Over the past decade, photoredox catalysis has been warmly embraced by the synthetic organic community for its ability to access unique reactivity using mild reaction conditions that harness energy from light. A major drawback in this field of chemistry is that many examples in the current literature use photocatalysts containing precious metals. By utilizing light-activated catalysts based on earth-abundant chromium, our group has been able to cultivate a more sustainable approach in the field of photocatalysis. To this end, a Cr photocatalyzed cyclopropanation using diazo reagents has been developed. The transformation proceeds through a radical cation mechanism that has distinct features from traditional diazo-based cyclopropanations. Furthermore, a direct (3+2) cycloaddition between olefins and vinyldiazo species using photocatalysis has been discovered. This process enables nucleophilic interception of radical cation species by vinyl diazo compounds which traditionally behave as electrophiles. Experimental insights refute a cyclopropanation/rearrangement cascade process and support a direct cycloaddition. Overall, these transformations are able to transform sp2-rich starting materials to more architecturally complex products containing multiple sp3 centers.
