Metal free synthesis of 1-azaspiro[4.4]nonane-3-one system via reactions of nitrones with 1,1-disubstituted allenes

Abstract

In the cycloaddition reaction between fluorenone N-aryl nitrones and 1,1-disubstituted allenes, the initially formed cycloadduct underwent facile [1,3] shift to give 1?-phenylspiro[fluorene-9,2?-pyrrolidin]-4?-ones. Although 1?-phenylspiro[fluorene-9,2?-pyrrolidin]-4?-ones are stable in solid state, a few of them underwent facile aerial oxidation in solution to give the corresponding 1?-phenylspiro[fluorene-9,2?-pyrrolidine]-4?,5?-diones in excellent overall yields. © 2019 Wiley Periodicals, Inc.