synthesis of dihydrooxepino[3,2-c]pyrazoles via claisen rearrangement and ring-closing metathesis from 4-allyloxy-1h-pyrazoles

synthesis of dihydrooxepino[3,2-c]pyrazoles via claisen rearrangement and ring-closing metathesis from 4-allyloxy-1h-pyrazoles

;Yoshihide Usami;Aoi Kohno;Hiroki Yoneyama;Shinya Harusawa
Journal of ethnopharmacology 2018 Vol. 23 pp. 592-
229
usami2018moleculessynthesis

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.

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243377
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