The reduction of α-halo ketones generates a variety of product structures that may exhibit unique substitution patterns and reactivity.
For instance, reduction of α,α'-dihalo ketones leads to 2-oxyallyl metal complexes, which participate in [4+3] and [3+2] cycloaddition reactions as the 2π component.
One-electron reducing agents, such as d6 or d1 transition metal complexes, initially donate a single electron to the halo ketone.
[7] (3)Treatment of enolates derived from either one- or two-electron reducing agents with an electrophile affords α-functionalized ketones as the final product.
[8] However, in the absence of a trapping electrophile or protic solvent, loss of the remaining halide from the enolate intermediate affords α-keto carbenes or carbenoids, which undergo C-H insertion reactions.
[1] Isomerization of 2-oxyallyl metal complexes to cyclopropanone and allene oxide forms is rapid and reversible; increasing the covalent character of the oxygen–metal bond favors the 2-oxyallyl isomer.
[15] (7)Reductive dimerization may result from the combination of two intermediate α-acyl radicals or nucleophilic attack of a metal enolate on unreacted halo ketone.
[19] (10)The 2-oxyallyl metal intermediates generated during reductions of α,α'-dihalo ketones with iron(0) complexes participate in [4+3] and [3+2] cycloaddition reactions to form cycloheptenones and cyclopentanones, respectively.