A new two-step synthesis of 2-alkylated 1,4-diketones and α-alkylated γ-keto esters

Article abstract of DOI:10.1055/s-1999-3533

2-Alkylated 1,4-diketones and α-alkylated γ-keto esters can be easily prepared by a two-step procedure which involves first the conjugate addition of a nitroalkane to an enedione derivative in acetonitrile with DBU as base, followed by chemoselective hydrogenation of the C-C double bond (H₂ 10% Pd/C) of the Michael adduct, obtained after elimination of nitrous acid.

Full text of DOI:10.1055/s-1999-3533

1236
PAPER
A New Two-Step Synthesis of 2-Alkylated 1,4-Diketones and a-Alkylated
g-Keto Esters
Roberto Ballini,* Giovanna Bosica, Lara Petrelli, Marino Petrini
Dipartimento di Scienze Chimiche dell'Università, Via S. Agostino 1, I-62032 Camerino, Italy
Fax +39(737)637345; E-mail: ballini@camserv.unicam.it
Received 18 November 1998; 6 February 1999
Although several methods have been reported4,5 for the
Abstract: 2-Alkylated 1,4-diketones and a-alkylated g-keto esters
synthesis of the above compounds, most of these suffer
can be easily prepared by a two-step procedure which involves first
from drawbacks such as the use of harsh conditions, em-
ployment of expensive chemicals, low yields and/or te-
the conjugate addition of a nitroalkane to an enedione derivative in
acetonitrile with DBU as base, followed by chemoselective hydro-
genation of the C–C double bond (H2, 10% Pd/C) of the Michael ad- dious procedures.
duct, obtained after elimination of nitrous acid.
Aliphatic nitro compounds can be considered as versatile
building blocks in organic synthesis,8 both the activating
effect of the nitro group and its facile transformation into
various functionalities have extended the importance of
nitro compounds in the preparation of complex molecules.
In the past the nitroalkanes have already been used to ob-
tain 1,4-diketones9 and g-keto esters10 through Michael
addition to electron-deficient alkenes, followed by the Nef
reaction.
Key words: 2-Alkyl 1,4-diketones, a-alkyl g-keto esters, nitro-
alkanes, conjugated addition, nitrous acid elimination
1,4-Diketones are important intermediates in the synthesis
of cyclopentenones and heterocyclic compounds such as
furans, pyrroles, thiophenes, and pyridazines.1–6 g-Keto
esters represent a valuable class of compounds as interme-
diates for various heterocycles such as lactones, b-lactam
antibiotics, isoquinolines and lactonic sex pheromones.7
In the course of our studies to explore the novel utilities of
nitroalkanes in the Michael reaction,11 we have disclosed
NO2
NO2
R1
DBU
CH3CN
R
R1
R
1
O
O
O
OMe
-HNO2
-HNO2
68-90%
75-99%
5
2
O
NO2
O
O
NO2
H
O
O
