Chloroiminium salt

Formation of angular-substituted dimethylene-bisimidazole derivatives 386 has been achieved by reaction of the parent bisimidazole 385 with either l-bromo-2-chloroethane or 1,2-dibromoethane (Equation 102) <1997CJC28>. Reaction of the bisimidazole with a bis-chloroiminium salt has also been used to generate a related core structure <2006T731>. 

Table 2.5. Heteroatom-substituted carbene complexes prepared from chloroiminium salts.

The Vilsmeier-Haack reagent, a chloroiminium salt, is a weak electrophile. Therefore, the Vilsmeier-Haack reaction works better with electron-rich carbocycles and heterocycles. 

Chloroiminium salts, for example (102), give either oxadiazoles (103) or (104) depending on the basicity of the solvent (Scheme 42) <65CB1293>. 

Thus, whilst acid-hydrolysis of 21 provided 27, N-methylation of the former followed by treatment of the resulting chloroiminium salt 29 with aqueous alkali generated 28. A later report [14] described a shorter route to 28 which involved a mild Bischler-Napieralsky reaction of the tertiary carbamate 30 secured from 20 by N-methylation, with a mixture of trifluoro-... 

Keywords amino carbene, bis(trimethylsilyl)mercury, chloroiminium salt... 

For this reaction, we added a solution of bis(trimethylsilyl)mercury (in THF) to the suspension of the chloroiminium salt in THF at low temperature and allowed the reaction mixture to warm to room temperature. After about one hour, we obtained a clear yellow solution and a drop of mercury. After separation of the metal and evaporation of the solvent the carbene was isolated. 

Starting from the chloroiminium salt we performed the reaction with bis(trimethylsilyl)mercury at low temperature in THF. 

Hexamethylphosphoramide, (MejN)3P=0, reacts with phosgene to give an interesting chlorophosphonium salt, in a manner similar to the formation of chloroiminium salts (Vilsmeier reagents) cf. Sections 10.2.2.3 and 10.2.7 [1638] ... 

Amides, for example Nyv-dimethylcarboxamides, represented by the general formula (109), react with salt (1) to yield chloroiminium salts (110 Scheme 9). Hydrolysis of these salts affords 2-dimethylamino-methylene amide derivatives (111). If group R in salt (110) is hydrogen, further reaction with salt (1) is possible, giving chloroiminium salts (112). Hydrolysis of these salts (112) affords aldehydes (113). 

Another acylation procedure uses iminium salts rather than acyl halides. The Vilsmeier-Haack reaction is a well-known process illustrated by reaction of pyrrole with the POCI3 complex of N,N-dimethylacetamide (207, which can decompose to a chloroiminium salt). The acylation reaction gave 208, which was converted to 2-acetylpyrrole by hydrolysis with aqueous sodium acetate.A synthetic example is taken from Lai s synthesis of indole analogs of mycophenolic acid,l in which 209 reacted with POCI3 and DMF to give a 77% yield of the aldehyde 210. 

Thwamides. Conversion of amides to thioamides is accomplished by exposing the corresponding chloroiminium salts to the tetrathiomolybdate reagent. 

Chloroiminium salts produced as shown below are excellent synthons for 1,3-dicarbonyl compounds and can be used in the context of reaction with glycinate. 

Formation of Chloroiminium Salts. Oxalyl chloride reacts... 

For example, efficient syntheses of thioamides and thio-lactams are based on this methodology. Certain types of chloroiminium salts can serve as precursors for high-energy synthetic intermediates. Thus, azomethine ylides were obtained by treatment of -acylamino carboxylic esters with oxalyl chloride (eq 24). ... 

Chloroiminium salts prepared from formaldehyde led to amino-chlorocarbenes when treated with base (eq 25). ... 

The Vilsmeier-H2iack reagent, a chloroiminium salt, is a weak electrophile. Therefore, the Vilsmeier-Haack reaction works better with electron-rich carbocycles and heterocycles. Since pyrrole is very electron-rich, the Vilsmeier-Haack reaction readily takes place. Formylation of methyl pyrrole-2-carboxylate was achieved using the Vilsmeier-Haack reaction. The mechanism is shown below. The resulting methyl 5-formylpyrrole-2-carboxylate, in turn, was converted into nonpeptidic analogues of neurotesin(8-13), which are potential treatment for neuropsychiatric diseases such as schizophrenia and Parkinson s disease. 

A soln. of the startg. unsatd. chloroiminium salt in morpholine heated 2 hrs. on... 

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