From Curtius degradation

These compounds are easily prepared from the appropriate 2-aminothiazole and acyl chloride (see Section III.2.D) or by general heterocydization methods. Acyl chlorides may be replaced by the corresponding anhydrides (471). Acids themselves may be used as acylating agents provided that the imidazole-triphenyl phosphine mixture is used as a catalyst (472). The Curtius degradation of 247 yields 2-acetamido-4-phenylthiazole (248) (Scheme 149) (473). 

Special reactions of hydrazides and azides are illustrated by the conversion of the hydrazide (205) into the azide (206) by nitrous acid (60JOC1950) and thence into the urethane (207) by ethanol (64FES(19)105Q) the conversion of the same azide (206) into the N-alkylamide (208) by ethylamine the formation of the hydrazone (209) from acetaldehyde and the hydrazide (205) and the IV-acylation of the hydrazide (205) to give, for example, the formylhydrazide (210) (65FES(20)259). It is evident that there is an isocyanate intermediate between (206) and (207) such compounds have been isolated sometimes, e.g. (211). Several of the above reactions are involved in some Curtius degradations. 

Pyrimidine-5-carboxamide, 4-amino-purine synthesis from, 5, 582 Pyrimidine-5-carboxamide, 4-amino- N- pheny synthesis, 3, 122 Pyrimidinecarboxamides Curtius degradation, 3, 82 dehydration, 3, 82 Hofmann degradation, 3, 82 hydrolysis, 3, 81 reactions, 3, 81 synthesis, 3, 127 Pyrimidinecarboxamides, thio-synthesis, 3, 128... 

Putrescine dihydrochloride has been prepared by the Hofmann degradation of adipamide 3.. s by the Curtius degradation of adipyl hydrazide through the urethane by the Curtius degradation of adipyl azide obtained from adipyl chloride and sodium azide by the Schmidt degradation of adipic acid with hydrogen azide by the reduction of succinonitrile, succinaldoxime, or 7-phthalimidobutyronitrile with sodium and from N-ben-zoyl-7-iodobutylamine ... 

Aminopyrazole has been prepared by a Curtius degradation of pyrazole-3(5)-carboxylic acid hydrazide,2 3 by saponification and decarboxylation of ethyl 3-aminopyrazole-4-carboxy-late 4 obtained from ethyl ethoxymethylenecyanoacetate and hydrazine, and by the present procedure.6,6... 

Conversion to carbamates. Cyclic carbamates derived from sugars and related compounds have repeatedly been encountered, the first being an inosamine derivative, obtained by Curtius degradation of dihydroshikimic acid.82,83... 

Cope and LeBel (60JA4656) prepared the cis laetone 81 from eyclo-pentane-c -l,2-dicarboxylic anhydride and converted it to the hydrazide 82. Curtius degradation of 82 gave the cyclic urethane 83. 

Several derivatives of lH-cycloprop[/]indene have been synthesized. The di-fluoro compounds 212 (X = 0,S) were obtained by the cycloaddition route from 188 in analogy to the synthesis of 191 and 192. The cycloaddition of diene 213 to 1,2-bromochlorocyclopropene (27) provided 214, which was aromatized to 217. Twofold Curtius degradation of 214 afforded the ketone 215. While attempted aromatization of 215 with base afforded no cycloproparene, the corresponding alcohol 216 reacted with base to 218 in acceptable yield. The alcohol 218 is also accessible from 219. ... 

Two examples illustrate the formation of amino groups at 1- or 2-positions of dibenzopyridoazepines the route from carboxylic acid 354c by Curtius degradation through mixed anhydride to yield amine 391... 

Indanone was first prepared by distillation of the calcium salt of o-phenylenediacetic acid2 3 and, more recently, by the action of acetic anhydride on its potassium salt.4 It has been obtained by the dilute sulfuric acid-catalyzed hydrolysis and decarboxylation of 2-iminoindan-l-carboxylate6 and ethyl 2-indanone-l-carboxylate.6 2-Indanone is commonly obtained by acid-catalyzed dehydration of an indene glycol,7 8 as illustrated in this preparation. Indene glycol has been obtained from indene via the bromohydrin.9-12 The most recent preparation of 2-indanont is by Curtius degradation of 2-indenecarboxylic acid.13... 

Support-bound isocyanates can be conveniently prepared from carboxylic acids by Curtius degradation. Because the reaction of the intermediate acyl azides with alcohols to yield esters is slow, Curtius degradation can be conducted in the presence of alcohols to yield carbamates directly (Entries 4 and 5, Table 14.8). 

Curtius degradation of acyl azides a. acyl azide from hydrazide... 

Curtius degradation of acyl azides (obtained from acid chlorides)... 

Aminoisothiazoles are readily available by direct ring synthesis (see Section I,B), and most of those described in the literature have been prepared in this way. However, those methods do not lead to 3-chloroisothiazoles, and 5-amino-3-chloro-4-cyanoisothiazole was prepared in excellent yield from 3,5-dichloro-4-cyanoisothiazole and ammonia.8,51 5-Aminoisothiazole itself has been prepared by Curtius degradation of isothiazole-5-carboxylic acid (Scheme 31),115 although a triketotriazine has also been obtained under Curtius conditions.116... 

Arylfurazancarboxamides on treatment with alkaline hypochlorite undergo Hofmann degradation to the amines likewise carbamates result from Curtius rearrangement of furazanylacyl azides in the presence of alcohols. 

Isocyanates of fluorinated compounds can readily be obtained either from trimethylsilyl isocyanate and, e.g. trifluoroacetyl chloride, with yields of isocyanate in the region of 64%. or more conveniently by Curtius degradation of fluorinated acid chlorides. ... 

The acid chloride of phenothiazine-1-carboxylic acid has been prejDared by treating the acid with the calculated amount of PCI5 in benzene, thus avoiding ring chlorination -(see Section V, A, 1, d). Another way to prevent ring chlorination in this reaction is first to acylate at position 10. ° Some amides have been prepared from phenothiazine carboxylic acid chlorides - ° and Curtius degradations performed. ... 

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