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16.22.6.2.2.1.2 By Substitution of Hydrogen

DOI: 10.1055/sos-SD-116-00573

Ishikawa, T.Science of Synthesis Knowledge Updates, (20122333.

Treatment of 6,8-dimethylpyrimido[4,5-c]pyridazine-5,7(6H,8H)-dione (18) with silver(I) permanganatepyridine complex in the presence of an amine affords aminated products, e.g. 19 (Scheme 10).[‌14‌,‌15‌] Additional cyclization to a three-ring system through CC bond formation is observed when a suitable carbon chain is present in the amine [e.g., to afford 19 (R1=Et; R2=H); 42% yield].[‌16‌,‌17‌] The 3-alkynyl-[‌13‌] or 3-amino-substituted analogues,[‌18‌] as well as the N-oxide 20,[‌19‌] can also be used as precursors. In the latter case, the oxidative amination using piperidine or morpholine can also proceed without an oxidant to give 3-amino-6,8-dimethylpyrimido[4,5-c]pyridazine-5,7(6H,8H)-diones 21, in which N-deoxygenation has occurred.[‌19‌]

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