Selective reduction of C=C bond in iminolactone ring by a system magnesium–methanol

Full text of DOI:10.1134/S1070428016050262

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2016, Vol. 52, No. 5, pp. 759–761. © Pleiades Publishing, Ltd., 2016.
Original Russian Text © G.G. Tokmadzhyan, L.V. Karapetyan, 2016, published in Zhurnal Organicheskoi Khimii, 2016, Vol. 52, No. 5, pp. 768–769.
SHORT
COMMUNICATIONS
Selective Reduction of С=С Bond
in Iminolactone Ring by a System Magnesium–Methanol
G. G. Tokmadzhyan and L. V. Karapetyan
Yerevan State University, ul. Alek Manukyan 1, Yerevan, 0025 Armenia
e-mail: tokmajyang@ysu.am
Received February 26, 2016
DOI: 10.1134/S1070428016050262
We formerly developed a convenient method of pre-
paration of unsatrurated γ-iminolactones by reaction in
the presence of sodium methylate of tertiary α-ketoalco-
hols and amides (nitriles) of acids containing an active
methylene group [1–6]. We attempted to perform a
transition from the unsaturated to saturated γ-imino-
lactones by selective reduction of the С=С bond in the
iminolactone ring not affecting the functional groups.
functionally substituted in the position 3 of 4,5,5-
trimethyl-(or 5,5-pentamethylene)-2,5-dihydrofuran-2-
one and 2Н-pyran-2-one in the preparation of saturated
lactones [13].
We applied the reducing system magnesium–
methanol for selective reduction of the С=С bond in
iminolactones 1а and 1b [1], where the С=С bond was
conjugated with a carbamoyl substituent in the position
С3 of the iminolactone ring. The reduction of com-
pounds 1а and 1b with the system magnesium–me-
thanol afforded saturated lactones 2а and 2b in 85–
88% yields. This reaction course apparently means that
first the С=С bond is reduced, and further at the
treatment of excess magnesium with diluted (1 : 1)
hydrochloric acid the imino group suffers the
hydrolysis with the formation of a lactone carbonyl.
For the preparation of saturated iminolactones the
excess magnesium was filtered off, and we obtained
compounds 3а and 3b in 65 and 68% yields.
The reduction with molecular hydrogen is sometimes
impossible, firstly, because of the hazards met when
working with it, and secondly, due to the inaccessi-
bility of reduction catalysts [7]. The use of complex metal
hydrides (LiAlH4, NaBH4) results in the cleavage of the
ring and glycol formation [8, 9]. A system magnesium–
methanol is used for reductive cyclization, reductive clea-
vage, for reduction of certain substituents (NO2, N3, Cl,
oxime group) and of conjugated С=С bond [10–12].
The system magnesium–methanol was excellently
suitable for selective reduction of the С=С bond in a
O
O
NH2
NH2
H3C
H3C
O
Mg_
Me
1
OH
HCl_H2O, 1 : 1
:
1
R2
R1
,
R2
R1
O
NH2
NH
O
H
O
H3C
l
O
C
O
H
Mg_MeOH
R2
R1
2a, 2b
4a, 4b
O
O
NH2
NH
1a, 1b
H3C
R2
R1
O
3a, 3b
R1 = R2 = CH3 (а); R1, R2 = (CH2)5 (b).
759

