A general and efficient synthesis of substituted fluorenes and heterocycle-fused indenes containing thiophene or indole rings utilizing a Suzuki–Miyaura coupling and acid-catalyzed Friedel–Crafts reactions as key steps

A general and efficient synthesis of fluorenes or heterocycle-fused indenes including 3-thia-cyclopenta[a]indenes, 9-thia-indeno[1,2-a]indenes, 5,6-dihydroindeno[2,1-b]indoles has been developed. This methodology is realized by a multistep protocol involving first preparation of ortho-formylbiaryls through Suzuki–Miyaura coupling of o-bromobenzaldehydes with arylboronic acids or the coupling of aryl halides with 2-formylbenzene boronic acid, this is followed by Grignard addition and Friedel–Crafts cyclization reactions catalyzed by Brønsted or Lewis acid to form the desired fluorene or indene rings. The method offers several advantages such as high yields, high selectivities, mild reaction conditions, easily accessible starting materials, and so on.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slide