Halogenated carbonyl compounds

The O-S exchange method in presence of a-halogenated carbonyl compound is a very good one for thiazole compounds. The thioamide is prepared in situ by the action of amide upon phosphorus pentasulphide with solvent. The a-halogenated aldehyde reacts directly. But the O-Se exchange cannot be performed with a-halogenated carbonyl compounds because of the apparition of phosphoric acid. (Scheme 3), The C-Se bond is very sensitive to add pH. 

The replacement of selenoamide by selenourea in the Hantzsch s synthesis. (1st method) leads to 2-aminoselenazoles 2, 14. 15). This series of compounds has been well developed, mainlv because selenourea is much more easily accessible than the selenoamides, but also because a wide variety of a-halogenated carbonyl compounds are available for the Hantzsch s evdization reaction (Scheme 5). 2-Aminoselenazole itself was prepared from commercially available chloroacetaldehyde semihydrate... 

Other important applications for organoboranes" include the Michael-like addition reaction to a ,/3-unsaturated carbonyl compounds, and the alkylation of a-halogenated carbonyl compounds. 

S-Alkylation of a thiocarboxylic acid with an a-halogenated carbonyl compound gives a thiol ester in which the two carbons to be connected... 

Thieno[2,3-. ]pyridines, 115, form via a condensation reaction with halogenated carbonyl compounds, as shown in Scheme 35. Depending on the base strength of the reagent and reaction conditions, intermediate 114 may be isolated <2005CCA63>. 

TABLE 13.8 Estimated Lifetimes of Halogenated Carbonyl Compounds in the Aqueous Phase11... 

The phosphonium salts derived from an o -hydroxybenzyl halide and triphenylphosphine react with a variety of a-halogenated carbonyl compounds in the presence of sodium methoxide to yield chromenes. The speed of the alkylation and the simplicity of the work-up make this an attractive route to 2- and 3-substituted chromenes. 

Aliphatic and aryl aliphatic amino ketones are made by the amination of the halogenated carbonyl compounds, - e.g., dimethylaminoacetone (74%), l-diethylamino-2-pentanone (79%), and a-methylaminopropio-phenone (57%). It is noteworthy that this system may undergo a rearrangement, viz., ArCOCH,Br+ (C,H,),NH— ArCHjCON(C,H5)a (45%). The reaction of a-halo ketones with arylamines is even more complex. Examples of the formation of a-aminoaldehydes by this method are few. However, the same results may be achieved by the amination of the halo acetals with subsequent hydrolysis. "... 

The hydroxy function may originate from the reduction of an a-halogenated carbonyl compound or a Grignard reaction. The oxirane oxygen is not always incorporated directly from a hydroxy group for instance, in the case of a carboxylic acid ester, it is derived with neighboring-group participation from an ortho-monoester intermediate. 

Feist-B6nary furan synthesis Synthesis of furans from p-keto esters and a-halogenated carbonyl compounds under basic conditions. 166... 

Photoeliminations of CO or CO2 from halogenated carbonyl compounds have been reported in Section 5. These include photolyses of COBr2," XC(0)SY (X = F, Cl Y = NCO, CF3), oxalyl chloride, fumaryl and maleoyl dichlor-ides," and dichloromaleic anhydride. ... 

The Passerini reaction of a-halogenated carbonyl compounds (8 X = Cl, Br) can be used for the protection of the C-terminal carboxyl groups of A -protected a-amino acid derivatives (7). ... 

The 8-mercaptohypoxanthine derivatives reacted similarly as the xanthines 96 with halogenated carbonyl compounds to afford 6-alkylthiazolo[2,3-/]purine-4(377)-one e.g., 105 (73CPB256) (Scheme 28). The structures of compounds 103 showing the f -bond fusion were proven by desulfuration with Raney- nickel yielding the 7-substituted purin-one or -dione. 

Between 1948 and 1952 Morris and Van Winkle (1952), Arbuzov and Alimov (1951), and Perkow et al. (1952) investigated independently the reaction of polyhalogen aldehydes, primarily of chloral, with trialkyl phosphites. The conversion was assumed by some workers to be a true Michaelis-Arbuzov reaction and, accordingly, it was thought erroneously that the product formed in the reaction of chloral and trimethyl phosphite is the phosphonate of formula 66. Perkow et al. (1952) established that a-halogen carbonyl compounds give with trialkyl phosphites an anomalous Michaelis-Arbuzov reaction, so that the actual reaction product is 2,2-dichlorovinyl phosphate, 67. This reaction is known in the literature as Perkow s reaction. 

From alkanesulphonyl chlorides and halogenated carbonyl compounds 811... 

A further, and more important, difficulty occurs in attempted Michaelis-Arbuzov reactions involving certain halogenated carbonyl compounds. In these cases, a reaction in... 

The reactions of alkoxyacetylenes with such electrophiles as halogens, carbonyl compounds, derivatives of boron, mercury, sulfur, silicon and germanium usually proceed regioselectively according to equation 49... 

Condensation of salicylaldehyde and its derivatives with a variety of esters of chloroacetic acids in the presence of TBAB led to the synthesis of benzo[b]furans by means of a solid-liquid PTC reaction under the action of microwave irradiation [39]. This was a modification of one of the most popular routes to substituted benzo[b]furans, i.e. O-alkylation of O-hydroxylated aromatic carbonyl compounds with a-halogenated carbonyl compounds then intramolecular condensation. The mixture of aldehydes and chloroacetic acid esters were absorbed on potassium carbonate then irradiated in an open vessel in a domestic MW oven for 8-10 min (Eq. 26). 

The formation of epoxides in this way complements their formation from alkenes with m-CPBA because it involves construction of a C-C bond. Epoxide formation from a-halogenated carbonyl compounds is known as the Darzens reaction. 

This reaction provides an alternative method for preparing cy-halogenated carbonyl compounds. 

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