R
R
R1
R1
R1
OMe
R1
H
-HNO2
R
β-elimination
-HNO2
R
β-elimination
O
O
R1
OMe
3a-j
6a-j
O
O
H2, 10% Pd/C
40 psi, 75-96%
H2, 10% Pd/C
40 psi, 73-99%
R
O
R
O
R1
OMe
4a-j
7a-j
O
O
Synthesis 1999, No. 7, 1236–1240 ISSN 0039-7881 © Thieme Stuttgart · New York

PAPER
A New Two-Step Synthesis of 2-Alkylated 1,4-Diketones and a-Alkylated g-Keto-Esters
1237
Table 1 Enone Derivatives 3 Prepared
Producta
Yield
(%)
IR (film)
1H NMR (CDCl3/TMS)
d, J (Hz)
13C NMR (CDCl3)
d
n (cm–1)
3a
68
1719, 1665
0.95 (t, 3H, J = 7.3), 1.4–1.6 (m, 2H), 2.15–2.25
(m, 2H), 2.2 (s, 3H), 2.46 (s, 3H), 3.5 (s, 3H),
6.8 (t, 1H, J = 7.3)
14.0, 18.7, 23.3, 29.5, 33.4, 138.5,
141.3, 199.2, 204.1
3b
3c
3d
72
75
85
1730, 1666
1715, 1681
1720, 1665
2.2 (s, 3H), 2.3 (s, 3H), 2.5–2.6 (m, 2H), 3.5
(s, 3H), 3.7 (s, 3H), 6.8 (t, 1H, J = 7.4)
18.6, 23.8, 32.6, 33.0, 51.6, 137.0,
139.5, 173.2, 200.0, 203.5
1.5–1.7 (m, 6H), 2.1 (t, 2H, J = 6.4), 2.2 (s, 3H),
2.3 (s, 3H), 2.4 (t, 2H, J = 7.5), 3.5 (s, 2H)
18.6, 26.5, 27.2, 28.2, 33.0, 34.1, 36.4,
132.8, 150.8, 203.3, 204.5
0.9 (t, 3H, J = 6.7), 1.2-1.5 (m, 6H), 1.2–1.5
(m, 2H), 2.2 (s, 3H), 2.4 (s, 3H), 3.4 (s, 1H), 6.8
(t, 1H, J = 7.2)
14.0, 18.6, 22.8, 23.9, 26.5, 29.3, 30.9,
33.0, 138.5, 140.1, 200.0, 203.5
3e
77
40
1717, 1665
1712, 1666
1.1 (t, 3H, J = 7.4), 2.1–2.3 (m, 2H), 2.2 (s, 3H),
2.4 (s, 3H), 3.4 (s, 2H), 6.8 (t, 1H, J = 7.4)
14.0, 18.6, 21.3, 24.4, 32.9, 139.7,
140.1, 199.2, 202.7
3f’
2.06 (s, 3H), 2.19 (s, 3H), 3.16 (s, 2H), 3.96
(d, 2H, J = 7.9), 7.15-7.4 (m, 5H)
18.5, 23.9, 33.2, 39.8, 127.4, 128.3,
129.0, 137.9, 140.6, 141.8, 199.8,
203.5
3f"
3g
33
90
1712
2.06 (s, 3H), 2.11 (s, 3H), 2.5–2.69 (m, 2H),
3.04–3.09 (m, 1H), 6.07–6.13 (dd, 1H, J = 9.2,
15.9), 6.6 (d, 1H, J = 15.9), 7.1–7.55 (m, 5H)
16.3, 29.3, 44.9, 56.7, 126.2, 127.6,
129.0, 132.4, 133.5, 136.4, 207.1,
210.4
1733, 1665
1.4–1.8 (m, 2H), 2.15 (t, 2H, J = 7.0), 2.2–2.4
(m, 2H), 2.2 (s, 3H), 2.35 (s, 3H), 3.4 (s, 2H), 3.7
(s, 3H), 6.8 (t, 1H, J = 7.2)
18.6, 23.9, 28.11, 32.6, 33.0, 51.4,
139.0, 139.1, 173.7, 199.9, 203.5
3h
3i
80
70
1706, 1661
1720, 1666
2.3 (s, 3H), 2.3-2.6 (m, 4H), 2.4 (s, 3H), 3.4
(s, 2H), 7.1 (t, 1H, J = 7.2)
18.5, 23.8, 29.7, 33.0, 43.2, 137.6,
140.5, 199.9, 203.5, 207.7
0.9 (d, 6H, J = 6.6), 1.7-1.9 (m, 1H), 2.09
(t, 2H, J = 7.1), 2.15 (s, 3H), 2.3 (s, 3H), 3.4
(s, 2H), 6.8 (t, 1H, J = 7.3)
18.6, 22.5, 23.9, 27.2, 33.1, 33.6,
136.8, 139.6, 200.8, 203.5
3j
77
1717, 1665
1.3 (s, 3H), 1.7-1.9 (m, 2H), 2.2-2.4 (m, 2H), 2.2
(s, 3H), 2.3 (s, 3H), 3.4 (s, 2H), 3.8-4.0 (m, 2H),
6.8 (t, 1H, J = 7.3)
18.6, 22.4, 23.8, 33.0, 38.8, 64.6,
110.3, 139.1, 140.2, 199.9, 203.5
a Satisfactory microanalyses obtained: C ± 0.18, H ± 0.14.
