Imidoyl ketenimines

Alkylidene-2,3-dihydro-l,3,5-thiadiazines (196) are produced slowly in [4-p2] cycloadditions of A-imidoyl ketenimines (195) with diarylthioketones in warm toluene (Equation (13)) <85LA2305>. 

Likewise, imidoyl ketenimines 153 react as 1-aza-1,3-dienes in [4-1-2] cycloaddition reactions with phenyl isocyanate to give the cycloadducts 154 (62-67 % yields) or with tosyl isothiocyanate to give the cycloadducts 155 (62-69 % yields) . ... 

Also, upon refluxing in benzene, the imidoyl ketenimine 156 undergoes intramolecular cyclization to give 157 in 71-82 % yield . 

Similarly, the imidoyl ketenimine 158 undergoes an intramolecular [4-1-2] cycloaddition to give the quinazoline derivative 159 in 65 % yield . 

Iminoalkylidenetriphenylphosphoranes result from the transylidation reaction of methylenetriphe-nylphosphorane with imidoyl chlorides (equation 76), or from Michael addition of ylides to the C—43 bond of ketenimines (formed from carbodiimide and ylides in the initial step). 

For example, Dimroth treated thioamides, derived from isothiocyanates and malonates, with phosphorus pentachloride, and he obtained the corresponding imidoyl chlorides (III), which can be dehydro-chlorinated to produce the ketenimines IV. 

In addition to azomethines and oximes, various heterocumulenes, such as ketenimines, isocyanates and isothiocyanates, can be used to synthesize imidoyl chlorides. For example, addition of chlorine to ketenimines LXIX affords a-chloroimidoyl chlorides LXX... 

The elimination of hydrogen chloride from imidoyl chlorides is also the standard method of synthesis of ketenimines CLXVIII (4 5,106,237,271 ... 

Imidoyl bromides are also obtained when oximes are treated with the phosphonium salt XV. For example, reaction of XV with the oxime XVI produces the imidoyl bromide XVII, which can be dehydrohalogenated to the ketenimine XVIII by means of triethylamine ( ). 

Yields are only moderate (20—49%) and the ketenimines are accompanied by resinous by-products. Alternative routes to bis(fluoroalkyi)ketenimines involve dehydrofluorination of 2Sf-imidoyl fluorides, or treatment of the dangerously toxic perfluoroisobutene with mixtures of primary and tertiary... 

Oxoketenimines (IR, 2076 cm ) are formed in a thermal rarrangement from imidoyl ketenes. The oxoketenimines are stable up to 0 °C. A-2-carbonylphenyl ketenimines undergo a [1,5] migration to produce vinylimino ketenes (see Section 4.1) . 

Some ketenimines, such as 169, undergo a thermal rearrangement to produce the isomeric imidoyl ketenes 170, which undergo intramolecular cyclization to give the quinolones 171. 

---