Triethylborane induced radical reaction of gallium enolates with α-halo esters

Article abstract of DOI:10.1246/bcsj.75.2049

Treatment of silyl enolates with methyllithium followed by an addition of gallium trichloride afforded the corresponding gallium enolates. The reaction of the resulting gallium enolates with α-halo carbonyl compounds in the presence of triethylborane as a radical initiator provided 1,4-dicarbonyl compounds in good yields.

Full text of DOI:10.1246/bcsj.75.2049

c. Jpn.
© 2002 The Chemical Society of Japan
Bull. Chem. Soc. Jpn., 75, 2049–2052 (2002) 2049
e Chemical
ciety of Ja-
n
e Chemical
ciety of Ja-
n
Triethylborane Induced Radical Reaction of Gallium Enolates with
α
-Halo Esters
Radical Reaction with Gallium Enolates
S. Usugi et al.
Shin-ichi Usugi, Hideki Yorimitsu, Hiroshi Shinokubo, and Koichiro Oshima*
02
49
52
Department of Material Chemistry, Graduate School of Engineering, Kyoto University,
Yoshida, Sakyo-ku, Kyoto 606-8501
SJA8
09-2673
071
(Received March 19, 2002)
Treatment of silyl enolates with methyllithium followed by an addition of gallium trichloride afforded the corre-
sponding gallium enolates. The reaction of the resulting gallium enolates with α-halo carbonyl compounds in the pres-
ence of triethylborane as a radical initiator provided 1,4-dicarbonyl compounds in good yields.
02
02
We have recently reported that allylgallium is an effective
reagent for radical allylation of α-iodo or α-bromo carbonyl
compounds.1 For instance, treatment of benzyl bromoacetate
with allylgallium, prepared from allylmagnesium chloride and
gallium trichloride, in the presence of triethylborane2 as a radi-
cal initiator in THF provided benzyl 4-pentenoate in good
yield (Scheme 1). Here we wish to report a triethylborane-in-
duced radical reaction of gallium enolates3 with α-haloesters4
providing γ-keto esters.5
Methyllithium (1.04 M ether solution, 1.01 mL, 1.05 mmol)
was added to a solution of 1-trimethylsiloxy-1-cyclohexene
(1a) in ether at 0 °C under argon atmosphere.6 After stirring
for 30 min at the same temperature, GaCl3 (1.0 M hexane solu-
tion, 1.0 mL, 1.0 mmol) was added to the resulting lithium
enolate. The reaction mixture was warmed to room tempera-
ture over a period of 30 min. Benzyl iodoacetate (2a, 0.5
mmol) and Et3B (1.0 M hexane solution, 0.2 mL, 0.2 mmol)
were added sequentially. Finally, air (5 mL) was introduced
via a syringe, and the resulting mixture was stirred for 3 h. Ex-
tractive workup followed by silica gel column purification pro-
vided benzyl (2-oxocyclohexyl)acetate (3a) in 70% yield
(Scheme 2).
ramethyl-1-piperidinyloxyl), none of expected products were
detected in the reaction mixture. These results suggest that the
reaction proceeds via a radical process. The results of the reac-
tion of benzyl iodoacetate (2a) with various gallium enolates,
generated from the corresponding silyl enolates in situ, are list-
ed in Table 1. Several characteristics of this reaction are note-
worthy. (1) γ-Keto esters were obtained in good yields starting
from a variety of silyl enolates. (2) In the case of silyl enolate
1g, prepared from cyclopropyl methyl ketone, benzyl 7-iodo-
4-oxo-heptanoate (3g) was obtained exclusively via cyclopro-
pane ring cleavage (entry 6). (3) An addition of benzyl iodo-
acetate to the lithium enolate instead of the gallium enolate
provided a complex mixture. (4) Only a trace amount of the
product was obtained from the reaction of the gallium enolate
derived from 1d (entry 3). In this case, the benzyl radical
(·C(Ph)(OGaCl2)CH2CH2COOCH2Ph), which resulted from
the addition of α-carbonyl radical (·CH2COOCH2Ph) to the
gallium enolate, would be unreactive due to stabilization by
the phenyl group.
0.1
Next, the reaction of various α-halo carbonyl compounds
with the gallium enolate prepared from 1a was examined
(Table 2). Not only primary α-iodo ester 2a but also primary
α-bromo ester 2b, α-iodo amide 2d, and α-iodo nitrile 2f af-
forded the corresponding adducts in good yields upon treat-
Without Et3B as a radical initiator, the reaction did not pro-
ceed at all. Moreover, in the presence of TEMPO (2,2,6,6-tet-
Scheme 1.
