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Lithium-Bromide Exchange Versus Nucleophilic Addition of Schiff's Base: Unprecedented Tandem Cyclisation Pathways

Lithium-Bromide Exchange Versus Nucleophilic Addition of Schiff's Base: Unprecedented Tandem Cyclisation Pathways

Samantha A Orr, Emily C Border, Philip C Andrews, Victoria L Blair

Chemistry. 2019 Sep 12;25(51):11876-11882.

PMID: 31282040

Abstract:

By exploring lithium-bromide exchange reactivity of aromatic Schiff's bases with tert-butyllithium (tBuLi), we have revealed unprecedented competitive intermolecular and intramolecular cascade annulation pathways, leading to valuable compounds, such as iso-indolinones and N-substituted anthracene derivatives. A series of reaction parameters were probed, including solvent, stoichiometry, sterics and organolithium reagent choice, in order to understand the influences that limit such ring-closing pathways. With two viable reactivity options for the organolithium on the imine; namely, nucleophilic addition or lithium-bromide exchange, a surprising competitive nature was observed, where nucleophilic addition dominated, even under cryogenic conditions. Considering the most commonly used solvents for lithium-bromide exchange, tetrahydrofuran (THF) and diethyl ether (Et2 O), contrasting reactivity outcomes were revealed with nucleophilic addition promoted in THF, while Et2 O yielded almost double the conversion of cyclic products than in THF.

Chemicals Related in the Paper:

Catalog Number	Product Name	Structure	CAS Number	Price
AP7550358	Lithium bromide		7550-35-8	Price

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