Light/inductive effect induced isomerization of chromeno-5-methyl-2,6,9-trioxabicyclo[3.3.1]nonadienes

Abstract

Light-mediated [1,3] sigmatropic shift of chromeno-5-methyl-2,6,9-trioxabicyclo[3.3.1]nonadienes to yield chromeno-3-methyl-2,6,9-trioxabicyclo[3.3.1]nonadienes was reported. The migration was observed to proceed without the requirement of UV light if a strong electron-withdrawing group on the benzene moiety or a strong electron-donating group on the coumarin moiety is present. A plausible stepwise ionic mechanism was proposed for the latter isomerization.