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26.9.1.1.4.2 Variation 2: Transition-Metal-Catalyzed Substitution with Acid Halides

DOI: 10.1055/sos-SD-026-00987

Marsden, S. P.Science of Synthesis, (2005261064.

Zerovalent palladium species insert readily into the CCl bond of acid chlorides to generate acylpalladium(II) chloride complexes. These usually undergo a rapid decarbonylation to give aryl-, vinyl-, or alkylpalladiums that undergo further reactions such as interception by alkenes in Heck processes. There are, however, two classes of reaction whereby the initially formed acylpalladium can be trapped by an alkene before decarbonylation takes place, allowing direct synthesis of α,β-unsaturated ketones (Scheme 22). The first example involves the use of bridgehead acid chlorides such as 90 to prepare enones, e.g. 91. In this case, the intermediate acylpalladium species are reluctant to undergo decarbonylation owing to strain in the potential products of the reaction.[‌86‌] Alternatively, aryl and hetaryl acid chlorides such as 92 react with alkyl vinyl ethers (e.g., 93) under palladium catalysis to generate vinylogous esters, e.g. 94.[‌87‌] The reactions are very highly regio- and stereoselective. Attempted extension to more substituted enol ethers or other alkene acceptors was unsuccessful, but the reaction tolerates a wide range of aromatic groups, provided there is no ortho substituent.

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