The reactivity of potassium carbanions with epoxides
The reaction of α-cumylpotassium and cyclohexene oxide produces trans-cumylcyclohexanol in high yield in the presence of excess cumene. Reactions of 1.1 and 2.0 equivalents of cumene with one equivalent of n-butylpotassium to make α-cumylpotassium were shown to take several days to reach a maximum yield in the subsequent reaction of α-cumylpotassium and cyclohexene oxide. Although it was initially hypothesized that the high yield was attributed to the interaction of the potassium with the aromatic rings of the α-cumyl anion and the excess cumene, which was confirmed by molecular modeling studies, these reactions demonstrated that no large excess of aromatic solvents were needed. Substituting benzene and tert-butylbenzene for cumene in this reaction gave lower yields of product. Cyclohexene oxide reacted with n-butylpotassium to unexpectedly produce 2-butylcyclohexanone in a 2 % isolated yield or in a 10 % isolated yield of its semi-carbazone derivative. Based on the literature, we hypothesized that we produced 2-butylcyclohexanone by first opening the epoxide ring of cyclohexene oxide by SN2 substitution with n-butylpotassium to give the alkoxide of trans-2-butylcyclohexan-1-ol as observed in the reaction of cyclohexene oxide and α-cumylpotassium. Next, a second equivalent of n-butylpotassium reacted with cyclohexene oxide to produce a carbene alkoxide. Finally, the carbene alkoxide oxidized the alkoxide of trans-2-butylcyclohexan-1-ol to 2-butylcyclohexanone. This mechanism implies that a greater than 33 % yield is not possible. The reaction of 2-methyl-1,2-epoxycyclohexane with n-butylpotassium and the reaction of cyclohexene oxide with sec-butyllithium did not lead to any ring opening products.
Inorganic chemistry|Organic chemistry
Dorado, Christina, "The reactivity of potassium carbanions with epoxides" (2011). ETD Collection for University of Texas, El Paso. AAI3469328.