Ketones halogenoketones

Water addition to the carbonyl group of aldehydes and ketones has been known for a long time. a-Halogenoketones react with water to form tetrahedral adducts (reaction 23). 

Recently Zbiral and Stroh reported that treatment of a-azido-ketones (obtained generally by reaction of the a-halogenoketone with sodium azide) with triphenylphosphine is a convenient route to 2,5-disubstituted pyrazines (Scheme 5). Thus, 2,5-diphenyl-, 2,5-bis(4-methoxyphenyl)-, and 2,5-diisopropylpyrazine have been obtained in 75, 45, and 44% yield, respectively. The intermediate P-iV-ylide undergoes intermolecular condensation to give a 2,5-dihydropyrazine which is subsequently aromatized.122... 

Borowitz and his co-workers have carried out a detailed comparative study of the reactions of phosphinites, phosphonites, and phosphites with -halogenoketones. The balance between keto-phosphorylation and enol-phosphorylation favours the former with increasing oxygen content of the phosphorus compound, higher temperature, more polar solvents, and bromo-rather than chloro-ketones. a -Dibromobiacetyl reacts with two moles of phosphite to give the double Perkow product (43) and no trace of the alternative Arbusov product or of the phosphorane (45). The rate of the first Perkow... 

The use of a-halogenoketones for cyclizing 2-aminoazines or 2-aminoazoles is well-known (see p. 276 and [B-45, 3533]), but the same result may be obtained by heating the heterocycle with a ketone, iodine or bromine and sodium hydro-gencarbonate in ethanol [2710]. In an extension of the reaction of 2-amino-thiazoles with a-bromoketones (p. 277), 1-bromomethyl 2-t-butyl ketone has been shown to give high yields of 6-t-butylimidazo[2,I-6]thiazoles, the presence... 

Conflicting reports relating to the products obtained from the Tiffeneau-Demjanov ring-expansion of 5a-cholestan-3-one have appeared. G.Lc. analysis has failed to reveal the presence of the A-homo-3-ketone, although it has been detected by o.r.d. and c.d. measurements. The pure A-homo-4-ketone has now been obtained via solvolysis of the dibromocarbene adduct (309) of 3-methoxy-cholest-2-ene to afford the unsaturated halogenoketone (310) which was then reduced to the 4-one. In a similar manner, 3-acetoxycholest-3-ene afforded the isomeric unsaturated halogenoketone (311) which on reduction produced A-homo-5a-cholestan-3-one. 

Boron fluoride I lithium iodide Ketones from a-halogenoketones 71. O... 

Palladium-carbon/triethylamine Ketones from halogenoketones... 

Selenium oxide chloride a-Halogenoketones from ketones... 

Dinitrophenylhydrazones of ketones including cycloheptanone are cleaved by aqueous solutions of TiCla." Only cis-cycloheptene was obtained by alkyl-lithium induced decomposition of cycloheptanone tosylbydrazone. Tosylhydrazones of a-halogenoketones react with phenyl copper at — 60 °C to give a-phenyl ketones after hydrolysis, thus a-chlorocycloheptanone was converted into a-phenylcyclohept-anone. ... 

Acyl cyanides have been prepared from acid chlorides,a-halogenoketones, and a,jS-unsaturated acyl cyanides. Syntheses of a-cyanoketones from ketones, a,jS-unsaturated ketones, pyrroles, and 3-acylthioisoxazoles have been reported. 

Titanium trichloride Replacement of halogen by hydrogen Ketones from a-halogenoketones... 

The allene-lithium (27), formed by metallation of methoxyallene, reacts with a-halogenoketones to give epoxides (28), which in turn give furans (29) on reaction with Bu OK in DMSO. Lithiated trimethylsilyl allyl ether (30) reacts with ketones to give 1,2-diol derivatives (31), or cyclizes if there is an appropriate electrophilic centre in the molecule. ... 

---