Scheme 2.

2050 Bull. Chem. Soc. Jpn., 75, No. 9 (2002)
Table 1. Reaction of Gallium Enolates with Benzyl Iodoacetate
Radical Reaction with Gallium Enolates
Entry
R1
R2
R3
Time/h
Product
Yield/%
1
2
3
4
5
1b
1c
1d
1ea
1f
n-C5H11
t-Bu
Ph
Pr
i-Pr
H
H
H
Et(H)
Me
H
H
H
H(Et)
Me
6
2
7
3
10
3b
3c
3d
3e
3f
76
50
trace
66
26
6
1g
H
H
9
3g
60b
a) A mixture of (E) and (Z)-stereoisomer
b) Product was ICH2CH2CH2C(O)CH2CH2C(O)OCH2Ph
Table 2.
Entry
1
Substrate
R–X
Time/h Product Yield/%
2a
3
3a
70
69
1a
2
3
2b
2c
4
3a
3h
7
12
(50/50)
4
2d
4
3i
51
5
6
2e
2f
9
4
3j
17
76
3k
7
2c
4
3l
49
1b
8
9
10
2d
2e
2f
3
5
4
3m
3n
3o
45
37
77
ment with gallium enolates. In contrast, the reaction of sec-
ondary α-iodo ester 2c and α-iodo ketone 2e provided the de-
sired products in only low yields. The use of alkyl halides
without an activating group, such as isopropyl iodide or t-butyl
iodide, resulted in the formation of a negligible amount of the
expected adducts.
radical, which is produced by the action of oxygen on trieth-
ylborane, abstracts the halogen atom from an α-halo carbonyl
compound 2 (R4-X) to give the alkyl radical 4 (R4•). Next, the
alkyl radical 4 adds to the carbon-carbon double bond of a gal-
lium enolate to give the alkyl radical 5. The radical 5 then re-
acts with 2 to yield the adduct 6 and regenerates the alkyl radi-
cal 4.7 The adduct 6 eventually eliminates gallium halide to
furnish the product 3. Elimination of gallium(Ⅱ) chloride from
We propose the reaction mechanism involving an iodine
atom transfer process that is depicted in Scheme 3. An ethyl

S. Usugi et al.
Bull. Chem. Soc. Jpn., 75, No. 9 (2002) 2051
Scheme 3.
sulfate and concentrated in vacuo. The residual oil was purified
by silica gel column chromatography to provide benzyl (2-oxocy-
clohexyl)acetate (3a, 86 mg) in 70% yield.
the alkyl radical 5 to afford 3 directly is an alternative pathway.
The resulting gallium(Ⅱ) species abstracts halogen from 2 to
regenerate the alkyl radical 4, and the radical chain reaction
continues.8
In conclusion, we have developed an alkylation reaction of
various gallium enolates via a triethylborane-induced radical
process. An addition of radicals to silyl enolates is limited to
polyhalogenated radicals such as perfluoroalkyl or trichloro-
methyl radicals. Conversion of silyl enolates to gallium eno-
lates enhances the reactivity of the enol moiety toward radi-
cals, and allows us to employ carbonyl- and cyano-substituted
alkyl radicals.
Benzyl (2-Oxocyclohexyl)acetate (3a) IR (neat) 2937, 2862,
1736, 1711, 1499, 1450, 1389, 1350, 1312, 1275, 1213, 1163,
1132, 978, 740, 698 cm−1; 1H NMR (CDCl3) δ 1.30–1.46 (m, 1H),
1.50–1.78 (m, 2H), 1.80–1.90 (m, 1H), 2.00–2.26 (m, 3H), 2.26–
2.46 (m, 2H), 2.76–2.92 (m, 2H), 5.10 (s, 2H), 7.24–7.36 (m, 5H);
13C NMR (CDCl3) δ 25.00, 27.57, 33.68, 34.27, 41.63, 46.95,
66.13, 128.08, 128.12, 128.51, 136.07, 172.44, 210.89. Found: C,
73.32; H, 7.45%. Calcd for C15H18O3: C, 73.15; H, 7.37%.
