Radical-Mediated Strategies for the Functionalization of Alkenes with Diazo Compounds

One
of the most common reactions of diazo compounds with alkenes
is cyclopropanation, which occurs through metal carbene or free carbene
intermediates. Alternative functionalization of alkenes with diazo
compounds is limited, and a methodology for the addition of the elements
of Z-CHR2 (with Z = H or heteroatom, and CHR2 originates from N2CR2) across a carbon–carbon
double bond has not been reported. Here we report a novel reaction
of diazo compounds utilizing a radical-mediated addition strategy
to achieve difunctionalization of diverse alkenes. Diazo compounds
are transformed to carbon radicals with a photocatalyst or an iron
catalyst through PCET processes. The carbon radical selectively adds
to diverse alkenes, delivering new carbon radical species, and then
forms products through hydroalkylation by thiol-assisted hydrogen
atom transfer (HAT), or forms azidoalkylation products through an
iron catalytic cycle. These two processes are highly complementary,
proceed under mild reaction conditions, and show high functional group
tolerance. Furthermore, both transformations are successfully performed
on a gram-scale, and diverse γ-amino esters, γ-amino alcohols,
and complex spirolactams are easily prepared with commercially available
reagents. Mechanistic studies reveal the plausible pathways that link
the two processes and explain the unique advantages of each.