REACTION OF N-VINYLINDAZOLIUM AND N-VINYLBENZOTRIAZOLIUM SALTS WITH NUCLEOPHILES

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, P2(1)/n, a=6.001(4)Angstrom;, b=13.601(8)Angstrom, c=17.452(6)Angstrom, beta=94.93(3)degrees, V=1419(1)Angstrom(3), 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.