Nitrogen reaction with, phosgene

Nucleophilic centers of trifunctional carboxylic components naturally have to be masked before the formation of synunetric anhydrides. Ddz-tryptophane, for example, shows several side reactions with phosgene, whereas the same compound with formyl masked indole nitrogen results in an excellently pure symmetric anhydride [71] (Fig. 46). 

This section deals with the reactions of amino compounds with phosgene generated from its common source or phosgene equivalents, by a direct transfer of the chlorocarbonyl group, giving carbamoyl chlorides. Reactions of imines and other unsaturated (cyclic) nitrogen compounds with phosgene will be discussed later. 

Phosgene reacts with a multitude of nitrogen, oxygen, sulfur, and carbon centers. Reaction with primary alkyl and aryl amines yield carbamoyl chlorides which are readily dehydrohalogenated to isocyanates. Secondary amines also form carbamoyl chlorides. 

N-benzylaniline with phosgene, and then with sodium azide to produce carbonyl azide 52. On heating, nitrogen is evolved and a separable mixture of nitrene insertion product 53 and the desired ketoindazole 54 results. The latter reaction appears to be a Curtius-type rearrangement to produce an N-isocyanate (54a), which then cyclizes. Alkylation of the enol of 54... 

Amidines with a more complicated substitution pattern have been prepared from amidines by alkylation—either at nitrogen or at nitrogen substituents. - Variations at these positions have been achieved by heteroarylation, acylation,vinylation or carboxylation with phosgene, thio-phosgene, isocyanide dichlorides or isothiocyanates. Some interesting amidines, e.g. (347)-(3S2) (Scheme 59), have been prepared in this manner. The amidine skeleton can also be varied by halogen-ation, - hydrolysis, isomerization or catalytic hydrogenation or other addition reactions if there are C=—C double bonds present as in (353 equation 173) for example. ... 

In a surprising reaction, A/,A/ -diphenylmethylene diamine (a possible intermediate formed in the commercial production of TDI, see Section 4.7.1.1) reacts with phosgene by cleavage of a carbon-nitrogen bond to give a mixture of products [2086] ... 

Diethyl esters of -alkylamino phosphoric acid react readily with phosgene. Carbon dioxide and chloroethane are liberated, reaction occurring at the phosphoryi group in preference to the nitrogen atom [508] ... 

Condensation of anthranilic acid with various ort/zo-esters and reaction of semicarbazides, gave 2-substituted benzoxazin-4-ones and also by the reaction of hydrazones with aryl-/alkyl-ureas and by salicylaldehyde or 2-hydroxyacetophenones with 4-aryl-/alkyl-semicarbazides. Hydrolysis of o-aminoesters and subsequent treatment with phosgene gave 40. Fused oxazine with bridge head nitrogen 41 and triazolo[3,4-Z>]thiazines 42 were also prepared . The 2,3-dihydrobenzoxazine 43, thiomorpholines 44 and phenothiazines 45 were prepared. ... 

A more recent development of the same general type of reagent is 2,2-difluoro-1,3-dimethylimidazolidine (DPI), which is even more reactive, because of the stabilizing effects of two nitrogen atoms at the active center [124] (Scheme 2.55). By reaction with the inexpensive phosgene and subsequent nucleophilic fluorination the reagent can be recycled on an industrial scale. 

The reaction of phosgene with l,l-dialkyl-2-arylazoguanidines (28) yields 6-dialkylamino-3-aryl-1,2,3,5-tetrazin-4-ones (29) (Equation (3)). These products decompose on heating at 120°C to give nitrogen, dialkylcyanamides, and aryl isocyanates. The tetrazinones decompose in the same way... 

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