8 - Addition of Hydride Donors and Organometallic Compounds to Carbonyl Compounds

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The acylations of hydride donors or of organometallic compounds, which give aldehydes or ketones, are often followed by an unavoidable second reaction: the addition of the hydride or organometallic compound to the aldehyde or the ketone. The addition of a hydride donor to an aldehyde or to a ketone gives an alcohol. This addition is therefore also a redox reaction, namely, the reduction of a carbonyl compound to an alcohol. Reagents that transfer a carbanion to the C atom of a C=O double bond are referred to as C nucleophiles. The most important nucleophiles of this kind are organolithium compounds and Grignard reagents. In the addition of hydride donors to aldehydes, the tetrahedral intermediate is a primary alkoxide. In the addition to ketones, it is a secondary alkoxide. Alkyllithium and alkyl Grignard reagents, alkenyllithium and alkenyl Grignard reagents, and aryllithium and aryl Grignard reagents, as well as alkynyllithium and alkynyl Grignard reagents, can be added to the carbonyl group of aldehydes and ketones.