Sulfur analogues, carbonic anhydride

Carbohydrate Esters of Carbonic Anhydride and Their Nitrogen and Sulfur Analogues... 

Nitration of pyridines in other than nitric or sulfuric acids is of little interest here because either no reaction or N-nitration takes place (see Section 2.05.2.10). However, pyridine 1-oxide is considerably more reactive and treatment with benzoyl nitrate ultimately leads to the 3-nitro derivative (Scheme 25) (60CPB28). Annelation of a benzene ring bestows greater reactivity on the 3-position in quinoline, compared with pyridine, and reaction with nitric acid in acetic anhydride furnishes the 3-nitro derivative (ca. 6%) (Scheme 26). This isomer has also been obtained, again at low yield (6-10%), by treatment of quinoline with tetranitratotitanium(IV) in carbon tetrachloride (74JCS(P1)1751>. Nitration of benzo analogues of pyridine occurs much more readily in the benzene ring, and Chapter 2.06 should be consulted for these reactions. 

Among the new carbocations generated, the first example was reported for a triazolyl-based, triaryl methylcation (41). This heterocyclic analogue of the trityl cation was prepared by ionization of the tris(3-benzyl-triazolyl-5-yl)methanol with trifluoroacetic anhydride. Cation (41) was trapped with varied carbon, nitrogen, oxygen, and sulfur nucleophiles. 

---