Isoindolo[2,1-a]indol-6-one—a new pyrolytic synthesis and some unexpected chemical properties

Abstract

Isoindolo[2,1-a]indol-6-one 1 is formed by a sigmatropic shift–elimination–cyclisation cascade by flash vacuum pyrolysis (FVP) of methyl 2-(indol-1-yl)benzoate 7 at 950 °C. The dihydro compound 16 is easily obtained by catalytic reduction of 1, but the reaction is very sensitive to steric effects at the 11-position. Attempted ring-opening of 1 in basic methanol provides an equilibrium of isoindolo[2,1-a]indol-6-one 1 and the ester 19. Lithium aluminium hydride reduction of 1 provides the alcohol 22 which can be dehydrated to a mixture of 23 and 24 by FVP at 800–950 °C.