ZnBr 2 /CuCN‐Promoted, Highly Regioselective S N 2′ Reactions of Some Functionalised Organolithium Compounds with Allylic and Propargylic Halides

Treatment of lithium (2‐lithiomethylphenyl)methoxide ( 2a ) and lithium 2‐(2‐lithiomethylphenyl)ethoxide ( 2b ) [easily prepared by ring opening of phthalan ( 1a ) and isochroman ( 1b ), respectively, by the use of lithium and a catalytic amount of 4,4′‐di‐ tert ‐butylbiphenyl (DTBB)] with zinc bromide and copper cyanide, both in equimolecular amounts, in THF at room temperature, followed by treatment with different allylic chlorides or bromides 3 at −78 or 20 °C, almost exclusively provides (after hydrolysis with water) the corresponding alcohols 4 ′ resulting from an S N 2′ displacement, the process being highly regioselective. The same procedure with intermediates 2a and 2b was applied to propargylic chlorides or bromides 5 , exclusively yielding the corresponding allenylic alcohols 6 ′ , resulting from an S N 2′ reaction. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)