An Intramolecular Iodine-Catalyzed C(sp$^{3}$)−H Oxidation as a Versatile Tool for the Synthesis of Tetrahydrofurans

The first iodine-catalyzed cyclization reaction of aliphatic primary and secondary alcohols gives access to tetrahydrofurans through an intramolecular C(sp$^{3}$)−H activation. The reaction proceeds under mild reactions using either a floodlight lamp or daylight.
The formation of ubiquitous occurring tetrahydrofuran patterns has been extensively investigated in the 1960s as it was one of the first examples of a non-directed remote C−H activation. These approaches suffer from the use of toxic transition metals in overstoichiometric amounts. An attractive metal-free solution for transforming carbon-hydrogen bonds into carbon-oxygen bonds lies in applying economically and ecologically favorable iodine reagents. The presented method involves an intertwined catalytic cycle of a radical chain reaction and an iodine(I/III) redox couple by selectively activating a remote C(sp$^{3}$)−H bond under visible-light irradiation. The reaction proceeds under mild reaction conditions, is operationally simple and tolerates many functional groups giving fast and easy access to different substituted tetrahydrofurans.