▎ 摘　　要

NOVELTY - Photocatalyst comprises a nitrogen-doped graphene nanosheet functionalized with a ruthenium complex, and a composite photocatalyst comprising a reaction catalyst, where the photocatalyst and the reaction catalyst comprises a nitrogen-doped graphene nanosheet functionalized with the ruthenium complex are covalently bonded. USE - The catalyst is useful for position-selective arylation or heteroarylation of imidazo(1,2- alpha ) pyrimidine (claimed). ADVANTAGE - The photocatalyst: selectively binds aryl or heteroaryl to position 3 of imidazo (1,2- alpha ) pyrimidine, and position 3 of imidazo (1,2- alpha ) pyrimidine can be usefully used to introduce various aryl or heteroaryl. DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for: (1) preparing the catalyst, comprising either: preparing a nitrogen-doped graphene nanosheet (NDGNs) comprising reacting the nitrogen-doped graphene nanosheet with a ruthenium complex to prepare (Ru-N-doped Graphene nanosheets, RuNDGNs) functionalized with a ruthenium complex, or (1) preparing a nitrogen-doped graphene nanosheet (NDGNs), (2) reacting the nitrogen-doped graphene nanosheet with a ruthenium complex to prepare a nitrogen-doped graphene nanosheet (Rudns) functionalized with a ruthenium complex, and (3) reacting a nitrogen-doped graphene nanosheet functionalized with the ruthenium complex with a reaction catalyst to prepare nitrogen-doped graphene nanosheets (fRuNDGNs) in which a nitrogen-doped graphene nanosheet and a reaction catalyst are covalently bonded; and (2) position-selective arylation or heteroarylation of imidazo (1,2- alpha ) pyrimidine, comprising reacting an aryl or heteroaryl compound and an imidazo (1,2- alpha ) pyrimidine compound in the presence of the composite photocatalyst.