Am etal-free generation of carbanion nucleophiles is of prime importance in organic synthesis. Herein we report ap hotocatalytic approacht ot he Corey-Seebach reaction. The presentedm ethod operates under mild redox-neutral andb ase-free conditions giving the desired product with high functional group tolerance. The reaction is enabled by the combination of photo-and hydrogen atom transfer (HAT) catalysis. Thisc atalytic merger allows aC ÀHt oc arbanion activation by the abstraction of ah ydrogen atom followed by radical reduction. The generated nucleophilici ntermediate is then capable of adding to carbonyl electrophiles.T he obtained dithiane can be easily convertedt ot he valuable a-hydroxy carbonyl in as ubsequent step. The proposed reaction mechanism is supported by emissionq uenching, radical-radical homocoupling and deuterium labeling studies as well as by calculated redox-potentials and bond strengths. Ketones bearing ah ydroxy group in alpha position are a common structuralm oiety in several natural productsa nd potential drugs. [1] Ac lassical method to synthesize this class of compound is the well-known Corey-Seebach umpolung first reportedi n1 965. [2] In their seminal ands ubsequentw ork, they describe the deprotonation of dithianes by as trong base, yieldinga na cyl anion equivalent. This intermediate is capable of reacting with variouse lectrophiles,i ncluding carbonyl compounds opening easy access to a-hydroxy ketones upon deprotection (Scheme 1A). [3] Am ore novel approach to generate acyl anion equivalents is N-heterocyclicc arbene (NHC) catalysis. [4] However,t he benzoin self-condensation is, in some cases, as evere side reaction, especially when ak etone is the targeted electrophile and so far,o nly specific activated ketones could be used in an intermolecular reactionu sing NHC catalysis. [5] Thus, the Corey-Seebach umpolung is still widely applied for the synthesis of natural products [6] as well as for the construction of smaller molecules today. [7] Accordingly, over the last two decades, significant efforts have been made to advance the dithiane method introduced by Corey and Seebach. Among others, [8] an anion relay strategy [9] andt he combinationw ith metal-[10] and organocatalysis [11] (Scheme 1B)h ave been developed. Additionally, specific dithianes could be used as radicalp recursors in photocatalytic transformations for an addition to double bonds (Scheme1C). [12] Scheme1.Corey-Seebachr eactiona nd the use of dithianes as substrate in different catalyticsystems.