ENE REACTIONS AND [2+2]CYCLOADDITIONS OF NITRILIUM SALTS WITH ALKENES

N-Alkylnitrilium salts (1) undergo ene reactions with electron-rich di -and higher substituted alkenes 2 to afford either 2-azoniaallene salt s (3, 6, 9, 11) (the nitrilium salt reacting as ene and the alkene rea cting as enophile) or 1-azonia-1,4-pentadiene salts (10, 12) (the alke ne reacting as ene and the nitrilium salt reacting as enophile). Compe ting with ene reactions tri-and tetrasubstituted alkenes and N-alkylni trilium salts undergo [2+2]cycloaddition to furnish azetinium salts (8 , 13). In solution, alkyl substituted 2-azoniaallene salts tautomerize to 2-azonia-1,3-butadiene salts (4, 5, 7). The constitutions of the 2 -azoniaallene salt 6c and the azetinium salt 8 were secured by X-ray c rystallographic analyses.