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Knorr, Rudolf; Behringer, Claudia; Ruhdorfer, Jakob; Roman, Ulrich von; Lattke, Ernst; Böhrer, Petra (2017): Conducted Tour Migration of Li+ during the cis/trans Stereoinversion of alpha-Arylvinyllithiums. In: Chemistry-A European Journal, Vol. 23, No. 52: pp. 12861-12869
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A "conducted tour" migration keeps a mobile client on a profitable route even though an occasional side-step may seem attractive. A stereochemical manifestation of such a migration had been suggested by Donald J. Cram (1964), and we present now a different example that concerns the cis/trans stereoinversion of monomeric H2C=C(Li)-aryl compounds: Upon tetrahydrofuran (THF)-assisted heterolysis of the Li-C bond with formation of a solvent-separated ion pair (SSIP), the unchained mobile client Li+(THF)(4) is proposed to surmount the rim of the electronically fixed aryl group and to disdain the less encumbered pathways across the H2C=C region. This interpretation is based on knowledge from a previously published series of monomeric -arylalkenyllithiums in combination with two new members: 4-(-lithiovinyl)-2,2-dimethylbenz[f]indane (1) revealed both a barrier against -aryl rotation and a route-distinguishing retardation as compared with the corresponding migration-dependent cis/trans stereoinversion rate constant of 1-(-lithiovinyl)naphthalene (2). Monomeric and dimeric ground states of 1 and 2 and their microsolvation numbers were determined by using the recently developed primary and secondary NMR criteria.