Visible‐Light‐Mediated Energy Transfer Enables the Synthesis of β‐Lactams via Intramolecular Hydrogen Atom Transfer

Abstract

The synthesis of 2‐azetidinones (β‐lactams) from simple acrylamide starting materials by visible‐light‐mediated energy transfer catalysis is reported. The reaction features a C(sp3)−H functionalization via a variation of the Norrish–Yang photocyclization involving a carbon‐to‐carbon 1,5‐hydrogen atom transfer (supported by deuterium labelling and DFT calculations) and can be used for the construction of a diverse range of β‐lactam products.

Visible-Light-Mediated Energy Transfer Enables Cyclopropanes Bearing Contiguous All-Carbon Quaternary Centers

“…Visible-light-mediated energy transfer (EnT) catalysis has emerged as an efficient and valuable alternative, enabling access to reactive triplet states and facilitating subsequent organic transformations. − Inspired by the remarkable progress in EnT catalysis, we reasoned that the EnT method may enable the activation of N -tosylhydrazone due to its inherent weak N–S bond strength. , With the release of sulfonyl groups and nitrogen, an in situ triplet-state carbene species should be formed and subsequently facilitate the generation of highly congested EWG-free cyclopropanes with 1,1-disubstituted alkenes. Considering this possibility, we undertook the challenge and designed an EnT-mediated σ-bond homolysis toward the activation of N -tosylhydrazones and the synthesis of highly congested cyclopropanes bearing contiguous all-carbon quaternary centers (Scheme D).…”

Catalyst-free intramolecular radical cyclization cascades initiated by the direct homolysis of Csp3–Br under visible light

“…Considering that C sp 3 –C sp 3 bond formation is a part of almost all synthetic efforts, 10 a C sp 3 –Br bond is introduced as the first domino of the cyclization cascade (Scheme 1C). 11 However, direct alkylation involving alkyl bromide usually requires the catalysis of transition metals or photocatalysts (Ru, Ir, Acr + , etc .)…”

Visible-light-induced cyclization of 2-alkenyl-1,1′-biphenyls

“…13 More recently, the Petersen group have further developed a visible-light-mediated convenient and straightforward procedure for the synthesis of β-lactams from simple and easy to obtain acrylamide precursors via intramolecular H-shift. 14 In continuation of our interest in visible-light photochemistry 15 and inspired by the remarkable advances in visible-light-mediated energy transfer (EnT) catalysis, we have directed our efforts toward the development of a visible light induced method for intramolecular hydroarylation. Reported herein is a novel and efficient protocol to access phenanthrene-9,9(10 H )-dicarbonitrile derivatives from 2-malononitrilemethylene-substituted 1,1′-biphenyls through visible light-induced cyclization involving [1,5] H-shift by using 2,4,5,6-tetrakis(carbazol-9-yl)-1,3-dicyanobenzene (4CzIPN) as a photocatalyst under mild conditions.…”