Abstract
Electrophilic aromatic bromination is the most common synthetic method used to prepare aryl bromides, which are very useful intermediates in organic synthesis. To understand the experimental results in electrophilic aromatic brominations, ab initio calculations are used here for a tentative analysis of the positional selectivity. The calculated results agree well with the corresponding experimental data, and the reliability of the resulting positional selectivity was verified by the corresponding experimental data.
Highlights
Aryl bromides have found widespread utility as substrates for Pd, Ni, and Cu-catalyzed cross-coupling reactions to form diverse C–C, C N, C O, and C S bonds [1,2,3,4,5,6,7,8,9]
Similar positional selectivity was usually found when the reactions were performed in the other electrophilic aromatic bromination systems [27,28]
The results based on ab initio calculations provide clear indication for the positional selectivity tendencies in an electrophilic aromatic bromination
Summary
Aryl bromides have found widespread utility as substrates for Pd-, Ni-, and Cu-catalyzed cross-coupling reactions to form diverse C–C, C N, C O, and C S bonds [1,2,3,4,5,6,7,8,9]. A π-donor substituent at one of these positions stabilizes the arenium ion and stabilizes the transition state and lowers the activation energy necessary for the electrophilic aromatic substitution, and acts as an ortho/para directing group. 2-bromo-5-methoxybenzaldehyde (4a) in 81% yield, while the potential isomer of 4-bromo-3methoxybenzaldehyde (4b) was not formed at all [45,46] As witnessed in these two examples, a π-donor substituent (πDS) usually tends to facilitate its para electrophilic aromatic bromination, whereas a π-acceptor substituent (πAS) usually tends to prevent the corresponding para electrophilic aromatic bromination. The results based on ab initio calculations are used to distinguish the ortho/para positional selectivity
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