Cyclic unsaturated compounds

Conclusions

• 1. The alkylation of cyclopentadienylsodium with 2-bromobutane in liquid ammonia gave an equilibrium mixture of sec-butylcyclopentadienes, which contained ∼60% and ∼40% of the 1- and 2-isomers, respectively.

• 2. The alkylation of sec-butylcyclopentadienylsodium leads to a mixture, composed of 33% and 77% of di-sec-butylcyclopentadienes, which contain substituents in the 1,2 and 1,3 positions. The 1,2-di-sec-butylcyclopentadiene in the equilibrium state represents a mixture of ∼60% of the 1,2-isomer and ∼40% of the 2,3-isomer. The equilibrium mixture of the 1,3-di-sec-butyl-substituted cyclopentadienes contains ∼15% and ∼85% of the 1,3- and 1,4-isomers, respectively.

• 3. A reversible 1,2-shift of hydrogen is observed when the equilibrium mixtures of the sec-butyl-substituted cyclopentadienes are reacted with maleic anhydride, as a result of which the adduct of the isomer with free 1 and (or) 4 positions is formed preferentially.

• 4. At 380–500° the 1,2- and 1,3-di-sec-butyl-substituted cyclopentadienes undergo a reversible skeletal isomerization, which leads to an equilibrium mixture of the mentioned structural isomers (15 and 85%, respectively).

• 5. The mono-sec-butylcyclopentadiene is thermally stable in the temperature range 300–500°.