Alkyl halides and related compounds azoles without a free NH group

9 Alkyl halides and related compounds azoles without a free NH group 

Pyrazoles and imidazoles carrying a substituent on nitrogen, as well as oxazoles, thiazoles, etc., are converted by alkyl halides into quaternary salts. This is illustrated by the preparation of thiamine (98) from components (96) and (97). 

Azoles having heteroatoms in the 1,3-orientation are more reactive than those in which the arrangement is 1,2. However, the magnitude of the factor varies. Thus oxazole is 68 times more reactive than isoxazole, whereas benzoxazole quatemizes 26 times faster than does 1,2-benzisoxazole 

Annulation of a five-membered aza ring to a benzo ring generally leads to rate retardation in N-quatemization reactions similar in magnitude to that for six-membered rings. Exceptions are known  

1- benzisoxazole undergoes A-methylation faster than isoxazole, and in 2,1,3-benzoxadiazole and 

---

Alkyl halides and related compounds azoles without a free NH group Alkyl halides and related compounds compounds with a free NH group. 3.10 Acyl halides and related compounds... 

---