Abstract
The structure in solution of an allylic lithium compound with attached chiral ligand, 4, is shown by NMR to be internally solvated, partially delocalized and with a small detectable C-Li covalence. Crystallization of 4 in the presence of O 2 produces a 1:1 complex of 4 with its alkoxide oxidation product 9. X-ray crystallography reveals the allylic lithium part of this complex to be fully delocalized.
Highlights
The allyl anion is the simplest of the conjugated carbanions
Just recently our studies of some allylic lithium compounds with attached ligands showed these compounds to be internally solvated.[6]
We describe some studies of a silyl substituted allylic lithium compound with an attached chiral auxiliary, the (S)-2-methoxymethylpyrollidino ligand
Summary
The allyl anion is the simplest of the conjugated carbanions. Numerous chemical,[1] spectroscopic[2] and calculational[3] and crystallographic[4] studies have established that solvated allylic lithium compounds are delocalized with the coordinated lithium centered and normal with respect to the allyl plane. NMR data for the unsolvated allylic lithium compounds 2a, 2b supports a more covalent structure.[5] Structures which exhibit a degree of delocalization between 1 and 2 are not well known. We show below how structure 4 (with 13C and 1H shifts) describes the compound in solution, crystals have been isolated which consist of a 1:1 complex of 4 with the lithium alkoxide formed by reaction of 4 with adventitious oxygen.
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