that the nitro group may, contemporaneously, behave both ene, or g-methylene protons, b-methylene, or g-methine
as an electron-withdrawing and as a leaving group.12 The protons of b-secondary alkyl substituents provides a reli-
latter result suggested us a new convenient, two-step way able guide for the assignment of the olefin configuration.
to prepare the title compounds. Our procedure involves
first the conjugate addition of the nitronate derived from
the nitro compound 1 to the enedione derivatives 2 and 5
(with this substrate a regiospecific addition occurs) in ac-
etonitrile and with DBU (1 equiv) as base (Scheme 1),
then chemoselective hydrogenation (10% Pd/C as cata-
lyst) of the C–C double bond of the enones 3 and 6 ob-
tained by the elimination of nitrous acid from the Michael
adducts, completes the conversion to the title compounds
4 and 7. The E-isomers were highly predominant (up to
93%, determined by NMR analysis of the crude reaction
mixture) in the intermediates 3 and 6. In fact, it is well
When 2-phenylnitroethane is used as starting material, the
conjugate addition to 2 or 5 produces (Scheme 2) a mix-
ture of isomers 3f’/3f" (5.5:4.5), and 6h’/6h" (7.3:3.7), re-
spectively. However, the hydrogenation of these mixtures
converts both the isomers to the saturated products 4f and
7h, respectively. By this procedure high yields (Tables 1–
4) are observed for each step (68–90% 1 to 3; 75–96% 3
to 4; 75–99% 1 to 6; and 75–99% 6 to 7) and several other
fuctionalities, such as ester, carbonyl, hydroxyl, and ketal
can be preserved, so that, our method allows the formation
of functionalized 2-alkylated 1,4-diketones and a-alkylat-
ed g-keto esters, both difficult to prepare by other ways.
documented that a b-alkyl substituent syn to a carbonyl
It is important to point out that while in the previous ap-
moiety in a,b-conjugated enones resonates downfield rel-
proach to obtain 1,4-diketones and g-keto esters from ni-
ative to the anti alkyl substituent in the NMR spectrum.13
Consequently, the NMR chemical shift of the b-methyl-
troalkanes [(i) conjugate addition, (ii) Nef reaction],9,10
Synthesis 1999, No. 7, 1236–1240 ISSN 0039-7881 © Thieme Stuttgart · New York

