Photocatalytic [3+2] Cyclization of Cyclopropylamines With <i>gem</i> ‐Difluoroalkenes: Accessing <i>gem</i> ‐Difluorinated Cyclopentylamines

ABSTRACT A photocatalyzed [3+2] cyclization protocol has been developed using cyclopropylamine and gem‐ difluoroalkene as the synthetic precursors. Frameworks of gem ‐difluorinated cyclopentylamines with the potential for pharmacodynamic promotion are produced in simple conditions and good yields. A certain iridium photocatalyst was carefully screened for the successful proceeding of this reaction. Mechanistic studies disclosed the quenching of the excited iridium photocatalyst by cyclopropylamine, and sequential radical addition to the double bond ensured the formation of cyclopentane. Functional groups such as halogens, esters, cyano, and aliphatic olefins were all tolerated to make this strategy an easy access to the fluorinated cyclopentylamines. Substrates employing heteroaryl‐substituted and tetra‐substituted gem‐ difluoroalkenes also make this strategy a method for preparing gem ‐difluorinated molecules with elaborate structures.