Ru(II)- or Rh(III)-Catalyzed Annulation of Aromatic/Vinylic Acids withAlkylidenecyclopropanes via C-H Activation

An efficient and new route for the synthesis of (E)-4-benzylideneisochroman-1-ones through tandem cascadeannulation of benzoic acids with alkylidenecyclopropanes using Ru(II) as a catalyst is demonstrated. It is important to note that thereaction delivers selectivelyE-stereoselective 4-benzylideneisochroman-1-one derivatives in moderate to good yields, which hascompletely diverse selectivity as compared with previous methods. Further, the annulation was explored with less-reactive beta C-Hactivation of vinylic acids with alkylidenecyclopropanes, leading to the highly useful alpha-pyrone derivatives in the presence of anRh(III) catalyst.

Automated summary

An efficient and novel synthesis route for (E)-4-benzylideneisochroman-1-ones has been demonstrated using Ru(II) as a catalyst for the tandem cascade annulation of benzoic acids with alkylidenecyclopropanes. The reaction selectively delivers E-stereoselective 4-benzylideneisochroman-1-one derivatives in moderate to good yields, exhibiting completely different selectivity compared to previous methods. Furthermore, annulation with less-reactive beta C-H activation of vinylic acids with alkylidenecyclopropanes has been explored, leading to the synthesis of highly useful alpha-pyrone derivatives in the presence of an Rh(III) catalyst.