Synthesis of hexahydroisobenzofuran-1(3H)-ones via pyridine-boryl radical-catalyzed intramolecular cascade cyclization of alkene-tethered cyclobutyl ketones.

Cyclobutane is a valuable C4 synthon, and the cycloaddition reactions involving donor-acceptor cyclobutanes have been extensively studied. However, the ring-opening cyclization reactions of acceptor-acceptor cyclobutanes remain largely unexplored due to the inherent difficulty in cleaving the carbon-carbon bonds. In this study, we report an intramolecular formal [4 + 2] cycloaddition reaction of alkene-tethered cyclobutyl ketones enabled by pyridine-boryl radical catalysis. This transformation tolerates aryl, alkyl, and terminal alkenes, affording hexahydroisobenzofuran-1(3H)-ones in moderate to good yields with acceptable diastereoselectivities.