proceed to generate the corre-
sponding carboxylic acid. In the case of 4a–c, the a-indi-
um intermediates would be so reactive that they would to
be easily protonated.
chromatography (SiO2: 14 g; hexane–EtOAc, 10:1) afforded
5d (55 mg, 0.31 mmol, 80%) and 6d (5.3 mg, 0.03 mmol,
7%).
In conclusion, we have demonstrated a new indium-medi-
ated Reformatsky–Claisen rearrangement of substituted
allyl bromodimethylacetates.9,10 The present method can
be applicable to the substrates having a base-sensitive
group (e.g. AcO), unlike the Ireland–Claisen rearrange-
ment. In addition, this method enables us to create func-
tionalized quaternary centers. Further exploration of this
chemistry is underway in our laboratory.
(10) 2: IR (neat): 3400(br), 2940, 2859, 1702, 1448, 1255, 1051,
925, 844, 761 cm–1. 1H NMR (400 MHz, CDCl3): d = 5.70–
5.81 (m, 1 H), 5.08 (d, J = 16.8 Hz, 1 H), 5.04 (d, J = 11.6
Hz, 1 H), 2.28 (d, J = 7.6 Hz, 2 H), 1.62–1.58 (m, 4 H), 1.35–
1.46 (m, 2 H), 1.26–1.30 (m, 4 H). 13C NMR (100 MHz,
CDCl3): d = 182.6, 133.3, 117.7, 47.1, 44.3, 33.4, 25.3, 22.9.
MS (EI): m/z = 123, 168 [M+]. HRMS (EI): m/z [M+] calcd
for C10H16O2: 168.1151; found: 168.1126.
5d: IR (neat): 3200(br), 2981, 1744, 1700, 1467, 1367, 1243,
1162, 1039, 929, 686, 606 cm–1. 1H NMR (300 MHz,
CDCl3): d = 5.64 (dt, J = 16.8, 10.4 Hz, 1 H), 5.21 (dd, J =
10.4, 1.6 Hz, 1 H), 5.19 (dd, J = 16.8, 0.6 Hz, 1 H), 4.03–4.20
(m, 2 H), 2.77–2.82 (m, 1 H), 2.00 (s, 3 H), 1.17 (s, 6 H).
13C NMR (75 MHz, CDCl3): d = 183.4, 170.8, 134.0, 119.7,
63.9, 49.7, 43.2, 24.4, 20.2. MS (EI): m/z = 200 [M+]. HRMS
(EI): m/z [M+] calcd for C10H16O4: 200.1048; found:
200.1027.
Acknowledgment
This work was financially supported by a Grants-in-Aid for Scien-
tific Research from the Ministry of Education, Culture, Sports, Sci-
ence and Technology, Japan (17590009) and by a Grant-in-Aid for
Scientific Research from the President of Nagasaki University.
References and Notes
8a: IR (neat): 2979, 1708, 1455, 1364, 1272, 1104, 923, 848,
737, 698, 605 cm–1. 1H NMR (300 MHz, CDCl3): d = 7.21–
7.35 (m, 5 H), 5.67 (dt, J = 17.8, 9.3 Hz, 1 H), 5.15–5.21 (m,
2 H), 4.47 (s, 2 H), 3.47 (dd, J = 15.9, 8.8 Hz, 2 H), 2.79 (dd,
J = 15.9, 6.6 Hz, 1 H), 1.16 (s, 3 H), 1.13 (s, 3 H). 13C NMR
(75 MHz, CDCl3): d = 183.7, 138.2, 135.3, 128.3, 128.3,
127.5, 119.1, 72.9, 70.5, 50.7, 43.5, 24.8, 20.4. MS (EI):
m/z = 248 [M+]. HRMS (EI): m/z [M+] calcd for C15H20O3:
248.1413; found: 248.1397.
8b: IR (neat): 2930, 1703, 1470, 1389, 1256, 1103, 1004,
921, 837, 776, 666 cm–1. 1H NMR (300 MHz, CDCl3): d =
5.69 (ddd, J = 16.8, 10.2, 9.9 Hz, 1 H), 5.17 (dd, J = 10.2, 1.9
Hz, 1 H), 5.15 (dd, J = 16.7, 1.9 Hz, 1 H), 3.68 (t, J = 5.4 Hz,
2 H), 2.56 (dt, J = 9.3, 6.0 Hz, 1 H), 1.19 (d, J = 7.1 Hz, 6 H),
0.88 (s, 9 H), 0.05 (s, 6 H). 13C NMR (75 MHz, CDCl3): d =
183.9, 135.4, 119.0, 63.7, 52.8, 43.2, 25.9, 20.4, 18.3, –5.6.
