RING FORMATION THROUGH INTRAMOLECULAR SN' DISPLACEMENT OF AN ALLYLIC METHOXY SUBSTITUENT

Intramolecular S(N)' displacement of an allylic methoxy substituent by an organomagnesium nucleophile selectively generated vinylcyclopentane and vinylcyclohexane products. This cyclization reaction was promoted by the addition of 5 mol % of CuI, CuBr, or CuBr-SMe2. The Z isomer resulted in more efficient five-membered ring formation than did the E isomer, while the E isomer cyclized to a greater extent than the Z isomer for six-membered ring formation. Formation of five- and six-membered rings from organolithium intermediates were more efficient processes and did not show a significant dependence on olefin geometry. The selectivity obtained for cyclization of acyclic secondary allylic ethers was dependent on olefin geometry, and selective product formation was much greater for the organolithium cyclizations than for the Cu(I)-promoted reactions. Bicyclic ring products formed from a secondary allylic ether substrate were generated stereoselectively with cis ring fusion.