Halo carbonyl compounds, formation

Alkylation of enolates with a-halo carbonyl compounds. (Formation of 1,4-dicarbonyl compounds)... 

A lot of methods are available for the synthesis of this heterocycle, and most of them rely on the formation of the five-membered ring. In this section, only the methodologies of reasonable scope will be reported. The most classical method involves the cyclocondensation of 2-aminopyridine with an a-halo carbonyl compound. Due to the broad availability of the required substrates and the efficiency of this cyclocondensation, it continues to be the method of choice to prepare this heterocycle. New examples highlighting the generality of this reaction are collected in Table 14. 

Dehalogenation.1 DMBI effects dehalogenation of a-halo carbonyl compounds in a variety of ethereal solvents with formation of DMBI+X in generally high yield. The order of relative reactivity is Br > Cl > F (halides) and primary > secondary > tertiary (for the a-substituted position). In combination with HO Ac (1 equiv.) the reagent also reduces acyl chlorides to aldehydes (70-90% yield). 

When a-halo carbonyl compounds are used, the Arbuzov reaction (a) has as competitor the formation of an enol phosphate (i.e., formation of a P-O... 

First designated in 1887 by Hantzsch, the cyclization of a-halo carbonyl compounds by a wide diversity of reactants attached to the N-C-S portion of the ring is the most extensively popular process for formation of thiazoles. 

The formation of metal carbonyl clusters by reduction of the metal halides appears to occur via the formation of halo-carbonyl compounds as intermediate species. Thus, the reduction of halide derivatives is often a good alternative for the formation of clusters ... 

There are three important routes to the formation of the mercury-transition metal bond (a) displacement of halogen or pseudohalogen from mercury(II) salts with carbonyl metallate anions (b) reaction of a halo-phenylmercury compound with a transition metal hydride and (c) oxidative addition of a mercury halide to neutral zero valent metals.1 We report here the syntheses of three compounds containing three-centre, two-electron, mercury-ruthenium bonds utilizing trinuclear cluster anions and mercury(II) halides.2-4... 

The amide ions are powerful bases and may be used (i) to dehydrohalogenate halo-compounds to alkenes and alkynes, and (ii) to generate reactive anions from terminal acetylenes, and compounds having reactive a-hydrogens (e.g. carbonyl compounds, nitriles, 2-alkylpyridines, etc.) these anions may then be used in a variety of synthetic procedures, e.g. alkylations, reactions with carbonyl components, etc. A further use of the metal amides in liquid ammonia is the formation of other important bases such as sodium triphenylmethide (from sodamide and triphenylmethane). 

The addition of a-deprotonated alkyl halides to alkenes or carbonyl compounds can, because of the good leaving-group properties of halides, also lead to formation of cyclopropanes [292] or epoxides [187, 304, 306, 310], respectively. Because of the inherent instability of a-halo organometallic compounds, these intermediates should be handled carefully and on a small scale only. The ketone produced by the last reaction in Scheme 5.34 is probably formed by Oppenauer oxidation of the intermediate alcohol by the excess benzaldehyde [310],... 

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 addition of hydrogenphosphonates to chloroketones, and also to other mono halo-genated carbonyl compounds, is aided by the presence of AI2O3, yields of 78-96% being achievable. However, reactions between dialkyl or diphenyl hydrogenphosphonates and chloroacetone " ", 5 m-dichloroacetone or a ym-dichloroacetone " do occur in the absence of a catalyst when mixtures of reactants are heated to 100-120 °C the products are the phosphonates 173 (R = H or Cl). Aryl trichloromethyl ketones are mon-odechlorinated by the action of trialkyl phosphites or dialkyl hydrogenphosphonates and both further dechlorination and the formation of phosphate esters have been... 

The formation of a,P-epoxy carboxylic esters from carbonyl compounds and a-halo esters is not just an undesired side reaction, but is also an important synthetic method known as Darzens reaction. 

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