From halo acyl halides

The thiazolidin-4-one ring system has a wide variety of physiological activity, and its chemistry has been well investigated. By contrast, the 5-ones have been little studied. They are readily formed from thioureas and a-halo-acyl halides, e.g. (312). However, a slight modification of the substrate can lead to a variety... 

Oxazoles (191) are producedwhen triphenylphosphine is treated simultaneously with an a-azidocarbonyl compound and an acyl halide. The intermediate iminophosphoranes (189) react with the acyl halide before they can react with themselves to give pyrazines. Elimination of phosphine oxide from the resulting salts may give the intermediate halo-genoimines (190), or the oxazoles may be formed via the betaines (192). 

Formation of Acyl Halides from Carboxylic Acids Halo-de-hydroxylation... 

Formation of Acyl Halides from Acid Derivatives Halo-de-acyloxy-substitution Halo-de-halogenation... 

Alkenes were reacted with thallium triacetate and azidotrimethylsilane to give 0-azidoalkyl thallium compounds, which were converted in situ to aziridinylazothallium compounds70,71. Only in the case of norbornene derivatives were the initial adducts (cxo.cw-azido-thallium compounds) isolated72. The aziridinylazothallium compound derived from cyclohexene 1 underwent thermal decomposition to give the trans-1,2-diazide, 2 in low yield. However, on treatment with acyl halides or trifluoroacetic anhydride, compound 1 afforded the corresponding 0-halo or 0-trifluoroacetoxy azides70. 

Although hydrolysis of acyl halides and anhydrides is infrequently used in the preparation of acids, several important examples are noted. The acyl chlorides, ArjC = CHCOCl, from the action of oxalyl chloride on di-arylethylenes are hydrolyzed to yS,yS-diarylacrylic acids by stirring with ice-cold sodium carbonate solution. a-Halo acids prepared by the Hell-Volhard-Zelinsky reaction are obtained from the a-halo acid halide by stirring with cold water (method 67). 

A thiazole ring may also be constructed from a lactam thiocarbonyl and one of the following reagents DMAD [3177], a 2-bromoacrylic acid or its nitrile [20S1, 3509], an aryl isothiocyanate and an alkyne [2706, 2915], a reactive a-methylene ketone such as dimedone [3944], an acyl halide [2433] or a halo ketone which is prepared in situ [2475]. 

This reaction was first reported by Nenitzescu in 1931. It is the formation of an a,p-unsaturated ketone directly by aluminum chloride-promoted acylation of alkenes with acyl halides. Therefore, it is known as the Darzens-Nenitzescu reaction (or Nenitzescu reductive acylation), or Nenitzescu acylation. Under such reaction conditions, Nenitzescu prepared 2-butenyl methyl ketone from acetyl chloride and 1-butene and dimethylacetylcyclohex-ene from acetyl chloride and cyclooctene. However, in the presence of benzene or hexane, the saturated ketones are often resolved, as supported by the preparation of 4-phenyl cyclohexyl methyl ketone from the reaction of cyclohexene and acetyl chloride in benzene, and the synthesis of 3- or 4-methylcyclohexyl methyl ketone by refluxing the mixture of cycloheptene and acetyl chloride in cyclohexane or isopentane. This is probably caused by the intermolecular hydrogen transfer from the solvent. In addition, owing to its intrinsic strain, cyclopropyl group reacts in a manner similar to an oleflnic functionality so that it can be readily acylated. It should be pointed out that under various reaction conditions, the Darzens-Nenitzescu reaction is often complicated by the formation of -halo ketones, 3,)/-enones, or /3-acyloxy ketones. This complication can be overcome by an aluminum chloride-promoted acylation with vinyl mercuric chloride, resulting in a high purity of stereochemistry. ... 

The P-halo ketone intermediates formed in the foregoing reactions arise from the capture of carbocationic intermediates by halide of the gegenions. In some cases, solvents such as acetonitrile can act as the competing nucleophilic species. For example, P-amido ketones could be obtained by the acylation of alkenes in acetonitrile (172). 

An efficient method for the formal abstraction of oxide from acyl ligands was developed in our laboratory 44). Oxalyl halides react directly with the pentacarbonylmetal acyl complexes of chromium, molybdenum, and tungsten to form the fra ,s-alkylidyne(halo)tetracarbonyl complexes [Eq. (5)]. Other suitable Lewis acids are COCI2, CI3COCI, CI3COCOCI, and... 

---