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Molecules 2018, 23(3), 592; https://doi.org/10.3390/molecules23030592

Synthesis of Dihydrooxepino[3,2-c]Pyrazoles via Claisen Rearrangement and Ring-Closing Metathesis from 4-Allyloxy-1H-pyrazoles

Laboratory of Pharmaceutical Organic Chemistry, Osaka University of Pharmaceutical Sciences, 4-20-1 Nasahara, Takatsuki, Osaka 569-1094, Japan
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Received: 14 February 2018 / Revised: 26 February 2018 / Accepted: 4 March 2018 / Published: 6 March 2018
(This article belongs to the Collection Heterocyclic Compounds)
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Abstract

Synthesis of novel pyrazole-fused heterocycles, i.e., dihydro-1H- or 2H-oxepino[3,2-c]pyrazoles (6 or 7) from 4-allyloxy-1H-pyrazoles (1) via combination of Claisen rearrangement and ring-closing metathesis (RCM) has been achieved. A suitable catalyst for the RCM of 5-allyl-4-allyloxy-1H-pyrazoles (4) was proved to be the Grubbs second generation catalyst (Grubbs2nd) to give the predicted RCM product at room temperature in three hours. The same reactions of the regioisomer, 3-allyl-4-allyloxy-1H-pyrazoles (5), also proceeded to give the corresponding RCM products. On the other hand, microwave aided RCM at 140 °C on both of 4 and 5 afforded mixtures of isomeric products with double bond rearrangement from normal RCM products in spite of remarkable reduction of the reaction time to 10 min. View Full-Text
Keywords: dihydrooxepino[3,2-c]pyrazole; synthesis; 4-allyloxy-1H-pyrazoles; RCM; Claisen rearrangement dihydrooxepino[3,2-c]pyrazole; synthesis; 4-allyloxy-1H-pyrazoles; RCM; Claisen rearrangement
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).
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Usami, Y.; Kohno, A.; Yoneyama, H.; Harusawa, S. Synthesis of Dihydrooxepino[3,2-c]Pyrazoles via Claisen Rearrangement and Ring-Closing Metathesis from 4-Allyloxy-1H-pyrazoles. Molecules 2018, 23, 592.

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