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

Abstract

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.

Ring expansion of spirocyclopropanes with stabilized sulfonium ylides: highly diastereoselective synthesis of cyclobutanes

“…3 The regioselectivity of these reactions may be attributed to the inherent difference between esters and ketones. Recently, we reported the ring-opening cyclization of spirocyclopropanes 4 with EWG-stabilized sulfonium ylides 1 to afford hexahydrobenzopyranone as a single isomer via the regioselective ring-opening of cyclopropane with sulfonium ylide 1 and subsequent S N 2-type O -cyclization (Scheme 1B, eqn (1)). 4 f Considering the similar reactivity of cyclopropane and carbon–carbon double bonds, we expected that the reaction of ester-derived spirocyclopropane 2 with stabilized sulfonium ylide 1 would provide spirocyclobutane 3 through C -cyclization (Scheme 1C).…”