Copper-Promoted Oxidative Intramolecular C-H Amination of Hydrazones to Synthesize 1<i>H</i>
-Indazoles and 1<i>H</i>
-Pyrazoles Using a Cleavable Directing Group
A facile and efficient copper‐promoted oxidative intramolecular C–H amination of hydrazones for the synthesis of 1H‐indazoles and 1H‐pyrazoles was developed using a tracelessly cleavable directing group. This reaction is characterized by its mild conditions, operational simplicity, readily available reagents, and excellent yields. A tentative mechanism for Cu‐mediated C–H‐oxidative amination was proposed
Pyrazoles direct: Propargyl alcohols undergo hydrazination when treated with p‐tosyl hydrazide in the presence of catalytic amounts of either Sc(OTf)3 or La(OTf)3 (see scheme; Tf=trifluoromethanesulfonyl). Propargylhydrazides are converted into either N‐tosyl or N‐H pyrazoles when treated with an acid or a base, respectively. The one‐step acid‐catalyzed hydrazination/cyclization of propargyl alcohols
been developed for the synthesis of pyrazole. Based on the analysis of UV‐Vis absorption of the substrate, the reaction was designed to avoid the use of external photocatalysis and proceeds via direct irradiation of N‐centred anion by sunlight. The key features of this reaction include operational simplicity, readily available reagents, and amenability to gram‐scale synthesis.
The palladiumcatalyzed one-pot synthesis of isoxazoles and pyrazoles from aryl iodides, terminal alkynes, chromium hexacarbonyl and hydroxylamine hydrochloride or aqueous hydrazine solution is described. The Sonogashira carbonylative coupling intermediate was trapped in situ by hydroxylamine hydrochloride or aqueous hydrazine to deliver isoxazoles or pyrazoles, respectively, in high yields. This efficient
Preparation of 3,5-Disubstituted Pyrazoles and Isoxazoles from Terminal Alkynes, Aldehydes, Hydrazines, and Hydroxylamine
作者:Ryo Harigae、Katsuhiko Moriyama、Hideo Togo
DOI:10.1021/jo4027116
日期:2014.3.7
provided the corresponding 3,5-disubstituted pyrazoles or isoxazoles in good yields with high regioselectivity, through the formations of propargyl secondary alkoxides and α-alkynyl ketones. The present reactions are one-pot preparation of 3,5-disubstituted pyrazoles from terminal alkynes, aldehydes, molecular iodine, and hydrazines, and 3,5-disubstitutedisoxazolesfrom terminal alkynes, aldehydes