Nikol’skiy VV, Minyaev ME, Bastrakov MA, Starosotnikov AM. Straightforward and Efficient Protocol for the Synthesis of Pyrazolo [4,3-
b]pyridines and Indazoles.
Int J Mol Sci 2023;
24:ijms24021758. [PMID:
36675281 PMCID:
PMC9860909 DOI:
10.3390/ijms24021758]
[Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2022] [Revised: 01/09/2023] [Accepted: 01/11/2023] [Indexed: 01/18/2023] Open
Abstract
An efficient method for the synthesis of pyrazolo [4,3-b]pyridines has been developed on the basis of readily available 2-chloro-3-nitropyridines via a sequence of SNAr and modified Japp-Klingemann reactions. The method offers a number of advantages including utilization of stable arenediazonium tosylates, operational simplicity as well as combining the azo-coupling, deacylation and pyrazole ring annulation steps in a one-pot manner. An unusual rearrangement (C-N-migration of the acetyl group) was observed and a plausible mechanism was proposed based on the isolated intermediates and NMR experiments. In addition, the developed protocol was successfully applied to the synthesis of 1-arylindazoles combining the Japp-Klingemann reaction and cyclization of the resulting hydrazone as a one-pot procedure.
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