In organic chemistry, α-halo ketones can be reduced with loss of the halogen atom to form enolates. The α-halo ketones are readily prepared from ketones by various ketone halogenation reactions, and the products are reactive intermediates that can be used for a variety of other chemical reactions. Introduction 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. 2-Oxyallyl metal intermediates may also intercept nucleophiles in a process that involves umpolung at the α carbon. In addition, because reduction of monohalo ketones produces enolates in a site-specific fashion, reactions associated with enolates (alkylation, aldol, Michael) may be carried out using halo ketone substrates under reductive conditions. (1) Mechanism Many reducing agents used in this type of reaction are commercially available. A few require preparation and immediate use, including zinc–copper couple and zinc/silver couples. and organocuprates Monohalo ketones Monohalo ketones are reduced by both one-electron and two-electron reducing agents to afford the parent ketones, derivatives functionalized with electrophiles, or products of dimerization. The mechanism of reduction itself depends on the nature of the reducing agent. One-electron reducing agents, such as d6 or d1 transition metal complexes, initially donate a single electron to the halo ketone. Fragmentation of the resulting radical anion yields an organic radical and halide anion. Donation of a second electron from a second equivalent of reducing agent leads to the formation of a metal enolate in which the oxidation state of the reducing agent has increased by one. (2) Two-electron reducing agents, the most prominent of which is zinc metal, undergo direct oxidative addition to monohalo ketones to afford metal enolates in which the oxidation state of the metal has increased by two. Subsequent disproportionation with unreacted halo ketone sometimes leads to the formation of two equivalents of enol radical, which may subsequently dimerize. (3) Treatment of enolates derived from either one- or two-electron reducing agents with an electrophile affords α-functionalized ketones as the final product. α,α-Dihalo ketones Similar to monohalo ketones, geminal dihalo ketones initially form metal enolates upon exposure to one- or two-electron reducing agents. In the presence of a protic solvent, reduction stops at this stage to afford the monohalo ketone (which may be further reduced to the parent ketone). However, in the