Stereo-defined saturated nitrogen heterocyles are important compounds found in medicines, building blocks, ligands and organocatalysts. In principle, azomethine ylide cycloadditions are the most direct entry into these compounds. The [3+2] cycloaddition with olefins has been thoroughly developed in the last decades but has been limited by the use of activated (electron-deficient) olefins. Important metal catalysts have been developed to achieve impressive regio-, diastereo- and enantioselectivities. However, it has been difficult to get any reactivity when unactivated olefins (like any alkyl-olefin) are used in this reaction, probably due to inaccessible overlap with their high energy LUMOs. Very recently we have reported on the first [3+3] approach to the direct assembly of piperazine compounds using the special reactivity of organoaluminum azomethine ylides under visible-light irradiation.1 Interestingly, we have now found that the principles of this system can be extended to the first general [3+2] cycloaddition of azomethine ylides involving unactivated olefins with various functionalities. This way, important pyrrolidine compounds can be assembled in one-step using a fundamentally interesting transformation that we are currently studying using various techniques. We have found this reaction to be surprisingly more tolerant to a broad range of functional groups (as compared to the parent [3+3] cycloaddition reported this year by us),1 thus enabling the stereocontrolled synthesis of interesting pyrrolidine compounds with substitution patterns never accomplished before. [1] Angew. Chem. Int. Ed. 2015, DOI:10.1002/anie.201505608

Organometallic aluminum azomethine ylides meet visible light: Unique reactivity for direct syntheses of heterocycles

251st National Meeting (2016)

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