Ru(II) Catalyzed Oxidative Dehydrogenative Annulation and Spirocyclization of Isoquinolones with N‐Substituted Maleimides

Abstract

A Ruthenium(II) catalyzed additive‐free oxidative, dehydrogenative annulation of different malemides on 3,4‐disubstituted isoquinolone to afford fused and spiro‐cyclized isoquinolo‐isoquinolone and isoindolo‐isoquinolone derivatives is reported here. By simply changing solvent and oxidizing agents, under two different conditions, this methodology produced two different poly‐N‐heterocyclized products. Isoquinolone‐NH was strategically used as the internal directing group in the ortho C‐H activation using Ru(II) catalyst. Mechanistically dehydrogenative, oxidative C‐C followed by C‐N cross‐coupling and aza‐michael reaction pathway led to the corresponding fused and spiro‐products respectively. A diversified library of eighty‐one (81) such two products were synthesized by employing this methodology. The fused and the spirocyclized polyheterocyclic compounds absorbed at λ<sub>max</sub> 240‐270 nm range, however only spiro‐compounds produced blue fluorescence at λ<sub>em</sub> 391‐450 nm range.