A rearrangement–cycloaddition approach to spiro-fused indanones

Spiro-fused indanones were constructed using a [4+2]-cycloaddition approach from α-methylene indanone dienophiles, which were elaborated from 4-chromanone in a number of steps including a key rearrangement process. This type of spiro-fused structure forms the central core ring system found in natural products such as coleophomone A. The cycloaddition reactions using an α-methylene indanone dienophile led to the exo diastereoisomer as the major cycloadduct, whereas the 1,4-dione based dienophile predominantly led to the endo diastereoisomer.