Chloroformamidinium chlorides

Synthesis of Carbocyclic and Heterocyclic 7r-Electron Systems with Pentafulvenoid Chloroformamidinium Chlorides K. Hafner and H.-P. Krimmer, Angew. Chem., Int. Ed. Engl., 1980,19, 199-201. 

Asymmetric esterification of benzoic acid with racemic (l-bromoethyl)benzene was performed with chiral cyclic guanidines as stoechiometric bases4 the ester was obtained with ee below 15%. The chiral guanidines 6 were obtained from a chiral diamine of C2 symmetry which was tranformed first to urea and then to several guanidines through an intermediate chloroformamidinium chloride (Figure 4). 

Acylation reaction which affords chloroformamidinium chloride is of great interest for the commercial synthesis of carbodiimides, especially dicyclohexylcarbodiimide (see volume 2). 

The reaction of phosgene with substituted ureas is well known. Phosgene reacts with tetrasubstituted ureas as a chlorinating agent to afford chloroformamidinium chlorides in high yields. This topic will be discussed in volume 2. 

In the case of N,N -dialkyl ureas, phosgene is attacked by both oxygen and nitrogen atoms to give a mixture of chloroformamidinium chlorides (A) (0-acylation of the ureas) and allophanoyl chlorides (B) (N-acylation) as shown in scheme 155 (Ref. 211). 

Chloroformamidinium chlorides (29) are generated from DMF and oxalyl chloride in acetonitrile. After addition of the carboxylic acid the activated ester (26f) is formed and treated with a solution of the alcohol in pyridine. Phenyl, alkyl and even r-butyl esters may be prepared in yields of greater than 80% (equation 11). Reagent (31), accessible from (30) and oxalyl chloride (equation 12) behaves quite similarly to (29). The use of silyl esters (26g), which are formed in situ in Ae presence of the alcohol and react then to the esters, has already been mentioned in Section 2.2.1.2.1. An application is described in Table 1. 

Since the cyclic ureas can be obtained from 1,2-diaminoalkanes and CO 2. this reaction represents a potentially useful method for the industrial production of diisocyanates. In contrast, a cyclic chloroformamidinium chloride is obtained from 1,3-dimethyl-... 

Owing to the greater nucleophilic character of sulfur relative to oxygen, reaction of 1,3-disubstituted thioureas with phosgene usually occurs at the sulfur atom, to give high yields of chloroformamidinium chlorides [2083a, 2087] ... 

Reaction of thioureas with phosgene is usually performed at room temperature in an inert solvent (such as benzene, chlorobenzene or 1,2-dichloroethane) in which the thiourea is soluble. By-products, if formed, are readily separated with ethoxyethane in which the chloroformamidinium chloride salts are insoluble. 

In the reaction of dialkyl cyanamides with carbonyl chloride 2 1 adducts XXV are initially formed, as evidenced by the isolated oligomeric chloroformamidinium chloride (XXVI), which is obtained in high yield ( ). 

The reaction of chloroformamidinium chlorides with alkoxide ion yields urea acetals XLV however, free alcohol has to be avoided, because solvolysis of the urea acetals to the ortho esters XLVI occurs ( ). 

The reaction of the chloroformamidinium chloride XLVIII with three moles of alcohol at 0°C produces the oligopseudo urea XLIX, which upon subsequent reaction with aqueous ammonium hydroxide at room temperature yields the triazine derivative L ( ). 

The reaction of the chloroformamidinium chloride LVII with ammonia produces, depending upon the reaction conditions, the triazine derivatives LVIII and LIX ( ). 

Heating of the chloroformamidinium chloride LXVII at 180-190°C produces the triazine derivative LXVIII in 80% yield ( ). 

The cyclic analogs of chloroformamidines are virtually unknown. Suzuki mentioned the synthesis of 2-chloroimidazolidine but reported no physical constants. The cyclic chloroformamidinium chloride XXV can be obtained from l,3-dimethylimidazolidine-2-one (XXVI) and carbonyl chloride, but this reaction is considerably slower than the phosgenation of the tetrasubstituted linear urea C ). 

Reaction of chloroformamidinium chloride (XXXVII) (cyanamide dihydrochloride) with diethyl iminocarbonate yields diethyl N-cyano-imidocarbonate (XXXVIII) ( ). 

Chloroformamidinium chloride also undergoes rapid reaction with (SbCl4N3)2 to produce the azide XXXIX... 

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