Preparation and Decomposition of Potassium Alkalide−Lipophilic Crown Ether Complexes in Tetrahydrofuran

Abstract

Cyclohexano-15-crown-5, cyclohexano-18-crown-6, dicyclohexano-15-crown-5, and dicyclohexano-18-crown-6, but not dicylohexano-16-crown-5, in THF dissolve potassium metal to form dark blue potassium alkalide solutions at ambient temperature. On standing, the potassium alkalide complexes decompose and the solutions turn colorless at differing rates. Identification of the products provides insight into the decomposition mechanism.

Decomposition of vinyl ethers by alkalide K−, K+(15-crown-5)2 via organopotassium intermediates

“…The direction of the ether bond cleavage depended on the kind of substituent. Unexpectedly, the scission of one of the linear ether bonds was found in some oxiranes possessing an oxygen atom in the substituent [7]. The highly strained oxirane ring remained undisturbed.…”

“…Then, it was found that the regioselective cleavage of the alkyl-oxygen bond occurred also in methyl phenyl ether, ethyl phenyl ether [2], and allyl phenyl ether [3] in their reactions with K À , K þ (15-crown-5) 2 1. It was shown in further works that various cyclic ethers as monosubstituted oxiranes [3][4][5][6][7][8][9], oxetane [10][11][12] and tetrahydrofuran [13,14] can also be opened by alkalides. The most interesting seemed to be the reaction involving oxiranes.…”

“…The highly strained oxirane ring remained undisturbed. The decomposition of cyclic ethers in a larger ring, e.g., 18-crown-6 [13], 15-crown-5 [14], and their monocyclohexano-and dicyclohexano-derivatives [15] was observed under the influence of potassium anions in tetrahydrofuran solution.…”

“…They were generally unstable and underwent various fast reactions, e.g., with crown ether or with the substrate [16]. Some of them eliminate potassium phenoxide [5] or unsaturated hydrocarbons, e.g., ethylene [12,14] or cyclohexene [15]. Most of the reactions mentioned above had been previously not described in the literature.…”

Photochemical, Electrochemical and Enzymatic Methods for Ether‐Bond Cleavage

“…[68][69][70][71] Similarly, potassium anions cleave exclusively the allyl-oxygen or benzyl-oxygen bond in some glycidyl ethers to give organopotassium compounds as intermediate reaction products. [72,73] The classical methods of allyl ether deprotection generally proceed through double-bond isomerization to enol ethers by potassium tert-butoxide [74] or rhenium complexes followed by acidic hydrolysis. [75,76] In the case of the electrochemical procedure a mechanism involving the allyl-oxygen cleavage with formation of a π-allylnickel intermediate has been suggested.…”