Benzyl 4-Oxononanoate (3b) IR (neat) 2932, 2860, 1736,
1717, 1499, 1456, 1410, 1354, 1163, 1080, 1003, 739, 698 cm−1
;
1H NMR (CDCl3) δ 0.86 (t, J = 7.2 Hz, 3H), 1.16–1.36 (m, 4H),
1.56 (tt, J = 7.5, 7.5 Hz, 2H), 2.41 (t, J = 6.0 Hz, 2H), 2.61 (t, J =
6.0 Hz, 2H), 2.71 (t, J = 6.0 Hz, 2H), 5.09 (s, 2H), 7.28–7.36 (m,
5H); 13C NMR (CDCl3) δ 13.74, 22.29, 23.35, 27.89, 31.25,
36.88, 42.68, 66.40, 128.23, 128.27, 128.60, 135.98, 172.79,
209.18. Found: C, 73.46; H, 8.65%. Calcd for C16H22O3: C,
73.25; H, 8.45%.
Experimental
1H NMR (300 MHz) and 13C NMR (75.3 MHz) spectra were
taken on a Varian GEMINI 300 spectrometer in CDCl3 as a sol-
vent, and chemical shifts are given in δ value with tetramethylsi-
lane as an internal standard. IR spectra were determined on a
JASCO IR-810 spectrometer. Mass spectra were recorded on a
JEOL JMS-700 spectrometer. TLC analyses were performed on
commercial glass plates bearing 0.25-mm layer of Merck Silica
gel 60F254. Silica gel (Wakogel 200 mesh) was used for column
chromatography. The analyses were carried out at the Elemental
Analysis Center of Kyoto University. Unless otherwise noted,
materials obtained from commercial suppliers were used without
further purification. THF was freshly distilled from sodium ben-
zophenone ketyl before use. Et3B was purchased from Aldrich
Chemicals and was diluted to prepare a 1.0 M hexane solution,
which was stored under argon.
Benzyl 5,5-Dimethyl-4-oxohexanoate (3c) IR (neat) 3034,
2970, 2935, 2874, 1738, 1707, 1499, 1479, 1456, 1384, 1350,
1
1315, 1161, 1086, 978, 739, 698 cm−1; H NMR (CDCl3) δ 1.15
(s, 9H), 2.63 (t, J = 6.6 Hz, 2H), 2.83 (t, J = 6.6 Hz, 2H), 5.12 (s,
2H), 7.30–7.42 (m, 5H); 13C NMR (CDCl3) δ 26.39, 28.08, 31.34,
43.83, 66.34, 128.25, 128.26, 128.59, 136.02, 172.96, 214.12.
Found: C, 72.71; H, 8.20%. Calcd for C15H20O3: C, 72.55; H,
8.12%.
Benzyl 3-Ethyl-4-oxoheptanoate (3e) IR (neat) 3034, 2964,
2936, 2878, 1736, 1713, 1499, 1456, 1407, 1385, 1354, 1329,
1228, 1175, 957, 750, 698 cm−1; 1H NMR (CDCl3) δ 0.88 (t, J =
6.9 Hz, 3H), 0.89 (t, J = 6.9 Hz, 3H), 1.36–1.72 (m, 4H), 2.37
(dd, J = 3.9, 16.5 Hz, 1H), 2.48 (t, J = 7.2 Hz, 2H), 2.82 (dd, J =
9.9, 16.5 Hz, 1H), 2.88–2.98 (m, 1H), 5.07 (s, 1H), 5.09 (s, 1H),
7.28–7.38 (m, 5H); 13C NMR (CDCl3) δ 11.15, 13.57, 16.72,
24.35, 34.68, 44.22, 48.42, 66.37, 128.29, 128.30, 128.61, 135.90,
172.53, 212.86. Found: C, 73.04; H, 8.58%. Calcd for C16H22O3:
C, 73.25; H, 8.45%.
General Procedure for the Reaction of Gallium Enolates
with -Halo Carbonyl Compounds. To a solution of 1-tri-
α
methylsiloxy-1-cyclohexene (170 mg, 1.0 mmol) in ether (2 mL),
methyllithium (1.04 M ether solution, 1 M = 1 mol dm−3, 1.01
mL, 1.05 mmol) was added dropwise via a syringe at 0 °C. After
the mixture was stirred for 30 min, gallium trichloride (1.0 mL,
1.0 M hexane solution, 1.0 mmol) was dropped at 0 °C. The mix-
ture was allowed to warm to room temperature over a period of 30
min, and then benzyl iodoacetate (138 mg, 0.5 mmol) and Et3B
(1.0 M hexane solution, 0.20 mL, 0.20 mmol) were added sequen-
tially. Finally, air (5 mL) was introduced via a syringe, and the re-
sulting mixture was stirred for 3 h at 25 °C. The mixture was then
poured into water and extracted with ethyl acetate (20 mL × 3).
