Photoredox chemistry is gaining traction in organic chemistry labs as it offers a mild approach for crafting carbon-carbon bonds. Relying on the ability of heavy metals to perform single-electron-transfer to an organic substrate, these methods generate unique reactive intermediates that can be harnessed to facilitate challenging bond formation. One reactive intermediate, the ketyl radical, is of particular interest. Generated via a proton-coupled electron transfer to a carbonyl, the ketyl radical exhibits a reversal of standard polarity roles, called an umpolung. A methodology which takes advantage of the unique umpolung reactivity of ketyl radicals is currently being developed. Using Ru(bpy)<sub>3</sub>PF<sub>6</sub> and a Hantzsch ester terminal reductant along with visible light, vinylogous carbonate substrates are cyclized into richly functionalized furans in high diastereomeric ratios. This cascade reaction, which furnishes a ring and two stereocenters from linear, achiral starting material, affords a vital synthetic precursor in the synthesis of a furanolactone motif present in many natural products. Access to both diastereomers of this transformation is available via an epimerization protocol. This epimerization-lactonization yields the desired bicyclic furanolactone.

Reductive ketyl radical cyclizations towards the total synthesis of the plakortone family of natural products

253rd National Meeting (2017)

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