Ultrasound-Promoted Synthesis of Spirocyclopropanes from Switchable Starting Materials via Azomethine Ylide [3+2]-Cycloaddition

An ultrasound-promoted green protocol to access a new series of spirocyclopropanes from indeno[1,2-b]quinoxaline derivatives and azomethine ylides, generated in situ from iodine-catalyzed reaction of acetophenones as well as 2-methylquinoline with pyridine in the presence of a base, is described. These transformations proceeded via a spirocyclopropanation reaction followed by elimination of pyridine. Clear evidence for the structure of a spirocyclopropane-linked indenoquinoxaline derivative was obtained from single-crystal X-ray analyses. The most important feature of this reaction is the fact it forms three stereogenic centers, one of which is quaternary with excellent selectivity.