Dinitrogen trioxide (N 2 O 3 ) is a powerful and efficient nitrosating agent that comes with an unprecedented atom economy. However, the synthetic application of N 2 O 3 is still underdeveloped mostly due to its inherent instability and the lack of reliable protocols for its preparation. This paper presents an open-source setup and procedure for the on-demand generation of anhydrous N 2 O 3 solution (up to 1 M), which can be further used for reactions under batch and flow conditions. The accuracy and stability of N 2 O 3 concentration are guaranteed with the absence of head-space in the setup and with the synchronization of the gas flows. The reliability of this protocol is demonstrated by > 30 worked examples in the nitrosative synthesis of heterocycles-a library of structurally diverse benzotriazoles and sydnones. Kinetic and mechanistic aspects of the Nnitrosative steps are also explored.

Dinitrogen trioxide (N 2 O 3 ) is a powerful and efficient nitrosating agent that comes with an unprecedented atom economy. However, the synthetic application of N 2 O 3 is still underdeveloped mostly due to its inherent instability and the lack of reliable protocols for its preparation. This paper presents an open-source setup and procedure for the on-demand generation of anhydrous N 2 O 3 solution (up to 1 M), which can be further used for reactions under batch and flow conditions. The accuracy and stability of N 2 O 3 concentration are guaranteed with the absence of head-space in the setup and with the synchronization of the gas flows. The reliability of this protocol is demonstrated by > 30 worked examples in the nitrosative synthesis of heterocycles-a library of structurally diverse benzotriazoles and sydnones. Kinetic and mechanistic aspects of the Nnitrosative steps are also explored.