Lithium 2-(2-lithiomethylphenyl)ethanolate from isochroman: Easy preparation of substituted benzoxepines and functionalised arenes

Article abstract of DOI:10.1016/0040-4020(95)00065-G

The reaction of isochroman (1) with an excess of lithium powder and a catalytic amount of DTBB (2.5 mol %) in THF at 20°C yields the title intermediate, which by reaction with different electrophiles (H₂O, D₂O, CO₂ and carbonyl compounds) at temperatures ranging between -78 and 20°C yields, after hydrolysis, the corresponding products 3. Diols 3h-m, derived from benzaldehyde or ketones, give upon treatment with 85% phosphoric acid the corresponding benzoxepines 5h-m. In the other cases, Friedel-Crafts products resulting from a rearrangement of the first carbenium ion formed, are obtained.