1238
R. Ballini et al.
PAPER
Table 2 2-Alkylated 1,4-Diketones 4 Prepared
Product
Yield
(%)
IR (film)
1H NMR (CDCl3/TMS)
d, J (Hz)
13C NMR (CDCl3)
d
n (cm–1)
4a
90
95
95
95
90
95
95
96
75
94
1710
1709
1712
1711
1709
1710
1710
1705
1712
1709
0.9 (t, 3H, J = 6.2), 1.1–1.7 (m, 6H), 2.15 (s, 3H),
2.21 (s, 3H), 2.4 (d, 1H, J = 14.1), 2.9 (d, 1H,
J = 9.8), 2.9-3.1 (m, 1H)
14.0, 22.3, 27.0, 29.8, 30.3, 31.1, 43.5,
53.1, 208.7, 210.9
4b
4c
4d
4e
4f
1.2–1.7 (m, 4H), 2.12 (s, 3H), 2.25 (s, 3H), 2.3
(t, 2H, J = 3.3), 2.45 (d, 1H, J = 9.8), 3.0–3.1 (m,
1H), 3.68 (s, 3H)
21.2, 23.2, 27.6, 29.7, 29.9, 43.2, 50.9,
51.3, 172.4, 208.1, 211.6
1.1–1.8 (m, 11H), 2.15 (s, 3H), 2.25 (s, 3H),
2.4 (d, 1H, J = 14.3), 2.9 (d, 1H, J = 9.6), 2.9–3.1
(m, 1H)
26.2, 26.5, 27.9, 28.9, 29.6, 29.9, 37.9,
42.3, 53.5, 207.1, 211.7
0.85 (t, 3H, J = 6.3 Hz), 1.2–1.6 (m, 10H), 2.15
(s, 3H), 2.25 (s, 3H), 2.4 (d, 1H, J = 14.3), 2.9
(d, 1H, J = 9.7), 2.9–3.1 (m, 1H)
14.1, 21.7, 22.7, 29.5, 27.6, 29.7, 30.3,
31.9, 43.2, 53.1, 208.1, 211.6
0.85–0.9 (t, 3H, J = 6.9), 1.2-1.4 (m, 4H), 2.1
(s, 3H), 2.2 (s, 3H), 2.4 (d, 1H, J = 14.2), 2.87
(d, 1H, J = 10.0 Hz), 2.95–3.1 (m, 1H)
15.8, 22.7, 27.1, 29.1, 31.7, 43.8, 51.0,
207.3, 211.1
1.5–1.8 (m, 4H), 2.15 (s, 3H), 2.25 (s, 3H), 2.4
(d, 1H, J = 14.0), 2.9 (d, 1H, J = 9.9), 3.0–3.2
(m, 1H), 7.0–7.4 (m, 5H)
27.6, 29.7, 30.6, 33.8, 43.3, 53.2,
125.7, 127.6, 128.2, 142.7, 208.1,
211.4
4g
4h
4i
1.2–1.8 (m, 6H), 2.15 (s, 3H), 2.22 (s, 3H), 2.3
(t, 2H, J = 4.2), 2.4 (d, 1H, J = 14.6), 2.9
(d, 1H , J = 10.1), 2.9–3.1 (m, 1H), 3.7 (s, 3H)
24.5, 26.6, 27.6, 29.7, 29.8, 32.8, 43.2,
51.3, 52.2, 174.1, 208.1, 211.6
1.2–1.4 (m, 4H), 2.1 (s, 3H), 2.2 (s, 3H), 2.4
(s, 3H), 2.4 (d, 1H, J = 14.7), 2.5 (t, 2H, J = 3.2),
2.9 (d, 1H, J = 9.9 Hz), 3.0–3.1 (m, 1H)
21.1, 27.6, 29.7, 30.0, 43.2, 43.7, 50.5,
208.1, 209.2, 211.6
0.9 (d, 6H, J = 6.6), 1.1–1.3 (m, 4H), 1.3–1.6
(m, 1H), 2.15 (s, 3H), 2.22 (s, 3H), 2.4 (d, 1H,
J = 14.2), 2.95 (d, 1H, J = 12.8), 2.9–3.0 (m, 1H)
22.7, 26.5, 27.3, 27.6, 29.7, 32.8, 43.3,
51.0, 208.1, 212.5
4j
1.3 (s, 3H), 1.31-1.7 (m, 6H), 2.12 (s, 3H), 2.21
(s, 3H), 2.45 (d, 1H, J = 13.9), 2.45 (d, 1H,
J = 9.2), 2.91-3.1 (m, 1H), 3.8–4.0 (m, 4H)
24.0, 25.4, 27.6, 29.7, 31.3, 37.6, 43.2,
52.2, 64.5, 110.0, 208.1, 211.6
a Satisfactory microanalysis obtained: C ± 0.13, H ± 0.16.
O
R
+
NO2
2, R =Me
the latter compounds are employed as acyl anion equiva-
lents a, this new procedure, here reported, utilises the ni-
troalkanes as alkyl anion synthons b (Scheme 3).
