Anilino-l-phenylimidazolin-4-one

The mixed anhydride obtained by reaction of ketene with monochloroacetic acid (12 g) is added to a suspension of 1,3-diphenylguanidine (21 g) in acetone (60 ml) cooled to 0°C. The temperature of the reaction mixture rises to 10-15°C, and a precipitate is deposited. This is filtered and washed with acetone, giving the hydrochloride salt of (18) (Ar = Ph) (11.2g, 40%), m.p. 235-236°C. Similarly prepared is (18) (Ar = p-tolyl) (38%). 

As mentioned earlier, the other main NCN synthons which are commonly available are ureas, thioureas and isothioureas, which condense with 

The common reaction of an a-bromoketone with excess urea and ammonium acetate in aqueous acetic acid (refluxed for about 3 h) to give 4-imidazolin-2-ones in 50-75% yields can be simplifled and adapted to a single-flask process from the original ketones. The ketone is initially brominated at 18-20°C in a mixture of acetic acid and urea, then, after the addition of 30% ammonia solution, the a-bromoketone which forms is heterocycUzed in about 40% yield by further heating ( 3 h) [42]. 

Cyanourea will react similarly with an a-haloketone to give 1-cyanoimidazolin-2-ones, which are readily hydrolysed to the 1-carbamoyl and ultimately to the 77-unsubstituted analogues [46]. 4-Amino-2(2//)-imidazolones can be made from urea and an o-ketonitrile [47]. 

5-Methylisothiourea is formally analogous to an amidine or guanidine (see also reactions of amidine sulfinic acids earlier in this chapter). It reacts readily with acylvinylphosphonium salts in much the same way as amidines to give 2-methylthio-4-imidazolylphosphonium salts, which can be converted into multifunctional imidazoles with recovery of triphenylphosphine [28]. 

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