The combined organic layers were dried over anhydrous sodium
Benzyl 3,3,5-Trimethyl-4-oxohexanoate (3f) IR (neat) 2972,
2936, 2874, 1738, 1705, 1499, 1462, 1381, 1346, 1177, 1128,
1028, 1003, 741, 698 cm−1; 1H NMR (CDCl3) δ 1.06 (d, J = 6.6
Hz, 6H), 1.27 (s, 6H), 2.62 (s, 2H), 3.10 (sept, J = 6.6 Hz, 1H),
5.08 (s, 2H), 7.30–7.40 (m, 5H); 13C NMR (CDCl3) δ 19.80,
24.60, 34.39, 43.72, 46.26, 66.15, 128.26, 128.35, 128.59, 135.97,

2052 Bull. Chem. Soc. Jpn., 75, No. 9 (2002)
Radical Reaction with Gallium Enolates
171.61, 218.42. Found: C, 73.44; H, 8.62%. Calcd for C16H22O3:
C, 73.25; H, 8.45%.
Calcd for C9H15NO: C, 70.55; H, 9.87%.
Compounds 3j9 and 3k5a are found in the literature.
Benzyl 7-Iodo-4-oxoheptanate (3g) IR (neat) 3032, 2957,
1736, 1717, 1499, 1454, 1408, 1354, 1202, 1169, 1094, 1003,
752, 698 cm−1; 1H NMR (CDCl3) δ 2.05 (tt, J = 6.6, 6.9 Hz, 2H),
2.58 (t, J = 6.9 Hz, 2H), 2.63 (t, J = 6.3 Hz, 2H), 2.72 (t, J = 6.3
Hz, 2H), 3.17 (t, J = 6.6 Hz, 2H), 5.09 (s, 2H), 7.28–7.40 (m, 5H);
13C NMR (CDCl3) δ 6.06, 26.96, 27.87, 37.10, 42.86, 66.48,
128.26, 128.32, 128.62, 135.87, 172.58, 207.41. This compound
was unstable and we could not obtain an analytically pure sample.
This work was supported by Grants-in-Aids for Scientific
Research (Nos. 12305058 and 10208208) from the Ministry of
Education, Culture, Sports, Science and Technology. H. Y.
acknowledges JSPS for financial support. H. S. also thanks
Banyu Pharmaceutical Co., Ltd.
References
Benzyl 2-(2-Oxocyclohexyl)propanoate (3h)
IR (neat)
1
a) S. Usugi, H. Yorimitsu, and K. Oshima, Tetrahedron
2939, 2864, 1736, 1711, 1499, 1454, 1381, 1155, 1042, 739, 698
cm−1; 1H NMR (CDCl3) δ 1.19 (d, J = 7.2 Hz, 3H), 1.48–1.72 (m,
3H), 1.82–2.06 (m, 3H), 2.20–2.42 (m, 2H), 2.58–2.68 (m, 1H),
2.70–2.90 (m, 1H), 5.09 (s, 2H), 7.26–7.38 (m, 5H); 13C NMR
(CDCl3) δ 14.52, 24.83, 27.45, 30.98, 39.25, 42.06, 63.21, 66.10,
128.13, 128.17, 128.56, 136.20, 175.22, 210.87. HRMS m/z calcd
for C16H20O3 260.1412, found 260.1412.
Lett., 42, 4535 (2001). b) S. Usugi, H. Yorimitsu, H. Shinokubo,
and K. Oshima, Bull. Chem. Soc. Jpn., 43, 841 (2002).
2
For triethylborane as a radical initiator, see: a) K. Nozaki,
K. Oshima, and K. Utimoto, J. Am. Chem. Soc., 109, 2547 (1987).
b) K. Nozaki, K. Oshima, and K. Utimoto, Tetrahedron Lett., 39,
923 (1989). c) K. Oshima and K. Utimoto, J. Syn. Org. Chem.,
Jpn., 47, 40 (1989). d) H. Yorimitsu and K. Oshima, “Radicals in
Organic Synthesis,” ed by P. Renaud and M. P. Sibi, WILEY-
VCH, Weinheim (2001), Vol. 1, Chap. 1.2, p. 11. e) C. Ollivier
and P. Renaud, Chem. Rev., 101, 3415 (2001).
