The palladium-catalyzed Suzuki-Miyaura cross-coupling reactions of halo derivatives of 4H-pyrido[1,2-a]pyrimidin-4-one with (het)arylboronic acids allow easy access to (het)aryl and vinyl derivatives of this bicycle in good to excellent yields, even from chloro derivatives. The sequence of reactivity of the halogen in the different positions of the ring system was also investigated. 6-Phenyl-4H-pyrido[1,2-a]pyrimidin-4-one could be prepared by thermal cyclization of isopropylidene (6-phenylpyrid-2-ylamino)methylenemalonate, together with a small amount of 7-phenyl-1,4-dihydro-1,8-naphthyridin-4-one.

Suzuki-Miyaura Cross-Coupling Reactions of Halo Derivatives of 4H-Pyrido[1,2-a]pyrimidin-4-ones.-The reactivity of chloro, bromo, and iodo substituents at different positions on the pyridopyrimidinone skeleton in Suzuki-Miyaura cross-coupling reactions is investigated. It is found, that the reaction sequence for the halogen atoms at different positions of this bicycle is 8 ≥ 2 > 9 > 7 > 3, which is in accordance with the rule of Handy and Zhang. The sequence of reactivity I > Br > Cl is observed at each position. -(MOLNAR, A.; KAPROS, A.; PARKANYI, L.; MUCSI, Z.; VLAD, G.; HERMECZ*, I.; Org. Biomol. Chem. 9 (2011) 19, 6559-6565, http://dx.doi.org/10.1039/c1ob05505d ; External Pharm. Dep., Budapest Univ. Technol. Econ., H-1045 Budapest, Hung.; Eng.) -Bartels 07-166