Terminal epoxides have been shown to dimerize to carboxylic esters at 180°C in the presence of some Rh(I) and Ru(II) catalysts. Mixing of two epoxides of different electronic nature gives as the main product "crossed" esters, in which the electron-donating substituents are attached to the carboxylic part and the electronegative groups to the alcoholic residue. Kinetic measurements were carried out using styrene oxide as substrate and RuCl2(PPh3)3 as catalyst. The reaction rate proved to increase either by increasing the electron density of the metal or by introduction of electron-donating groups in the substrate. The proposed reaction mechanism includes (a) dissociation of RuCl2(PPh3)3; (b) oxidative addition of the epoxide (through the less-substituted carbon atom) to the activated catalyst; (c) slow hydrogen transfer from the metal to the β-oxirane carbon, followed by ring cleavage of the epoxide; (d) α-hydrogen transfer and formation of a ruthenium-acyl complex; (e) addition of the second epoxide molecule to the acyl carbonyl carbon; (f) reductive elimination of ester RCH2CH2OCOCH2R from the rearranged ruthenium complex.
|Number of pages||7|
|Journal||Journal of Organic Chemistry|
|Publication status||Published - 1978|
ASJC Scopus subject areas
- Organic Chemistry