N-Benzyl-2-(2-oxocyclohexyl)ethanamide (3i) IR (nujol)
3298, 1697, 1639, 1556, 1348, 1312, 1286, 1236, 1132, 1080,
1
1018, 741, 698 cm−1; H NMR (CDCl3) δ 1.20–1.42 (m, 1H),
1.48–1.78 (m, 2H), 1.78–1.90 (m, 1H), 2.00–2.22 (m, 3H), 2.26–
2.42 (m, 2H), 2.58–2.68 (m, 1H), 2.86–3.00 (m, 1H), 4.38 (d, J =
5.8 Hz, 1H), 4.39 (d, J = 5.8 Hz, 1H), 6.53 (bs, 1H), 7.20–7.36
(m, 5H); 13C NMR (CDCl3) δ 25.05, 27.79, 34.32, 36.49, 41.86,
43.48, 47.66, 127.38, 127.64, 128.64, 138.20, 172.31, 212.76.
HRMS m/z calcd for C15H19NO2 245.1416, found 245.1415.
Benzyl 2-Methyl-4-oxononanoate (3l) IR (neat) 3067, 3034,
2934, 2874, 1736, 1717, 1499, 1456, 1408, 1379, 1259, 1165,
1138, 1030, 970, 910, 750, 698 cm−1; 1H NMR (CDCl3) δ 0.86 (t,
J = 7.2 Hz, 3H), 1.17 (d, J = 7.2 Hz, 3H), 1.12–1.32 (m, 4H),
1.53 (tt, J = 7.5, 7.2 Hz, 2H), 2.36 (t, J = 7.5 Hz, 2H), 2.43 (dd, J
= 17.1, 5.1 Hz, 1H), 2.87 (dd, J = 17.1, 8.1 Hz, 1H), 2.99 (m,
1H), 5.08 (s, 1H), 5.10 (s, 1H), 7.26–7.40 (m, 5H); 13C NMR
(CDCl3) δ 13.76, 16.95, 22.30, 23.29, 31.26, 34.66, 42.88, 45.61,
66.33, 128.10, 128.19, 128.59, 136.16, 175.76, 209.14. Found: C,
73.73; H, 8.85%. Calcd for C17H24O3: C, 73.88; H, 8.75%.
N-Benzyl-4-oxononanamide (3m) IR (nujol) 3314, 1701,
1639, 1551, 1412, 1236, 1030, 723, 696 cm−1; 1H NMR (CDCl3)
δ 0.87 (t, J = 7.2 Hz, 3H), 1.16–1.36 (m, 4H), 1.54 (tt, J = 7.2,
7.2 Hz, 2H), 2.40 (t, J = 7.2 Hz, 2H), 2.44 (t, J = 6.6 Hz, 2H),
2.75 (t, J = 6.6 Hz, 2H), 4.36 (s, 1H), 4.38 (s, 1H), 6.36 (bs, 1H),
7.20–7.32 (m, 5H); 13C NMR (CDCl3) δ 13.68, 22.22, 23.31,
29.67, 31.17, 37.49, 42.63, 43.44, 127.37, 127.86, 128.62, 138.31,
172.15, 210.53. HRMS m/z calcd for C16H23NO2 261.1729, found
261.1734.
3
For reactions involving gallium enolates, see: a) M.
Yamaguchi, T. Tsukagoshi, and M. Arisawa, J. Am. Chem. Soc.,
121, 4074 (1999). b) Y. Han and Y. Z. Huang, Tetrahedron Lett.,
39, 7751 (1998).
4
Et3B-catalyzed radical reactions with α-halo carbonyl
compounds, see: a) T. Nakamura, H. Yorimitsu, H. Shinokubo,
and K. Oshima, Synlett, 1998, 1351. b) H. Yorimitsu, K.
Wakabayashi, H. Shinokubo, and K. Oshima, Bull. Chem. Soc.
Jpn., 74, 1963 (2001). c) H. Yorimitsu, T. Nakamura, H.
Shinokubo, K. Oshima, K. Omoto, and H. Fujimoto, J. Am. Chem.
Soc., 122, 11041 (2000).
