Manganese-mediated coupling reactions

Pathways available to the adduct radical include further oxidation to a carbocation (and subsequent β-elimination or trapping with a nucleophile) and hydrogen abstraction to generate a saturated carbonyl compound containing a new carbon-carbon bond.

[3] Yields of these reactions are generally moderate, particularly in the intermolecular case, but tandem intramolecular radical cyclizations initiated by Mn(III) oxidation may generate complex carbocyclic frameworks.

Because of the limited functional group compatibility of Mn(OAc)3, radical couplings employing this reagent have mainly been applied to the synthesis of hydrocarbon natural products, such as pheromones.

The fate of 2 is primarily determined by reaction conditions—in the presence of copper(II) acetate, this intermediate undergoes further oxidation to a carbocation and may eliminate to form β,γ-unsaturated ketone 4.

This section describes the scope and limitations of inter- and intramolecular manganese-mediated radical coupling reactions and is organized according to the carbonyl compound employed as the substrate.

[8] (3)When Cu(OAc)2 is present, further oxidation to carbocations followed by elimination takes place, leading to the formation of β,γ-unsaturated carbonyl compounds in moderate yields.

[14] (8)The stereochemical course of tandem reactions can be understood in some cases by invoking a chairlike transition state with as many substituents as possible in pseudoequatorial positions;[15] however, a number of examples exhibiting unpredictable stereochemistry are known.