Acyl radicalsa re invaluablei ntermediates in organic synthesis, however theirg eneration remains challenging.H erein, we presenta nu nprecedented light-driven, cobalt-catalysed method for the generation of acyl radicals from readilya vailable 2-S-pyridyl thioesters.T he synthetic potential of this methodology was demonstrated in the Giese-type acylation of activatedo lefinsi nt he presence of heptamethylc obyrrinate.T his vitaminB 12 derivative provedtobethe most efficient catalyst in the studied process.T he developedm ethod featuresb road sub-strate scope (38 examples), good functional group tolerance,a nd mild reactionc onditions.M oreover, it is easily scalable( illustrated on a2 0-folds cale-up procedure), enabling its preparative use.M echanistic studies revealedt hat the reactionp roceeds via ar adical pathway with the key steps involving the formation of an acyl-vitamin B 12 complexa nd subsequent photolysis of the Co À Cb ond.

Co complex – Cby(OMe)7 ‐ enables consecutive generation of alkyl and acyl radicals from adequately designed carboxylic acids possessing a halogen atom in theirs structures. Mechanistic studies reveal that alkyl corrins forms at much higher rate than the respective acyl derivatives enabling selective reactions with activated olefins.