5, R =OMe
O
DBU, CH3CN
In conclusion, the principal advantages of the methodolo-
gy presented here are high yields, high purity and the sim-
ple procedure using inexpensive chemicals.
O
O
O
R
R
+
3f", R = Me (33%)
6h", R = OMe (32%)
3f', R = Me (40%)
6h', R = OMe (55%)
O
All the reactions were monitored by TLC and gas chromatographic
analyses, performed on a Carlo Erba Fractovap 4160 using a capil-
lary column of duran glass (0.32 mm × 25 mt), stationary phase
H2, 10% Pd/C
40 psi,
1
OV1 (film thickness 0.4–0.45 nm). All H NMR and 13C NMR
spectra were recorded in CDCl3 at 200 and 75 MHz, respectively,
on a Varian Gemini 200. Chemical shifts are expressed in ppm
downfield from TMS. IR spectra were recorded with a Perkin-Elm-
er 257 spectrophotometer. All the products were purified by flash
chromatography on Merck silica gel using EtOAc/cyclohexane as
eluent. Elementary analyses were performed using a C, H, N, S An-
alyzer Model 185 from Hewlett-Packard.
O
R
4f, R = Me (95%)
7h, R = OMe (99%)
O
Scheme 2
Synthesis 1999, No. 7, 1236–1240 ISSN 0039-7881 © Thieme Stuttgart · New York

PAPER
A New Two-Step Synthesis of 2-Alkylated 1,4-Diketones and a-Alkylated g-Keto-Esters
1239
Hydrogenation of the C–C Double Bond of the Enone Deriva-
tives 3 and 6; General Procedure for the Synthesis of 4 and 7
The substrate 3 or 6 (11 mmol) was dissolved in EtOAc (120 mL)
and 10% Pd/C (0.2 g) was added. The suspension was hydrogenated
(40 psi) at r.t. for 5 h. The catalyst was removed by filtration through
a Celite pad and was washed with EtOAc (10 × 3 mL). After evap-
oration of the solvent the crude product was purified by flash chro-
matography (EtOAc/cyclohexane) giving the pure product 4 or 7.
H
O
NO2
R
R
R
b
a
Scheme 3
Acknowledgement
Conjugate Addition of Nitroalkanes 1 to 2-Ene-1,4-dione Deriv-
atives 2 and 5; General Procedure for the Synthesis of 3 and 6
DBU (3.04 g, 20 mmol) was added at r.t. to a solution of nitroalkane
1 (20 mmol) and enedione 2 or 5 (20 mmol) in MeCN (100 mL) .
The solution was stirred for 7 h at r.t., then silica gel (Merck 0.04–
0.063 mm, 5–6 g) was added and the solution was evaporated. The
residue, consisting of crude silica gel, was flash chromatographed,
using a suitable ratio of EtOAc/cyclohexane as eluent, affording the
pure compound 3 or 6.
This work was carried out in the framework of the National Project
"Stereoselezione in Sintesi Organica. Metodologie ed Applicazioni’
supported by Ministero dell'Università e della Ricerca Scientifica e
Tecnologica - Rome, and by University of Camerino.
