Ortho-selectivity in SNAr substitutions of 2,4-dihaloaromatic compounds. Reactions with anionic nucleophiles
作者:Michael D. Wendt、Aaron R. Kunzer
DOI:10.1016/j.tetlet.2010.03.124
日期:2010.6
in a variety of solvents. Substrates showed strong preferences for ortho substitution in most cases. Evidence is presented for activating group-dependent coordination, which contributes to very high ortho-selectivity in nonpolar solvents. This also drives the overall reaction rate in these solvents, and is of close to the same magnitude of rate increase derived from polar solvents. para-Products are
The Reactivity of 2-Fluoro- and 2-Chloropyridines toward Sodium Ethoxide: Factors Governing the Rates of Nucleophilic (Het)Aromatic Substitutions
作者:Manfred Schlosser、Thierry Rausis
DOI:10.1002/hlca.200590104
日期:2005.6
5-substituents enhance the rate of the nucleophilic substitution occurring at the 2-position. The sole exception concerns the F-atom at the 5-position which retards the reaction, presumably by lone-pair/lone-pairrepulsion with the negative charge building up at the central C-atom of the intermediate Meisenheimer complex. The substituent effects are additive. Therefore, by using the increments derived from the