Reaction of N-vinylindazolium and N-vinylbenzotriazolium salts with nucleophiles |
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Authors: | Jos Elguero Enrique Gutierrez-Puebla Angeles Monge Carmen Parco Mar Ramos |
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Institution: | a Instituto de Química Médica, CSIC, Juan de la Cierva 6, 28006 Madrid, Spain b Instituto de Ciencia de los Materiales, Sede C, CSIC, Laboratorio de Difracción de Rayos X, Facultad de Química, Universidad Complutense, 28040 Madrid, Spain c Departamento de Química Orgánica I,Facultad de Química, Universidad Complutense, 28040 Madrid, Spain |
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Abstract: | Reaction of N-vinylindazolium tetrafluoroborates with aqueous potassium carbonate or sodium borohydride affords 2,3-dihydroquinazolines which evolve to 1,2,3,4-tetrahydroquinazolines by intra or intermolecular nucleophilic attack. The X-ray structure of one tetrahydroquinazoline, the tricyclic compound 17a, was determined (C14H16N2O5, P21/n, a=6.001(4)Å, b=13.601(8)Å, c=17.452(6)Å, β=94.93(3)°, V=1419(1)Å3, Z=4, R=0.078 for 1541 observed reflexions). Only open-chain compounds are obtained when these salts react with methanol. 2-Vinylindazolium and 3-vinylbenzotriazolium tetrafluoroborates react with aqueous potassium carbonate and with sodium borohydride yielding the corresponding neutral benzazoles by cleavage of the azole-vinyl bond. They add methanol to the exocyclic double bond and, in the case of indazole derivative, an expansion to a 1,2-dihydroquinazoline is observed in basic medium.A general mechanism is proposed for the reaction of vinylpyrazolium and indazolium salts with nucleophiles. |
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