Electronically-controlled diastereoselective synthesis of spirocycles via [4 + 2] cycloaddition of 2-arylidene-1-indenones with benzyne.

A one-pot electronically controlled [4 + 2] cycloaddition reaction of in situ generated benzyne with 2-arylidene-1-indenone is unveiled to construct novel spirocyclic frameworks in a regio- and diastereoselective fashion. This protocol features operational simplicity, good functional group tolerance and avoids the use of metal catalysts and external additives. This methodology has extended the synthetic application of 2-arylidene-1-indenones enabling easy access to valuable 10'H-spiro[indene-2,9'-phenanthren]-1(3H)-ones in good yields.