Orr SA, Border EC, Andrews PC, Blair VL. Lithium-Bromide Exchange versus Nucleophilic Addition of Schiff's base: Unprecedented Tandem Cyclisation Pathways.
Chemistry 2019;
25:11876-11882. [PMID:
31282040 DOI:
10.1002/chem.201902140]
[Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2019] [Revised: 07/04/2019] [Indexed: 12/15/2022]
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.
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