Metal-Free Photocatalytic [4+2] Annulation of Acrylamides with 2-Benzyl-2-bromocarbonyls to Assemble Tetralin-1-carboxamides

Tetralin-1-carboxamides are frequently incorporated in myriad medicinally important molecules. However, their existing synthetic routes not only suffer from some drawbacks such as tedious procedures, harsh reaction conditions, narrow substrate scope, low yields, and environmental problems, but are also based upon the elaboration of uneasily available non-linear tetralin derivatives. Herein, we describe a metal- and additive-free visible light-induced [4+2] annulation of two simple linear starting materials, namely acrylamides and 2-benzyl-2-bromocarbonyls, through a cascade C(sp(3))-Br/C(sp(2))-H bond cleavage, double C-C bond formation, and aromatization sequence. The developed protocol provides a convenient, efficient, and green approach to a variety of tetralin-1-carboxamide derivatives with good functional group compatibility. Importantly, the resulting products could also undergo the LiCl-mediated mono-decarboxylative cyclization process to further furnish the architecturally novel bridged polycyclic imides with excellent cis-diastereoselectivities.