Diethylamide, lithium, structure

The effect of substrate structure on product profile is further illustrated by the reactions of cis- and trons-stilbene oxides 79 and 83 with lithium diethylamide (Scheme 5.17) [32]. Lithiated cis-stilbene oxide 80 rearranges to enolate 81, which gives ketone 82 after protic workup, whereas with lithiated trans-stilbene oxide 84, phenyl group migration results in enolate 85 and hence aldehyde 86 on workup. Triphenylethylene oxide 87 underwent efficient isomerization to ketone 90 [32]. 

The heterocycle 3-methyl-1,2-benzisoxazole, whilst structurally distinct from the phenolic aryl ethers underwent cleavage at the 0-N bond by slow addition in tetrahydrofuran to 1M lithium diethylamide at -75 C followed by isolation of crude 1,6-dihydropyridazine and its oxidation with manganese dioxide over 1 hour to give 3,5-bis(2-hydroxyphenyl)pyridazine in 61% yield (ref.96). 

Collum and co-worker studied the solution structure of lithium diethylamide (16) in THF and in ether. Not only dimers and trimers, but also four-, five-, and six-rung ladder structures such as 22 were detected. 

---