Ketones, polyhalo

Unlike Its acid catalyzed counterpart a halogenation m base cannot normally be limited to monohalogenation Methyl ketones for example undergo a novel polyhalo genation and cleavage on treatment with a halogen m aqueous base... 

Polyhalo ketones, reductive dehalogenation of, 29, 2 Pomeranz-Fritsch reaction, 6, 4 Prevost reaction, 9, 5 Pschorr synthesis, 2, 6 9, 7 Pnmmerer reaction, 40, 3 Pyrazolines, intermediates in diazoacetic ester reactions, 18, 3 Pyridininm chlorochromate, 53, 1 Pyrolysis ... 

For a review of reductive dehalogenalion of polyhalo ketones, see Noyori Havakawa Org. React. 1983, 29, 163-344. 

The reaction of a polyhalo ketone with base (equation 3) was described several years before Favorskii described a similar rearrangement (equation 4). Simple a,a- and a,a -dihalo ketones yield the same product (Scheme 14), so dibromination can be followed by Favorskii rearrangement without purification. These rearrangements are usually stereospecific, though subsequent cis to trans isomerization, under the influence of base, often obscures this feature. Various explanations have been provided for this stereospecificity, but the one due to Rappe (illustrated in Scheme 15) seems most plausible. ... 

Trimethylsilyl alkenyl ethers (511), prepared by reaction of the corresponding ketones with trimethylsilyl chloride in DMF, react with polyhalo-geno-compounds in boiling DMF-chlorobenzene in the presence of cuprous chloride to give halogeno-ajJ-unsaturated ketones (512). The ethers (511) also react with phenylsulphenyl chloride to give / -keto-sulphides (513) and with di- and tri-chloroacetyl chlorides to give 1,3-diketones (514). ... 

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