Oximes are valuable synthetic intermediates for the preparation of a variety of functional groups. To date, the stereoselective synthesis of oximes remains a major challenge as most current synthetic methods provide either mixtures of E- and Z-isomers or furnish the thermodynamically preferred E-isomer. Herein, we report a mild and general method to achieve Z-isomers of aryl oximes by photoisomerization of oximes via visible-light-mediated energy transfer (EnT) catalysis. Facile access to Z-oximes provides opportunities to achieve regio-/chemo-selectivity complementary to widely used transformations employing oxime starting materials. We show an enhanced one-pot protocol for photocatalyzed oxime isomerization and subsequent Beckmann rearrangement, which enables novel reactivity with alkyl groups migrating preferentially over aryl groups, reversing the regioselectivity of the traditional Beckmann reaction. Chemodivergent N-/O- cyclizations of alkenyl oximes are also demonstrated, leading to nitrones or cyclic oxime ethers respectively.

Photocatalyzed triplet sensitization of oximes using visible light provides a route to non-classical Beckmann rearrangement products

ACS Spring 2022

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