Jona Mirnik, Uroš Grošelj, A. Novak
Oct 18, 2013
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Journal
Synthesis
Abstract
A novel simple five-step synthesis of 1,6-disubstituted tetrahydropyrazolo[1,5- c ]pyrimidine-2,7(1 H ,3 H )-diones has been developed. The synthetic protocol starts with ‘ring switching’ transformation of commercially available 5,6-dihydro-2 H -pyran-2-one into the 5-(2-hydroxyethyl)pyrazolidin-3-one, followed by addition of the latter to isocyanates, Appel bromination, cyclization, and N(1)-alkylation with alkyl halides to give the title compounds. In comparison to a 12-step synthesis reported recently, the present method is clearly superior with respect to the number of synthetic steps and versatility of substituents at position 6.