NITRATION IN THE IMIDAZO[1,2-ALPHA]PYRAZINE SERIES - EXPERIMENTAL ANDCOMPUTATIONAL RESULTS

Nitration was carried out on a series of imidazo[1,2-a]pyrazine deriva tives. The reactivities of diversely substituted derivatives and of al l positions of substitution were analysed and experimental results com pared with C-13-nmr data and semi empirical calculations (AMl). Althou gh the unsubstituted heterocycle is highly resistant to nitration, ele ctron-donating groups such as alkoxy or alkylamino on position 8 enhan ce the reactivity of the imidazo[1,2-a]pyrazine derivatives towards el ectrophilic substitution and, more specifically, nitration. The C-13-n mr experiments, electronic distributions and Molecular Electrostatic P otential isodensity surfaces calculated on the neutral forms are in go od agreement with experimental results indicating position 3 is the mo st reactive position towards nitration.