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.

Synthesis of 1-azaazulenes using ring-opening cyclization of spirocyclopropane with a primary amine was accomplished. The reaction of cycloheptane-1,3-dione-2-spirocyclopropane with 2,4-dimethoxybenzylamine in refluxing acetonitrile resulted in a 94% yield of 1,2,3,6,7,8hexahydrocyclohepta[b]pyrrol-4(5H)-one. The obtained product was successfully converted into 1-azaazulenes by deprotecting the amino-protecting group followed by oxidation.Azaazulenes, aza-analogues of azulene, have intriguing physical and chemical properties and potential biological activities. 1 Of the many azaazulenes, 1-azaazulenes have attracted considerable attention from chemists because of their stabilities and pharmacological activities. [2][3][4] While many examples of 1-azaazulene syntheses have been reported, [5][6][7][8][9][10][11] in most cases, troponoid compounds were used as starting materials. For example, Nitta and co-workers successfully synthesized various 1-azaazulene derivatives 3 from tropones 1 using the aza-Wittig reaction followed by the oxidation of the bicyclic intermediates 2 (Scheme 1, A). 8 Narasaka and co-workers reported the synthesis of 1-azaazulenes 3 from cycloheptatrienylmethyl ketone O-pentafluorobenzoyloximes 4 by palladium(0)-catalyzed cyclization and sequential oxidation (Scheme 1, A). 9 Although these synthetic methods are direct and efficient, tropone derivatives are expensive and difficult to prepare.Meanwhile, we have developed a synthetic method of indole employing the ring-opening cyclization of cyclohexane-1,3-dione-2-spirocyclopropanes 5 with primary amines 6 to provide 2,3,6,7-tetrahydro-1Hindol-4(5H)-ones 7 followed by its oxidation into indole 8 (Scheme 1, B). 12 Based on this approach, we envision that the use of cycloheptane-1,3-dione-derived spirocyclopronane instead of a cyclohexane-1,3-dione derivative can construct a 1-azaazulene skeleton. Herein, we report the synthesis