Imidazo triazine, bromination

Bromination of (269a) (as the free base) with NBS produced (269b) in the only example of an electrophilic substitution on a fully aromatic imidazo[l,2-a][l,3,5]triazine (70M724). Ribosidation of (270) (as the bis-trimethylsilyl derivative) with l-0-acetyl-2,3,5-tri-0-benzoyl-jS-D-ribofuranose in 1,2-dichloroethane containing SnCU produced the 8-substituted isomer (271a), which was readily debenzoylated to (271b) (78JMC883). 

Bromination of enamine ketone 792 leads to the formation of 793 (Scheme 197). The Br in 793 can be replaced with hydrazine to give 2-(l-hydrazino-l,2-oxopropylidene)imidazoline 794. Cyclization between the nitrogen termini in 810 with aldehyde or acid chlorides affords 795, imidazo[2,T [l,2,4]triazine 796 and imidazo[2,Tr/ [l,2,4]triaze-pines 797 and 798, respectively <1997SC2433>. 

In the case of the imidazo[l,2-fe][l,2,4]triazine ring system (20), brominations, nitrations, and hydroxymethylations have been reported. Compound (57) reacted with bromine at position 2, i.e., (58) was formed, (Equation (5)), and the nitration of the same starting compound showed similar selectivity <84KGS413>. Hydroxymethylation of the isomeric diphenyl derivative (59) was found to take place at positions 3 and 7 <84KGS1565>. 

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