Hydrogenation imidoyl chlorides

As in the Skraup quinoline synthesis, loss of two hydrogen atoms is necessary to reach the fully aromatic system. However, this is usually accomplished in a separate step, utilising palladium catalysis to give generalised isoquinoline 6.14. This is known as the Bischler-Napieralski synthesis. The mechanism probably involves conversion of amide 6.12 to protonated imidoyl chloride 6.15 followed by electrophilic aromatic substitution to give 6.13. (For a similar activation of an amide to an electrophilic species see the Vilsmeier reaction, Chapter 2.)... 

A practically useful method for synthesis of selenoesters has been developed by Barton et al. A wide range of aliphatic and aromatic selenoesters have been synthesized from the appropriate N -disuh-stituted imidoyl chlorides (58) using sodium hydrogen selenide to introduce seleniumJ Imidoyl chlorides (58) can be obtained by the reaction of amides with phosgene. Representative results are shown in Scheme 17 (formulae 59-61). 

The reaction of an imidoyl chloride with sodium hydrogen selenide gave high yield of the selenoamide (equation 33). ° ... 

Nitriles react with phosgene only in the presence of hydrogen chloride, to give either 1,2-unsaturated isocyanates or N-heterocyclic derivatives. The reactions are really those between COClj and the imidoyl chlorides or 1-chloroenamines, since these are the materials formed, reversibly, as equilibrium mixtures when hydrogen chloride adds to nitriles [2229] ... 

EtCN and PrCN gave the pyrimidine derivatives as major products, and PhCHjCHjCN gave the isocyanate as the major product when the quantity of benzene solvent was increased. Isocyanates may be considered to be produced via the formation of the imidoyl chloride and subsequent reaction to give the corresponding (V-carbamoyl chloride, followed by the loss of hydrogen chloride. 

The cyclotrimerization of nitriles can be catalyzed by acids resulting in symmetrically substituted 1,3,5-triazines. These reactions proceed via adducts of the acid and the nitrile or via the corresponding imidoyl chloride,141 145 e.g. 29 for the hydrogen chloride catalyzed reaction. 

Huisgen and his co-workers190 have recently reported that the addition of aromatic nitrile ylides to carbonyl compounds results in the formation of A3-oxazolines, which are easily oxidizable to oxazoles. Typically, benzonitrile 4-nitrobenzylide (131, Ar = p-OsNC6H4), generated from the imidoyl chloride (130) by 1,3-elimination of hydrogen chloride with triethylamine, reacts smoothly with benzaldehyde to give a pair of... 

Sohn and Muller458 have allowed ethereal hydrogen tetrachlorostannate(n) to react with imidoyl chlorides, obtaining thereby good yields of aldehydes in... 

In the reaction of N-substituted carboxylic acid amides with phosphorus pentachloride generally the corresponding free imidoyl chlorides (I) or their hydrochlorides (II) (iminium chlorides) are formed. If the iminium chlorides are obtained initially, dehydrochlorination can be achieved by simply heating or using a stronger base, such as triethylamine, as the hydrogen chloride scavenger. 

The isomerization of the imidoyl chlorides, having adjacent hydrogens, is also evidenced by their rapid reaction with bromine. The bromine adducts XII can eliminate hydrogen chloride to form the imidoyl bromide XIII, or eliminate hydrogen bromide to yield the imidoyl chloride XIV ( ). 

If an excess of phosphorus pentahalides is used on aliphatic carboxylic acid amides, having a-hydrogens, further halogenation occurs. For example, the reaction of propionic acid ethylamide (XV) with 3 equivalents of phosphorus pentachloride yields the imidoyl chloride XVI, which can also be obtained from a,a-dichloropropionic acid ethylamide (XVII) and one equivalent of phosphorus pentachloride (5 ). 

Imidoyl chlorides of aromatic carboxylic acids ( ). An equimolar mixture of the N-monosubstituted amide and phosphorus pentachloride is heated for 15-180 min at 60-140 C. After completion of the reaction, which is indicated by the cessation of hydrogen chloride evolution, the phosphoryl chloride is removed under reduced pressure, and the remaining imidoyl chloride is distilled under vacuum. The reported yield ranges from 41-96%, but generally yields of 80-90% are obtained. 

The generation of imidoyl chlorides from nitriles and hydrogen halides in the presence of a suitable Lewis acid accounts for the formation of ketones in the Houben-Hoesch reaction (see Section IVD). 

Cyclization of o,cu-dinitriles in the presence of anhydrous hydrogen halides affords cyclic imidoyl chlorides. For example, addition of hydrogen bromide to succinonitrile causes an immediate precipitation of the imidoyl bromide XL, ... 

The elucidation of the structure of the hydrogen halide adducts of nitriles is rather difficult, because imidoyl chlorides and iminium chlorides which are unsubstituted on nitrogen are rather labile. They generally undergo... 

In the reaction of o-thiocyanatobenzoyl chloride with hydrogen chloride the thiazinone LIII is obtained, presumably via the imidoyl chloride LIV. In the absence of hydrogen chloride no reaction occurs ( " ). 

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