A 4-[6,7-dimethoxybenzopyranyl]5-[4-hydroxy-2-isopropyl benzofuranyl]ketone obtained by catalytic hydrogenation of rotenone

Full text of DOI:10.1007/s10600-010-9745-8

Chemistry of Natural Compounds, Vol. 46, No. 5, 2010
A 4-[6,7-DIMETHOXYBENZOPYRANYL]5-[4-HYDROXY-2-ISOPROPYL
BENZOFURANYL]KETONE OBTAINED BY CATALYTIC
HYDROGENATION OF ROTENONE
1*
2
1
Ph. Petit, M. Grignon-Dubois, and P. Bourgeois
UDC 547.972
Rotenone was hydrogenated by H /chloroplatinic acid in absolute ethanol, yielding three products: dihydrorotenone
2
(1) and dihydrodehydrorotenone (2), which have already been identified [1, 2], and 4-[6,7-dimethoxybenzopyranyl]5-[4-
hydroxy-2-isopropyl benzofuranyl]ketone (3) for which to our knowledge no analytical data have been published yet, although
similar structures have been described elsewhere [3, 4], which mentioned that the compound was obtained as a result of the
opening of the C-ring in basic medium [5–8]. In our case the mechanism of formation of 3 was not clearly manifested as we did
not operate in basic conditions; we then hypothesized that our catalyst might have contained a basic impurity. Compound 3
was obtained as a white solid and recrystallized from absolute ethanol to give white needles melting at 129ꢀC. The structure
1
13
of 3 was deduced by comparison of its H NMR, C NMR, and DEPT spectral data with those of an authentic standard of
rotenone and those of the literature [9]. The spectral data of compound 3 are listed in Table 1.
1
The H NMR spectrum of 3 showed the absence of the ethylenic protons in position 7ꢁ and the appearance of an
isopropylic system indicating that the double bond at position C-6ꢁ–C-7ꢁ was hydrogenated. Those results were in agreement
2
with those of the DEPT experiment which exhibited the signals of an additional CH and of one more CH, whereas no sp CH
3
2
was observed. The assignments of the protons of the isopropylic system were confirmed by irradiation of the multiplet at
1.99 ppm, reducing the two doublets of three protons each (1.04 and 0.99 ppm) into two singlets. We also noticed that upon
irradiation of that multiplet at 1.99 ppm a simplification of the multiplet at 4.71 ppm occurred. We deduced from that experiment
that only a proton close to H-6ꢁ could give such a result; we then assigned the signal at 4.71 ppm to H-5ꢁ. The placement of H-5ꢁ
was confirmed by irradiation of its signal, which led to the simplification of the signals of H-4ꢁ as the two doublets of doublets
collapsed into two doublets with a geminal coupling constant of 15.70 Hz. The DEPT experiment showed that 3 contained one
more CH at 27.2 ppm compared to rotenone and that the CH in position C-6a has disappeared, which was consistent with the
2
ring opening. The proton spectrum exhibited two multiplets of one proton each at 2.34 and 2.21, which we assigned to the
protons in position 6a considering, that their chemical shifts were consistent with the fact that they were not anymore under the
influence of O-7a. Irradiation of the multiplet at 4.20 ppm simplified those two multiplets into two doublets of doublets,
whereas irradiation at 4.71 ppm did not lead to any simplification. We assigned then the multiplet at 4.20 ppm to the H-6
protons because only a simultaneous irradiation of those protons could lead to such a simplification. The 14.06 and 7.42 Hz
and the 14.06 and 6.30 Hz coupling constants observed for H-12a in 3 were consistent with an axial-axial and an axial-equatorial
relationship of this proton to the CH methylene group at C-6a.
2
The HR-MS showed a molecular formula of C H O , and the EI-MS showed prominent fragment ions at m/z 205
23 26
6
(90%) and m/z 193 (100%).
These fragmentations are consistent with the structure assignment of 3.The IR spectrum exhibited a band at
–1
3400 cm , in agreement with an OH moiety. Therefore, the structure of 3 was assigned as 4-[6,7-dimethoxybenzopyranyl]5-
[4-hydroxy-2-isopropyl benzofuranyl]ketone.
1) UMR Qualitrop UFR SEN Campus de Fouillole, Universite desAntilles-Guyane F97159 Pointe-a-Pitre, Guadeloupe,
F. W. I.; 2) Laboratoire PhyValBio, Universite de Bordeaux I, 33405 Talence Cedex Fance, fax:+590 938 787, e-mail:
philippe.petit@univ-ag.fr. Published in Khimiya Prirodnykh Soedinenii, No. 5, pp. 669–670, September–October, 2010.
Original article submitted May 5, 2009.
0009-3130/10/4605-0795 02010 Springer Science+Business Media, Inc.
795

1
13
TABLE 1. H and C NMR Spectroscopic Data (CDCl , 300 MHz) for Compounds 3 (ꢂꢃ ppm, J/Hz)
3
Position
Position
ꢄ
ꢂC
ꢂH
ꢂCꢄ
ꢂHꢄ
1
2
3
4
4a
6
111.9
143.2
149.4
100.9
149.3
63.1
6.47 (s)
11
11a
12
12a
12b
132.0
113.9
205.4
41.2
109.8
29.0
7.77 (d, J = 8.74)
4.71 (m)
6.36 (s)
4
ꢁ
4.20 (m)
3.20 (dd, J = 8.51; 15.70, H-4 anti)
2.91 (dd, J = 8.01; 15.70, H-4 syn)
4.71 (m)
1.99 (m)
1.04 (d, J = 6.70); 0.99 (d, J = 6.70)
3.72 (s); 3.84 (s)
ꢁ
ꢁ
6a
27.2
2.34 (dd, J = 6.30; 14.06, H-6a syn)
2.21 (dd, J = 7.42 ; 14.06, H-6a anti)
ꢁ
90.9
33.2
17.8; 17.5
56.3; 55.7
5
7a
8
9
161.2
112.7
167.4
102.1
6
ꢁ
7
ꢁ
2-OCH3, 3-OCH3
10
6.43 (d, J = 8.74)
7'
.
6'
7'
+
.
+
4'
8
O
5'
O
E
6
OH
O
OH
O
O
6a
9
7a
D
12a
B
4a
10
4
11a
OMe
12b
11
A
O
1
OMe
3
OMe
2
OMe
3
m/z193
m/z205
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