From hydrazides

2-Formylpyrazine has been prepared by the McFadyen-Stevens method. 2-(2 -Benzenesulfonylhydrazino)carbonylpyrazine heated with sodium carbonate at 150-170° gave formylpyrazine (isolated as its thiosemicarbazone) (138), also obtained as distillate when the reactants were heated at 120°/3mm (1201), but Fand and Spoerri (1323), from the attempted reaction with sodium carbonate in ethylene glycol at 160°, were unable to isolate 2-formylpyrazine instead 2-(2 -pyrazinoyl-hydrazinocarbonyl)pyrazine, 2-carboxypyrazine, and other products were obtained. 

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The esters 35 are obtained by reaction of hydrazides 34 with chloroformate esters or carbonic diesters 3 23 28 42 as previously discussed for the special case of the activated esters (see Section 10.4.2). The amides 36, on the other hand, are formed from hydrazides 34 with isocyanic acid 3,43,44 or with trimethylsilyl isocyanate 42 (Scheme 10). 

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

Another approach to the synthesis of simultaneously b- and e-fused heterosystems containing l,3-thiazin-4-one fragments is based on the use of a thiazinone ring prepared in advance. Thus, 2-imino-3-amino-TA 79, obtained from hydrazide 198, was applied to the syntheses of triazolobenzo-TAs 199,200, and 201 (75MI1). Amine 201 may be obtained from hydrazide... 

Scheme 6.1.8. Detachment of peptides from hydrazide resins.

Scheme 4 Synthesis of hydrazone linkages from hydrazide and aldehyde compounds...

Alkyl nitrites and nitrogen tetroxide together with acid are also effective for the formation of acyl azides from hydrazides under anhydrous conditions. As shown in Scheme 16, the Curtius reaction is especially suitable for the formation of complex reactive molecules. 

Spiroquinazolines (114) can be obtained from hydrazides 104 and cyclohexanone (X = CH2) or l-methyl-4-piperidone (X = NMe).176 y-Ketocarbox-ylic acids as 2-acetylpropionic acid (115) form the condensed quinazolones 116 or 117, depending on the substitution of the ring and hydrazine nitrogens. With 2-acetylbenzoic acid (118), the analogous tetracyclic derivative 119 is obtained176,177 (Scheme 20). Half a mole of hydrazine hydrate with one mole... 

Waldmann s safety-catch hydrazide linker is also part of the class of traceless linkers [55]. Starting from hydrazide resin 126, which is converted into an activated species by oxidation with Cu(OAc)2, the molecules are cleaved by the addition of nucleophiles like amines to give arenes 127 (Scheme 16.30). 

The synthesis of diazenes, R3E—N=N—ER3, from hydrazides, R3E—NLi—NLi—ER3, with oxidants (e.g., 0=C6H4=0, HgO, 02, or Me3NO) is not recommended in view of rapid further oxidation to molecular nitrogen. 

Acyl azides are obtained from hydrazides by the action of nitrous acid or alkyl nitrites 269... 

Carboxylic acid azides from hydrazides GONHNHg CON3... 

Figure 36 (a) Reversible decoration of guanosine hydrazide 1 and of its G-quartet assembly Q1 by condensation with various aldehydes (2-8) (b) Generation of a dynamic library of acylhydrazones C, D and of the acylhydrazone G-quartets A and B from hydrazides 1, 9 and aldehydes 6 and 8. (Reproduced from Ref. 113. National Academy of Sciences, 2005.)... 

Other possibilities include the reaction of hydrazides with hydrogen chloride in nitromethane or methylene chloride. Also thionyl chloride or sulfuryl chloride will produce acid chlorides from hydrazides, although these reactions seem to be of limited scope. 

Pyr, and 2. A dihydrazide monomer unit is given by a code such as O-T-0. Thus, the mode of combination in the synthesis from hydrazides and diacid chlorides can be shown by the codes. 

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