Abstract
A versatile multistep continuous flow setup is reported for the four-step conversion of anilines into pyrazole products. The synthesis machine incorporates the use of amine-redox chemistry through diazotization and a metal-free vitamin C mediated reduction. The machine can be used for the synthesis of an array of analogues or the scale up of an individual target.
Highlights
The synthesis of heterocyclic compounds continues to serve as a cornerstone for the preparation of materials necessary for our modern society
We describe the first report of an end-to-end multistep[6] continuous flow process[7] for the amine-redox cycle followed by hydrolysis of the hydrazine surrogate and ensuing cyclo-condensation, a process characterised by low inventories of both diazonium salt and hydrazine at any one time and the use of vitamin C as reductant.[8]
Aiming for N-arylated pyrazoles, we tested the performance of the setup by injecting 0.8 mmol segments of 4-trifluoromethylbenzenediazonium tetrafluoroborate (2, 0.2 M in MeCN) and L-ascorbic acid (3, 0.2 M in H2O) which were
Summary
The synthesis of heterocyclic compounds continues to serve as a cornerstone for the preparation of materials necessary for our modern society. The scope has been increased by the development of important ligands that permit a difficult reductive elimination step.[2] this cross-coupling approach may have some way to go before its application on scale becomes economically and environmentally sustainable, some headway has been made with the development of a continuous flow approach.[3] An alternative option, which permits access to a vast range of substituted hydrazines centres on the use of amine-redox chemistry.
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