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. (4) α,α'-Dihalo ketones Initial reduction of α,α'-dihalo ketones leads to metal enolate intermediates. Loss of the remaining halide generates 2-oxyallyl metal complexes, which undergo [4+3] and [3+2] cycloaddition reactions in the presence of dienes or olefins. 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. (5) Scope and Limitations Reductions of α-halo ketones may afford the parent ketones, partially reduced halo ketones, or products arising from interception of intermediates along the reduction pathway with nucleophiles or electrophiles. The products obtained depend on both the reducing agent and the substitution pattern of the halo ketone. Monohalo ketones Monohalo ketones may be reduced to the corresponding parent ketone with lithium metal, followed by protonation of the enolate. Other useful reducing agents for this transformation include lithium dialkylcuprates and molybdenum hexacarbonyl-alumina. (6) Alkylation of enolates generated through the reduction of monohalo ketones is limited to the most reactive alkyl halides. However, reduction in the presence of an aldehyde leads to reductive aldol products, analogous to the Reformatsky reaction of haloesters. Zinc dust may be used alone; or as an amalgam, in combination with diethylaluminum chloride, or with catalytic amounts of copper(I) bromide. (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. Although complex reaction mixtures often result, selective dimerization is possible in some cases. In the example below, the product distribution is solvent dependent (8) α,α-Dihalo ketones Depending on the conditions employed, geminal dihalo ketones may be reduced to the parent ketone, monohalo ketone, or functionalized monohalo ketone with organocuprates. Warming functionalized α-halo ketones produced under these conditions from −40 °C to room temperature leads to the corresponding α,β-unsaturated ketone. (9) α,α'-Dihalo ketones Organocuprates may also be employed for the reduction of α,α'-dihalo ketones to alkylated ketones. In the absence of an electrophile the monoalkyl ketone is isolated in good yield; when an alkyl iodide is added, the dialkyl ketone is isolated (geminal alkylation is a problematic side reaction). (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