MS (EI): m/z = 273 [M + H+]. HRMS (EI): m/z [M+] calcd
for C14H28O3Si: 272.1808; found: 272.1785.
(1) For examples, see: (a) Ziegler, F. E. Acc. Chem. Res. 1977,
10, 227. (b) Tadano, K.-I. In Studies in Natural Products
Chemistry: Stereoselective Synthesis, (Part F); Atta-Ur-
Rahman, Ed.; Elsevier: Amsterdam, 1992, 405. (c) Ito, S.;
Tsunoda, T. Pure Appl. Chem. 1994, 66, 2071.
(d) Nubbemeyer, U. Top. Curr. Chem. 2005, 244, 149.
(2) (a) For reviews, see: The Claisen Rearrangement: Methods
and Applications; Hiersemann, M.; Nubbemeyer, U., Eds.;
Wiley-VCH: Weinheim, 2007. See also: (b) Bennett, G. B.
Synthesis 1977, 589. (c) Blechert, S. Synthesis 1989, 71.
(d) Wipf, P. In Comprehensive Organic Synthesis, Vol. 5;
Trost, B. M., Ed.; Pergamon Press: Oxford, 1991, 827.
(e) Martin Castro, A. M. Chem. Rev. 2004, 104, 2939.
(3) Baldwin, J. E.; Walker, J. A. J. Chem. Soc., Chem. Commun.
1973, 117.
(4) Ireland, R. E.; Mueller, R. H.; Willard, A. K. J. Am. Chem.
Soc. 1976, 98, 2868.
(5) (a) Ireland, R. E.; Mueller, R. H. J. Am. Chem. Soc. 1972, 94,
5897. (b) Ireland, R. E.; Wipf, P.; Armstrong, J. D. J. Org.
Chem. 1991, 56, 650. (c) Ireland, R. E.; Wipf, P.; Xiang,
J.-N. J. Org. Chem. 1991, 56, 3572. (d) For a review, see:
Pereira, S.; Srebnik, M. Aldrichimica Acta 1993, 26, 17.
(6) (a) Wada, M.; Shigehisa, T.; Akiba, K. Tetrahedron Lett.
1985, 26, 5191. (b) Greuter, H.; Lang, R. W.; Romann, A. J.
Tetrahedron Lett. 1988, 29, 3291. (c) Zaman, S.; Kitamura,
M.; Narasaka, K. Bull. Chem. Soc. Jpn. 2003, 76, 1055.
(d) Yang, Y.-Y.; Meng, W.-D.; Qing, F.-L. Org. Lett. 2004,
6, 4257. (e) Yang, Y.-Y.; Xu, J.; You, Z.-W.; Xu, X.-H.;
Qiu, X.-L.; Qing, F.-L. Org. Lett. 2007, 9, 5437. (f) Zheng,
F.; Zhang, X.; Qing, F.-L. Chem. Commun. 2009, 1505.
(7) Chao, L.-C.; Rieke, R. D. J. Org. Chem. 1975, 40, 2253.
(8) (a) Babu, S. A.; Yasuda, M.; Shibata, I.; Baba, A. Org. Lett.
2004, 6, 4475. (b) Babu, S. A.; Yasuda, M.; Shibata, I.;
Baba, A. J. Org. Chem. 2005, 70, 10408. (c) Babu, S. A.;
Yasuda, M.; Okabe, Y.; Shibata, I.; Baba, A. Org. Lett. 2006,
8, 3029.
8c: IR (neat): 2943, 1704, 1469, 1354, 1265, 1122, 1034,
908, 815, 685, 545 cm–1. 1H NMR (300 MHz, CDCl3): d =
5.59–5.75 (m, 1 H), 5.17 (dd, J = 17.6, 1.7 Hz, 1 H), 5.16 (dd,
J = 11.3, 2.2 Hz, 1 H), 4.59 (s, 2 H), 3.69–3.90 (m, 2 H),
3.29–3.55 (m, 2 H), 2.79 (dt, J = 6.9, 2.2 Hz, 1 H), 1.42–1.89
(m, 6 H), 1.17 (s, 3 H), 1.13 (s, 3 H). MS (EI): m/z = 243
[M + H+]. HRMS (EI): m/z [M+] calcd for C13H22O4:
242.1518; found: 242.1518.
