Photocatalyzed [3sigma + 2sigma] and [3sigma + 2pi] cycloadditions for the synthesis of bicyclo[3.1.1]heptanes and cyclopentenes.

We report the use of photocatalysis for the homolytic ring-opening of carbonyl cyclopropanes. In contrast to previous studies, our approach does not require a metal co-catalyst or a strong reductant. The carbonyl cyclopropanes can be em-ployed for both [3sigma + 2sigma] and [3sigma + 2pi] cycloaddition with either bicyclo[1.1.0]butanes and alkenes, yielding bicy-clo[3.1.1]heptanes and cyclopentanes respectively. Bicyclo[3.1.1]heptane (BCHs) have been recently highlighted as bi-oisosteres for meta-substituted aromatic rings. Our protocol provides a convergent way to synthesize them from bench stable bicyclo[1.1.0]butanes and cyclopropanes.