The arylative oxygenation of the
electron-rich olefins styrene,
α-methylstyrene, vinyl pyrrolidinone, and vinyl oxazolidinone
was accomplished using arenediazonium salts and catalytic amounts
of FeSO4 in an effective single electron transfer radical
process. A broad range of aryldiazonium salts was tolerated using
water, methanol, or their combination with acetonitrile to furnish
the corresponding carbohydroxylated and carbomethoxylated products
(42 examples), including functionalized dihydroisocoumarin and dihydrobenzofuran
systems in good to excellent yields (up to 88%). The protocols developed
for the Fe(II)-catalyzed carbohydroxylation were also compared to
Ru(II) and Ir(III) photoredox carbooxygenations of these electron-rich
olefins. The Fe(II)-catalyzed process proved to be highly competitive
compared to the photoredox and the uncatalyzed processes. The proposed
mechanism for the Fe(II)-catalyzed reactions involves the synergic
combination with an effective Fe+2/Fe+3 redox
system and a radical polar crossover mechanism featuring an unprecedented
capture of the reactive N-acyliminium in the case
of vinyl pyrrolidinone and vinyl oxazolidinone.