Journal of Organic Chemistry p. 5680 - 5685 (1988)
Update date:2022-07-29
Topics:
Pommelet, Jean-Claude
Dhimane, Hamid
Chuche, Josselin
Celerier, Jean-Pierre
Haddad, Mansour
Lhommet, Gerard
The title compounds 9 were synthesized in three steps from cyclic lactams 2.After treatment of 2a-h with phosgene followed by the addition of Meldrum's acid to the chloroiminium chloride intermediates 3a-h, derivatives 4a-h were isolated in good yields.Compounds 4a-g were quantitatively converted to bicyclic enaminones 7a-g by flash-vacuum pyrolysis in the temperature range 480-600 deg C.In contrast, 4h provided 8h, the hydroxyprrole tautomer of 7h.The reaction takes place through the initial formation of (aminomethylene)ketenes 5a-h followed by a 1,4-hydrogen migration from the carbon adjacent to the nitrogen atom to the central carbon of the cumulenone.The lower temperature (480 deg C) needed for benzyl and N-carboalkoxy derivatives 4e-h in comparison with N-alkyl derivatives 4a-d (600 deg C) is correlated with gas-phase acidity of the migrating hydrogen atom.The hydroxypyrroles 8a-g, tautomers of 7a-g (7<-->8), were trapped with acetic anhydride, affording O-acetylated bicyclic
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Doi:10.1055/s-1988-27500
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