Nitrophenyl isocyanate reagent

Nitroindole 418 Nitrophenyl isocyanate reagent 77 1-Nitropyrene 61 N-Nitrosamines 107... 

British Drug Houses Ltd. or Matheson Laboratory reagent-grade phenyl isocyanate was used without further purification. When using other isocyanates, care should be taken to ensure their purity as the yield is greatly dependent upon this, commercially available p-nitrophenyl isocyanate being a case in point. 

Amines can be linked to polymeric alcohols as carbamates. Carbamate attachment of amines can be achieved by reaction of isocyanates with alcohol linkers, or by treatment of alcohol linkers with phosgene [339,427,428] or a synthetic equivalent thereof, followed by exposure to the amine (Figure 3.26). The reagents most commonly used for the activation of alcohol linkers are 4-nitrophenyl chloroformate [69,429-436] and carbonyl diimidazole [427,437-440], The preparation of support-bound carbamates is discussed in Section 14.6. 

New 2-aryl-l,2,4-triazin-3-ones and 2-aryl-l,2,4-tri-azepin-3-ones were prepared in a three step reaction sequence from readily available aryl isocyanates and aminoacetals or ketals. The key step in the reaction scheme was the formation of 2-arylsemicarbazides by the treatment of arylureas with the aminating reagent 0-(4-nitrophenyl)hydroxylamine. 2-Aryl-1,2,4-triazin-3-ones... 

The results of this reaction sequence are summarized in Scheme 3. Reaction of phenyl isocyanates with methylaminoacetaldehyde dimethyl acetal gave the corresponding ureas (5) in 90-95% yields. The urea was then treated with sodium hydride, and after the reaction mixture had cooled to 5°C, the aminating reagent was added all at once. Of three aminating reagents-O-(mesitylenesulfonyl) hydroxylamine (2), 0-(2,4-dinitrophenyl)hydroxylamine (3.) and 0-(4-nitrophenyl)hydroxylamine (2), the latter was preferred as it is a stable, recrystallizable solid. The crude product from this reaction mixture consisted of the semicarbazide and the urea which are conveniently separated by flash chromatography (silica gel). 

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