10a: IR (neat): 2980, 1698, 1470, 1413, 1281, 1184, 926,
742, 706, 513 cm–1. 1H NMR (300 MHz, CDCl3): d = 7.20–
7.31 (m, 5 H), 6.25 (dt, J = 17.6, 9.6 Hz, 1 H), 5.15 (dd, J =
10.9, 0.6 Hz, 1 H), 5.14 (dd, J = 17.5, 0.6 Hz, 1 H), 3.63 (d,
J = 9.6 Hz, 1 H), 1.18 (s, 3 H), 1.13 (s, 3 H). 13C NMR (75
MHz, CDCl3): d = 183.9, 140.0, 136.6, 129.3, 128.0, 126.8,
117.8, 57.3, 46.7, 23.2, 21.8. MS (EI): m/z = 204 [M+].
HRMS (EI): m/z [M+] calcd for C13H16O2: 204.1150; found:
204.1146.
10b: IR (neat): 2979, 1702, 1611, 1513, 1469, 1250, 1180,
1037, 922, 832, 540 cm–1. 1H NMR (300 MHz, CDCl3): d =
7.13 (d, J = 8.8 Hz, 2 H), 6.83 (d, J = 8.8 Hz, 2 H), 6.21 (dt,
J = 17.6, 10.1 Hz, 1 H), 5.13 (d, J = 11.0 Hz, 1 H), 5.12 (dd,
(9) General Procedure: A mixture of TMSCl (0.7 mL, 5.5
mmol) and Et3N (0.7 mL, 5.0 mmol) was centrifuged at 3000
rpm for 5 min. The supernatant (0.64 mL, containing 2.5
Synlett 2009, No. 14, 2351–2355 © Thieme Stuttgart · New York

LETTER
J = 15.9, 0.9 Hz, 1 H), 3.71 (s, 3 H), 3.59 (d, J = 9.6 Hz, 1
A New Variant of Reformatsky–Claisen Rearrangement
2355
Hz, 1 H), 4.13 (d, J = 11.1 Hz, 1 H), 2.02 (s, 3 H), 1.20 (s, 3
H), 1.19 (s, 3 H), 1.16 (s, 3 H). 13C NMR (75 MHz, CDCl3):
d = 182.8, 171.0, 139.5, 115.7, 68.1, 46.8, 44.4, 21.6, 20.8,
16.7. MS (EI): m/z = 214 [M+]. HRMS (EI): m/z [M+] calcd
for C11H18O4: 214.1205; found: 214.1197.
H), 1.17 (s, 3 H), 1.12 (s, 3 H). 13C NMR (75 MHz, CDCl3):
d = 183.7, 158.4, 136.9, 132.0, 130.2, 117.5, 113.4, 56.5,
55.1, 46.8, 23.1, 21.8. MS (EI): m/z = 234 [M+]. HRMS (EI):
m/z [M+] calcd for C14H18O3: 234.1255; found: 234.1237.
10c: IR (neat): 2980, 1707, 1489, 1404, 1276, 1076, 1011,
925, 828, 516 cm–1. 1H NMR (300 MHz, CDCl3): d = 7.42
(d, J = 8.5 Hz, 2 H), 7.09 (d, J = 8.5 Hz, 2 H), 6.18 (dt, J =
16.8, 9.9 Hz, 1 H), 5.17 (dd, J = 11.2, 0.9 Hz, 1 H), 5.14 (dd,
J = 16.7, 0.8 Hz, 1 H), 3.60 (d, J = 9.3 Hz, 1 H), 1.18 (s, 3
H), 1.12 (s, 3 H). 13C NMR (75 MHz, CDCl3): d = 183.6,
139.0, 136.0, 131.2, 130.9, 120.8, 118.3, 56.6, 46.6, 22.9,
22.0. MS (EI): m/z = 282 [M+]. HRMS (EI): m/z [M+] calcd
for C13H1579BrO2: 282.0255; found: 282.0270.
16: IR (neat): 2978, 1700, 1468, 1375, 1293, 1131, 1009,
915, 740, 553 cm–1. 1H NMR (300 MHz, CDCl3): d = 5.98
(dd, J = 17.3, 11.0 Hz, 1 H), 5.04 (dd, J = 10.7, 1.1 Hz, 1 H),
5.00 (dd, J = 17.3, 1.4 Hz, 1 H), 1.16 (s, 6 H), 1.10 (s, 6 H).
13C NMR (75 MHz, CDCl3): d = 183.9, 144.4, 112.5, 47.8,
40.9, 22.9, 21.4. MS (EI): m/z = 156 [M+]. HRMS (EI): m/z
[M+] calcd for C9H16O2: 156.1150; found: 156.1142.
