Synthesis of Highly Functionalized Spirocycles and Pentafulvene‐Containing Dyes Involving 2‐(2′‐ketoalkyl)‐1,3‐indandiones

Abstract Synthesis of highly functionalized spiro[4.4]nonane and spiro[4.5]decane motifs by the reaction of dimethylacetylenedicarboxylate (DMAD) with 2‐(2′‐ketoalkyl)‐1,3‐indandiones and 2‐(3′‐ketoalkyl)‐1,3‐indandiones, respectively, has been developed by utilizing a catalytic amount of DABCO. The tertiary hydroxy‐containing spiro[4.4]nonane products were converted into fully conjugated pentafulvene π‐systems in an acidic medium through dehydration and unprecedented C−C bond rearrangement.