Synthesis 2023; 55(06): 945-958
DOI: 10.1055/a-1961-8504
paper

Synthesis of 5,6-Dihydro-4H-pyrrolo[1,2-b]pyrazoles and Homologs from 5-Substituted 2-(Alkynyl)tetrazoles via Microwave-Induced Intramolecular Nitrile-Imine–Alkyne 1,3-Dipolar Cycloaddition

Hiroki Yoneyama
,
Mano Adachi
,
Aoshi Morita
,
Maki Nakagawa
,
Miho Baba
,
Kanako Yamawaki
,
Noboru Hayama
,
Shinya Harusawa
,
This work was financially supported by research funds from Osaka Medical and Pharmaceutical University.


Abstract

Microwave irradiation of 2-alkynyl-5-(phenyl or alkyl)tetrazoles affords 2-(phenyl or alkyl)-5,6-dihydro-4H-pyrrolo[1,2-b]pyrazoles via intramolecular [3+2] cyclization of nitrile-imine intermediates. In the present method, the use of 5-alkyltetrazoles as the starting materials is more advantageous because of the difficulties associated with conventional photoreactions. From 2-phenylalkynyl-5-methylthio-1H-tetrazoles, the reaction efficiently produces 2-methylthio-3-phenyl-5,6-dihydro-4H-pyrrolo[1,2-b]pyrazoles. The procedure using the methylthio group is applied to the total synthesis of three naturally occurring withasomnines. The method is also extended to the construction of molecules in which bicyclic pyrazoles are fused to six- to eight-membered rings.

Supporting Information



Publication History

Received: 26 August 2022

Accepted after revision: 17 October 2022

Accepted Manuscript online:
17 October 2022

Article published online:
16 November 2022

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