Ring-Opening Cyclization of Spirocyclopropanes with Stabilized Phosphorus Ylides: Access to Indane and Azulene Skeletons

In this study, regio- and diastereoselective ring-opening cyclization of spirocyclopropanes with phosphorus ylides stabilized by electron-withdrawing groups were developed. The reaction of various cyclohexane-1,3-dione-2-spirocyclopropanes with phosphorus ylides bearing alkoxycarbonyl groups proceeded smoothly without any additives to provide the corresponding 6,7-dihydroindan-4-ones in 32–87% yields. Cycloheptane-1,3-dione-2-spirocyclopropanes were also used in this reaction, producing the corresponding products 1,2,3,6,7,8-hexahydroazulen-4-ones in 52–67% yields. The resulting [5.6]- and [5.7]-fused carbocyclic products were readily converted into highly substituted indanes and azulenes, respectively, by oxidation.