A Convenient Synthesis of Functionalized 2,3-Diazaspiro[4.4]nona-1,6,8- trienes

Among pyrazolone derivatives, spirocyclic pyrazolone systems [1] have attracted extensiveinterest because of their remarkable bioactivities. Despite many efforts devoted to the developmentof new preparative methods for these heterocyclic systems, the development of syntheticallyeffective protocols for such compounds is still a challenge [2]. In view of our interestin the synthesis of spiroheterocycles [3], we now report a convenient Michael addition/cyclization sequence of alkyl isocyanide–acetylenic ester adducts with various pyrazolones,leading to the formation of diazaspiro[4.4]nona-1,6,8-trienes in moderate to goodyields. The structures of all molecules were confirmed by NMR spectroscopic data.