The obtained experimental and spectral data make it possible to put forward a possible reaction scheme.
If compounds containing an activated methyl group are used as addend in the Michael condensation it is possible
in view of published data [3] to expect an unambiguous reaction path.
The 1,5-dioxo compounds A containing the heterocyclic fragment are initially formed under the
condition of base catalysis. The process does not stop at the intermediate, and the reaction goes further, leading
to the formation of carbocyclization products. This is due to the mobility of the protons in the neighboring
methyl group, subsequent dehydration, and the formation of the hypothetical structures C and D. It was also not
possible to rule out possible cleavage of the furan (pyrrolone) ring, leading to compounds E and F.
However, after analysis of the data from the IR spectra and the 1H and 13C NMR spectra it was possible
to rule out the formation of compounds of the E and F type (Tables 3 and 4) and confirm the formation of
structure D out of the two most likely forms (C and D).
This is fully supported by comparison of the chemical behavior of 5-R-3-arylmethylene-3H-furan-2-ones
and N-aryl-5-R-3-arylmethylene-3H-pyrrol-2-ones as acceptors in the Michael condensation. It should be noted
that the N-heteroanalogs react under milder conditions and the reaction products are formed with higher yields.
Thus, the experimental data fully support the earlier calculations.
EXPERIMENTAL
The IR spectra were recorded on a Specord instrument (Germany) in the region of 400-4000 cm−1 with
1
the crystalline compounds as suspensions in vaseline oil. The H and 13C NMR spectra were obtained on a
Bruker MSL-400 spectrometer (400 and 50 MHz respectively) at 25°C in deuterochloroform with TMS as
internal standard. Thin-layer chromatography was conducted on Silufol UV-254 plates in the 2:1:1 chloroform–
hexane–ether and 2:2:1 ethyl acetate–hexane–chloroform systems with iodine vapor as eluant. Chromatographic
separation was realized on a column of silica gel with isopropyl alcohol, ethanol, and hexane as eluants.
The quantum-chemical calculations were performed with MOPAC software by the LCAO-MO SCF
method in the MNDO approximation with PM3 parametrization.
The arylmethylene-substituted 3H-furan-2-ones 1a-c were obtained by the procedure in [4], and N-aryl-
3H-pyrrolo-2-ones 2a,b by the procedure in [5].
8-R-4-Acyl-5-aryl-3-oxo-9-oxabicyclo[4.3.0]nona-1,7-dienes 3a-c and N-Tolyl-8-R-4-acyl-5-aryl-
3-oxo-9-azabicyclo[4.3.0]nona-1,7-dienes 4a,b (General Method). To a mixture of the furanone 1a-c [or
pyrrolone 2a,b] (5.4 mmol) and acetylacetone (5.4 mmol) we added dropwise solution of freshly prepared
sodium ethoxide in alcohol (5.4 mmol). The reaction mixture was heated for 3-7 h, poured into cold water,
neutralized with dilute hydrochloric acid, and extracted with diisopropyl ether. The extract was evaporated, and
the crystalline residue was recrystallized from hexane (Table 2).
The work was carried out with support from a grant of the President of the Russian Federation for young
scientists MK-3581.2007.3.
REFERENCES
1.
2.
A. Yu. Egorova, P. V. Reshetova, N. A. Morozova, and V. A. Sedavkina, Khim. Geterotsikl. Soedin.,
1043 (1997). [Chem. Heterocycl. Сотр., 33, 910 (1997)].
Z. Yu. Timofeeva, Thesis for Candidate of Chemical Sciences [in Russian], Saratov (2002).
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