18: IR (neat): 2979, 1955, 1705, 1455, 1360, 1284, 1069,
851, 739, 699 cm–1. 1H NMR (300 MHz, CDCl3): d = 7.23–
7.38 (m, 5 H), 4.94 (t, J = 2.1 Hz, 2 H), 4.59 (s, 2 H), 4.13 (t,
J = 1.9 Hz, 2 H), 1.38 (s, 6 H). 13C NMR (100 MHz, CDCl3):
d = 207.4, 182.0, 137.9, 128.3, 127.7, 127.5, 104.5, 78.1,
71.9, 68.8, 43.0, 24.9. MS (EI): m/z = 246 [M+]. HRMS (EI):
m/z [M+] calcd for C15H18O3: 246.1255; found: 246.1257.
20: IR (neat): 2929, 1702, 1469, 1367, 1279, 1149, 942, 859,
721, 619 cm–1. 1H NMR (300 MHz, CDCl3): d = 5.79 (dd,
J = 10.3, 3.2 Hz, 1 H), 5.53 (d, J = 9.9 Hz, 1 H), 2.46–2.60
(m, 1 H), 1.40–2.20 (m, 6 H), 1.26 (s, 6 H). MS (EI): m/z =
168 [M+]. HRMS (EI): m/z [M+] calcd for C10H16O2:
168.1150; found: 168.1168.
22: IR (neat): 2928, 1732, 1469, 1370, 1225, 1131, 1080,
1043, 794, 642, 605 cm–1. 1H NMR (300 MHz, CDCl3):
d = 5.85 (s, 2 H), 5.26 (dd, J = 9.2, 2.9 Hz, 1 H), 4.42 (d, J =
2.3 Hz, 1 H), 4.25 (dd, J = 11.8, 2.7 Hz, 1 H), 4.17 (dd, J =
11.8, 5.5 Hz, 1 H), 3.74 (dt, J = 2.7, 3.1 Hz, 1 H), 2.09 (s, 3
H), 2.07 (s, 3 H), 1.21 (s, 3 H), 1.18 (s, 3 H). 13C NMR (75
MHz, CDCl3): d = 180.5, 171.2, 170.6, 128.6, 127.6, 78.7,
74.1, 65.4, 63.2, 46.3, 21.0, 21.7, 20.5. MS (EI): m/z = 300
[M+].
10e: IR (neat): 2981, 1706, 1471, 1274, 1167, 1030, 925,
874, 793, 602 cm–1. 1H NMR (300 MHz, CDCl3): d = 7.35
(s, 1 H), 7.26 (s, 1 H), 6.30 (s, 1 H), 6.00 (dt, J = 17.6, 9.3
Hz, 1 H), 5.15 (d, J = 11.8 Hz, 1 H), 5.14 (d, J = 15.1 Hz,
1 H), 3.61 (d, J = 9.1 Hz, 1 H), 1.19 (s, 3 H), 1.14 (s, 3 H).
13C NMR (75 MHz, CDCl3): d = 183.7, 142.5, 140.1, 136.1,
123.5, 117.8, 110.8, 48.0, 29.7, 22.6, 22.2. MS (EI): m/z =
194 [M+]. HRMS (EI): m/z [M+] calcd for C11H14O3:
194.0943; found: 194.0939.
12: IR (neat): 2974, 1709, 1473, 1409, 1383, 1241, 1201,
1162, 943, 557 cm–1. 1H NMR (300 MHz, CDCl3): d = 5.12
(tt, J = 7.7, 1.4 Hz, 1 H), 2.26 (d, J = 7.7 Hz, 2 H), 1.72 (s, 3
H), 1.61 (s, 3 H), 1.19 (s, 6 H). 13C NMR (75 MHz, CDCl3):
d = 184.7, 134.6, 119.6, 42.7, 38.4, 26.0, 24.5, 17.9. MS (EI):
m/z = 156 [M+]. HRMS (EI): m/z [M+] calcd for C9H16O2:
156.1151; found: 156.1131.
14: IR (neat): 2984, 1742, 1700, 1471, 1417, 1385, 1242,
1037, 921, 606, 452, 440 cm–1. 1H NMR (300 MHz, CDCl3):
d = 5.90 (dd, J = 17.4, 10.9 Hz, 1 H), 5.20 (dd, J = 10.9, 0.8
Hz, 1 H), 5.08 (dd, J = 17.3, 0.8 Hz, 1 H), 4.26 (d, J = 11.1
Synlett 2009, No. 14, 2351–2355 © Thieme Stuttgart · New York