Chemistry of Dienyl Anions. I. Crystalline Dienyl Anions by Direct Reaction of Conjugated and Non-conjugated Dienes with Alkali Metals in the Presence of Et3N

Abstract Series of acyclic and cyclic dienyl anions were prepared from both conjugated and non-conjugated dienes by direct metalation with alkali metals (Li, Na, K, Rb, and Cs) in tetrahydrofuran in the presence of triethylamine or N,N,N′,N′-tetramethylethylenediamine. Eight different dienyl anions of open chain or cyclic structures were isolated as crystals. All the acyclic potassium dienides of pentadienes, 2-methylpentadienes, 3-methylpentadienes, hexadienes and 2,4-dimethylpentadienes gave the corresponding 1,3-dienes upon hydrolysis, while the potassium cyclic dienide of cycloheptadienes and cyclooctadienes gave 1,4-dienes exclusively. The result of methylation of dienyl anions with methyl iodide agreed with that of hydrolysis. The reaction path for formation of these dienyl anions was studied based on the carbon skeleton and the molar ratio of the reduced diene dimers produced together with the dienyl anions. Selective oxidative coupling of the dienyl anions occurred with CuX or CuX2 to give linear tetraenes in good yield.