another name for organocopper compounds used for carbon-carbon bond formation in organic synthesis. Compounds of this type were first described in the 1930s by the American chemist Henry Gilman, for whom they are named. The most widely used organocopper compounds are the lithium diorganocuprates, which are prepared by the reaction between organolithium reagents (RLi) and copper(I) halides (CuX); for example, ArLi gives Ar₂CuLi.

The copper(I) salt is normally the iodide or bromide. Diethyl ether (ethyl ether) and tetrahydrofuran are the preferred solvents for the preparation and further reactions of Gilman reagents. Reaction temperatures below about –20 °C (−4 °F) are customary.

Lithium diorganocuprates react with alkyl halides; for example, Ar₂CuLi gives Ar—R. Secondary alkyl halides give much lower yields than primary alkyl halides, and tertiary alkyl halides react mainly by elimination. Aryl halides (ArX) and vinylic halides (C=CX) react similarly with alkyl halides (R′X) to give R—Ar and R—C=C, respectively. The major application of lithium diorganocuprates is in carbon-carbon bond formation by addition to α,β-unsaturated aldehydes (aldehyde) and ketones (ketone). Other functional groups (functional group) that react with lithium diorganocuprates include epoxides (epoxide) and acyl chlorides.

When organolithium reagents are treated with copper(I) cyanide (CuCN), so-called higher-order cuprates 【R₂Cu(CN)Li₂】 result. In general, higher-order cuprates react with the same kind of substances as lithium diorganocuprates but are often more effective.