Table 3 Enone Derivatives 6 Prepared
Producta
Yield
(%)
IR (film)
1H NMR (CDCl3/TMS)
d, J (Hz)
13C NMR (CDCl3)
d
n (cm–1)
6a
75
1713, 1670
0.92 (t, 3H, J = 7.3), 1.38–1.59 (m, 2H), 2.02-2.2
(m, 2H), 2.18 (s, 3H), 3.41 (s, 3H), 3.71 (s, 3H), 6.98
(t, 1H, J = 7.5)
14.0, 19.4, 24.0, 30.6, 37.0, 51.9,
127.5, 147.0, 167.0, 207.0
6b
6c
6d
6e
88
93
92
99
1718, 1656
1713, 1650
1710, 1630
1717, 1640
1.8 (s, 3H), 2.12 (s, 3H), 2.15 (s, 3H), 3.45 (s, 2H), 3.7
(s, 3H)
20.6, 20.9, 24.4, 34.5, 52.3,
125.2, 144.3, 173.2, 205.9
1.05 (t, 3H, J = 7.5), 2.0–2.15 (m, 2H), 2.2 (s, 3H), 3.4
(s, 2H), 3.7 (s, 3H), 6.95 (t, 1H, J = 7.5)
13.6, 19.4, 21.2, 36.6, 51.9,
127.1, 136.6, 167.0, 205.6
1.52–1.65 (m, 6H), 2.14–2.16 (m, 2H), 2.18 (s, 3H),
2.6–2.7 (m, 2H), 3.45 (s, 2H), 3.69 (s, 3H)
20.6, 26.5, 29.1, 32.6, 35.5, 36.1,
52.3, 123.8, 151.9, 172.9, 205.9
2.2 (s, 3H), 2.4–2.5 (m, 4H), 3.4 (s, 2H), 3.67 (s, 3H),
3.71 (s, 3H), 6.97 (t, 1H, J = 7.2)
19.3, 23.6, 33.5, 36.6, 51.6, 51.9,
128.2, 143.0, 167.7, 173.2,
206.4
6f
98
85
55
32
82
98
1712, 1649
1712, 1649
1716, 1640
1710
1.3 (s, 3H), 1.8–1.9 (m, 2H), 2.2 (s, 3H), 2.21–2.26
(m, 2H), 3.44 (s, 2H), 3.72 (s, 3H), 3.86–3.98 (m, 4H),
7.0 (t, 1H, J = 7.5)
19.4, 22.1, 23.8, 39.7, 51.9, 64.6,
110.3, 127.8, 146.1, 167.7,
206.4
6g
6h’
6h"
6i
1.18 (d, 3H, J = 6.2), 1.5–1.6 (m, 2H), 2.2 (s, 3H),
2.18–2.3 (m, 2H), 3.45 (s, 3H), 3.7 (s, 3H), 3.71–3.8
(m, 1H), 6.95 (t, 1H, J = 7.6)
19.4, 23.4, 24.5, 36.7, 37.0, 51.9,
66.3, 127.8, 145.9, 167.7, 206.4
2.2 (s, 3H), 3.16 (s, 2H), 3.7 (s, 3H), 3.75
(d, 2H, J = 2.9), 6.3 (t, 1H, J = 7.8), 7.15–7.4
(m, 5H)
19.4, 36.8, 39.5, 51.9, 127.4,
128.3, 128.8, 129.2, 138.4,
141.2, 167.5, 206.4
2.2 (s, 3H), 2.65–2.75 (m, 2H), 3.05–3.2 (m, 2H), 3.7
(s, 3H), 6.1 (dd, 1H, J = 8.4, 15.9), 6.55
(d, 1H, J = 15.9), 7.1–7.4 (m, 5H)
27.9, 45.5, 51.6, 51.9, 127.0,
127.6, 128.9, 131.6, 136.8,
174.1, 206.9
1712, 1651
1720, 1654
2.15 (s, 3H), 2.2 (s, 3H), 2.3–2.5 (m, 2H), 2.6
(t, 3H, J = 7.2), 3.5 (s, 2H), 3.7 (s, 3H), 6.9
(t, 1H, J = 7.6)
19.4, 23.3, 29.7, 36.7, 44.1, 51.9,
129.2, 143.4, 167.7, 206.4,
207.7
6j
1.4–1.8 (m, 2H), 2.15 (t, 2H, J = 7.0), 2.2 (s, 3H), 3.4
(s, 2H), 3.65 (s, 3H), 3.7 (s, 3H), 6.95 (t, 1H, J = 7.5)
19.4, 23.2, 28.1, 29.8, 36.7, 42.9,
51.9, 127.8, 142.8, 167.7, 206.4,
208.2
a Satisfactory microanalyses obtained: C ± 0.13, H ± 0.10.
