Imines photochemistry with the exception for studies of the carbon-nitrogen double bond geometrical isomerization has long remained in the shadow of its more widely used and well-known relatives – aldehydes and ketones. Here we report synthetically useful [4+2] and [4+4] cycloadditions of aminoazaxylylenes photogenerated from imines resulting in unprecedented piperazine-spiro-quinoline and piperazine-spiro-azocane molecular architectures. Distinct structures of the photoproducts, in which diverse heterocyclic functionalities are held rigidly or semi-rigidly in a well-defined 3D spatial arrangement, plausibly offer access to unexplored chemical space.<br/>We have developed a direct access to imine-based photoprecursors starting from readily available isatins through a one-pot sequence of their N-acylation and ring opening with aromatic diamines. The scope of the shown photochemical transformation was probed using various aromatic and aliphatic imines.<br/>We show that Lewis acids dramatically accelerate these photoinduced intramolecular cycloadditions, which provides opportunity of using chiral ligands to control enantioselectivity of [4+4] and [4+2] cycloadditions.<br/>Alternatively, chiral oxazolines based on commercial enantiopure 2-aminoalcohols have been utilized as chiral auxiliaries to directly access shown ketones with up to 98% ee.

Enantioselective cycloadditions of aminoazaxylylenes photogenerated via proton transfer in aromatic imines and oxazolines offer expedited access to diverse polyheterocyclic moleculararchitectures

249th National Meeting (2015)

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