Regioselective synthesis of polycyclic sulfones via radical-induced three-component bicyclization cascades.

New radical-triggered three-component bicyclization cascades of 2-alkynyl aryldiazonium tetrafluoroborates with a sulfur dioxide surrogate DABCO·(SO2)2 and internal alkynes such as haloalkynes and ynones have been reported for the first time, leading to 49 examples of polycyclic sulfones with moderate to good yields and high levels of regioselectivity. This transformation initiated by an in situ generated arylsulfonyl radical proceeds efficiently under mild and neutral redox conditions, which provide an easy and metal-free pathway toward the formation of a range of richly decorated indeno[1,2-c]thiochromene 5,5-dioxides.