Tetrabutylammonium azide

As in the pyranoside series, the substitution at C-2 of furanoside derivatives is also difficult (87], Treatment of the 2-imidazylate ester of a benzyl 5-deoxy-a-D-hexofurano-side derivative with tetrabutylammonium azide or benzoate in refluxing toluene led to the formation of substitution products in 82 and 53% yields, respectively [88] (Scheme 11). 

Alterati vely, tetrabutylammonium azide, which is not available commercially, can be replaced by tetrabutylammonium chloride and sodium azide according to the following protocol ... 

An attempt has been made to obtain the elusive thiobenzoyl azide at low temperature.19 Ethanolic solutions of thiobenzoyl chloride and tetrabutylammonium azide were mixed at —115° directly in a low-temperature UV cell. On slight warming (to ca. —100°) a reaction took place with formation of thiatriazole, but no new absorptions due to thiocarbonyl chromophore were observed. This most probably means that the ring closure to thiatriazole, not unexpectedly, is more rapid than the bimolecular formation of thiocarbonyl azide. 

Attempts have been made to obtain 5-phenylthiatriazole-l-oxide (the 5-oxide) for thermal and photochemical studies.24 A nonoxidative route was investigated by mixing ethanolic solutions of either cis- or trans-thiobenzoyl chloride 5-oxide and ammonium or tetrabutylammonium azide. At room temperature a rapid evolution of gas takes place, and besides nitrogen, both sulfur and sulfur dioxide are formed in amounts approximately according to Eqs. (11) and (12). 

As example of introduction of amino and a carboxylic functions in a rigid bicyclic glyco-structure, compound 14-S was treated with tetrabutylammonium azide in toluene at 70 °C, affording the azide 30-S in 87 % yield (Scheme 9). 

The same sequence of reactions was accomplished on the bicyclic iodide 16-R (Scheme 10), the reaction of which with tetrabutylammonium azide in toluene at 60 °C afforded the azide 33-R in 76% yield. Selective deprotection of the primary hydroxyl group of compound 33-R and Jones oxidation, finally afforded compound 35-R as masked glyco-aminoacid. The azido group was maintained in these compounds as protected equivalent of the amino group. 

General Procedure (68J. A solution of imidazylate (1 mmol) and tetrabutylammonium azide [109] (0.85 g, 3 mmol, 3 eq.) in 8 mL of toluene was heated during 1-6 h, depending on the substrate. The reaction mixture was washed with water, dried (Na2S04), and evaporated. 

In place of sodium azide, which has low solubility in common organic media, use of a mixture of hy-drazoic acid and pyridine, tetrabutylammonium azide or tetramethylguanidinium azide has been recommended. One of the most useful and safe alternatives is trimethylsilyl azide (50), which reacts with various acyl chlorides or anhydrides to give isocyanates directly, under thermal conditions (Scheme... 

Tebbe reaction, 231 Tetrabutylammonium azide, 133 Tetramethylurea (TMU), 436 2-Thiopyridylcarbonate (TOPCAT) glycosyl donors, 431 preparation, 434, 440 design, 432 reactivity, 435... 

Table 2.6 Tetrabutylammonium azide (TBAA) physical and chemical properties...

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