Cobalt-Catalyzed Chemoselective Transfer Hydrogenative Cyclization Cascade of Enone-Tethered Aldehydes.

The ligand-free Co-catalyzed chemoselective reductive cyclization cascade of enone-tethered aldehydes with -PrOH as the environmentally benign hydrogen surrogate is developed by this study. Mechanistic studies disclosed that such a protocol is initiated by an -enone-assisted Co(I)-catalyzed reduction of the aldehyde functionality with -PrOH. Meanwhile, the selectivity from the Michael-Aldol cycloreduction cascade to the oxa-Michael cascade is feasible and readily adjusted by the addition of steric Lewis bases, such as TEMPO and DABCO, delivering substituted 1-indenes and dihydroisobenzofurans, respectively.