Tetrazoles quaternization

For both azole and benzazole rings the introduction of further heteroatoms into the ring affects the ease of quaternization. In series with the same number and orientation of heteroatoms, rate constants increase in the order X = 0requires stronger reagents and conditions methyl fluorosulfonate is sometimes used (78AHC(22)71). The 1-or 2-substituted 1,2,3-triazoles are difficult to alkylate, but methyl fluorosulfonate succeeds (7IACS2087). 

Alkyl groups and halogen atoms in tetrazoles are not highly activated unless the ring is quaternized. 

Treatment of a THF solution of trimethylenetetrazole 44 with a solution of BuLi in hexane affords a yellow to orange solution of the lithiated tetrazole 45 (structure tentatively assigned). Alkylation with Mel gives 7-methyl-6,7-dihydro-5//-pynolo[ 1,2-c]tetrazolc 46 in 73% yield. Quaternization of 46 with dimethyl sulfate affords a mixture (3 1) of tetrazolium salts 47 and 48 from which PFg- salts were obtained by crystallization (Scheme 2) <1997MI671>. 

Structures comprising Two Five-Membered Rings (5,5).—Thiazolo[3,2-d]-tetrazoles [CA/4-C,7V5 ]. A " C n.m.r. study of the products of quaternization... 

Both 1- and 2-substituted tetrazoles are susceptible to quaternization. Selective 1-alkylation of 5-alkyltetrazoles can be accomplished via quaternization of 5-alkyl-2-(tri-n-butylstannyl)tetrazole followed by destannylation [522] ... 

The reagent has been employed as a quaternizing agent for a variety of N-heterocycles. Regioselective IV-methylation has been observed (eq 4). Thiazoles are exclusively IV-methylated, whereas tetrazoles yield regioisomeric products. The dication of squaric acid bis(amidine) is prepared by regioselective N-methylation (eq 5). ... 

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