Synthesis 1999, No. 7, 1236–1240 ISSN 0039-7881 © Thieme Stuttgart · New York

1240
R. Ballini et al.
PAPER
Table 4 a-Alkylated g-Ketoesters 7 Prepared
Producta
Yield
78
IR (film)
1H NMR (CDCl3/TMS)
d, J (Hz)
13C NMR (CDCl3)
d
n (cm–1)
7a
1732
0.9 (t, 3H, J = 6.7 Hz), 1.2–1.7 (m, 6H), 2.11
(s, 3H), 2.4 (d, 1H, J = 12.9), 2.9 (d, 1H, J = 17.3),
2.81-2.9 (m, 1H), 3.65 (s, 3H)
13.9, 22.8, 28.7, 29.0, 30.1, 43.6,
45.1, 51.4, 174.2, 205.8
7b
75
1719
0.9 (d, 3H, J = 6.8), 0.95 (d, 3H, J = 6.9), 1.8–2.0
(m, 1H), 2.2 (s, 3H), 2.4 (d, 1H, J = 12.3 Hz),
2.7–2.8 (m, 1H), 2.9 (d, 1H, J = 17.1), 3.68
(s, 3H)
18.2, 20.2, 30.8, 30.9, 41.9, 46.9,
52.2, 175.1, 207.8
7c
7d
7e
73
99
99
1735
1732
1735
0.9 (t, 3H, J = 7.1), 1.2–1.6 (m, 4H), 2.15 (s, 3H),
2.45 (d, 1H, J = 12.3), 2.9 (d, 1H, J = 17.3),
2.8–2.9 (m, 1H), 3.69 (s, 3H)
14.1, 20.0, 28.2, 34.8, 43.4, 45.3,
50.9, 174.5, 204.3
1.5–1.8 (m, 11H), 2.15 (s, 3H), 2.5 (d, 1H,
J = 12.1), 2.9 (d, 1H, J = 17.3 Hz), 2.91–3.1
(m, 1H), 3.4 (s, 3H)
26.8, 27.3, 30.0, 31.7, 33.7, 37.3,
42.5, 44.8, 51.1, 176.9, 207.5
1.5–1.7 (m, 4H), 2.18 (s, 3H), 2.3 (t, 2H, J = 6.7),
2.5 (d, 1H, J = 12.4), 2.9 (d, 1H, J = 15.2),
2.8–2.91 (m, 1H), 3.6 (s, 3H), 3.7 (s, 3H)
22.1, 22.4, 28.8, 30.4, 41.9, 44.7,
51.4, 51.5, 172.4, 174.9, 205.1
7f
99
99
1718
1.3 (s, 3H), 2.15 (s, 3H), 2.5 (d, 1H, J = 12.3), 2.9
(d, 1H, J = 15.3), 3.68 (s, 3H), 3.85–4.0 (m, 4H)
24.0, 25.1, 28.8, 31.9, 38.5, 42.8,
44.7, 51.5, 64.5, 110.0, 174.9, 205.1
7g
3400, 1715
1.18 (d, 3H, J = 6.0), 1.3–1.7 (m, 6H), 2.18
(s, 3H), 2.55 (d, 1H, J = 12.3), 2.9 (d, 1H,
J = 17.1), 2.8–2.9 (m, 1H), 3.7–3.8 (m, 1H)
22.7, 23.5, 28.8, 30.3, 40.2, 42.8,
44.7, 51.5, 67.9, 174.9, 205.1
7h
7i
99
95
99
1717, 1603
1710
1.7–2.0 (m, 4H), 2.15 (s, 3H), 2.6 (d, 1H,
J = 12.5), 2.9 (d, 1H, J = 17.3), 2.9–3.1 (m, 1H),
3.7 (s, 3H), 7.1–7.3 (m, 5H)
28.8, 31.4, 34.2, 43.7, 44.9, 51.5,
125.7, 128.0, 129.1, 142.6, 174.8,
205.1
1.5–1.6 (m, 4H), 2.12 (s, 3H), 2.15 (s, 3H), 2.5
(t, 2H, J = 6.7), 2.6 (d, 1H, J = 12.6), 2.9 (d, 1H,
J = 15.3 Hz), 2.8–2.9 (m, 1H), 3.63 (s, 3H)
21.3, 28.9, 29.4, 30.0, 41.0, 44.3,
44.7, 51.5, 174.9, 205.1, 209.1
7j
1732
1.2–1.7 (m, 6H), 2.2 (s, 3H), 2.3 (t, 2H, J = 6.7),
2.5 (d, 1H, J = 12.5), 2.9 (d, 1H, J = 15.2),
2.8–2.9 (m, 1H), 3.69 (s, 3H), 3.71 (s, 3H)
22.9, 26.6, 28.5, 28.76, 29.8, 43.87,
44.7, 51.5, 175.0, 205.1, 207.7
a Satisfactory microanalyses obtained: C ± 0.15, H ± 0.14.
