From a-bromo ketones

Joly s method (or modifications) is the best procedure for preparing A " -3-ketones and can be extended to the elimination of hydrogen bromide from a-bromo ketones of all types. Rearrangement is sometimes observed but is not often serious. Selectivity can be improved in some instances by lowering the reaction temperature. The method has been found useful for the preparation of A" -3-ketones from 6-halo-A" -3-ketones ... 

The methods previously used to obtain single aldol products (or their dehydrated derivatives) from reactants where several aldol products are possible8 include the reaction of bromozinc enolates, from a-bromo-ketones, with aldehydes 9 the reaction of bromomagnesium enolates, from either a-bromoketones or from ketones and bromomagnesium... 

This is the first time that the biotransformation of a-bromo and a,a -dibromo ketone using S. platensis has been successfully accomplished. Although enantioselective a-hydroxy ketones were not obtained, it was found that the hydroxylative biotransformation of a-bromo and o ,Q -(jibromo alkanones using S. platensis affords a new synthetic method, which is more convenient, cleaner, and of lower energy than the chemical method used heretofore (see Tables 12.7 and 12.8). Biotransformation for a-hydroxy ketone from a-bromo ketone is no doubt attributable to the special properties of S. platensis system. 

Reaction of halides with silver nitrate to give nitrate esters has been known for years, but its synthetic application is more recent. Komblum showed that the nitrate esters derived from a-bromo ketones and esters decompose smoothly with catalytic sodium acetate in DMSO to give the a-dicarbonyl compounds in high yield. It was found unnecessary to isolate the nitrate ester after reaction of the halide with silver nitrate the solution was filtered to remove AgBr, concentrated, and added to DMSO containing catalytic sodium acetate. The method complements the others for the synthesis of a-dicarbonyl compounds since it employs nonacidic, nonbasic conditions. Unfortunately, the method gave variable results with benzyl halides. The application of the method to bromo esters other than bromoacetates was not reported. Some related oxidations are shown in equations (41) and (42), and Schemes 9 and 10. The oxidation of an iminium salt is notable. 

Recently, Shchepin and coworkers described Michael addition reactions with zinc ketone enolates (144) for the preparation of chroman-2-one derivatives 146. The enolates were generated in situ from a-bromo ketones 143 by addition of excess zinc (equation 40), and subsequent conjugate addition to a, S-unsaturated ketones (145) (equation 40 ) provided chroman-2-ones (146a, b) in yields up to 82% . 

Alternatively, the ketone may be converted to the enol acetate and this may be brominated (Scheme 3.85). Elimination of hydrogen bromide from a-bromo ketones leads to a,P-unsaturated ketones. 

Vinylogous thioamides 33 (NRj = dimethylamino or morpholino) react with benzyl chloride to give thiophenes, while thienyl ketones are produced from a-bromo ketones (equation 22). 

A versatile method to generate p-ketophosphonates that cannot be generated through the Arbuzov reaction has been developed a-phosphonate enolates of cyclic ketones are obtained through sequential treatment of ketones wiA LDA, diediyl phosphorochloridate and LDA (Scheme Acyclic P-ketophosphonates can also be formed from a-bromo ketones (Scheme 8) and in a similar reaction a-trialkylsilyl enolates can also be obtained (Scheme 9).3 -36 Kuwajima and Takeda employed the reaction of ot-phenylselenylvinyl silyl ethers with lithium and di-methylaminoniq>hthalene (DMAN) to generate ot-silyl enolates (Scheme 10). ... 

Acyclic P-ketophosphonates can also be formed from a-bromo ketones (Scheme 8)35 and in a similar reaction a-trialkylsilyl enolates can also be obtained (Scheme 9).35,36... 

Aldol reaction. TrichlorosiloxyaUcenes are generated in a dehrominative silylation process from a-bromo ketones. Condensation with ArCHO leads to p-aryl enones. In the presence of the Lewis base Ph3PO the reaction is optimized. 

Conventionally the acyl derivatives of acyloins and benzoins may readily be obtained by reaction with acid anhydrides. The acyloin esters can more conveniently be prepared by allowing the corresponding a-bromo ketones and the sodium or potassium salts of the appropriate carboxylic acid to react, either in ethanol or in the acid to be esterified. The esters may not necessarily be isolated, and the oxazoles are obtained directly by adding the ammonium salt to, or passing ammonia through, the mixture, which is then boiled.84 The reaction then becomes useful for the preparation of oxazoles (53) from a-bromo ketones and carboxylic acids.84 121... 

Isoquinolinium salts (2) derived from a-bromo-ketones undergo Michael addition to ajS-unsaturated ketones in acetic acid, in the presence of ammonium acetate, to give 2,4,6-triaryl-pyridines (3) in yields ranging from 40 to 60% (Scheme 2). ... 

OAr From PTBD-resin (cf. Table 1.6.7, polymeric bases) by treatment with ArOH in MeCN.198 Alkyl aryl ethers from primary, allylic and benzylic bromides as well as from a-bromo ketones, esters and amides. Bis-aryl ethers from aryl fluorides. ... 

CyeUe 1,4-diketones from a-bromo ketones (cf. 5, 758). The intramolecular coupling of o-bromo ketones has been extended to synthesis of cyclic 1,4-dikc-tones (equations I and II). ... 

Sodium borate I potassium bromide I tetra-n-butylammonium iodide a-Imido- from a-bromo-ketones... 

A general route to 3-substituted butenolides (72), which could have considerable potential, is the cyclization of phosphonium salts (71), simply by treatment with triethylamine in methylene chloride. The salts are easily obtained from a-bromo-ketones and bromoacetic acid and, in the examples quoted in this preliminary study, overall yields are high except when 2-bromocyclohexanone was used as the ketonic component (c/. 3, 133). The 3-substituted butenolide group present in naturally occurring cardenolides can be built up from an a-methylthioketone residue by a Reformatsky reaction, followed by acid- and base-catalysed rearrangements. ... 

P-Ketophosphonates are valuable intermediates in the realm of Homer-Emmons alkenation methodology. Acyclic variants are difficult to obtain from enol phosphates due to competing alkyne and allene formation. One solution utilized the dianion derived from a-bromo ketones and trapping with diethyl phosphorochloridate however, only moderate yields of P-keto phosphonates were reported. The most efficient procedure utilizes the anion derived from dialkyl methylphosphonate, addition to an aldehyde, followed by oxidation (eq 8). ... 

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