Intermolecular [3+2] cycloaddition of cyclopropylamines with olefins by visible light photocatalysis
by Shinabery, Ryan S.; Zheng, Nan; Maity, Soumitra; Zhu, Mingzhao
In an environmentally responsible world, we must utilize readily available, renewable resources such as solar energy in the form of visible light (390-750 nm). Unfortunately, the majority of org. mols. are unable to absorb visible light, limiting the use of visible light in org. chem. Ru(II) and Ir(III) polypyridyl complexes have been shown to generate nitrogen radical cations from amines in a variety photoredox reactions. With this in mind, we desired to create a substrate that would undergo a downstream irreversible reaction upon oxidn. to a nitrogen radical cation. Cyclopropylamines were found to be an ideal substrate for this task. With substrate in hand, we sought to use an olefin to capture the resulting radical species and promote C-C bond formation. After screening a variety of reaction conditions (e.g., solvent, catalyst loading, etc.), the optimal conditions were found to be 2 mol% [Ru(bpyrz)3](PF6)2·2H2O in degassed nitromethane irradiated by a 13W fluorescent light bulb. A variety of mono and bicyclic cyclopropylamines were synthesized using Buchwald-Hartwig Cross Coupling and Kulinkovich-de Meijere reactions resp. The cyclopropylamines were then subjected to the optimized conditions with several terminal olefins to give the corresponding [3+2] cycloaddn. products in good yields. These cycloaddn. products are useful as building blocks in a variety of synthetic applications and as mol. scaffolds in medicinal chem.