Metal-/solvent-free oxidative [4 + 2]/[3 + 2] annulation of 2-ethynylbenzaldehydes with arylalkenes: facile synthesis of benzo[a]fluoren-5-ones

Abstract

We report here a DTBP-mediated oxidative [4 + 2]/[3 + 2] annulation between 2-alkynylbenzaldehydes and terminal arylalkenes enabled by aldehyde C(sp²)–H functionalization for assembling a range of benzo[a]fluoren-5-ones with high step-economy, simple operation under metal-/solvent-free conditions and excellent functional group tolerance. This method is initiated from 2-alkynylbenzaldehyde reaction partners and provides a useful new strategy to construct complex benzo[a]fluoren-5-one scaffolds compared to existing protocols initiating from alkene reaction partners.