Synthesis of Spirocyclohexadienones through Radical Cascade Reactions Featuring 3-Fold Carbon-Carbon Bond Formation

The radical 5-exo cyclization starting from 2-allyloxyphenyl-diazonium ions can be employed for the diastereoselective synthesis of ortho-spirocyclohexadienones through a consecutive addition to alkynes. The spirocyclic systems are formed in a radical [2 + 2 + 1] cycloaddition comprising three carbon carbon formations, of which the final one is an ipso attack onto the aromatic system at the original position of the diazonium-derived aryl radical.