Pivaloyl chloride Friedel-Crafts reaction

Sometimes acylium ions lose carbon monoxide to generate an ordinary carbonium ion. It will be recalled that free acyl radicals exhibit similar behavior at high temperatures. Whether or not the loss of carbon monoxide takes place seems to depend on the stability of the resulting carbonium ion and on the speed with which the acylium ion is removed by competing reactions. Thus no decarbonylation is observed in Friedel-Crafts reactions of benzoyl chloride, the phenyl cation being rather unstable. But attempts to make pivaloyl benzene by the Friedel-Crafts reaction produce tert-butyl benzene instead. With compound XLIV cyclization competes with decarbonylation, but this competition is not successful in the case of compound XLV in which the ring is deactivated.263... 

Pivaloylindole gives high yields of 6-substituted ketones on reaction with a-halo-acid-chlorides and aluminium chloride simple acid chlorides react only at 0-3. The sequence below shows how a 1-pivaloyl-3-(indol-3-yl)propanoic acid undergoes Friedel-Crafts cyclisation to C-4, away from the deactivated heterocyclic ring. °... 

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