Α-halo ketones

A haloketone in organic chemistry is a functional group consisting of a ketone group or more general a carbonyl group with a α-halogen substituent. The general structure is RR'C(X)C(=O)R where R is an alkyl or aryl residue and X any one of the halogens. The preferred conformation of a haloketone is that of a cisoid with the halogen and carbonyl sharing the same plane as the steric hindrance with the carbonyl alkyl group is generally larger.

Efforts are reported in asymmetric synthesis of halocarbonyls through organocatalysis. In one study an acid chloride is converted into an α-halo-ester with a strong base (sodium hydride), a bromine donor and an organocatalyst based on proline and quinine:

In the proposed reaction mechanism the base first converts the acid chloride to the ketene, the organocatalyst then introduces chirality through its quininoid tertiary amine, forming a ketene adduct.

Haloketones take part in several reaction types. In reaction with a nucleophile, two electrophilic sites are available and in reactions with a base several acidic protons exist due to the presence of two electron withdrawing groups. The carbon halogen bond experiences increases polarity from the inductive effect of the carbonyl group making the carbon atom more electropositive.

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