Chlorodimethylformiminium chloride

Isonitriles.1 Isonitriles can be prepared in 70-95 % yield by dehydration of forma-mides in a DMF solution of chlorodimethylformiminium chloride, prepared in situ from... 

Another interesting application of iminium chlorides in organic synthesis involves their use as catalysts in the conversion of carboxylic acids to carboxylic acid chlorides ( ), carbamates to isocyanates ( ), amino-acids to isocyanato acid chlorides and arylamine hydrochlorides to isocyanates In these reactions chlorodimethylformiminium chloride is being used, because it is readily available. However, other imidoyl halides could react in a like manner. 

A recent study related to the structure of chlorodimethylformiminium chloride and chlorotetramethylformamidinium chloride showed that both compounds are completely in the polar form as evidenced by spin-spin coupling between the olefinic proton in the former, which appears at lower field, and the N-methyl protons, which are at higher field. Likewise, the carbon-13-proton coupling constant indicated a positive charge on the nitrogen ( ). 

Martin and Martin ( ) have also investigated the NMR spectra of intermediate complexes formed in the Vilsmeier-Haack reaction. These authors show that the NMR spectrum of chlorodimethylformiminium chloride is similar to that of the DMF-POCI3 complex. The chemical shift... 

Evaporation of the solvent affords the pure chlorodimethylformiminium chloride, m.p. 140-145 C, in virtually quantitative yield. 

The iminium halides, with the exception of the fluoro compounds, have a polar structure, as evidenced by conductivity measurements single-crystal neutron defraction studies nd NMR work (206.215 For example, chlorodimethylformiminium chloride in sulfur dioxide was shown to be completely in the polar form. Further evidence is provided by the salt-like character of the compound, and by its characteristic C=N absorption at 1621-1681 cm (see Table VI). 

N,N-Dimethylforrmmide dimethylacetal To a solution of 128 g (0.1 mole) of chlorodimethylformiminium chloride (see page 63) in 640 ml chloroform a solution of 48 g of sodium in 1000 ml of methanol is added dropwise at 0°C. After stirring for one hour at room temperature the solvent is evaporated, and vacuum distillation of the residue yields 65 g (55 %) of N,N-dimethylformamide dimethylacetal, b.p. 104°C. 

The reaction of chlorodimethylformiminium chloride with alcohols has been utilized to synthesize the corresponding alkyl halides (122,234,235 and only a catalytic amount of N,N-dimethylformamide is necessary for conversion of an alcohol into the corresponding alkyl halide, using carbonyl chloride or thionyl chloride as the halogenating agent ( 22.143 p j. example. 

It is not necessary to use phosphorus oxychloride complexes of formamides, because Roh and Kochendorfer in 1937 demonstrated that the iminium chlorides themselves react similarly and Bosshard and Zollinger have shown that comparable yields can be obtained using chlorodimethylformiminium chloride as the reagent. However, in the synthesis of diarylketones good yields are only obtained when the phosphorus oxychloride complex of the corresponding arylcarboxylic acid amide has been used The synthesis of ketones from carboxylic acid amides, phosphorus oxychloride and suitable substrates predates the aldehyde synthesis by approximately 40 years but it is of only limited usefulness because side reactions are very often encountered... 

Methylenecyclohexan (CXXXIV) affords the 1 2 adduct CXXXV upon treatment with chlorodimethylformiminium chloride... 

Acetylenes undergo rapid reaction with chlorodimethylformiminium chloride (233,3io example, phenylacetylene yields a-chlorocinnamic aldehyde (CXXXVI)... 

Similar reactions occur on treatment of benzalaniline, carbodiimides, phenyl isocyanate and N-sulfinylaniline with iminium chlorides For example, from chlorodimethylformiminium chloride and phenyl isocyanate the 1 1 adduct CXXXVII is obtained, which on thermolysis (with elimination of carbonyl chloride) or hydrolysis yields the formamidine CXXXVIH... 

Ketones which have hydrogen atoms adjacent to the carbonyl group, react with chlorodimethylformiminium chloride to afford jS-chlorovinyl-aldehydes (i i5 3i2j Yot example, cyclohexanone and chlorodimethylformiminium chloride afford l-formyl-2-chlorocyclohexene (CXXXIX) (224.312 ... 

In contrast, cyclic ethers afford the corresponding a-chloroalkyl-formates on treatment with chlorodimethylformiminium chloride ( o.sio For example, reaction of ethylene oxide and chlorodimethylformiminium chloride gives rise to the formation of the formate CLI... 

In some instances ring closure with formation of aromatic compounds occurs when unsaturated ketones are treated with chlorodimethylformiminium chloride (28-154 example, the ketone CLIII affords the dialdehyde CLIV upon reaction with DMF and carbonyl chloride... 

Likewise, nicotine aldehyde can be obtained from 1-dimethylamino-butadiene and chlorodimethylformiminium chloride ( ). 

Another cyclization sequence involves the reaction of propioveratrone (CLV) with chlorodimethylformiminium chloride, in which the intermediate iminium chloride CLVI cyclizes at elevated temperature to yield the indene derivative CLVII ( ). 

Tris-formylmethane (CLVIII) is obtained upon reaction of ) -dimethyl-aminoacroleine with chlorodimethylformiminium chloride ( ). 

Arnold treated chlorodimethylformiminium chloride with hydrogen cyanide, and he obtained dimethylaminomalonitrile (CLXII) in 45-50% yield. 

The reaction of imidoyl chlorides with 4-dimethylaminophenyllithium occurs in a similar manner, affording the corresponding ketone Iminium chlorides, such as chlorodimethylformiminium chloride, react with phenylmagnesium bromide to yield a mixture of benzene and the tertiary amine CLXXX... 

The reaction of chlorodimethylformiminium chloride (XXII) with diazoketones and ethyl diazoacetate gives rise to the formation of a-diazo-aldehydes XXIII ( ). In contrast, diazomethane undergoes reaction with XXII to yield 2-dimethylamino-l,3-dichloropropane ( ). 

The extremely useful and reactive isocyanides have received considerable attention. Walborsky has reported that chlorodimethylformiminium chloride, prepared in situ from thionyl chloride and DMF, dehydrates a wide range of formamides to isocyanides (Scheme 66) the requisite formamides... 

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