Asymmetric Radical Cyclopropanation of Alkenes with In Situ-Generated Donor-Substituted Diazo Reagents via Co(II)-Based Metalloradical Catalysis

Donor-substituted diazo reagents,
generated in situ from sulfonyl
hydrazones in the presence of base, can serve as suitable radical
precursors for Co­(II)-based metalloradical catalysis (MRC). The cobalt­(II)
complex of D2-symmetric chiral porphyrin
[Co­(3,5-DitBu-Xu­(2′-Naph)­Phyrin)]
is an efficient metalloradical catalyst that is capable of activating
different N-arylsulfonyl hydrazones for asymmetric
radical cyclopropanation of a broad range of alkenes, affording the
corresponding cyclopropanes in high yields with effective control
of both diastereo- and enantioselectivity. This Co­(II)-based metalloradical
system represents the first catalytic protocol that can effectively
utilize donor-type diazo reagents for asymmetric olefin cyclopropanation.