TOKMADZHYAN, KARAPETYAN
760
The structure of obtained compounds was
established from the data of IR and Н NMR spectra.
Rf 0.54, mp 147–149°С (from xylene). IR spectrum,
ν, cm–1: 3300 (NH), 1760 (С=О), 1680 (С=О).
1Н NMR spectrum, δ, ppm: 1.19 d (3Н, СН3, J
7.0 Hz), 1.27 m (1Н) and 1.58–1.82 m (7Н,
С6Н10), 2.68 d.q (1Н, СН, J 12.8, 7 Hz), 4.37 d (1Н,
СН, J 12.8 Hz), 7.23 br.s (1Н) and 8.22 br.s (1Н,
NH2).
1
IR spectra of saturated iminolactones 3а and 3b lacked
the band corresponding to the С=С bond of imino-
lactone ring in the region 1640–1660 cm–1, and in the
1Н NMR spectra in contrast to the spectra of the initial
compounds 1а and 1b signals of the protons Н3 and Н4
were present at 2.68 and 4.35 ppm. In the IR spectra of
saturated lactones 2а and 2b the absorbance of the
С=С bond in the region 1640–1660 cm–1 was also
absent, and the absorption band appeared of the
carbonyl group of the saturated lactone ring at 1760–
A mixed sample of compounds 2а and 2b obtained
by procedures a and b melts without depression of the
melting point thus proving the identity of the
compounds.
1
1780 cm–1. In the Н NMR spectra in contrast to the
Saturated iminolactones 3а and 3b. A mixture of
0.01 mol of unsaturated iminolactone 1а and 1b, 2.4 g
(0.1 mol) of magnesium turnings, and 50 m of
anhydrous methanol was stirred for 8–9 h at a room
temperature. Excess magnesium was filtered off,
methanol was removed from the filtrate at a reduced
pressure, the solid residue was recrystallized.
spectra of the initial compounds 1а and 1b signals
were observed of protons H3 and H4 at 2.54 and
4.32 ppm.
The structure of compounds 2а and 2b was proved
by a chemical reaction: the reduction of lactones
4а and 4b [14] by the system magnesium–methanol
afforded compounds 2а and 2b in high yields (90–
92%).
2-Imino-4,5,5-trimethyltetrahydrofuran-3-car-
boxamide (3а). Yield 1.10 g (65%), Rf 0.57, mp 126–
128°С (from petroleum ether). IR spectrum, ν, cm–1:
Saturated lactones 2а and 2b. a. A mixture of
0.01 mol of unsaturated iminolactone 1а and 1b, 2.4 g
(0.1 mol) of magnesium turnings, and 50 mL of
anhydrous methanol was stirred for 8–9 h at a room
temperature. Excess magnesium was dissolved in
diluted (1 : 1) hydrochloric acid, reaction products
were extracted with ethyl ether, the extract was dried
with magnesium sulfate, the solvent was evaporated,
the residue was recrystallized.
1
3300 (NH), 3130 (NH), 1680 (С=О), 1640 (С=N). Н
NMR spectrum, δ, ppm: 1.15 d (3Н, СН3, J 7.0 Hz),
1.22 s (3Н, СН3), 1.44 s (3Н, СН3), 2.54 d.q (1Н,
СН, J 12.8, 7 Hz), 4.32 d (1Н, СН, J 12.8 Hz),
7.21 br.s (1Н, NH), 7.34 br.s (1Н) and 8.26 br.s (1Н,
NH2).
2-Imino-4-methyl-1-oxaspiro[4.5]decane-3-car-
boxamide (3b). Yield 1.43 g (68%), Rf 0.55, mp 180–
182°С (from xylene). IR spectrum, ν, cm–1: 3300
b. A mixture of 0.01 mol of unsaturated lactone 4а
and 4b, 2.4 g (0.1 mol) of magnesium turnings, and
50 mL of anhydrous methanol was stirred for 8–9 h at
a room temperature. Excess magnesium was dissolved
in diluted (1 : 1) hydrochloric acid, reaction products
were extracted with ethyl ether, the extract was dried
with magnesium sulfate, the solvent was evaporated,
the residue was recrystallized from xylene.
1
(NH), 3135 (NH), 1680 (С=О), 1640 (С=N). Н NMR
spectrum, δ, ppm: 1.15 d (3Н, СН3, J 7.0 Hz), 1.27 m
(1Н), 1.47 m (2H), 1.58–1.82 m (7Н, С6Н10), 2.54 d.q
(1Н, СН, J 12.8, 7 Hz), 4.32 d (1Н, СН, J 12.8 Hz),
7.21 br.s (1Н, NH), 7.36 br.s (1Н) and 8.28 br.s (1Н,
NH2).
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4,5,5-Trimethyl-2-oxotetrahydrofuran-3-carbox-
amide (2a). Yield 1.5 g (88%) (a), 1.54 g (90%) (b), Rf
0.56, mp 92–93°С (from xylene). IR spectrum, ν, cm–1:
3300 (NH), 1760 (С=О), 1680 (С=О). 1Н NMR
spectrum, δ, ppm: 1.18 d (3Н, СН3, J 7.0 Hz), 1.26 s
(3Н, СН3), 1.45 s (3Н, СН3), 2.68 d.q (1Н, СН, J 12.8,
7 Hz), 4.35 d (1Н, СН, J 12.8 Hz), 7.23 br.s (1Н) and
8.20 br.s (1Н, NH2).
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SELECTIVE REDUCTION OF С=С BOND IN IMINOLACTONE RING
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