Picture of two heads

Open Access research that challenges the mind...

The Strathprints institutional repository is a digital archive of University of Strathclyde research outputs. Strathprints provides access to thousands of Open Access research papers by University of Strathclyde researchers, including those from the School of Psychological Sciences & Health - but also papers by researchers based within the Faculties of Science, Engineering, Humanities & Social Sciences, and from the Strathclyde Business School.

Discover more...

After-effects of lithium-mediated alumination of 3-iodoanisole: isolation of molecular salt elimination and trapped-benzyne products

Crosbie, Elaine and Kennedy, Alan and Mulvey, Robert E. and Robertson, Stuart D. (2012) After-effects of lithium-mediated alumination of 3-iodoanisole: isolation of molecular salt elimination and trapped-benzyne products. Dalton Transactions, 41 (6). pp. 1832-1839. ISSN 1477-9226

Full text not available in this repository. (Request a copy from the Strathclyde author)

Abstract

Gaining a deeper understanding of the modus operandi of heterometallic lithium aluminate bases towards deprotonative metallation of substituted aromatic substrates, we have studied the reactions and their aftermath between our recently developed bis-amido base '(Bu2Al)-Bu-i(mu-TMP)(2)Li' 3 and 3-halogenated anisoles. Ortho-metallation of 3-iodoanisole with 3 results in a delicately poised heterometallic intermediate whose breakdown into homometallic species and benzyne cannot be suppressed, even at low temperature or in a non-polar solvent (hexane). Homometallic components [LiI center dot TMP(H)](4) (5) and (Bu2Al)-Bu-i(TMP)center dot THF (6) have been isolated while the reactive benzyne intermediate has been trapped via Diels-Alder cyclization with 1,3-diphenylisobenzofuran yielding 1-methoxy-9-10-diphenyl-9-10-epoxyanthracene (7). In polar THF solution, nucleophilic addition of LiTMP across the benzyne functionality followed by electrophilic quenching with iodine yields the trisubstituted aromatic species 1-(2-iodo-3-methoxyphenyl)-2,2,6,6-tetramethylpiperidide (8). Compounds 5-8 have been characterized by single-crystal X-ray diffraction in the solid state and multinuclear NMR spectroscopy in solution. By considering these collated results, a plausible reaction mechanism has been proposed for the breakdown of the aforementioned intermediate bimetallic framework. Interestingly, the metallation reaction can be controlled by changing to 3-chloroanisole with an excess of base 3, as evidenced by electrophilically trapping the deprotonated aromatic with iodine to give 2-iodo-3-chloroanisole (9).