Metal-free [3+3] benzannulation of 1-indanylidene-malononitrile with Morita-Baylis-Hillman carbonates: direct access to functionalized fluorene and fluorenone derivatives

An efficient [3+3] benzannulation of Morita-Baylis-Hillman carbonates with 1-indanylidenemalononitrile was achieved under metal-free reaction conditions selectively delivering a wide range of functional multi-substituted fluorene or fluorenone compounds in high yields, respectively (up to 86% yield). Moreover, experiments and quantum chemical calculations were also performed to study the mechanism of the transformation.