Isolation and crystal structure of a presumed intermediate in the reaction of an organolithium compound with an epoxide.
The organolithium-epoxide complexes tetrakis(1-lithio-2-methoxybenzene)bis(ethylene oxide) and tetrakis(1-lithio-2-methoxybenzene)bis(propylene oxide), which are thought to be intermediates in the b-hydroxyalkylation of organolithium compds., have been isolated and characterized. NMR studies on these complexes in nonpolar solvents such as C6H6 and PhMe provide evidence for epoxide O to Li coordination. Addnl., the propylene oxide complex has been characterized by single-crystal x-ray diffraction at 100 K. The structure consists of a tetrameric aggregate of 1-lithio-2-methoxybenzene and two disordered propylene oxide mols., which coordinate to Li as external Lewis bases. Since ab initio calcns. (RHF; SV 3-21G) show the activation of the epoxide by Li coordination to be very small, the question of whether such complexes are intermediates in the nucleophilic ring opening of epoxides remains unanswered.
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