Reversed steric order of reactivity for tert‐butyl and adamantyl‐3‐cyanomethylene‐1,2,4‐triazines

Reactions of 2‐(6‐ tert ‐butyl‐5‐oxo‐4,5‐dihydro‐1,2,4‐triazin‐3(2 H )‐ylidene)‐3‐oxo‐3‐R‐propanenitriles (R = t ‐Bu, Ad‐1) with tert ‐butyl bromoacetate gave the corresponding N(2), C(5)O bis‐alkylation products. Treatment of the latter with t ‐BuLi, in the case of R = t ‐Bu, led to intramolecular condensation at the exocyclic nitrile group. However, in the case of R = Ad‐1, the condensation with the sterically more hindered carbonyl group was observed to give diastereomerically pure 8‐cyanopyrrolo[1,2‐ b ][1,2,4]triazine‐6‐carboxylate derivatives. The structures of the isolated products were confirmed by spectral methods and X‐ray single‐crystal diffraction.