Diastereoselective\nConstruction of Spirocyclic Isobenzofurans\nvia a Tandem Michael Addition/5-Exo-dig Cyclization Reaction

A practical\napproach for rapid and efficient access to\nspirocyclic\nisobenzofurans is described. The reaction proceeds through the cycloaddition\nof 1,6-ynenone derivatives and 4-nitro-1,3-diarylbutan-1-ones, promoted\nby Cs<sub>2</sub>CO<sub>3</sub> in the presence of <i>l</i>-proline as a catalyst. The advantages of this reaction include\nthe formation of two C–C bonds and one C–O bond as well\nas mild reaction conditions. Extended spirocyclic isobenzofurans are\nobtained with good efficiency and diastereoselectivity under these\nmild conditions, and this new protocol avoids the use of any transition-metal\nreagents.