(b) Rosini, G.; Ballini, R. Synthesis 1988, 833.
References
(c) Ballini, R. In Studies in Natural Products Chemistry; Vol.
19; Atta-ur-Rahman Ed.; Elsevier: Amsterdam, 1997, p 117.
(9) (a) Ballini, R.; Petrini, M.; Marcantoni, E.; Rosini, G.
Synthesis 1988, 231, and references cited therein.
(b) Ballini, R.; Bartoli, G. Synthesis 1993, 965.
(c) Ballini, R. Synthesis 1993, 687.
(10) (a) Ballini, R.; Petrini, M. Synthesis 1986, 1024.
(b) Ballini, R.; Petrini, M.; Rosini, G. Synthesis 1987, 711.
(c) Ballini, R.; Bosica, G. J. Chem. Res. (S) 1993, 435.
(11) (a) Rosini, G.; Marotta, E.; Ballini, R.; Petrini, M. Synthesis
1986, 237.
(b) Ballini, R.; Marziali, P.; Mozzicafreddo, A. J. Org. Chem.
1996, 61, 3209.
(c) Ballini, R. Bosica, G. Eur. J. Org. Chem. 1998, 355.
(12) Ballini, R.; Rinaldi, A. Tetrahedron Lett. 1994, 35, 9247.
(13) Dieter, R. K.; Silks, III, L. A.; Fishpang, J. R.; Kastner, M. E.
J. Am. Chem. Soc. 1985, 107, 4679.
(1) Bossard, P.; Engster, C. H. Adv. Heterocycl. Chem. 1986, 30,
384.
(2) Dean, F. M. Adv. Heterocycl. Chem. 1982, 30, 172.
(3) Sundberg, R. J. In Comprehensive Heterocyclic Chem.; Vol.
4; Katritsky, A. R.; Rees, C. W., Eds; Pergamon: Oxford,
1984; p 329.
(4) Ellison, R. A. Synthesis 1973, 397.
(5) Ho, T. L. Synth. Commun. 1974, 4, 265.
(6) Stetter, H.; Kuhlmann, H. Org. React. 1991, 40, 407.
(7) See for example:
(a) Cardellach, J.; Font, J.; Ortuno, R. M. J. Heteocyclic
Chem. 1984, 21, 327.
(b) Short, K. M.; Mjalli, M. M. A. Tetrahedron Lett. 1997, 38,
359.
(c) Frenette, R.; Monette, M.; Bernstein, M. A.; Young, R. N.;
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(d) Ohkuma, T.; Kitamura, M.; Noyori, R. Tetrahedron Lett.
1990, 31, 5509.
Article Identifier:
1437-210X,E;1999,0,07,1236,1240,ftx,en;Z08598SS.pdf
(8) (a) Seebach, D.; Colvin, E. W.; Lehr, F.; Weller, T. Chimia
1979, 33, 1.
Synthesis 1999, No. 7, 1236–1240 ISSN 0039-7881 © Thieme Stuttgart · New York