REACTION OF ZINC ENOLATES OF ALKYL ESTERS
601
1
Table 3. Yields, melting points, elemental analyses, and H NMR spectra of ethyl 5-R-2-R-2-ethyl-3-oxo-4-pentenoates
mp, C or
1H NMR spectrum, , ppm
Comp. Yield,
bp,
C
no.
%
(
p, mm)
R2
CH=
=CHCO
Et
R1
OEt
XVa
73
93 94
7.35 t, 7.52 s,
7.52 d
7.04 d
1.93 q (CH ), 1.93 q (CH ), 4.18 q (CH ),
2
2
2
7
.65 d, 7.93 s (J 16 Hz) (J 16 Hz) 0.76 t (Me) 0.76 t (Me) 1.20 t (Me)
(
3-BrC H )
6
4
XVb
XVc
XVd
45
68
72
117 119
210 215
6.69 d, 7.45 d
7.50 d
7.57 d
6.61 d
6.67 d
1.90 q (CH ), 1.90 q (CH ), 4.15 q (CH ),
2 2 2
(
4-Me NC H ) (J 16 Hz) (J 16 Hz) 0.75 t (Me) 0.75 t (Me) 1.20 t (Me)
2
6 4
7.23 m (Ph)
1.80 q (CH ), 3.10 s (CH ), 4.03 q (CH2),
2 2
(
2 3)
(J 16 Hz) (J 16 Hz) 0.77 t (Me) 7.00 s (Ph) 1.10 t (Me)
7.47 d 6.57 d 1.80 q (CH ), 3.10 s (CH ), 4.07 q (CH2),
80 81
7.33 s
2
2
(
4-BrC H )
(J 16 Hz) (J 16 Hz) 0.77 t (Me) 7.03 s (Ph) 1.10 t (Me)
6
4
Table 3. (Contd.)
XVc, XVd) or CDCl (VIIIc, VIIIg) on an RYa-2310
3
(
60 MHz) instrument or in DMSO-d (IVd IVo,
6
Found, %
Calculated, %
VIIIa, VIIIb, VIIIe, VIIIh VIIIk, VIIIm VIIIo,
Comp.
no.
Formula
XVa, XVb) on a Bruker AM-300 spectrometer.
C
H
C
H
The quantum-chemical calculation was carried out
by the SCF MO LCAO method in the MNDO ap-
proximation [7] included in the MOPAC 6.0 program
package.
XVa
XVb
XVc
XVd
57.65
71.80
78.65
63.50
5.80
8.43
7.08
5.49
C H BrO
57.79
71.92
78.57
63.61
5.94
8.52
7.14
5.54
1
7
21
3
C H NO
1
9
27
3
C H O
2
2 24 3
C H BrO
2
2 23
3
6
-R-2,2,4,4-Tetramethyl-2,3,5,6-tetrahydro-
pyran-2,4-diones IVa IVl and IVp. a. A mixture of
0.05 mol of ethyl 4-bromo-2,2,4-trimethyl-3-oxo-
pentanoate and 0.045 mol of an aldehyde was added
to 10 g of fine zinc chips in 10 ml of ether and 30 ml
of ethyl acetate. After adding the whole amount of the
reactants, the mixture was refluxed for 30 min. After
cooling, it was hydrolyzed with 10% HCl and ex-
tracted with ether. The organic layer was separated,
washed to the neutral reaction, and dried with sodium
sulfate; the solvent was distilled off. The products
were purified by double recrystallization from hexane.
Compound IVa was purified by vacuum distillation.
our case, due to the absence of substituents in position
of bromozinc alcoholate XIV, the major reaction
pathway is elimination of the zinc subsalt from inter-
4
mediate XIV and formation of ethyl 5-R-2-R-2-ethyl-
3-oxo-4-pentenoates XV as the only products in the
yields of 45 73% (Table 3), regardless of the solvent
(ether HMPA) and the radical in position 2.
The composition and structure of XVa XVd were
1
determined by elemental analysis and H NMR and
1
IR spectroscopy. The H NMR spectra of XVa XVd
contain typical doublet signals of protons at the
double bond in the regions 6.57 7.04 and 7.47
b. Compounds IVm IVo. A 0.05-mol portion of
ethyl 4-bromo-2,2,4-trimethyl-3-oxopentanoate was
added to 10 g of activated fine zinc chips in 20 ml of
ether and 20 ml of ethyl acetate. The reaction mixture
was refluxed for 30 min and separated from zinc by
decanting; 0.035 mol of an aldehyde was added.
Further work-up was similar to procedure a. The
products were purified by double recrystallization
from methanol.
7
.57 ppm. The spin spin coupling constant of the
olefin protons (16 Hz) is indicative of the E conforma-
tion of the above compounds. Their IR spectra contain
characteristic absorption bands in the regions 1600
1
1
610, 1680 1690, and 1720 1725 cm belonging to
the double bond and the ketone and lactone carbonyl
groups, respectively.
EXPERIMENTAL
1
2
5
-R -6-R -3,3-Dimethyl-2,3,5,6-tetrahydro-
The IR spectra were taken on a UR-20 spectro-
photometer using neat samples. The H NMR spectra
pyran-2,4-diones. Compounds VIIIa, VIIIc, VIIIj,
VIIIn, and VIIIo were prepared similarly to procedure
a starting from ethyl 4-bromo-4-R -3-oxoalkanoates.
1
1
were recorded for solutions in CCl (IVa IVc, VIIIf,
4
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 73 No. 4 2003
Shchepin
