Vinyl‐to‐Benzyl Isomerization and Electrocyclizations in Lithio Derivatives of o‐Tolylstilbenes

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Abstract
(Z)‐2‐(2‐Methylphenyl)‐1,2‐diphenylvinyllithium (1) isomerizes in THF solution to give 1‐[2‐(lithiomethyl)phenyl]‐1,2‐diphenylethene (2). Although 2 cannot be observed directly in this case, its intermediacy becomes evident from the independent preparation by metallation of 1‐[2‐(ethoxymethyl)phenyl]‐ (5) and 1‐(2‐methylphenyl)‐1,2‐diphenylethene (7), with formation of the same sequential products from all three sources. 2 cyclizes by reversible attack on the syn‐phenyl group to give a cyclohexadienide anion 3 containing a seven‐membered ring. 3 exhibits 1H NMR coalescence phenomena and rearranges under thermodynamic control to the 1,2‐diphenyl‐1‐indanide anion 10.

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