Deoxygenative Photocyclizations

Deoxygenative Photocyclizations

Author: Charlotte Gers-Panther

Chiral tetrahydrofurans and pyrrolidines have diverse biological activities and can be found in a large number of natural products and pharmaceuticals. Amongst many other methods, their synthesis can be accomplished by visible-light-mediated photoredox catalysis, which involves the formation of a C–O bond (tetrahydrofurans) or a C–N bond (pyrrolidines).

Oliver Reiser, University of Regensburg, Germany, and colleagues have developed a synthesis protocol for a large variety of chiral tetrahydrofuran and pyrrolidine derivatives (pictured, X = O, N). The method involves C–C-bond forming 5-exo-dig and 5-exo-trig cyclizations of activated 1,2-diols or β-amino alcohols in the presence of an iridium catalyst under visible-light irradiation. The proposed mechanism proceeds through a carbon-centered radical, formed after single-electron transfer and C–O-bond mesolysis, which cyclizes to give the five-membered heterocycle.

The method is inexpensive, uses readily available starting materials, and involves a sustainable, halogen-free activation of the hydroxy group towards radical reactions, which is achieved by its transformation into either recyclable 3,5-bis(trifluoromethyl)benzoate or inexpensive ethyl oxalate esters.


 

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