Synthesis and nitrogen elimination of the linearly fused tetrazolo (1 ,5-b) isoquinolinium salts : Formation of a new tetracycle: Indazolo (2,3-b) isoquinoline

Abstract

Treatment of 3-aminoisoquinoline ( 1 ) with aryldi-azonium salts gave 2-amino-4-arylazoisoquinolines ( 2 ) which reacted with aromatic aldehyde to yield imidazo(4,5-c) iso-quinolines. With 3-amino-4-methylisoquinoline ( 4 ), however, the same reaction led to 3-isoquinolyltriazenes ( 5 ), and these could then be cyclized by the use of “TBB” to give tetrazolo(1,5-b)-isoquinolinium salts ( 6 ). The latter azolium salt ( 6 ) showed ambident reactivity in the presence of hydroxide ion manifested by simultaneous formation of tolualdehyde derivative 10 and indazolo (3,2-b) isoquinoline system ( 8 ). This ambidency as well as the difference in behaviour between the new linearly fused system ( 6 ) and its formerly studied angularly fused isomers (“annelation effect”) is interpreted in terms of the frontier molecular orbital theory.