5
For radical reactions of metal enolates, see: a) K. Miura, N.
Fujisawa, H. Saito, D. Wang, and A. Hosomi, Org. Lett., 3, 4055
(2001). b) G. A. Russell and L. L. Herold, J. Org. Chem., 50,
1037 (1985). c) Y. Watanabe, T. Yoneda, Y. Ueno, and T. Toru,
Tetrahedron Lett., 31, 6669 (1990). d) K. Miura, M. Taniguchi, K.
Nozaki, K. Oshima, and K. Utimoto, Tetrahedron Lett., 31, 6391
(1990). e) K. Miura, Y. Takeyama, K. Oshima, and K. Utimoto,
Bull. Chem. Soc. Jpn., 64, 1542 (1991). f) J. Sugimoto, K. Miura,
K. Oshima, and K. Utimoto, Chem. Lett., 1991, 1319. g) K.
Miura, J. Sugimoto, K. Oshima, and K. Utimoto, Bull. Chem. Soc.
Jpn., 65, 1513. h) S. Tanaka, T. Nakamura, H. Yorimitsu, H.
Shinokubo, and K. Oshima, Org. Lett., 2, 1911 (2000). i) T.
Nakamura, S. Tanaka, H. Yorimitsu, H. Shinokubo, and K.
Oshima, Computes Rendus Acad. Sci. Paris, Chim., 4, 461 (2001).
1-Phenylnona-1,4-dione (3n) IR (neat) 2932, 2860, 1713,
1688, 1597, 1582, 1448, 1400, 1358, 1238, 1211, 1180, 1126,
6
C. H. Heathcock, C. T. Buse, W. A. Kleschick, M. C.
Pirrung, J. E. Sohn, and J. Lampe, J. Org. Chem., 45, 1066 (1980).
For atom-transfer radical reactions, see. a) D. P. Curran,
1
1003, 754, 691 cm−1; H NMR (CDCl3) δ 0.87 (t, J = 6.9 Hz,
7
3H), 1.20–1.38 (m, 4H), 1.60 (tt, J = 7.2, 7.5 Hz, 2H), 2.50 (t, J =
7.5 Hz, 2H), 2.83 (t, J = 6.3 Hz, 2H), 3.26 (t, J = 6.3 Hz, 2H),
7.40–7.46 (m, 2H), 7.50–7.58 (m, 1H), 7.92–8.00 (m, 2H); 13C
NMR (CDCl3) δ 13.77, 22.33, 23.45, 31.31, 32.27, 36.10, 42.90,
128.11, 128.62, 133.16, 136.84, 198.87, 209.93. HRMS m/z calcd
for C15H20O2 232.1463, found 232.1454.
Synthesis, 1988, 417; D. P. Curran, M.-H. Chen, and D. Kim, J.
Am. Chem. Soc., 108, 2498 (1986). b) D. P. Curran and C.-T.
Chang, Tetrahedron Lett., 28, 2477 (1987). c) J. Byers, “Radicals
in Organic Synthesis,” ed by P. Renaud and M. P. Sibi, WILEY-
VCH, Weinheim (2001), Vol. 1, Chap. 1.5, p. 72.
8
Gallium(Ⅱ) species has been proposed to be involved in a
4-Oxononanenitrile (3o) IR (neat) 2959, 2934, 2862, 2249,
1
1717, 1468, 1414, 1377, 1128, 1082 cm−1; H NMR (CDCl3) δ
HGaCl2-mediated radical reduction reaction, see: S. Mikami, K.
Fujita, T. Nakamura, H. Yorimitsu, H. Shinokubo, S. Matsubara,
and K. Oshima, Org. Lett., 3, 1853 (2001).
0.86 (t, J = 6.9 Hz, 3H), 1.16–1.36 (m, 4H), 1.57 (tt, J = 7.5, 7.5
Hz, 2H), 2.41 (t, J = 7.5 Hz, 2H), 2.55 (t, J = 7.2 Hz, 2H), 2.76 (t,
J = 7.2 Hz, 2H); 13C NMR (CDCl3) δ 11.20, 13.68, 22.22, 23.23,
31.13, 37.55, 42.37, 119.08, 206.49. Found: C, 70.60; H, 9.85%.
9
M. Yasuda, T. Oh-hata, I. Shibata, A. Baba, and H.
Matsuda, J. Chem. Soc., Perkin Trans. 1, 1993, 859.