Abstract
A series of tetrahydropyrazolo[1,5- c ]pyrimidine-2,7(1 H ,3 H )-diones 3a – h as the first representatives of the so far unexplored saturated heterocyclic system have been synthesized, formally in 12 steps from methyl acrylate ( 4 ). The synthesis comprises a four-step preparation of methyl N -Cbz-5-alkylamino-3-oxopentanoates 9a–c , their three-step transformation into 5-{2-[(alkyl)(benzyloxycarbonyl)amino]ethyl}pyrazolidin-3-ones 12a – c , three-step selective alkylation of the amidic N-2 to give 2-alkyl-5-{2-[(alkyl)(benzyloxycarbonyl)amino]ethyl}pyrazolidin-3-ones 16b – h , followed by hydrogenolytic Cbz-deprotection and subsequent cyclization of the intermediate 1,4-diamine with CDI to furnish the title compounds 3 . Most of the synthetic steps were performed as a one-pot transformation.
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