Dehalogenation of a-haloketones

Dehalogenation of a-haloketones. In the presence of fluoride ion the effective dehalogenation of a-haloketones by (PhjSnljSe in MeCN at room temperature is accomplished. The reagent is easy to handle as it has no significant odor and is not sensitive to water. 

Carbon - heteroatom bonds can be cleaved by an appropriate combination of a hard acid and a soft nucleophile. Synthetically useful selective C-0 bond cleavage in the presence of other C-0 bond(s) is described. Reductive dehalogenation of a-haloketones is presented as an example that illustrates the concept of hard-soft affinity inversion. Finally, regio- and stereoselective functionalization of 1,3-di-enes is demonstrated by the thienium cation Diels-Alder cyclization involving the C-S bond cleavage. 

Table I. Dehalogenation of a-Haloketones with AlCl3 and EtSH...

Dehalogenation of a-haloketones. The reduction can be conducted in 57% HI without solvent. 

Another application of [pmim][BFJ for the debromination reaction has been reported by Ranu et al. (2007). a-Bromoketones were selectively debrominated to either monobromo or debromoketones under microwave irradiation. The utilization of [pmim][BF J was also found appropriate for the dehalogenation of a-haloketones esters and v/c-bromoacetals. 

This reaction was first reported by Hantzsch and Weber in 1887. It is the formation of thiazole derivatives by means of condensation of a-haloketones (or aldehydes) and thioamides. Therefore, it is generally known as the Hantzsch thiazole synthesis. In addition, other names, including the Hantzsch synthesis, Hantzsch reaction, and Hantzsch thiazole reaction are also used from time to time. Besides thioamides, other thio-ketone derivatives such as thiourea, dithiocarbamates, and ketone thiosemicarbazone can also condense with a-halo ketones (or aldehydes) to form thiazoles. This reaction occurs because of the strong nucleophilicity of the sulfur atom in thioamides or thioureas, and normally gives excellent yields for simple thiazoles but low yields for some substituted thiazoles, as of dehalogenation. This reaction has been proven to be a multistep reaction, and the intermediates have been isolated at low temperatures, in which the dehydration of cyclic intermediates seems to be the slow step. It is found that a variety of reaction conditions might result in the racemized thiazoles that contain an enolizable proton at their chiral center, and it is the intermediate not the final product that is involved in the racemization. Therefore, some modifications have been made to reduce or even eliminate the epimeriza-tion upon thiazole formation. In addition, this reaction has been modified using a-tosyloxy ketones to replace a-haloketones. ... 

The Hantzsch synthesis of thiazoles is an excellent method for the synthesis of simple thiazoles, however for some substituted examples low yields have been reported as a result of dehalogenation of the a-haloketone. An alternative method for the synthesis of highly substituted thiazoles has been reported, thus starting from the 2-bromo-5-chlorothiazole 76 it was possible to introduce substituents selectively at the 2-position by a palladium-catalysed cross coupling reaction to give 77 (74-92%). In order to introduce a substituent into the 5-position,... 

Another example of the formation of tellurirane using a nonheterocyclic tellurium compound has been shown in the reaction of sodium 0,0-diethyl phosphorotelluroate (45) with a-haloketones (62). As shown in Scheme 11, the starting a-haloketones (62) are converted into the corresponding dehalogenated parent ketones (63) via epitelluride intermediate (64) together with the formation of elemental tellurium. 

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