10.1016/S0040-4020(01)87794-2
The research explores the role of X=Y-ZH systems as potential 1,3-dipoles, focusing on the cycloadditions of arylidene imines of α-amino acid esters with a range of dipolarophiles. The study investigates the substantial rate enhancements observed in the presence of both Bronsted and Lewis acids. The purpose of the research is to understand the catalytic effects of these acids on the cycloaddition reactions and to determine the relationship between the rate of reaction and the pKa of the acid for Bronsted acids, as well as the order of rate acceleration for Lewis acids. The conclusions drawn from the research indicate that these reactions are regio- and stereo-specific, and the rate acceleration for Lewis acids follows the order Zn(OAc)2 > AgOAc > LiOAc > MgOAc, with anion dependence also playing a role. The chemicals used in the process include arylidene imines of α-amino acid esters, various dipolarophiles, Bronsted acids (such as 2,4-dinitrophenol, acetic acid, and others), and Lewis acids (such as Zn(OAc)2, AgOAc, LiOAc, and MgOAc). The study provides insights into the formation of metallo-1,3-dipoles and their role in cycloaddition reactions, contributing to the understanding of catalytic processes in organic chemistry.
10.1016/j.tet.2008.01.100
This research investigated the cyclisation mechanisms of a series of ethyl 3-phenyl-4,6-dimethoxyindol-7-yl-2-(hydroxyimino)acetates to form ethyl 6,8-dimethoxypyrazolo[4,5,1-hi]indole-5-carboxylates. The study aimed to determine the electronic requirements of the reaction and the mechanism of formation using 1H NMR spectroscopy. The researchers found that the reaction proceeds through a concerted intramolecular substitution, with the rate of cyclisation being faster for electron-donating substituents and slower for electron-withdrawing substituents, as evidenced by a linear Hammett plot. Key chemicals used in the process included various substituted indole precursors, triethylamine as a base, tetrahydrofuran as a solvent, and 2,4-dinitrophenol as a reagent in the cyclisation process. The research concluded that the cyclisation of the ethers 1aee occurs through a concerted intramolecular substitution mechanism, leading to the formation of the desired indoles 2aee.
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