Syntheses of condensed polycyclic azonia aromatic compounds by photocyclization

Abstract

Stilbene-type photocyclization provides a good route to new condensed polycyclic azonia aromatic compounds. The structures of the new compounds so formed have been confirmed by direct comparison with independently prepared samples. The photocyclization of the 2-styrylisoquinolinium salt (11) and 1-[β-(2-naphthyl)vinyl] pyridinium salt (12) gave the dibenzo[a,h]quinolizinium salt (14) and the naphtho[1,2-a]quinolizinium salt (16) in 24 and 45% yields, respectively. The 2-[β-(2-naphthyl)vinyl]isoquinolinium salt (13) was photocyclized to afford 2a-azoniabenzo[ghi]perylene perchlorate (24) in 30% yield. It was also found that 4-methyl-2a-azoniadibenzo[c,g]phenanthrene perchlorate (27), prepared from 1-(1-napthylthio)isoquinoline, upon photocyclization gave the methyl derivative of (24), compound (28). Bond formation via a conrotatory photocyclization is possible when the bond order (P_rs*) between the atoms r and s, involved in the cyclization in the excited state, has a negative value.